A novel single-chip and multiplexed read-out circuit for multi-electrode electrochemical sensors, in standard 0.18 μm UMC CMOS technology, is presented. The circuit is a part of a fully-integrated biochip (in design) for the detection of multiple metabolites. The proposed topology is based on the potentiostat approach, and it is devoted to detect currents within the range of 250 pA - 650 nA for an electrode active area of 0.25 mm2. The need of multi-metabolites monitoring asks for a system with multi-working electrodes. In the proposed configuration, switches select one working electrode at each clock phase, while the others are short-circuited to the reference one, in order to nullify the injected current inside the counter. Low noise and low energy topology (50μW at 1.5V of voltage supply) is employed for the control amplifier. The linearity of the proposed read-out circuit allows accuracy better than 0.1%.