Smartphone-integrated sensing platform based on a “one-stone-three-birds” strategy for real-time quantitative detection of Ag(I) ions

Heavy metal ion contamination poses a serious threat to human health and ecological balance, emphasizing the need for sensitive detection methods to maintain water quality and safeguard public safety. To meet this challenge, an integrated quantitative detection platform based on smartphone image capture and a built-in RGB color analysis app, following a “one-stone-three-birds” strategy, was developed. It allows for rapid, sensitive, and on-site detection of silver ions (Ag(I)) in actual water samples. In the presence of Ag(I) ions, the aggregation of AuNPs with ammonium thioglycolate (ATG), which acts as a multifunctional agent (an aggregation inducer, charge modulator, and recognition unit), is inhibited, resulting in a notable hypsochromic shift in the surface plasmon resonance (SPR) spectrum of AuNPs and a color change from gray-blue to pink-red, depending on the target level. Quantitative analysis is performed by measuring the color signal intensity of AuNPs after adding Ag(I) ions with a smartphone equipped with an RGB color detector. The detection mechanism was verified further through transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV-Vis spectrophotometry (UV-Vis). The smartphone-integrated detection method exhibited a linear range of 0.1 to 8 µM and a detection limit of 10.4 nM. Results from this platform, paired with a smartphone, were validated against data from atomic absorption spectrometry (AAS). This smartphone-based detection approach offers the benefits of simplicity, speed, and low cost, making it suitable for environmental monitoring of Ag(I) ions.