Portable on-site colorimetric kit using stable gold nanorod powder for tracing hydrogen sulfide in various environmental samples

Abstract

On-site detection of hydrogen sulfide (H₂S), a toxic byproduct of microbial decomposition, is essential for environmental surveys, sewage tracing, and occupational safety. While existing gold nanorods (Au NRs)-based colorimetric methods offer portability and sensitivity, their practicality is hindered by the instability of enzymes and colloidal nanoparticles. Herein, we present an enzyme-free, portable H₂S detection device using Au NRs powder, ensuring highly sensitive and reliable colorimetric detection while enhancing long-term applicability. The sensing strategy involves two steps: H₂S microextraction and colorimetric assay. First, H₂S is accumulated into a NaOH aqueous drop from a complex sample matrix via headspace single-drop microextraction (HS-SDME) using sulfamic acid. In the colorimetric assay, dissolved H₂S reduces KIO₃ to I₂ in glycine-HCl buffer (pH 2.6), which etches Au NRs in the presence of Br^- and CTA⁺, causing a blue shift in the plasmon band with a distinct color change. This method achieves a visual detection limit of 0.05 μM, approximately 10 times lower than the Methylene Blue method. The use of HS-SDME ensures excellent selectivity against coexisting ions (≥10-fold) and small organic molecules (100-fold). Validation with real samples yielded recoveries of 92.40 %-109.51 %, demonstrating reliability in environmental monitoring and river pollution tracing. To simplify detection, we developed a liquid-free test kit containing an H₂S microextraction tube (sulfamic acid powder), a colorimetric assay tube (Au NRs powder and solid buffer), and a portable heating device. This enzyme-free sensor ensures long-term stability and practicality, advancing Au NRs-based sensors for environmental monitoring.