A portable paper-based colorimetric sensor for palladium detection via β-Cyclodextrin-capped silver nanoparticles

Monitoring of aquatic environments contaminated with heavy metals requires rapid, selective, and sensitive analytical methods. This study reports the development of a novel paper-based colorimetric sensor utilising silver nanoparticles (AgNPs) synthesised via a green route and stabilised by β-Cyclodextrin (β-CDs). The AgNPs were synthesised under optimised conditions (1.5 × 10−4 M AgNO3, 5.0 × 10−3 M β-CDs, and pH 12) and adsorbed onto a paper substrate. The synthesised nanomaterials were characterised using UV-Visible (UV-Vis) spectrophotometry, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy with energy-dispersive X-ray analysis (FESEM-EDX), particle size analysis (PSA), and zeta potential analysis. The AgNPs exhibited a maximum absorbance at 407 nm, spherical morphology with diameters of 17.06–29.5 nm, and a zeta potential of −15.5 ± 0.1 mV, indicating moderate colloidal stability. The developed sensor demonstrated rapid and highly selective detection of Pd2+ ions within 10 minutes, driven by an aggregation-induced colorimetric transition from yellowish-orange to greyish-white. Digital image analysis of red, green, and blue (RGB) intensities revealed a strong linear correlation (R2 = 0.9994) within the optimal working range of 1–5 ppm, achieving low limits of detection (0.11 ppm) and quantification (0.38 ppm). Furthermore, application to real lake water samples confirmed excellent recovery and precision, consistent with Inductively Coupled Plasma Mass Spectrometry (ICP-MS) validation. This simple, selective, and low-cost sensor demonstrates strong potential for sustainable, on-site monitoring of Pd2+ contamination in aquatic systems.