Plasmonic property of gold nanoparticles to predict nanozyme activity: towards the colorimetric detection of manganese(ii).

Because of its remarkable versatility and indispensable properties, the need for manganese for different applications has grown tremendously. The ever-growing need and the beneficiation of manganese ore, however, have increased the emission of manganese into the environment, such as into water sources, negatively affecting human and animal health. This necessitates a simple method for the analysis of manganese in water resources. The intrinsic peroxidase-like activity of gold nanoparticles (AuNPs) is considered for the detection of Mn2+. The peroxidase-like activity of AuNPs using 3,3',5,5'-tetramethylbenzidine (TMB) as a chromogenic substrate decreased upon the addition of Mn2+ to the AuNP nanozyme sensing system. The decrement in the peroxidase-like activity is related with the enlargement of the AuNP size and is dependent on the concentration of Mn2+. A linear relationship between absorbance intensity and Mn2+ concentration was established for the concentration ranges of 5-60 µM and 60-90 µM. Using the slope and the standard deviation of the linear line for the concentration range of 5-60 µM, the limit of detection (LOD) was determined to be 0.227 µM. The sensing system exhibited excellent selectivity for Mn2+. In conclusion, the proposed method opens an avenue for the detection of different target analytes based on the enzyme-like activities of metallic nanoparticles, which could be tuned by aggregation.