Modified carbon black as label in a colorimetric on-chip immunoassay for histamine

Abstract

The present study demonstrates the modification of carbon black and its usage as a detection label in colorimetric immunoassays on a microarray format. We show the feasibility using a binding inhibition assay for histamine, which is a marker of food freshness and quality. The modified carbon nanoparticles (CNPs) were characterized by determining functional surface groups, elemental composition, size, surface charge and dispersion stability to investigate the influence of modification on the assay performance with the overall goal to optimize assay conditions and enhance signal strength. Carbon nanoparticles were oxidized and further modified with silanes with different functional end groups (thiol, epoxy, amine) 3-glycidoxypropyltrimethoxysilane being the most effective modification. Additionally, 1-pyrenebutanoic acid N-succinimidyl ester (PSE) was tested as conjugation agent allowing semi-quantitative read-out by naked eye over a broad histamine range (0-600 μg/mL), similar to just oxidized CNPs. The dispersion stability was enhanced with acrylic polymer Atlox and dispersion agent xanthan. However, no concentration dependent response towards histamine was observed. With oxidized CNPs read-out could be done by naked eye; otherwise an office scanner was needed for detection. Lower zeta potential was recorded after oxidation, resulting in better colloidal stability. Electrostatic stabilization was enough to create stable suspensions, and further modification was not necessary for the antibody coupling and stability in the assay.