Biosensor membranes composed of polymers containing heterocyclic nitrogens

Biosensor membranes composed of polymers containing heterocyclic nitrogens

Field of the Invention

This invention relates, in general, to a membrane that limits the flow of analytes. More particularly, the invention relates to such a membrane composed of polymers containing heterocyclic nitrogens. The membrane is a useful component of biosensors and, more particularly, of biosensors that can be implanted in a living body.

Background of the invention

Although the biosensors themselves are not in accordance with the present invention, enzyme-based biosensors are devices in which a signal from a biochemical reaction that depends on the concentration of an analyte is converted into a physical signal that can measured, such as an optical or electrical signal. Such biosensors are widely used in the detection of analytes in clinical, environmental, agricultural and biotechnology applications. Analytes that can be measured in clinical analyzes of human body fluids include, for example, glucose, lactate, cholesterol, bilirubin and amino acids. The detection of analytes in biological fluids, such as blood, is important for the diagnosis and monitoring of many diseases.

Biosensors that detect analytes by means of electrical signals, such as current (amperometric biosensors) or charge (culombimetric biosensors), have a special interest because in the biochemical reactions of many important bioanalites the transfer of electrons is involved. For example, the reaction of glucose with glucose oxidase leads to the transfer of electrons from glucose to the enzyme producing gluconolactone and reduced enzyme. In an example of an amperometric glucose biosensor, glucose is oxidized by the oxygen in the body fluid by a reaction catalyzed by glucose oxidase that generates gluconolactone and hydrogen peroxide, after which the hydrogen peroxide is electro-oxidized and correlated with the glucose concentration of body fluid (Thomé-Buret, V., et al., Anal. Chem. 68, 3822 (1996) and US Patent No. 5,882,494, of Van Antwerp.). In another example of an amperometric glucose biosensor, the electro-oxidation of glucose to gluconolactone is mediated by a polymeric redox mediator that electrically "wire" the reaction center of the enzyme to an electrode. (Csöregi, E., et al., Anal. Chem. 66, 3131 (1994); Csöregi, E., et al., Anal. Chem. 67, 1240 (1995); Schmidtke, DW, et al., Anal Chem. 68, 2845 (1996); Schmidtke, DW, et al., Anal. Chem. 70, 2149 (1998); and Schmidtke, DW et al., Proc. Natl. Acad. Sci. USA 95, 294 (1998).)

Amperometric biosensors typically employ two or three electrodes, which include at least one measuring electrode or working electrode and another reference electrode. In two electrode systems, the reference electrode also serves as a counter electrode. In three electrode systems, the third electrode is a counter electrode. The measuring electrode or working electrode is composed of a non-corroding conductor, carbon or metal, and is connected to the reference electrode by means of a circuit, such as a potentiostat.

Although the biosensors, by themselves, are not in accordance with the present invention, some biosensors are designed to implant in the body of a living animal, such as a mammal or a human body, simply by way of example. In an implantable amperometric biosensor, the working electrode is typically constructed with a detection layer, which is in direct contact with the electrode conductive material, and with a membrane layer that limits diffusion, over the detection layer. The detection layer typically consists of an enzyme, an enzymatic stabilizer such as bovine serum albumin (BSA), and a crosslinking agent (crosslinking agent) that performs the polymeric crosslinking (crosslinking) of the components of the detection layer. Alternatively, the detection layer consists of an enzyme, a polymeric mediator, and a crosslinking agent that cross-links the components of the detection layer, as in the case of the "wired enzyme" biosensor cited.

In an implantable glucose amperometric sensor, the membrane is often beneficial or necessary to regulate or limit the flow of glucose into the detection layer. By way of explanation, in a glucose sensor without a membrane, the flow of glucose to the detection layer increases linearly with the glucose concentration. When all the glucose that reaches the detection layer has been consumed, the measured output signal is directly proportional to the glucose flow and, therefore, to the glucose concentration. However, when glucose consumption is limited by the kinetic characteristics of chemical or electrochemical activities of the detection layer, the measured output signal is not regulated by glucose flow and is not directly proportional to glucose flow or concentration. -In this case, only a fraction of the glucose that reaches the detection layer is consumed before the sensor becomes saturated, after which the measured signal stops increasing, or increases only slightly, with the concentration of glucose. On the other hand, in a glucose sensor provided with a membrane that limits diffusion, the membrane reduces the flow of glucose to the detection layer so that the sensor does not become saturated and, therefore, can operate effectively within a much wider range of glucose concentrations.

More particularly, in these membrane-provided glucose sensors, the rate of glucose consumption is regulated by the diffusion or flow of glucose through the membrane rather than by the kinetic characteristics of the detection layer. The flow of glucose through the membrane is defined by the permeability of the membrane to glucose, which is usually constant, and by the concentration of glucose in the solution or the biological fluid being investigated. When all of the glucose that reaches the detection layer has been consumed, the flow of glucose through the membrane to the detection layer varies linearly with the glucose concentration of the solution, and determines the conversion or signal rate output that have been measured in such a way that this is also directly proportional to the glucose concentration of the solution. Even when it is not necessary, a linear relationship between the output signal and the glucose concentration of the solution is ideal for the calibration of an implantable sensor.

Implantable glucose amperometric sensors that rely on hydrogen peroxide electro-oxidation, as described above, require an excess oxygen reactant to ensure that the sensor's output is regulated only by the concentration of glucose in the fluid or body tissue being investigated. That is, the sensor is designed so that it is not affected by oxygen typically present in the fluid or body tissue. In body tissue in which, typically, the glucose sensor is implanted, the oxygen concentration can be very low, such as from about 0.02 mM to about 0.2 mM, while the glucose concentration can be as high as about 30 mM or more. Without a membrane that limits glucose diffusion, the sensor would saturate very quickly at very low glucose concentrations. Thus, the sensor benefits from being provided with a membrane sufficiently permeable to oxygen, which reduces the flow of glucose to the detection layer, so that it is minimized or the so-called "oxygen deficiency problem" is eliminated. , a state in which there is insufficient oxygen for proper detection to take place.

In implantable amperometric glucose sensors that employ electrodes of "wired" enzymes, as described above, there is no problem of oxygen deficiency, because oxygen is not a necessary reactant. However, these sensors require membranes that limit glucose diffusion because, typically, for glucose sensors that lack such membranes, the current output reaches a maximum level around or below a glucose concentration of 10 mM, which is well below that of 30 mM, the high end of clinically important glucose concentrations.

A membrane that limits diffusion is also beneficial in a biosensor that uses a wired enzyme electrode, since the membrane significantly reduces the chemical and biochemical reactivity of the detection layer and, therefore, reduces the production of radical species that They could damage the enzyme. The membrane that limits diffusion can also act as a mechanical protector that prevents the leakage of components from the sensor out of the detection layer, and decreases the noise associated with the movement.

