This paper presents a neuromorphic CMOS Delta-Sigma modulator for the robust and energy-efficient readout of amperometric electrochemical sensors. The circuit makes use of an adaptive integrate-and-fire scheme to deliver asynchronous A/D conversion and attenuation of background currents with minimal power requirements. The modulator reuses the dynamic characteristics of the electrode-electrolyte interface for quantization noise shaping, and it offers potentiostatic control of the voltage difference between working and reference electrodes of a three-electrode electrochemical cell. Electrical simulation results are reported at transistor level for a smart electrochemical sensor currently being integrated in a 1.2-V 65-nm 9-metal CMOS technology. The frontend exhibits a tunable off-band rejection of 20dB with a peak SNR of 61dB and 70-uW power consumption.