Förster Resonance Energy Transfer between Multicolor Emissive N-Doped Carbon Quantum Dots and Gold Nanorods for the Detection of H₂O₂, Glucose, Glutathione, and Acetylcholinesterase

Multicolor emissive nitrogen-doped carbon quantum dots (CQDs) were synthesized by the hydrothermal method and characterized using spectroscopic and electron microscopic techniques. Förster resonance energy transfer (FRET) between CQDs and gold nanorods (AuNRs) has been investigated that occurs due to the distinctive overlap of transverse and longitudinal bands of AuNRs with the fluorescence (FL) spectra of CQDs. Significant FL quenching (turn-off) of CQDs by AuNRs and their recovery (turn-on) have been observed due to etching of AuNRs and end-to-end assemblies that lead to the detection of biomolecules like H2O2, glucose, glutathione (GSH), and acetylcholinesterase (AChE). The redox reaction of Au(0) with H2O2 results in the decomposition of AuNRs to give Au(I) ions, thereby inducing the fluorescence recovery of CQDs (turn-on). The interruption of the FRET phenomenon by the production of H2O2 from the reaction of glucose oxidase in the presence of glucose and a thiol-containing compound from the reaction of acetylthiocholine and the AChE enzyme causes the FL recovery of CQDs, respectively. Moreover, the assembly of AuNRs leads to the FRET disruption, and FL turn-on signals were found to be measures of GSH. In comparison to the UV–visible approach, the FL measurements through the FRET process are found to be more sensitive under the same reaction conditions. The practical applicability of the proposed sensing system has been verified using human plasma samples.