Deep eutectic solvent-driven self-assembly of metal mercaptide complexes with enzyme-mimicking activities for detection of uric acid through one-step cascade catalytic reaction

This work presents a generic strategy to create a series of metal mercaptides complexes via coordination self-assembly between transition metals (Mn, Cu, Co, Fe, and Ni) and cysteine (Cys) by forming the sulfur-metal bridges. This strategy involves dissolving metal chlorides and Cys into deep eutectic solvents (DES), followed by the precipitation of metal mercaptides complexes (such as Cys-Mn) by adding water as an antisolvent, where DES serves as the solvent, shape directing, and capping agent, thereby preventing the formation of other metal impurities. Interestingly, the prepared complexes possess both laccase and peroxidase-like properties, allowing the design of a technique for the detection of L-3,4-dihydroxyphenylalanine ( l -DOPA) and uric acid, respectively. The prepared Cys-Mn can linearly oxidize l -DOPA with its concentrations from 0.1 to 130 μM and the detection limit was calculated to be 75.5 nM. Additionally, the Cys-Mn can mimic the activity of peroxidase towards oxidization of o-phenylenediamine at neutral pH, allowing single-step and one-pot cascade reactions for visual and fluorometric measurements of uric acid (UA) that could work in the range of 0.2–500 μM UA with a detection limit of 0.06 μM and 0.054 μΜ, respectively. The assay was successful in detecting UA in serum and urine samples with relative standard deviation (RSD) ranging from 7.3% to 10.2% and 3.0%–8.5% respectively, suggesting that it may prove useful in medical diagnostic testing.