NADPH-mediated seedless in situ formation of gold or gold-platinum nanoparticles for the enzymatic determination of atropine

The without-seeds in situ formation of gold nanoparticles from NADPH and its application to the colorimetric determination of atropine (a tropane alkaloid) in cereals is reported. The method is based on a chemical hydrolysis, followed by an enzymatic oxidation by NADP catalyzed by tropinone reductase in the presence of Au(III) or Au(III)/Pt(II). During this reaction, the formed NADPH reduces the metal ion precursor to AuNPs (or AuPtNPs) and the absorption due to the plasmon band (550 nm or 575 nm) is measured. The method (AuPtNPs) allows the determination of the analyte in the concentration range 0.025 to 0.09 mM with an RSD of 3% (n = 5) and is applied to its determination in spiked buckwheat samples using the standard addition method, with 96.9 ± 2.0% recovery. It is also demonstrated that NAD(P)H and NADH have different kinetics for AuNP generation, which could be used to discriminate between these two cofactors.