There have been several attempts to develop a membrane that limits glucose diffusion, is mechanically robust, biocompatible and easily manufactured. For example, a stratified microporous membrane with mechanical holes has been described (US Patent No. 4,759,828, by Young et al.) And membranes formed from polyurethane are also known (Shaw, GW, et al. , Biosensors and Bioelectronics 6. 401 (1991); Bindra, DS et al., Anal. Chem. 63, 1692 (1991); Shichiri, M., et al., Horm. Metab Res., Suppl. Scr. 20, 17 (1988)). Supposedly, glucose diffuses through the mechanical holes or fissures of these various membranes. In addition, by way of example, a heterogeneous membrane with discrete, hydrophobic and hydrophilic regions (US Patent No. 4,484,987 to Gough), and homogeneous membranes with both functionalities, hydrophobic and hydrophilic (US patents) have been described. U.S. Nos. 5,284,140 and 5,322,063, to Allen et al.). However, all these known membranes are difficult to manufacture and have inadequate physical properties.

An improved membrane formed from a complex mixture of a diisocyanate, a diol, a diamine and a silicone polymer, has been described in US Pat. Nos. 5,777,060 (Van Antwerp), 5,786,439 (Van Antwerp et al).) And 5,882,494 (Van Antwerp). As described therein, the membrane material is polymerized and crosslinked simultaneously in a flask; The resulting polymeric material is dissolved in a strong organic solvent, such as tetrahydrofuran (THF) and the resulting solution is applied to the detection layer to form the membrane: Unfortunately, a very strong organic solvent such as THF can denature the enzyme in the detection layer and also dissolve conductive ink materials as well as any plastic materials that can be part of the sensor. In addition, since polymerization and cross-linking reactions are completed in the reaction flask, no additional reactions occur that produce bonds when the solution is applied to the detection layer to form the membrane. As a result, the adhesion between the membrane layer and the detection layer may not be adequate.

In Application (PCT) of the Patent Cooperation Treaty underpinning International Publication No. WO 01/57241 A2, Kelly and Schiffer describe a method of manufacturing a membrane that limits glucose diffusion, photolytically polymerizing small hydrophilic monomers. The sensitivities of the glucose sensors that employ such membranes are, however, very widespread, which indicates a lack of control in the membrane manufacturing process. On the other hand, since polymerization involves very small molecules, it is quite possible that small, soluble molecules remain after polymerization, which can leach out of the sensor. Therefore, glucose sensors that employ such membranes that limit glucose diffusion may not be suitable for implantation in a living body.

US 4,929,313 describes electrochemical devices that can be used to convert an ionic flow into an electric current, for the determination of ionic concentrations. The devices are operated without the need for a reference electrode and are specific based on known ionic transfer agents. The operation of the devices entails the use of pairs of electrodes modified with electroactive redox materials coated with selective ionic coatings. A potential applied between a pair of appropriately modified electrodes results in the circulation of an electric current between the electrodes that depends on the concentration of the ion to be detected. The devices constructed by combining electrodes coated with electroactive polymers and different ion selective films, allow the simultaneous determination of various ions. For example, these devices are useful for measuring the concentration of total cations, total anions, H +, Li +, K +, Ca ++, Na +, HCO3-, Cl-, other cations and anions, and combinations thereof. The devices are small and stable enough to be used in vivo, for example, as means of determination in the blood or in large-scale checks of water quality or in purification / separation techniques.

US 5,543,326 describes oxidoreductases that are chemically modified to change their net charge at a given pH. By such modification, the adsorption of enzymes on surfaces, their retention in membranes of polymers of similar or opposite charge, and their binding with charged macromolecules of the same or opposite sign, in particular redox macromolecules, are regulated. The modified enzymes, of which the modified recombinant glucose oxidase is an example, are useful in biosensors, for example of glucose, as antigen marker enzymes or antibodies in immunodetection., And as labels of nucleotide sequences in probes, for example , for DNA nucleotide sequences.

Kabanov et al., (1996), Journal of Controlled Release 39, 173-189, describe the interaction of polyions with species that simulate cells. Vuillaume et al., (2000), Macromolecules 33, 781-790 describe the synthesis and characterization of pyridinium polymethacrylates capped in an amphiphilic tail.

Summary of the invention

The present invention is directed to membranes composed of cross-linked polymers containing nitrogenous heterocyclic groups, in particular poly (vinylpyridine) and poly (vinylimidazole) polymers. The membranes are useful for limiting the flow of an analyte to the working electrode of an electrochemical sensor so that the sensor responds linearly over a large range of analyte concentrations and is easily calibrated. The electrochemical sensors provided with membranes of the present invention demonstrate considerable sensitivity and stability and a large signal to noise ratio, in a variety of conditions.

According to one aspect of the invention, the membrane is formed by cross-linking in situ of a polymer, modified with a zwitterionic moiety, a non-pyridine copolymer component, and, optionally, another moiety that is either hydrophilic or hydrophobic, and / or has other desirable properties, in an alcoholic solution of a buffer. The modified polymer is produced from a precursor polymer that contains nitrogenous heterocyclic groups. Preferably, the precursor polymer is poly (vinyl pyridine) or poly (vinylimidazole). When used in an electrochemical sensor, the membrane limits the flow of an analyte that reaches the sensor's detection layer, such as the enzyme-containing detection layer of a "wired enzyme" electrode, and also protects the detection layer . These membrane qualities significantly extend the linear detection range and the stability of the sensor.

In the membrane formation process, the copolymer component that is not pyridine generally intensifies the solubility of the polymer and can also provide additional physical and chemical properties to the resulting polymer or membrane. Optionally, hydrophilic or hydrophobic modifiers can be used for "fine tuning" of the membrane permeability that results for an analyte of interest. They can be used to enhance the biocompatibility of the resulting polymer or membrane, optional hydrophilic modifiers such as polyethylene glycol and hydroxylated or polyhydroxylated modifiers. In the formation of a membrane of the present invention, it is believed that the zwitterionic moiety of the polymer provides an additional crosslinking layer, by means of intermolecular electrostatic junctions, in addition to the basic crosslinking attributed, in general, to covalent bonds, and is opined , therefore, that the membrane is reinforced.

Another aspect of the invention concerns the preparation of a membrane that limits the diffusion of substantially homogeneous analytes, which can be used in a biosensor, such as an implantable amperometric biosensor. The membrane is formed in situ by applying a buffered alcoholic solution of a crosslinking agent and a modified polymer, on a detection layer containing an enzyme, and allowing the solution to cure for one or two days. The crosslinking agent-polymer solution can be applied to the detection layer by placing one or more droplets of the solution on the sensor, immersing the sensor in the solution, or similarly. Generally, the thickness of the membrane is regulated by the concentration of the solution, by the number of droplets of the solution that have been applied, by the number of times the sensor has been immersed in the solution, or by any combination of these. factors. The amperometric glucose sensors provided with membranes that limit diffusion, of the present invention, demonstrate excellent stability and a rapid, linear response to glucose concentration over a wide range of glucose concentrations.

Brief description of the drawings

Figure 1 is an illustration of a typical structure of a section of a membrane that limits the diffusion of analytes, according to the present invention.

Figure 2 is a schematic illustration of the side view of a part of a two electrode glucose sensor having a working electrode, a combined electrode, counter-electrode / reference electrode, and a dip-coated membrane according to the present invention, which encapsulates both electrodes. Figures 2B and 2C are schematic illustrations of views of the top and bottom part, respectively, of the glucose sensor part of Figure 2A. In this report, Figures 2A, 2B and 2C can be referred to collectively as Figure 2.

