Label-free colorimetric immunoassay for the simple and sensitive detection of neurogenin3 using gold nanoparticles

Neurogenin3 (ngn3), as a marker for pancreatic endocrine precursor cells and an essential ingredient in the development of islet cells, was quantitatively detected for the first time. Based on a non-cross-linking specific interaction mechanism, a label-free colorimetric immunoassay for the synthetic peptide fragment of ngn3 (SKQRRSRRKKAND) using glutathione (-Glu-Cys-Gly, GSH) functionalized gold nanoparticles (GNPs) is reported. The anti-ngn3 antibody conjugated GNPs (GNP-Ab) was formed through electrostatic interaction upon the addition of anti-ngn3 antibody to the GSH-modified GNPs solution. Monobinding of the positively charged ngn3 to the negatively charged GNP-Ab will minimize the electrostatic repulsion between nanoparticles by neutralizing the surface charge, and then agglomeration is induced by an increasing salt concentration. Under the optimal conditions, the assay showed a linear response range of 50–300 ng/mL for the peptide with a detection limit being 20 ng/mL. The preliminary study on ngn3 opens up an innovative insight to detect short synthetic peptide fragment of antigen, and may own an opportunity for practical applications in clinical diagnosis and therapeutics.