A Nanoelectronic Enzyme-Linked Immunosorbent Assay for Detection of Proteins in Physiological Solutions

Semiconducting nanowires are promising ultrasensitive, label‐free sensors for small molecules, DNA, proteins, and cellular function. Nanowire field‐effect transistors (FETs) function by sensing the charge of a bound molecule. However, solutions of physiological ionic strength compromise the detection of specific binding events due to ionic (Debye) screening. A general solution to this limitation with the development of a hybrid nanoelectronic enzyme‐linked immunosorbent assay (ne‐ELISA) that combines the power of enzymatic conversion of a bound substrate with electronic detection is demonstrated. This novel configuration produces a local enzyme‐mediated pH change proportional to the bound ligand concentration. It is shown that nanowire FETs configured as pH sensors can be used for the quantitative detection of interleukin‐2 in physiologically buffered solution at concentrations as low as 1.6 pg mL−1. By successfully bypassing the Debye screening inherent in physiological fluids, the ne‐ELISA promises wide applicability for ligand detection in a range of relevant solutions. An electronic alternative to the enzyme‐linked immunosorbent assay (ELISA) is demonstrated by using enzymatic conversion of a substrate into a local pH change (see image) and an indium oxide nanowire in an FET configuration as a pH sensor. Concentrations of cytokine (IL‐2) as low as 1.6 pg mL−1 are successfully detected in physiological solutions.