Nanoscale potassium sensing based on valinomycin-anchored fluorescent gold nanoclusters

Gold nanoclusters are a smart platform for sensing potassium ions (K⁺). They have been synthesized using bovine serum albumin (BSA) and valinomycin (Val) to protect and cap the nanoclusters. The nanoclusters (Val-AuNCs) produced have a red emission at 616 nm under excitation with 470 nm. In the presence of K⁺, the valinomycin polar groups switch to the molecule's interior by complexing with K⁺, forming a bracelet structure, and being surrounded by the hydrophobic exterior conformation. This structure allows a proposed fluorometric method for detecting K⁺ by switching between the Val-AuNCs' hydrophilicity and hydrophobicity, which induces the aggregation of gold nanoclusters. As a result, significant quenching is seen in fluorescence after adding K⁺. The quenching in fluorescence in the presence of K⁺ is attributed to the aggregation mechanism. This sensing technique provides a highly precise and selective sensing method for K⁺ in the range 0.78 to 8 µM with LOD equal to 233 nM. The selectivity of Val-AuNCs toward K⁺ ions was investigated compared to other ions. Furthermore, the Val-AuNCs have novel possibilities as favorable sensor candidates for various imaging applications. Our detection technique was validated by determining K⁺ ions in postmortem vitreous humor samples, which yielded promising results.