An apparatus and methods for electrostatic-based sensing and detection of charges and charged materials displayed on a surface. In a general embodiment, a method for electrostatically sensing charges or charged materials by comparing the electrostatic interaction between a capture surface and a reference surface. Assays to detect binding or interactions between a capture surface and a material to be detected are also described. We also describe a sensitive and label-free electrostatic readout of DNA or RNA hybridization in a microarray format and using a microfluidic device. The electrostatic properties of the hybridized particles are measured using the positions and motions of charged microspheres. This approach enables sensitive, non-destructive electrostatic imaging. Changes in surface charge density as a result of specific molecular interaction can be detected and quantified with great sensitivity, and in the presence of a complex background.
STATEMENT OF GOVERNMENTAL SUPPORT
 This invention was made with government support under Contract No. DE-AC02-05CH11231 awarded by the U.S. Department of Energy. The government has certain rights in the invention.