A device for monitoring the concentration level of a constituent in tissue or a
body fluid sample, such as glucose concentration in blood, has a
laser light source which is modulated about a center emission frequency to probe the absorption spectrum of the constituent being monitored, a
laser driver circuit for tuning and modulating the
laser light, a
photodetector for detecting light from the
laser light source transmitted through the sample as the modulation frequency of the laser is tuned, and a demodulator for demodulating the
transmitted light and detecting variations in magnitude at
harmonics of the modulation frequency to assess the concentration level of that constituent. The device utilizes short-
wavelength near-
infrared laser light to monitor blood glucose levels, and could also be used for
drug screening and diagnosis of other medical conditions as well. In one embodiment, the device is used to monitor blood glucose level externally from the body and non-invasively by trans-illumination through a
thin layer of
skin, without the need for physical penetration of the
skin. In another embodiment, the device is used as an intravenous sensor deployed through a
catheter, and its output can be used to control an
insulin pump to stabilize the patient's blood glucose levels.