Noninvasive determination of blood constituents using an array of modulated laser diodes and a photoacoustic sensor head.

Using photoacoustic laser spectroscopy, the noninvasive determination of blood constituents like hemoglobin and glucose is feasible. The aim of our investigations is the development of a sensor which is suitable for continuously noninvasive monitoring of blood glucose concentrations in diabetic patients. For this purpose a photoacoustic sensor head was developed and coupled via an optical fiber bundle to an array of 8 laser diodes emitting at various wavelengths in the near infrared region. Applying a special modulation scheme, the tiny changes of the absorption coefficient of whole blood caused by the variations of blood glucose concentrations could be measured. A resolution of 70 mg/dl was achieved, a value which is already close to the clinical requirements for a continuously working glucose sensor.