A simple and sensitive colorimetric biosensor based on three different hydrothermally synthesized AuNP-CQD nanocolloids functionalized with aptamer for the biosensing of diclofenac in serum samples

This study emphasizes upon the synthesis of three different types of gold nanoparticles-Carbon quantum dots (AuNP-CQD) nanocolloids, which were named as AuNP-CQD (EA), AuNP-CQD (G) and AuNP-CQD (S). Primarily, before conjugating AuNP with different types of CQD, CQD were synthesized via hydrothermal method with varying precursors as the carbon source. Ethanolamine, Glycine, and Serine were used as the carbon sources for AuNP-CQD (EA), AuNP-CQD (G), and AuNP-CQD (S), respectively, and citric acid was used as the reducing agent. The aforementioned AuNP-CQD were further functionalized with diclofenac specific aptamer (DCL Apt ) for the colorimetric detection of diclofenac sodium. For optical characterisation, UV–Visible spectroscopy was used. For further characterization of the colorimetric system, FTIR and DLS techniques were used. Advanced analytical techniques such as XRD and XPS were utilized to outline the extensive details of structural and surface characteristics of the prepared nanocolloids. Microscopic evaluation techniques such as SEM and TEM were utilized to visualize the morphologies of AuNP, CQDs and AuNP-CQDs. AuNP are bound to CQD through electrostatic interactions. The prepared nanocolloids were utilized for the colorimetric detection of diclofenac in diclofenac sodium formulations. The LOD for AuNP-CQD (EA), AuNP-CQD (G) and AuNP-CQD (S) were recorded at 53.08 nM, 27.12 nM and 18.85 nM, respectively. The prepared nanocolloids were also utilized for the quantification of diclofenac sodium in human serum samples with recovery rates ranging from 94.27 – 98.79 % for AuNP-CQD (EA), 97.84 – 105.25 % for AuNP-CQD (G) and 95.17 – 99.23 % for AuNP-CQD (S) with RSD values ranging from 6.87 – 3.46 %, 2.1 – 2.04 % and 5.86 – 1.22 % for AuNP-CQD (EA), AuNP-CQD (G) and AuNP-CQD (S) respectively. This performance of AuNP-CQD surpasses the biosensing capabilities of pristine AuNP and other nanocomposites which establish the dominance of CQD and AuNP-CQD in colorimetric biosensing and providing a basis for future studies and multifarious applications.