A CMOS sensor platform with 1.2 µm × 2.05 µm electroless-plated 1024 × 1024 microelectrode array for high-sensitivity rapid direct bacteria counting

A CMOS sensor platform with a bacteria-sized (1.2 μm × 2.05 μm) Au electroless-plated 1024 × 1024 microelectrode array for high-sensitivity rapid direct bacteria counting is demonstrated. For high-sensitivity direct pathogen counting, Au microelectrodes are required to be as small as the target cell. In this work, by improving a self-aligned electroless plating technique, the size of microelectrodes on a CMOS sensor chip was successfully reduced to 1.2 μm × 2.05 μm, corresponding to 1/20th of the smallest size reported in literature. Two test chips with 1024 × 1024 and 32 × 32 sensor arrays were fabricated in a 0.6-μm CMOS process and microelectrodes were formed on them using electroless plating. The uniformity among the 1024 × 1024 electrodes arranged with a pitch of 3.6 μm × 4.45 μm was optically verified. In addition, the trenches on each microelectrodes for improving sensitivity were developed and optically verified for the first time. Cyclic voltammetry (CV) measurements made using the 32 × 32 sensor array chip with 6-μm square electroless-plated microelectrodes successfully demonstrated the platform´s effectiveness in the direct counting of HeLa cells.