Visual and photometric determination of histamine using unmodified gold nanoparticles

The authors describe a colorimetric approach for on-site monitoring of histamine based on the use of gold nanoparticles (AuNPs) that have a negatively charged surface due to the presence of adsorbed citrate ions. Histamine has two basic functional groups, an aliphatic amino group and an imidazole ring. Under the experimental conditions, the protonated aliphatic amino group drives the imidazole ring into close proximity to the AuNPs due to electrostatic attraction. This accelerates the replacement of citrate ions by the imidazole ring because of the strong affinity between imidazole and AuNPs. As a consequence, the two groups synergistically induce the aggregation of the AuNPs and trigger a visible color change from red to blue. The minimum visually detectable histamine concentration is 1.81 μM, which is comparable to the limit of detection (LOD) of the electrochemical approaches at a signal-to-noise ratio of 3:1. When using absorbance at 522 nm, the LOD is lowered to 38 nM. The method was applied to the determination of histamine in fish samples.