Figure 3 is a graph of current versus glucose concentration of sensors that have membranes that limit the diffusion of glucose according to the present invention, and of sensors that lack such membranes, based on average values.

Figure 4 is a graph of current output versus time, at a fixed glucose concentration, of a sensor having a membrane that limits glucose diffusion, according to the present invention, and of a sensor lacking such a membrane.

Figure 5 is a graph of current output versus time at different levels of glucose concentration, of sensors having membranes that limit the diffusion of glucose according to the present invention, based on average values.

Figure 6 is a graph of current output versus time, at different levels of glucose concentration, with and without stirring, of a sensor having a membrane that limits the diffusion of glucose according to the present invention, and of a sensor that It lacks such a membrane.

Figure 7A is a graph of current output versus glucose concentration of four batches of sensors, prepared separately, having membranes that limit the diffusion of glucose according to the present invention, based on average values. Figures 7B-7E are graphs of current output versus glucose concentration, of individual sensors of each of the four batches of sensors referred to above, which have membranes that limit the diffusion of glucose according to the present invention, respectively. In this report, Figures 7A, 7B, 7C, 7D and 7E can be referred to collectively, as Figure 7.

Description of the invention

When used herein, quoted terms and expressions are defined as explained below.

The term "alkyl" includes saturated, linear or branched aliphatic hydrocarbons. Examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl and the like. Unless otherwise indicated, the term "alkyl" includes alkyl groups and cycloalkyl groups.

The term "alkoxy" describes an alkyl group attached to the rest of the structure by an oxygen atom. Examples of alkoxy groups include methoxy, ethoxy, n-propoxy, isopropoxy, butoxy, tert-butoxy, and the like. In addition, unless otherwise indicated, the term "alkoxy" includes alkoxy groups and cycloalkoxy groups.

The term "alkenyl" describes an unsaturated, linear or branched aliphatic hydrocarbon, which has at least one carbon-carbon double bond. Examples of alkenyl groups include ethenyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-methyl-1-propenyl, and the like.

A "reactive group" is a functional group of a molecule that is capable of reacting with another compound to couple at least a part of such another compound to the molecule. Reactive groups include carboxy, activated ester, sulfonyl halide, sulfonate ester, isocyanate, isothiocyanate, epoxide, aziridine, halide, aldehyde, ketone, amine, acrylamide, thiol, acyl azide, acyl halide, hydrazine, hydroxylamine, halide alkyl, imidazole, pyridine, phenol, alkyl sulfonate, halotriazine, imido ester, maleimide, hydrazide, hydroxy, and photo-reactive aryl azido groups. Activated esters, as understood in the art, generally include succinimidyl, benzotriazolyl, or aryl esters substituted by groups that capture electrons such as sulfo, nitro, cyano or halo groups; carboxylic acids activated by carbodiimides.

A "substituted" functional group (for example, an alkyl, alkenyl or substituted alkoxy group) includes at least one substituent selected from the following: halogen, alkoxy, mercapto, aryl, alkoxycarbonyl, alkylaminocarbonyl, dialkylaminocarbonyl, -OH, -NH2, alkylamino , dialkylamino, trialkylammonium, alkanoylamino,

arylcarboxamido, hydrazino, alkylthio, alkenyl, and reactive groups.

A "crosslinking agent" (crosslinking agent) is a molecule that contains at least two reactive groups capable of binding at least two molecules, or linking at least two parts of the same molecule. The bond of at least two molecules is called intermolecular crosslinking, while the bond of at least two parts of the same molecule is called intramolecular crosslinking. A crosslinking agent having more than two reactive groups may be capable of both intermolecular and intramolecular crosslinking.

The term "precursor polymer" refers to the starting polymer before joining the various modifying groups to form a modified polymer.

The expression "nitrogen heterocyclic group" refers to a cyclic structure containing a sp2 hybridized nitrogen in a ring of the structure.

The term "polyvinylpyridine" refers to poly (4-vinylpyridine), poly (3-vinylpyridine), or poly (2-vinylpyridine), as well as to any copolymer of vinylpyridine and a second or third copolymer component.

The term "polyvinylimidazole" refers to poly (1-vinylimidazole), poly (2-vinylimidazole), or poly (4-vinylimidazole)

A "membrane solution" is a solution that contains all the necessary crosslinking and membrane formation components, including a modified polymer containing nitrogenous heterocyclic groups, a crosslinking agent and a buffer or a mixed alcohol-buffer solvent.

A biological fluid "or" biofluid "is any body fluid or derivative of a body fluid in which the analyte can be measured, for example, blood, intestinal juice, plasma, dermal fluid, sweat and tears.

An "electrochemical sensor" is a device configured to detect the presence or measure the concentration or amount of an analyte in a sample through electrochemical oxidation or reduction reactions. Typically, these reactions can be transduced to an electrical signal that can be correlated with the amount or concentration of the analyte.

A "redox mediator" is an electron transfer agent for transporting electrons between an analyte, an enzyme reduced or oxidized by the analyte, and an electrode, either directly, or by means of one or more additional electron transfer agents. A redox mediator that includes a polymeric main chain can also be referred to as a "redox polymer".

The term "reference electrode" includes a) reference electrodes and b) reference electrodes that also act as counter-electrodes (ie counter-electrodes / reference electrodes), unless otherwise indicated.

The term "counter-electrode" includes a) counter-electrodes and b) counter-electrodes that also act as reference electrodes (ie counter-electrodes / reference electrodes), unless otherwise indicated.

In general, the membrane of the present invention is formed by crosslinking a modified polymer containing nitrogenous heterocyclic groups within a mixed alcohol-buffer solvent and allowing the membrane solution to cure over time. The polymer comprises poly (nitrogen-containing heterocyclic constituent) as part of its main chain, and additional elements, which include a zwitterionic moiety, a hydrophobic moiety and, optionally, a biocompatible moiety. The resulting membrane is capable of limiting the flow of an analyte from a space, such as a space associated with a biofluid, to another space, such as a space associated with an enzyme-containing detection layer. An amperometric glucose sensor constructed with a wired enzyme detection layer and a layer that limits the diffusion of glucose of the present invention, is very stable and has a wide range of linear detection.

Polymers containing heterocyclic nitrogen

The polymer of the present invention has the general formula that follows

Formula 1a in which the horizontal line represents the main polymer chain, A is an alkyl group substituted with a water-soluble group, preferably a negatively charged group, such as sulphonate, phosphate or carboxylate, and more preferably, a group of a strong acid such as sulfonate, so that the quaternized heterocyclic nitrogen to which it is attached is zwitterionic; D is a copolymer component of the polymer, as described

5 additionally later; each of n, l and p, is independently an average number of a polymer unit or associated polymer units, shown in the parentheses closest to the left; and q is a number of a unit or units of the polymer indicated in square brackets.

