Smartphone-assisted fluorometric detection of heavy metals using gold nanoclusters with sequential addition of carbon dots

Abstract

A smartphone-assisted fluorometric method was developed for the detection of lead (Pb²⁺), mercury (Hg²⁺), and copper (Cu²⁺) using gold nanoclusters (AuNCs) as fluorescent probes. The detection mechanism is based on fluorescence enhancement by Pb²⁺ and quenching by Hg²⁺ and Cu²⁺. To enhance detection sensitivity and visual contrast, carbon dots (CDs) were added into the reaction mixture through serial addition at AuNCs/CDs ratio of 1:0.02 and 1:0.05. A key novelty of this work is the integration of tunable AuNCs/CDs ratios with smartphone-based RGB analysis, enabling semi-quantitative detection without the need for advanced instrumentation. RGB values extracted using smartphone application facilitated both quantitative and qualitative analysis of heavy metal ions. The method demonstrated selectivity for Pb²⁺, Hg²⁺, and Cu²⁺ with limits of detection (LOD) of 220 μg·L⁻¹, 100 μg·L⁻¹, and 390 μg·L⁻¹, respectively. In addition, flow field-flow fractionation coupled with inductively coupled plasma mass spectrometry (FlFFF-ICP-MS) revealed AuNC aggregation in response to increasing Pb²⁺ concentrations. The AuNCs/CDs probe provide the high %recovery with relative standard deviations (RSDs) below 10 %, indicating good precision and effective detection of Hg²⁺ and Pb²⁺ for water samples. This proposed method offers a simple, low-cost, and portable approach for detecting heavy metals in water samples.