Non-invasive apparatus and method for determining and monitoring glucose concentrations in human subjects. Glucose level is estimated through the effect of glucose on biological cells with glucose dependencies, e.g., red blood cells. The invention is based on the interaction of such cells with oscillating electric field gradients. The response of biological cells depends on factors including shape, size, and electrical charge distribution. The field gradient causes the cells to undergo characteristic motion which is detected by light beam scattering. The autocorrelation of the scattered light is computed, and the Fourier transform (FT) is performed to produce a characteristic velocity spectrum in which the peaks are characteristic of the cell &ldquo；bio-electrical&rdquo； states. The glucose level is estimated through measurements of changes of FT with changes in glucose levels after calibration with standard glucose methods.
