Azure A embedded in carbon dots as NADH electrocatalyst: Development of a glutamate electrochemical biosensor

Carbon nanodots modified with azure A (AA-CDs) have been synthesized and applied as redox mediator of bioelectrocatalytic reactions. A deep characterization of AA-CDs nanomaterial has been carried out, proving the covalent attachment of azure A molecules into the carbon dots nanostructure. Disposable screen-printed carbon electrodes (SPCE) have been modified with AA-CDs, through the action of chitosan polymer (Chit-AA-CDs/ SPCE). The Chit-AA-CDs/SPCE electrocatalytic activity towards the oxidation of NADH has been proved, obtaining excellent results regarding the low oxidation potential achieved (-0.15 V vs. Ag) and low detection and quantification limits (LOD and LOQ) for NADH, 16 and 53 mu M, respectively. The developed electrochemical platform has been applied for the construction of a glutamate biosensor by immobilizing L-glutamic dehydro-genase (GLDH/Chit-AA-CDs/SPCE). The morphology of GLDH/Chit-AA-CDs/SPCE platform was analysed by AFM at each different step of the electrode modification process. The resulting biosensing platform is capable of detect NADH enzymatically generated by GLDH in the presence of glutamate and NAD+. Good analytical pa-rameters were obtained for glutamate analysis using GLDH/Chit-AA-CDs/SPCE, as LOD and LOQ of 3.3 and 11 mu M, respectively. The biosensor has been successfully applied to the analysis of food and biological samples.

Automated summary

Carbon nanodots modified with azure A were synthesized and applied as a redox mediator for bioelectrocatalytic reactions. The modified electrodes demonstrated excellent electrocatalytic activity and analytical performance for the detection of NADH and glutamate. The developed biosensor based on immobilized enzyme showed good analytical parameters and successfully analyzed food and biological samples.