Nitrogenous heterocyclic groups of Formula 1a include, although not limited to, pyridine, imidazole, oxazole, thiazole, pyrazole or any of its derivatives. Preferably, the nitrogen heterocyclic groups are,

10 independently, vinylpyridine, such as 2-, 3-, or 4-vinylpyridine, or vinylimidazole, such as 1-, 2-, or 4-vinylimidazole. More preferably, the nitrogen heterocyclic groups are independently 4-vinylpyridine, so that the most preferable polymer is a poly (4-vinylpyridine) derivative. An example of such a poly (4-vinylpyridine) of the present invention has the following general formula,

Formula 1b;

in whose formula A, D, n, l, p and q are as described above with respect to Formula 1a,

Although the polymer of the present invention has the above general Formula 1a or Formula 1b, it should be noted that when A is a strong acid, such as a stronger acid than a carboxylic acid, component D is optionally, so that p can be equal to zero. Such a polymer of the present invention has the

twenty General formula that follows:

Form 1c:

in which formula A is a strong acid and the nitrogen heterocyclic groups, n, lyq are all as described above. A sulfonated and fluorinated carboxylic acid are examples of suitably strong acids. It is believed that when A is a sufficiently strong acid, the heterocyclic nitrogen to which it is attached becomes zwitterionic and is therefore capable of forming intermolecular electrostatic bonds with the crosslinking agent during membrane formation. It is believed that these intermolecular electrostatic junctions provide another level of cross-linking, beyond the covalent bonds typical of cross-linking, and therefore make the membrane that is obtained more robust. As a result, when A is a properly strong acid, component D, which is often

30 a reinforcing component, such as styrene, can be omitted from the polymers of Formulas 1a and 1b above. When A is a weaker acid, so that heterocyclic nitrogen is not zwitterionic or capable of forming intermolecular electrostatic bonds, the polymer of the present invention includes D, as illustrated in Formulas 1a and 1b above.

Examples of A include, but are not limited to, sulfopropyl, sulfobutyl, carboxypropyl and carboxyphenyl. In one embodiment of the invention, group A has the formula -LG, in which L is a linear or branched alkyl linking agent of C2-C12, optionally and independently substituted with an aryl, alkoxy, alkenyl group , alkynyl, -F, -Cl, -OH, aldehyde, ketone, ester or amido, and G is a negatively charged carboxy or sulfonate group. The alkyl part of the substituents of L have 1-6 carbon atoms and are preferably an aryl group, -OH or amido.

5 A may be attached to the nitrogen heterocyclic group by quaternization with an alkylating agent containing a suitable L-binding agent and a negatively charged G group, or a precursor group that can be converted to a negatively charged G group at a later stage. Examples of suitable alkylating agents include, although not limited to, 2-bromoethanesulfonate, propanosultone, butanosultone, bromoacetic acid, 4-bromobutyric acid and 6-bromohexanoic acid. Examples of alkylating agents containing

10 a precursor group includes, although not limited to, ethyl bromoacetate and methyl 6-bromohexanoate. Ethyl and methyl ester groups of these precursors can easily be converted into a negatively charged carboxy group by standard hydrolysis.

Alternatively. A can be attached to the nitrogen heterocyclic group by quaternizing the nitrogen with an alkylating agent containing an additional reactive group, and subsequent coupling by standard methods, of

fifteen this additional reactive group to another molecule that contains a negatively charged G group and a reactive group. Typically, one of the reactive groups is an electrophilic group and the other reactive group is a nucleophilic group. Selected examples of reactive groups and the bonds formed by their interactions are set forth in Table 1.

Table 1: Examples of reactive groups and resulting bonds By way of example, A can be linked to the nitrogen heterocyclic groups of the polymer by quaternization of the heterocyclic nitrogens with 6-bromohexanoic acid and subsequent coupling of the carboxyl group to the amino group of the 3- acid amino-1-propanesulfonic acid, in the presence of a carbodiimide coupling agent.

<dl><dt>First reactive group </dt><dd>Second reactive group Resulting link </dd></dl>

<dl><dt>Ester activated ** </dt><dd>Amine Friend </dd></dl>

<dl><dt>Acrylamide </dt><dd>Thiol Thioether </dd></dl>

<dl><dt>Acyl azide </dt><dd>Amine Friend </dd></dl>

<dl><dt>Acyl halide </dt><dd>Amine Friend </dd></dl>

<dl><dt>? Carboxylic acid </dt><dd>Amine Friend </dd></dl>

<dl><dt>Aldehyde or Ketone </dt><dd>Hydrazine Hydrazone </dd></dl>

<dl><dt>Aldehyde or Ketone </dt><dd>Hydroxyamine Oxime </dd></dl>

<dl><dt>Alkyl halide </dt><dd>Amine Alkylamine </dd></dl>

<dl><dt>Alkyl halide </dt><dd>? Carboxylic acid Ester </dd></dl>

<dl><dt>Alkyl halide </dt><dd>Imidazole Imidazolium </dd></dl>

<dl><dt>Alkyl halide </dt><dd>Pyridine Pyridinium </dd></dl>

<dl><dt>Alkyl halide </dt><dd>Alcohol / phenol Ether </dd></dl>

<dl><dt>Alkyl halide </dt><dd>Thiol Thioether </dd></dl>

<dl><dt>Alkyl sulfonate </dt><dd>Thiol Thioether </dd></dl>

<dl><dt>Alkyl sulfonate </dt><dd>Pyridine Pyridinium </dd></dl>

<dl><dt>Alkyl sulfonate </dt><dd>Imidazole Imidazolium </dd></dl>

<dl><dt>Alkyl sulfonate </dt><dd>Alcohol / phenol Ether </dd></dl>

<dl><dt>Anhydride </dt><dd>Alcohol / phenol Ester </dd></dl>

<dl><dt>Anhydride </dt><dd>Amine Friend </dd></dl>

<dl><dt>Aziridine </dt><dd>Thiol Thioether </dd></dl>

<dl><dt>Aziridine </dt><dd>Amine Alkylamine </dd></dl>

<dl><dt>Aziridine </dt><dd>Pyridine Pyridinium </dd></dl>

<dl><dt>Epoxy </dt><dd>Thiol Thioether </dd></dl>

<dl><dt>Epoxy </dt><dd>Amine Alkylamine </dd></dl>

<dl><dt>Epoxy </dt><dd>Pyridine Pyridinium </dd></dl>

<dl><dt>Halotriazine </dt><dd>Amine Aminotriazine </dd></dl>

<dl><dt>Halotriazine </dt><dd>Alcohol Triazinyl ether </dd></dl>

<dl><dt>Imido ester </dt><dd>Amine Amidine </dd></dl>

<dl><dt>Isocyanate </dt><dd>Amine Urea </dd></dl>

<dl><dt>Isocyanate </dt><dd>Alcohol Urethane </dd></dl>

<dl><dt>Isothiocyanate </dt><dd>Amine Thiourea </dd></dl>

<dl><dt>Maleimide </dt><dd>Thiol Thioether </dd></dl>

<dl><dt>Sulfonyl halide </dt><dd>Amine Sulfonamide </dd></dl>

<dl><dt>* Activated esters, as understood in the art. they generally include succinimidyl esters, benzotriazolyl. or aryl substituted by groups that capture electrons such as sulfo, nitro, cyano or halo; or carboxylic acids activated by carbodiimides.</dt><dd /></dl>

