Highly specific fingerprinting of alkaline earth metal ions by a tunable plasmonic nanosensor array based on nanoaggregation of metallochromic dyes-AuNPs.

Metal ions, specifically alkaline earth metal ions (AEMIs; Mg, Ca, Sr, and Ba), have essential roles in industrial processes, medical testing, and environmental evaluation; therefore, developing sensitive detection methods capable of their contents is highly required. To this aim, we have designed an absorbance nanosensor array using three metallochromic dyes decorated on AuNPs and have monitored variations in AuNP plasmonic profiles upon the addition of AEMIs in different buffer and pH solutions. The array is designed in a tunable size of 2 × 3 × 1(2/3); as the type buffer and pH of solution are fixed, the number of dyes can be changed in three individual modes, three binary modes, and a ternary mode, respectively. Owing to the different binding affinities of AEMIs toward dyes in different buffer and pH solutions, fingerprint-like plasmonic profiles with different levels of aggregation AuNPs were generated for all modes of array. These aggregation AuNP-based fingerprint profiles in the wavelengths of 500, 525, 550, 575, 600, 625, 650, 675, 700, 725, and 750 nm were used to discriminate the AEMIs by applying pattern recognition methods including linear discrimination analysis (LDA) and hierarchical clustering analysis (HCA) to identify each AEMI in the range 2.1-24.7 μM. Accordingly, limits of detection (LODs) values of 0.013 (±3.13), 0.014 (±2.99), 0.020 (±4.17), and 0.017 (±4.31) μM were obtained the Mg, Ca, Sr, and Ba, respectively. The results revealed that all the modes of array could well differentiate complex mixtures of the AEMIs. Our suggested array also exhibited a good performance in the differentiation of AEMIs in real samples and a certified reference material (CRM) sample.