An AuNP-based indicator for rapid on-site detection of strontium ion

Strontium (Sr) has attracted significant attention due to its radioactivity and physiological toxicity. Rapid and precise detection of Sr²⁺ was critical for risk mitigation, particularly in accidents involving strontium leaks. However, the existing methods often compromise accuracy, speed, and user-friendliness, making on-site detection of Sr²⁺ challenging. Herein, we developed a gold nanoparticle (AuNP)-based indicator for Sr²⁺ through leveraging high-affinity binding between Sr²⁺ and G-quadruplex (G4) DNA to regulate the thioflavin T (ThT)-induced charge neutralization assembly of AuNPs. The proposed indicator achieved a detection limit of 2.5 nM, significantly lower than the maximum allowable concentration of Sr²⁺ in drinking water (17.1 μM). To enable on-site detection of Sr²⁺, we designed a self-constructed portable suitcase housing all necessary components of the indicator (∼0.14 $ per test), and a smartphone app for colorimetric analysis. The proposed indicator was successfully explored for on-site detection of Sr²⁺ in rivers across Chengdu, Kunming, and Xishuangbanna, China, demonstrating its reliability for environmental monitoring.