D is a component of a poly (nitrogen heterocyclic-co-D) polymer of formula 1a or 1b. The examples of D

5 they include, even when not limited to, phenylalkyl, alkoxystyrene, hydroxyalkyl, alkoxyalkyl, alkoxycarbonylalkyl, and a molecule containing polyethylene glycol or a polyhydroxy group. Some poly (heterocyclic-co-D) polymers suitable as starting materials for the present invention are commercially available. For example, poly (2-vinylpyridine-co-styrene), poly (4-vinylpyridine-co-styrene) and poly (4-vinylpyridine-butyl methacrylate) polymers can be purchased from Aldrich Chemical Company, Inc. Other polymers

10 Poly (heterocyclic nitrogen-co-D) can be easily synthesized by any person skilled in the art of polymer chemistry, using well known methods. Preferably, D is a styrene component or a C1-C18 alkyl methacrylate component of a polyvinylpyridine-poly-D such as poly (4-vinylpyridine-co-styrene)

or poly (4-vinylpyridine-co-butyl methacrylate), more preferably, the first. D can contribute to various desirable membrane properties, including, but not limited to, hydrophobic properties,

fifteen hydrophilic, solubility, biocompatibility, elasticity and resistance. D may be selected for the optimization or "fine tuning" of a membrane obtained with the polymer in terms of its permeability for an analyte and its non-permeability for an undesirable interfering component, for example.

The letters n, l and p designate, respectively, the average number of each copolymer component in each polymer unit. The letter q is one for a block copolymer or a number greater than one for a copolymer

twenty with a number of repeating polymer units. By way of example, the value of q for a polymer of the present invention can be; 950, approximately, when n, l and p are, respectively, 1, 8 and 1. The letter q is therefore related to the overall molecular weight of the polymer. Preferably, the average molecular weight of the polymer is greater than about 50,000, more preferably, more than about 200,000, and, most preferably, more than about 1,000,000.

25 The polymer of the present invention may further comprise an optional copolymer, as illustrated by the general formula that follows:

Formula 2a

in whose formula the main polymer chain, A, D, n, l, p and q are as described above in what

30 regards Formulas 1a-1c; m is the average number of a unit or several associated polymer units set forth in the parentheses closest to the left; and B is a modifier. When the nitrogenous heterocyclic groups are substituted pyridine at position 4, as preferred, the polymer of the present invention is a derivative of poly (4-vinylpyridine) and has the following general formula, Formula 2b, set forth below:

Formula 2b

On the other hand, when A is a suitably strong acid, as described above, copolymer D is optional, in which case the polymer of the present invention has the general formula that follows:

Formula 2c:

In any of Formulas 2a-2c, B is a modifying group that can add to the membrane any desired chemical, physical or biological properties. Such desired properties include analyte selectivity, hydrophobic, hydrophilic, elasticity and biocompatibility. Examples of modifiers include the following: negatively charged molecules that can minimize the entry into the membrane of interfering negative charge chemical compounds; Hydrophobic hydrocarbon molecules that can increase the adhesion between the membrane and the sensor material that serves as a substrate; hydrophilic, hydroxylated or polyhydroxylated molecules that can help hydrate and add biocompatibility to the membrane; silicone polymers that can add elasticity and other properties to the membrane; and constituents of polyethylene glycol, which are known to increase the biocompatibility of biological materials (Bergstrom, K., et al., J. Biomed. Mat. Res. 26, 779 (1992)). Other examples of B include, although not limited to them, a metal chelating agent, such as a calcium chelating agent, and other biocompatible materials. A polyethylene glycol suitable for modifying the biocompatibility of the membrane generally has a molecular weight of from about 100 to about 20,000, preferably from about 500 to about 10,000, and more

twenty preferably, from about 1,000 to about. 8,000

Modifier B can bind to the heterocyclic nitrogens of the polymer, directly or indirectly. In direct binding, nitrogen heterocyclic groups can be reacted with a modifier containing an alkylating group. Suitable alkylating groups include, although not limited to, alkyl halide, epoxide, aziridine and sulfonate esters. In indirect binding, the heterocyclic nitrogens of the polymer can be

25 quaternized with an alkylating agent that possesses an additional reactive group, and then binds to a molecule that has the desired property and a suitable reactive group.

As described above, the B-containing copolymer is optional in the membrane of the present invention, so that when m of Formula 2a-2c is zero, the membrane has the general formula of Formulas 1a-1c, respectively. The relative amounts of the four copolymer components, the nitrogen heterocyclic group 30 containing A, the optional nitrogen heterocyclic group containing B, the nitrogen heterocyclic group, and D, may be expressed as percentages as follows: [n / ( n + m + l + p)] x 100%, [m / (n + m + l + p)] x 100%, [l / (n + m + l + p)] x 100 y [p / ( n + m + l + p)] x 100%, respectively. Suitable percentages are 1-25%, 0-15% (when the nitrogen heterocyclic group containing B is optional) or 1-15%, 20-90% and 0-50% (when D is optional), or 1- 50%, respectively, and the preferable percentages are 5-20%,

35 0-10% (when the nitrogen heterocyclic group containing B is optional) or 1-10%, 60-90% and 5-20%, respectively.

Specific examples of suitable polymers of the general formulas, Formulas 3 –6, are shown below.

Examples

Synthesis Examples of Polyvinylpyridine Polymers

Examples that illustrate the syntheses of various polyvinylpyridine polymers according to the present invention are given below. The figures provided are approximate.

Example 1: Synthesis of a polymer of Formula 3

By way of illustration, an example of the synthesis of a polymer of Formula 3 is now provided. A solution of poly (4-vinylpyridine-co-styrene) (styrene content: 10%) (20 g, Aldrich) was stirred in 100 ml of dimethylformamide (DMF), at 90 ° C, and 6-bromohexanoic acid (3.7 g) in 15-20 ml of DMF was added-The resulting solution was stirred at 90 ° C for 24 hours and then poured in 1.5 liters of ether, after which the solvent was dried. The remaining gummy solid was dissolved in MeOH (150-200 ml) and filtered with suction through a funnel with a medium poroside sintered glass filter plate to separate the undissolved solid. The filtrate was added slowly to rapidly stirred ether (1.5 liters) in a beaker. The resulting precipitate was collected by suction filtration and dried at 50 ° C under high vacuum for 2 days. The polymer had the following parameters: [n / (n + l + p)] x 100% '10%; [l / (n + l + p)] x 100% '80%; and [p / (n + l + p)] x 100% '10%.

Example 2: Synthesis of a polymer of Formula 5

By way of illustration, an example of the synthesis of a polymer of the above Formula 5 is now provided. A solution of poly (4-vinylpyridine-co-styrene) (10% styrene) (20 g, Aldrich) was stirred in 100 ml of anhydrous DMF at 90 ° C, methanesulfonic acid (80 mg) was added and then 2 g of methoxylated PEG epoxide (5,000 molecular weight) (Shearwater Polymers, Inc.) in 15-20 ml of anhydrous DMF. The solution was stirred at 90 ° C for 24 hours and 1,3-propanosultone (2.32 g) was added within 10 ml of anhydrous DMF. The resulting solution was continuously stirred at 90 ° C for 24 hours and then cooled to room temperature and poured into 800 ml of ether. The solvent was decanted and the remaining precipitate was dissolved in hot MeOH (200 ml), filtered with suction, precipitated again in 1 liter of ether, and then dried at 50 ° C under high vacuum for 48 hours. The resulting polymer had the following parameters: [n / (n + m + l + p)] x 100% '10%, [m / (n + m + l + p)] x100%' 10%; [l / (n + m + l + p)] x 100% '70%; and [p / n + m + l + p)] x 100% '10%.

