A bipolar photodiode array (PDA) protein chip is presented for the detection of E. coli O157:H7. Through unique design of the bipolar PDA microchip, the device was able to detect E. coli O157:H7 directly on the surface of the bipolar PDA. The bipolar PDA microchip maintained low noise level in the entire process of on-chip protein assay and demonstrated high performance of analog signal processing. At every reaction step of the on-chip bioassay, stability of wet photodiode detection elements was confirmed by monitoring the variance of their photosignals with respect to the irradiated red beam. The background signal represented less than 1.8% variance with respect to maximum signal of photodiode detection elements. As a result of using the on-chip bioassay, any complicated optical alignment and components could be removed in the constructed protein chip. This protein chip enables direct optical detection of E. coli O157:H7 eliminating the need of conventional expensive microplate reader that is incompatible with size of sampling platform of protein chip. The independence of the constructed protein chip on conventional microplate reader can contribute greatly to further miniaturization of protein chip and field usable lab-on-a-chip.