We introduce a facile assessment of binding kinetics at bioreceptive redox-active interfaces as a means of quantifying target proteins. This is achieved by monitoring the redox capacitance (Cr) of a receptor-modified conductive polymer interface under continuous flow. Exemplified with the quantification of C-reactive protein (CRP), capacitance analyses resolve both the association and dissociation regimes in real-time. Significantly, the rate of electrochemical signal change within the association regime is a sensitive function of target concentration, enabling marker assaying down to picomolar levels, comparable to end-point assays, in 15 s. This reagentless proof-of-principle methodology is envisioned to be widely applicable to the facile quantification of a range of other pertinent, clinically relevant targets.