An On-chip Chemiluminescent Immunoassay for Bacterial Detection using in Situ-synthesized Cadmium Sulfide Nanowires with Passivation Layers

The passivation layers of an in situ-synthesized cadmium sulfide (CdS) nanowire (NW) photosensor were prepared for two reasons: (1) to improve the physical stability of the NW on an interdigitated electrode and (2) to enhance the immobilization efficiency of proteins for the on-chip immunoassay. The passivation layer was estimated to have suitable optical properties, and the photoresponse of photosensor was increased after the formation of passivation layer. The immobilization efficiency of a parylene-H film through covalent bonding was compared with the immobilization of Z-domains through physical adsorption. Finally, on-chip chemiluminescent immunoassay of bacteria was carried out by immobilizing antibodies against Escherichia coli through Z-domains for the orientation control of antibodies. The limit of detection was determined to be less than 10⁴E. coli/mL (n=3), and the sensitivity of bacterial detection was estimated to be 0.339 pA/E. coli/mL (n=3) with a linearity factor (R²) of 0.999. These results showed that the on-chip chemiluminescent immunoassay for bacterial detection could be performed using passivation layer coated CdS NW photosensor.