Blood glucose optical bio-implant: Preliminary design guidelines

A preliminary investigation into the design of a near-infrared (NIR) optical bio-implant for accurate measurement of blood glucose concentration is reported. The use of an array of electrically pumped vertical-cavity surface-emitting laser (VCSEL) diodes at specific wavelengths for high-power narrow single-frequency emission leads to a high signal-to-noise ratio (SNR) in the measured NIR absorption spectrum while maximizing the sensor's sensitivity to small absorption changes. A Quantum well infrared (QWI) photodetector senses the received optical power after passage through the blood sample, followed by an artificial neural network (ANN) for the measurement of glucose in a whole blood matrix. For an independent test set made with bovine blood, the optimal ANN topology for processing the two selected spectral bands yielded a standard error of prediction of 0.42 mM (i.e., 7.56 mg/dl) over the concentration range of 4–20 mM.