Example 3: Synthesis of a polymer having a polyhydroxylated B modifier

By way of illustration, an example of the synthesis of a polymer having a polyhydroxy B modifier is now provided, as schematically illustrated below. Various polyhydroxy compounds that have biocompatibility properties are known. (U.S. Patent No. 6,011,077). The synthesis below illustrates how a modifying group that possesses a desired property can be attached to the polymer backbone by means of a linker.

1,3-propanosultone (0.58 g, 4.8 mmol) and 6-bromohexanoic acid (1m85 g, 9.5 mmol) are added to a solution of poly (4-vinylpyridine-co-styrene) (10% of styrene) (10 g) dissolved in 60 ml of anhydrous DMF. The resulting solution is stirred at 90 ° C for 24 hours and then cooled to room temperature. Then, O- (N-succinimidyl) -N, N, N ', N'-tetramethyluronium tetrafluoroborate (TSTU) (2.86 g, 9.5 mmol) and N, N- are successively added to the solution diisopropylethylamine (1.65 ml, 9.5 mmol). After stirring the solution for 5 hours, N-methyl-D-glucamine (2.4 g. 12.4 mmol) is added and the resulting solution is stirred at room temperature for 24 hours. The solution is poured into 500 ml of ether and the precipitate is collected by suction filtration. The collected precipitate is then dissolved in MeOH / H2O and the resulting solution is subjected to membrane ultrafiltration

10 using the same solvent MeOH / H2O. The dialyzed solution is evaporated to dryness to obtain a polymer with the following parameters: [n / (n + m + l + p)] x 100% '10%; [(m / (n + m + l + p)] x 100% '10%; [l / (n + m + l + p)] x 100%' 70%; and [p / (n + m + l + p)] x 100% '10%.

Crosslinking Agents

The crosslinking agents of the present invention are molecules that possess at least two reactive groups, by

fifteen for example, bi-, tri-, or tetra-functional groups, capable of reacting with the nitrogen heterocyclic groups, (pyridine groups), or other reactive groups contained in A, B or D of the polymer. Preferably, the reactive groups of the crosslinking agents are slow reaction alkylating groups that can quaternize the nitrogenous heterocyclic groups, such as the pyridine groups of the polymer. Alkylating groups include, but are not limited to, derivatives of polyethylene glycol or polypropylene glycol, epoxide (glycidyl group), aziridine, alkyl halide and sulphonate esters. The alkylating groups of the crosslinking agents are preferably glycidyl groups. Preferably, the glycidyl crosslinking agents have a molecular weight of from about 200 to about 2,000 and are water soluble or soluble in a water miscible solvent, such as an alcohol. Examples of suitable crosslinking agents include, but are not limited to, diglycidyl ether of polyethylene glycol with a molecular weight of about 200 to about 600, and N, Ndiglycidyl-4-glycidyloxyaniline.

It is desirable to have a slow crosslinking reaction during the distribution of the membrane solution so that the membrane coating solution has a reasonable life span for large-scale fabrications. A faster crosslinking reaction results in a coating solution that changes viscosity rapidly, which makes coating difficult. Ideally, the crosslinking reaction is slow during the distribution of the membrane solution, and accelerated during the curing of the membrane at room temperature or at elevated temperature, when possible.

Membrane formation and sensor manufacturing

An example of a process for producing a membrane of the present invention is now described. In this example, the polymer of the present invention and a suitable crosslinking agent are dissolved in a solvent containing a buffer, typically a mixed solvent of alcohol-buffer, to obtain a membrane solution. Preferably, the buffer has a pH of about 7.5 to about 9.5 and the alcohol is ethanol. More preferably, the buffer is a 10 mM 2- (4- (2-hydroxyethyl) -1-piperazine) ethanesulfonate (HEPES) buffer (pH 8), and the volume ratio of ethanol to buffer is from about 95 to 5 to about 0 to

100 A minimum amount of buffer is necessary for the chemical crosslinking reaction, especially if an epoxy or aziridine crosslinking agent is used. The amount of solvent needed to dissolve the polymer and the crosslinking agent may vary depending on the nature of the polymer and the crosslinking agent. For example, a higher percentage of alcohol may be needed to dissolve a polymer and / or a relatively hydrophobic crosslinking agent.

The ratio of polymer to crosslinking agent is important for the nature of the final membrane. By way of example, if an inadequate amount of crosslinking agent or an extremely large excess of crosslinking agent is used, the crosslinking is insufficient and the membrane is weak. On the other hand, if an amount of crosslinking agent is used greater than adequate, the membrane is too crosslinked so that the membrane is very brittle and / or prevents diffusion of the analyte. Therefore, there is an optimal ratio of a given polymer with respect to a crosslinking agent since it must be used to prepare a desirable or useful membrane. By way of example, the optimum weight ratio of polymer to crosslinking agent is typically from about 4: 1 to about 32: 1 for a polymer of any of the above Formulas 3-6 and a crosslinking agent of the type of diglycidyl ether of polyethylene glycol, which has a molecular weight of about 200 to about

400 More preferably, this range is from about 8: 1 to about 16: 1. In addition, by way of example, the optimum ratio, by weight, of polymer to crosslinking agent is typically about 16: 1 for a polymer of the above Formula 4, in which [n / (n + l + p)] x 100% '10%; [l / (n + l + p)] x 100% '80%, and [p / (n + l + p)] x 100%' 10%, or for a polymer of the above Formula 5, in which [n / (n + m + l + p)] x 100% '10%, [m / (n + m + l + p)] x 100%' 10%, [l / (n + m + l + p)] x 100% '70%, [p / (n + m + l + p)] x 100%' 10%, yr '110, and a crosslinking agent of the polyethylene glycol diglycidyl ether type, which has a weight molecular of about 200.

The membrane solution can be deposited as a coating on a variety of biosensors that can benefit from being provided with a membrane placed on the detection layer containing an enzyme. Examples of such biosensors include, although not limited to, glucose sensors and lactate sensors. (See U.S. Patent No. 6,134,461 to Heller et al.). The coating process may comprise any commonly employed technique, such as rotating coating, immersion coating or by depositing droplets of the membrane solution on the detection layers, and similar processes, followed by curing in ambient conditions for 1-2 days. typically. Particular details of the coating process (such as duration of immersion, frequency of dives, number of dives, or similar details) may vary, depending on the nature (ie, viscosity, concentration, composition,

or the like) of the polymer, the crosslinking agent, the membrane solution, the solvent and the buffer, for example. Conventional equipment, such as the DSG DIL-160 immersion or molding system from NIMA Technology in the United Kingdom, can be used for the coating process.

