Beyond the benefit afforded to supermarket shoppers and food manufacturers, nanotechnology-based sensors have the potential to revolutionize the speed and accuracy with which industries or regulatory agencies can detect the presence of molecular contaminants or adulterants in complex food matrices.
Many of these assays are based on observed color changes that occur to metal nanoparticle solutions in the presence of analytes.
For example, gold nanoparticles (AuNPs) functionalized with cyanuric acid groups selectively bind to melamine (Fig. 10), an adulterant used to artificially inflate the measured protein content of pet foods and infant formulas; the melamine-induced aggregation causes AuNPs to undergo a reproducible, analyte-concentration-dependent color change from red to blue, which can be used to precisely measure the melamine content in raw milk and infant formula at concentrations as low as 2.5 ppb with the naked eye.
A similar approach examined test samples for the presence of melamine by adding in sequential fashion separate solutions of gold ions and a chemical reductant .
In this system, when melamine is present in a sample, it binds to the reductant and prevents AuNP formation; thus, test samples with no melamine turn fully red during the assay due to AuNP formation via reaction between the gold ions and the reductant.
Colorimetric detection of melamine in raw milk using AuNPs and crown-ether-modified thiols with a limit of detection of 6 ppb has also been reported