Analyte Sensor, and Associated System and Method Employing a Catalytic Agent

Abstract

An analyte sensor for use in connection with a biofluid is described. The analyte sensor may comprise any suitable interface between the biofluid and a derivative of the biofluid and any suitable transducer of information concerning an analyte. At least one catalytic agent is provided in a locale or vicinity of the interface. The catalytic agent, such as a proteinaceous agent or a non-proteinaceous, organic-metal agent, is sufficient to catalyze the degradation of reactive oxygen and / or nitrogen species that may be present in the vicinity of the interface. An analyte-sensing kit and a method of sensing an analyte are also described.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of pending application no. 11 / 007,617 filed on Dec. 7, 2004, which is a continuation in part of application no. 10 / 819,498 filed Apr. 6, 2004, which is a continuation in part of application No. 10 / 775,604 filed on Feb. 9, 2004 now abandoned, the disclosure of each of which are incorporated herein by reference for all purposes, and each of which are assigned to assignee, Abbott Diabetes Care, Inc., of Alameda, Calif.FIELD OF THE INVENTION [0002] This invention generally relates to the provision of catalytic agents within the locale of an interface between a biofluid and derivatives of the biofluid, where the derivative of the biofluid contacts the sensing mechanism of an analyte sensor. The invention additionally relates to analyte sensors that make use of any of a variety of transducing mechanisms, and which may be placed internally, transcutaneously, or externally, relative to a body. BACKGROUND OF TH...

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Benefits of technology

[0010] This invention generally relates to the provision of biocompatibility-promoting catalytic agents to in vivo analyte sensors within the locale of an interface between a biofluid and a derivative of the biofluid, where the derivative of the biofluid is the fluid that contacts the transducing mechanism sensor. The locale of the interface includes locations that may be within the interface or chemically incorporated into it, immediately adjacent to or in contact with the interface, or at a distance near enough to the interface that the effect of the catalytic agents is such that it alters the composition or population of chemical species that comprise the chemical environment surrounding the interface. These catalytic agents include both organic, proteinaceous compounds, such as enzymes, as well as non-proteinaceous organic-metal compounds that degrade reactive oxygen species or reactive nitrogen species in the locale of the sensor. In this catalytic degradation process, such a reactive species moves through a metabolic pathway in which it is a reactant. In this manner, the concentration of such a reactive species in solution may be reduced. According to some aspects of the invention, catalytic agents engage reactive oxygen and nitrogen species of biological origin within the biofluid. Further, according to some aspects of the invention, that catalytic activity enhances the biocompatibility of sensors, more particularly, one or more aspects of biocompatibility that may manifest in the form of improvements in sensor performance. Improvement or enhancement of sensor performance may coincide or be associated with higher quality data, as determined by various statistical methods that evaluate internal consistency or agreement with data from other sources. Higher quality data may include, for example, data that are more accurate with respect to reference data from standard strip-reading sensors, data more reflective of actual systemic levels of analyte, or data that are more internally consistent and as such contain less noise. Enhanced sensor performance may also include a lengthening of the effective lifetime of a sensor, the effective lifetime being reflected in an extended period of the delivery of accurate data.

[0015] The catalytic agents, or more particularly, the organic-metal catalysts of the present invention, catalyze the degradation of reactive oxygen species and reactive nitrogen species, such as superoxide, hydrogen peroxide, and peroxynitrite, by way of example. Examples of such catalysts include superoxide dismutase / catalase catalysts, including catalytic enzymes and non-proteinaceous mimics of such enzymes. One particular example of a superoxide / dismutase catalyst is manganese 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine chloride (MnTPyP). Such a catalyst may be incorporated into a membrane that covers the sensing surface of a transcutaneous electrochemical sensor, or incorporated into the dialysis membrane of microdialysis-based sensing systems. As a result of its presence in the locale of the interface between the biological fluid and the sensing mechanism, the catalyst reduces the local concentration of reactive oxygen species, such as those mentioned above. While this invention is not bound by any proposed theory, it is thought that reactive oxygen species are present in the locale of the interface by virtue of metabolic activity of cells of the immune system, such as neutrophils, which are generally engaged in the initial phases of a foreign body response to the presence of the sensor. The reactive oxygen species in the locale of sensors may have effects that are deleterious to the sensor and may also further accelerate the recruitment of immune cells to the sensor site. The reactive oxygen species may further have effects on the metabolism of other cells in the locale, which may create local areas that are depleted of glucose, which, in turn, would disconnect local glucose values from systemic glucose values. Through the action of the superoxide dismutase / catalase catalysts and the consequent reduction of local concentrations of reactive oxygen species, the sensor may be rendered more biocompatible and its performance may be improved. Examples of enhanced sensor performance include a decrease in failure rate, an increase in operating lifetime, a decrease in the level of signal-interfering noise, and the prevention or decrease in incidence of spurious hypoglycemic incident reporting, by way of example.

Problems solved by technology

For example, the operation and performance of an in vivo enzyme-based biosensor may be complicated by high rates of analyte flux, such that the relationship between the concentration of glucose in a sample fluid and the response from the biosensor becomes non-linear.

Still other challenges, such as usage limitations, have become evident.

For example, data from studies of the recently available, transcutaneous CGMS system of Medtronic MiniMed, indicate spurious, low-glucose-reading incidents, particularly during periods of stillness, such as when a subject is asleep.

While nocturnal hypoglycemic events are indeed a clinical reality, especially in patients being aggressively treated with insulin, it has become recognized that false indications of such events are particular fallibilities of the CGMS system that complicate the interpretation of the data obtained using this system.

Spurious low-glucose-reading incidents are very problematic in the monitoring and treatment of a diabetic subject, as such incidents wrongly indicate that a euglycemic subject is hypoglycemic.

As an example, when a spurious, low-glucose reading is used as a signal to control insulin dosage, a subject may receive an improper or a reduced dose of insulin and thus be put at risk for becoming hyperglycemic.

Spurious low glucose readings can be further problematic as they may lead to incorrectly calibrated sensors, resulting in subsequent false, high glucose readings, which may reduce the credibility and usefulness of the alarm function, by way of example.

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