Sensor manufacturing example

Although the sensors themselves are not in accordance with the present invention, the manufacture of sensors typically consists in depositing a detection layer containing an enzyme on a working electrode, modeling the detection layer on the detection layer. membrane that limits diffusion and, optionally but preferably, also on the counter electrode and the reference electrode. The operative procedure given below refers to the manufacture of a two electrode sensor such as that shown in Figures 2A-2C. Sensors that have other configurations such as a three electrode design can be prepared using similar methods.

A particular example of manufacturing a sensor in which the figures are approximate is now provided. A solution of the detection layer was prepared from a 7.5 mM HEPES solution (0.5 µL, pH 8), containing

5 1.7 µg of compound L, polymeric osmium mediator, described in the published application, of the Patent Cooperation Treaty (PCT), international publication no. WO 01/36660 A2; 2.1 µg glucose oxidase (Toyobo); and 1.3 µg of polyethylene glycol diglycidyl ether (molecular weight 400). The formula of compound L is shown below.

10 The detection layer solution was deposited on carbon-ink working electrodes and cured at room temperature for two days to produce several sensors. A membrane solution was prepared by mixing 4 volumes of a polymer of the above Formula 4, dissolved at 64 mg / l in EtOH buffer solution, 60% / HEPES, 20% (10 mM, pH 8), and one volume of ether polyethylene glycol diglycidyl (molecular weight 200), dissolved at 4 mg / ml in EtOH buffer solution, 80% / HEPES, 20% (10 mM, pH 8). The sensors described were

fifteen immersed three times in the membrane solution, approximately 5 seconds per dive, with a time period of approximately 10 minutes between consecutive dives. The sensors were then cured at room temperature and normal humidity for 24 hours.

An approximate chemical structure of a section of a typical membrane prepared according to the present invention

is illustrated in Figure 1. Such a membrane can be used in a variety of sensors, such as

twenty two or three electrode sensors that have been described herein. By way of example, the membrane can be used in a two-electrode amperometric glucose sensor, as shown in Figure 2A-2C (collectively, Figure 2) and described below.

The amperometric glucose sensor, 10, of Figure 2, comprises a substrate, 12, located between a working electrode, 14, typically based on carbon, and an Ag / AgCl reference counter electrode / electrode, 16 . A

25 sensor or detection layer, 18, is placed on the working electrode. A membrane or membrane layer, 20, encapsulates the complete glucose sensor, 10, including the Ag / AgCl reference counter electrode / electrode.

The detection layer, 18, of the glucose sensor, 10, consists of glucose oxidase and a polymeric mediator constituted by a cross-linked osmium complex, as described in the published PCT Application, cited above, international publication no. WO 01/36660 A2. The formulation containing the enzyme and the mediator, which can be used in the detection layer, and methods for applying it to an electrode system, are known in the art, for example, according to US Pat. No. 6,134,461. According to the present invention, the

membrane layer was formed by immersing the sensor three times in a membrane solution comprising 4 mg / ml of polyethylene glycol diglycidyl ester (molecular weight 200, approximately) and 64 mg / ml of a polymer of the above Formula 4, in which [n / (n + l + p)] x 100% '10%; [l / (n + l + p)] x 100% '80%; and [p / (n + l + p)] x 100% '10%, and curing at room temperature and normal humidity for at least 24 hours, for example approximately 1 to 2 days, the sensor submerged three times. The value of q for such a membrane layer can be; 950, approximately, where n, l and p are 1, 8 and 1, respectively.

Membrane surface modification

The polymers of the present invention have a large number of nitrogen heterocyclic groups, such as pyridine groups, only a small percentage of which is used in crosslinking during membrane formation. Thus, the membrane has an excess of these groups present both within the membrane matrix and on the membrane surface. Optionally, the membrane can then be modified by placing another layer of material on the surface of the membrane rich in nitrogenous heterocyclic groups or rich in pyridine. For example, the membrane surface can be modified by adding a layer of polyethylene glycol to enhance biocompatibility. In general, the modification may consist of coating the membrane surface with a modification solution, such as a solution comprising the desired molecules that possess a reactive alkylating group, then washing the coating solution with a suitable solvent to remove the molecules. in excess. This modification should result in a monolayer of the desired molecules.

The membrane, 20, of the glucose sensor, 10, which is illustrated in Figure 2, can be modified as described above.

Experimental examples

Examples of experiments that demonstrate the properties and / or efficacy of sensors that have membranes that limit diffusion according to the present invention are provided below. The figures provided are approximate.

Calibration experiment

In a first example, a calibration experiment was carried out in which fifteen sensors that lacked membranes were tested simultaneously (Group 1) and, separately, eight sensors that had membranes that limit diffusion according to the present invention, were tested at the same time (Group 2), all at 37 ° C. In Group 2, the membranes had been prepared from polymers of the above Formula 4 and crosslinking agents of the polyethylene glycol diglycidyl ether type (PEGDGE) of molecular weight 200, approximately. In the Group 1 and Group 2 calibration experiment, the sensors were placed in a PBS buffered solution (pH 7) and the output current of each of the sensors was measured as the glucose concentration was increased. The measured output currents (! A for Group 1; nA for Group 2) were then averaged for the two groups, 1 and 2, and plotted against glucose concentrations (mM) as illustrated in the graph of Calibration of Figure 3.

As illustrated, the calibration curve of Group 1 sensors that lack membranes is approximately linear over a very small range of glucose concentrations, from zero to approximately 3 mM, or 5 mM at most: This result indicates that membrane-free sensors are insufficiently sensitive to changing glucose concentrations at elevated glucose concentrations such as 10 mM, which is well below the upper limit of glucose concentration, important from the point of view. 30 mM clinical, approximately. On the contrary, the calibration curve of the Group 2 sensors that had membranes that limit diffusion according to the present invention is substantially linear over a relatively wide range of glucose concentrations, for example, from zero to 30 approximately mM, as demonstrated by the line of best fit (y = 1,2502x + 1,1951; R2 '0.977), which is also illustrated in Figure 1. This result demonstrates the considerable sensitivity of the sensors provided with membranes for glucose concentrations, in low, medium and high glucose concentrations, and of particular importance in the high limit of clinically relevant glucose concentrations of 30 mM, approximately.

Stability experiment

In a second example, a stability experiment was carried out in which a sensor lacking a membrane and a sensor having a membrane limiting diffusion according to the present invention were tested simultaneously at 37 ° C. The membrane-provided sensor had a membrane prepared starting from the same polymer and the same crosslinking agent as those of the Group 2 sensors described above in the calibration experiment. In this stability experiment, each sensor was placed in a buffered solution containing PBS (pH 7) that had a fixed concentration of glucose, 30 mM, and the output current of each sensor was measured. The measured output currents (! A for the membraneless sensor; nA for the membrane-provided sensor) were plotted against time (hours) as illustrated by the stability graph in Figure 4.

