PEI-capped osmium nanoclusters (Os NCs) for dual-mode fluorescence and electrochemical detection of cyanide: A robust platform for environmental sensing.

Cyanide (CN-), a pervasive and highly toxic industrial pollutant, poses acute environmental and health risks due to its high bioavailability and disruption of cellular respiration. Conventional detection methods often lack sensitivity, portability, or real-time applicability, underscoring the need for advanced sensing technologies. Herein, we report the development of polyethyleneimine (PEI)-capped osmium nanoclusters (Os NCs) as a dual-mode sensor for highly sensitive fluorescence and electrochemical detection of CN-. The PEI-assisted synthesis yielded biocompatible, solvent-free Os NCs with uniform ultrasmall sizes (2-3 nm, confirmed by TEM) and remarkable stability (up to 3 months) exhibiting with detection limits of 12 nM (fluorescence) and 12.93 nM (electrochemistry), with broad linear ranges of 0.03-24.0 μM and 0.01-200 μM, respectively. The detection mechanism is based on electrostatic interaction between the positively charged amine groups (-NH2) of PEI and the negatively charged CN-, forming a conjugated structure that quenches fluorescence via metal to ligand charge transfer (MLCT) while enhancing electrochemical current. The electrochemical sensor was successfully applied to real samples, including roof tiles leachates, with validation of results by ion chromatography (IC). Additionally, CN- recoveries from spiked food and biological samples ranged from 93.65 to 102.66 % and 89.46-97.43 %, respectively. These results establish Os NCs as a cost-effective, robust platform for sustainable CN- monitoring in environmental and biological matrices.