Ultrasensitive and facile electrochemical detection of hydrogen sulfide in rat brain microdialysate based on competitive binding reaction.

In this study, a sensitive and facile method with wide linear range and low detection limit for detecting hydrogen sulfide in rat brain microdialysate was developed. The design of the sensor is based on the competitive binding reaction principle, in which cysteine was self-assembly immobilized on the surface of gold electrode, and then the Cu2+ as the electrochemical probe was anchored to the cysteine film through coordination bonding with carboxyl (-COOH) and amino group (-NH2) to form the Cu2+/Cys/Au electrode. The Cu2+/Cys/Au electrode can serve as an electrochemical H2S sensor through a ligand exchange reaction, which may come from the greater affinity of H2S than cysteine to the gold surface due to a steric hindrance reason. The hydrogen sulfide cuts off the S-Au bonds between cysteine and Au electrode and leads to the Cu2+ drop off from electrode, resulting in a decrease in the redox signal of Cu2+, thereby creating a current that is indirectly proportional to the logarithm of the concentration of H2S dissolved at the sensor surface. The current response, i.e., signal output, is in wide linearity to logarithm of the concentration of H2S in the range of 0.01-100.0 μM with ΔI/μA = 0.0857 lgCH2S(nM) +0.124 and very low detection limit 5 nM (S/N = 3). The assay demonstrated here is highly selective with respect to alleviating the interference of other thiol-containing species such as glutathione (GSH), homocysteine (Hcy), and cysteine commonly existing in the brain. The basal level of H2S in the microdialysate from the hippocampus of rats is determined to be around 8.6 ± 3.2 μM. The method demonstrated here is facile but reliable and durable and is envisaged to be applicable to understanding the chemical essence involved in physiological and pathological events associated with H2S. Graphical abstract By rationally tailoring the gold electrode surface through the competitive binding interaction of gold electrode between cysteine and H2S, we have successfully designed a simple, highly sensitive, and selective method for electrochemical sensing of H2S in brain microdialysate.