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Abstract

A method for determining the concentration of an analyte in a biological sample comprising the steps of: (1) providing an optical measuring instrument that comprises at least one thermally controllable optical measuring element that comes into contact with the surface of the biological sample; (2) applying an inert, thermally conductive, optically transparent coupling agent to the at least one optical measuring element or to the surface of the biological sample or both so that the coupling agent will be disposed at the interface of the surface of the biological sample and the at least one optical measuring element; (3) measuring optical properties of the biological sample by means of the optical measuring instrument; and (4) correlating the optical properties of the biological sample with the concentration of the analyte in the biological sample. A coupling agent suitable for this invention must have several properties to enable it to help decrease measurement variation, especially drift. One of the most important properties is sufficiently high optical stability that the optical properties of the coupling agent do not change even during prolonged experiments, such as oral glucose tolerance tests. Secondly, the coupling agent should have sufficiently high thermal conductivity to allow fast, efficient heat transfer between the optical probe and the biological sample. Third, the coupling agent should have sufficiently high viscosity to prevent it from migrating from the measurement area. Yet, it should also have sufficiently low viscosity to allow sufficient contact between the optical probe and the biological sample and to permeate into any small pockets between the probe and the biological sample that would otherwise be filled with the air. Fourth, the coupling agent should be inert. Material from the coupling agent should not diffuse into the biological sample and material from the biological sample should not diffuse into the coupling agent.

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