Polypyrrole nanoribbon based chemiresistive immunosensors for viral plant pathogen detection

Label-free chemiresistive sensors based on a polypyrrole (PPy) nanoribbon (width: 500 nm, thickness: 25–100 nm) were batch-fabricated by a lithographically patterned nanowire electrodeposition (LPNE) technique. A plant pathogen specific antibody was covalently conjugated on the surface of the structure via N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide (EDC)/N-hydrosuccinimide (NHS) crosslinking. The sensing performance was investigated by the detection of cucumber mosaic virus (CMV). The sensitivity of the nano-immunosensors was enhanced by reducing the electrical conductivity from 1 to 0.005 S cm−1 or by decreasing the thickness of the nanoribbon from 100 nm to 25 nm. The reduction in the ionic strength of the pH buffer solutions (i.e., 10 mM PBS to 10 mM PB) also enhanced the sensitivity. However, the reliability and reproducibility of the sensors were significantly reduced by the buffer change. The optimum sensor showed excellent sensitivity with a low and upper detection limit of 10 ng ml−1 and 100 μg ml−1, respectively, which is much lower than the low detection limit of traditional enzyme-linked immunosorbent assays (ELISAs) (i.e., 3 μg ml−1).