A chemical sensor for analyte solutions utilizes AC excitation of a sample distributed in one or more micro-wells of a measurement device. The sensors utilize narrowband filtering of the measured signal(s), resulting in a large reduction in noise. Synchronous detection is utilized to provide high discrimination of the desired signal from noise or interfering sources. Conductance and by extension impedance is measured by applying a constant alternating current (AC) voltage across the electrodes of each micro-well and measuring the resulting current.