A micromechanical electrometer is applied to the label-free detection of biomolecular interactions and electrochemical charge sensing. The primary element of the electrometer is a micromechanical variable capacitor to modulate and convert a dc charge to an ac voltage output, thereby limiting the effects of low frequency noise on charge detection. At room temperature and ambient pressure the noise-limited charge resolution of a micromechanical electrometer based on this principle is found to be 3 e/ sqrt(Hz), enabling the potential detection of charged single molecule binding on electrode surfaces. The detection principle is validated by several experiments. Biomolecular binding experiments are conducted on an external gold electrode situated within a custom-designed flow cell and electrically connected to the micromachined electrometer. The concepts are validated by demonstrating the detection of biotin-streptavidin binding and DNA hybridization. Furthermore, it is shown that the electrometer can be applied for the detection of the redox system ferrocyanide/ferricyanide to describe Nernstian behaviour due to well defined charge transfer on the electrode surface at different concentration ratios as expected.