As shown, the stability curve of the membraneless sensor decays rapidly over time, at a fall rate of approximately 4.69%! A per hour. This result indicates lack of stability of the membraneless sensor. On the contrary, the stability curve of the membrane-provided sensor according to the present invention shows a relative constancy over time, or with no appreciable fall over time, the falling rate being only 0.06% nA per hour. . This result demonstrates the considerable stability and reliability of these sensors. That is, at a concentration of 30 mM glucose, while the membraneless sensor loses sensitivity at a rate of almost 5% per hour over a period of approximately 20 hours, the membrane-provided sensor according to the present invention showed virtually no loss of sensitivity during the same period.

Response Capability Experiment

Ideally, the membrane of an electrochemical sensor should not prevent communication between the sensor's detection layer and the biological fluid or fluid that contains the analyte of interest. That is, the membrane must respond rapidly to changes in analyte concentration.

In a third example, a response capacity experiment was carried out in which eight sensors having diffusion membranes according to the present invention were tested simultaneously (Group 3), all at 37 ° C. The Group 3 sensors had membranes prepared from the same polymer and the same crosslinking agents as those of the Group 2 sensors described in the previous calibration experiment. In this response capacity experiment, the eight sensors were placed in a buffered solution containing PBS (pH 7) whose glucose concentration was increased stepwise over time, as illustrated by the glucose concentrations indicated in Figure 5, and The output current of each of the sensors was measured. The measured output currents (nA) were then averaged for Group 3 and plotted against time (real time, hour: minute: second), as shown in the graph of response capacity in Figure 5.

The response capacity curve of the Group 3 sensors, which had membranes that limit diffusion according to the present invention, have discrete steps that quickly simulate staggered increases in glucose concentration. As illustrated, the output current quickly jumps from one plateau to the next once the glucose concentration increases. This result demonstrates the considerable responsiveness of the sensors provided with membranes of the present invention. The responsiveness of these electrochemical sensors fitted with membranes makes them ideal for detecting analytes, such as for detecting glucose.

Motion Sensitivity Experiment

Ideally, the membrane of an electrochemical sensor should not be affected by the motion or movement of biological fluids or fluids that contain the analyte of interest. This is particularly important for a sensor that is implanted in a body, such as a human body, since movement can cause noise associated with the motion and can be quite frequent.

In this fourth example, a motion-sensitivity experiment was conducted in which a sensor A lacking a membrane was tested and, separately, a sensor B having a membrane limiting diffusion according to the present invention was tested, all at 37 ° C. Sensor B had a membrane prepared starting from the same polymer and the same crosslinking agent as those of the Group 2 sensors described in the calibration experiment. In this experiment, for each of the tests, the sensor was placed in a beaker with a buffered solution containing PBS (pH 7) and a magnetic stirrer. The glucose concentration of the solution was increased stepwise over time, in the same manner described in the previous response capacity experiment, as indicated by the various mM marks in Figure 6. The agitator was activated during each stepwise increase in glucose concentration and was inactivated some time later, as illustrated by the "agitation" and "unstirred" signs indicated in Figure 6. This activation and deactivation of the agitator was repeated cyclically to several levels of glucose concentrations and the output current of each of the sensors was measured throughout the experiment. The measured output currents (! A for sensor A; nA for sensor B) were plotted against time (minutes), as shown in the motion-sensitivity graph of Figure 6.

As indicated, the output current of the sensor A, without membrane, is greatly affected by the conditions of agitation versus those of without stirring over the range of glucose concentrations used in the experiment. On the contrary, the output current of the sensor B, which has membranes that limit diffusion according to the present invention, is virtually unaffected by the conditions of agitation versus those of without stirring up to a glucose concentration of approximately 10 mM, and only slightly affected by these conditions at a glucose concentration of approximately 15 mM. This result demonstrates the considerable stability of the sensors provided with membranes of the present invention in both agitated and non-agitated environments. The stability of these electrochemical sensors provided with membranes in a fluid movement environment makes them idelaes to detect an analyte within a moving body.

Sensor Reproducibility Experiment

Immersion coating, or molding, of membranes is typically carried out using immersion machines such as the DSG DIL-160 from NIMA Technology of the United Kingdom. Reproducible molding of membranes has been considered quite difficult to achieve (Chen, T., et al., In Situ Assembled Mass-Transport Controlling Micromembranes and Their Application in Implanted Amperometric Glucose Sensors, Anal .. Chem., Vol. 72, No 16, Pages 3757-3763 (2000)). Surprisingly, the sensors provided with membranes of the present invention can be produced quite reproducibly, as demonstrated in the experiment described now.

Four batches of sensors (Lots 1-4) were prepared separately by immersing the sensors three times in a membrane solution using molding equipment and then allowed to cure. In each of the four batches, the membrane solutions were prepared starting from the polymer of Formula 4 and diglycidyl ether of polyethylene glycol (PEDGE) as a crosslinking agent, of molecular weight 200, approximately (as in Group 2 and the other Groups described above ), using the same operating procedure. The membrane solutions for Lots 1 and 2 were prepared separately for each and separately from the membrane solution used for Lots 3 and 4. The membrane solution for lots 3 and 4 was the same, even when the Lot 3 and Lot 4 sensors were coated by immersion at different times using a different molding equipment. That is, Lots 1, 2 and 3 were coated by immersion using a constructed, non-commercial system, and Lot 4 was coated by immersion using the DSG D1L 160 system referred to above.

Calibration tests were carried out on each batch of sensors, at 37 ° C. For each batch, the sensors were placed in buffered solution containing PBS (pH 7) and the output current (nA) of each of the sensors was measured as the glucose concentration (mM) was increased. For each sensor in each of the four lots, a calibration curve was prepared based on a graph of the current output versus glucose concentration, as shown in Figure 7B (Lot 1: 5 sensors), Figure 7C (Lot 2: 8 sensors), Figure 7D (Lot 3: 4 sensors) and Figure 7E (Lot 4: 4 sensors). The average slopes of the calibration curves of each batch were as follows:

Lot 1: average slope = 1.10 nA / mM (CV = 5%);

Lot 2: average slope = 1.27 nA / mM (CV = 10%);

Lot 3: average slope = 1.15 nA / mM (CV = 5%); and

Lot 4: Average slope = 1.14 nA / mM (CV = 7%).

In addition, for each batch, the current output of the batch sensors was averaged and plotted against glucose concentration as shown in Figure 7A. The average slope of lots 1-4 was 1.17 nA / mM (CV = 7.2%).

The slopes of the curves within each lot and from lot to lot are grouped very closely, which shows a considerably small variation. The results demonstrate that the sensors prepared with membranes according to the present invention provide quite reproducible results both within a batch and from batch to batch.

The above examples demonstrate many of the advantages of the membranes of the present invention and of the sensors employing such membranes. Particular advantages of the sensors employing the membranes of the present invention include sensitivity, stability, responsiveness, movement compatibility , ease of calibration and ease and reproducibility of manufacturing.

Various aspects and features of the present invention have been explained or described with respect to opinions or theories, even though it is to be understood that the invention is not subject to a particular opinion or theory. Various modifications and processes, as well as numerous structures to which the present invention may be applicable, will be readily apparent to those skilled in the art to which the present invention is directed, by reviewing the specification. Although the various aspects and features of the present invention have been described with respect to various embodiments and specific examples herein, it is to be understood that the invention is entitled to protection within the full scope of the appended claims.