Graphene quantum dots-based nanocomposite for electrocatalytic application of L-cysteine in whole blood and live cells

•Graphene quantum dots stabilized AuNPs-metal-free organic framework has been designed and modified on GC electrode via drop coating.•GQDs-AuNPs-MFOF/GCE was utilized for oxidation of L-Cysteine and showed a wide linear range from 1 nM - 0.5 mM with LOD of 0.124 nM.•The present sensor showed excellent selectivity and practical application was demonstrated in human whole blood, biofluids, and live-cells. Driven by the urgent need to detect amino acids in live cells at trace levels, as they are an important biomarker for various diseases. For this purpose, we have developed a nanomolar level detection of l-cysteine (L-Cys) and real-time cellular quantification from live cells based on graphene quantum dots (GQDs)-AuNPs-metal-free organic framework (MFOF). Different analytical and microscopic techniques were used to confirm the synthesized nanocomposite. The sensitive electrochemical sensing system of l-Cys-was detected synergistically with GQDs-AuNPs-MFOF/GCE by voltammetry and amperometric i-t curve. The electrocatalytic oxidation signal of l-Cys-at Epa = none, +0.45, +0.36 and +0.21 V (vs. Ag/AgCl) with enhanced current responses were observed at control GCE, MFOF, GQDs-MFOF, and GQDs-AuNPs-MFOF/GCEs by DPV. The nanocomposite modified sensor probe showed a wide linear range concentration from 1 nM to 0.5 mM with LOD of 0.124 nM (S/N = 3), LOQ of 0.863 nM (S/N = 10) and sensitivity of 2.364 μA μM−1 cm−2. Subsequently, the selective detection of l-Cys-in the presence of possible other interfering biothiols. amino acids, and metal ions were achieved. The practical application was demonstrated in human whole blood and bio-fluid samples. Finally, the endogenous real-time detection of cellular cysteine in live cells was demonstrated. Ultrasensitive electrochemical determination of L-Cysteine in biological media using GQDs-AuNPs embedded in a metal-free organic scaffold [Display omitted]