We report here on in vitro and in vivo experiments that are intended to explore the feasibility of photoacoustic spectroscopy as a tool for the noninvasive measurement of blood glucose. The in vivo results from oral glucose tests on eight subjects showed good correlation with clinical measurements but indicated that physiological factors and person-to-person variability are important. In vitro measurements showed that the sensitivity of the glucose measurement is unaffected by the presence of common blood analytes but that there can be substantial shifts in baseline values. The results indicate the need for spectroscopic data to develop algorithms for the detection of glucose in the presence of other analytes.

A preliminary study of using a gelatin-based in vivo tissue model to investigate some of the near infrared photoacoustic characteristics that may influence the sensitivity of non-invasive photoacoustic detection of blood glucose in human tissue is described. It is shown that the optical absorption change due to glucose in the near infrared region is small and that the pulsed photoacoustic technique may offer a better detection sensitivity than other conventional optical transmission measurement systems being developed for blood glucose monitoring.

A glucose concentration analysis of human whole blood samples has been accomplished using pulsed laser photoacoustic spectroscopy (LPAS). Using a CO2 laser operating with microJ pulse energies, the technique has shown the required discrimination and sensitivity to determine glucose concentrations within the physiological range (18-450 mg dl-1) in whole blood samples. The sensitivity achieved with this system is comparable to that of the existing commercial enzyme-based diagnostic systems presently used in hospital clinical chemistry environments. The technique is compared with other optical methods that have recently been used for glucose determination, and its applicability for use in the development of an in vivo monitor is discussed.

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A time-resolved photoacoustic technique has been applied to the study of dissolved and dispersed absorbers in aqueous systems. The temporal pressure profiles generated from colloidal graphite and glucose solutions were measured, and it was found that the amplitude of the photoacoustic signal of both the glucose and the colloidal graphite solutions increase linearly with concentration and that acoustic signal time delay yields the acoustic velocity. The logarithm of the photoacoustic signal amplitude changes linearly with the time delay, with a slope that is proportional to the product of the acoustic velocity and the optical absorption that can thus be determined.