Carbon Quantum Dots/Gold Nanoparticle Dual-Mode Aptasensor for Smartphone-Based Gentamicin Detection in Food Samples

Abstract

A dual-mode smart colorimetric and fluorometric aptasensor is reported for the sensitive and selective detection of gentamicin (GENTA) in milk and egg samples. Gold nanoparticles (AuNPs) and carbon quantum dots (CQDs) formed a fluorescence resonance energy transfer pair to develop a dual-mode aptasensor. The aptasensor utilized the distance-dependent color-changing properties of AuNPs, energy transfer between CQDs (donor) and AuNPs (acceptor), and the change in the aptasensor’s emission intensity. With the optimized concentration of CQDs, AuNPs start to agglomerate due to electrostatic interactions between positively charged CQDs and negatively charged AuNPs. When aptamers (Apta) are immobilized on the surface of AuNPs, they provide a protective layer that prevents their agglomeration in the presence of CQDs. With GENTA, the Apta bind to it, detach from the AuNPs’ surface, and change the color and emission intensity of the aptasensor. The dual-mode response was analyzed with GENTA concentrations ranging from 0.09 μM to 8.17 μM, with lower detection limits (LOD) of 0.425 μM and 0.519 μM in the colorimetric and fluorometric modes, respectively. The concentration of GENTA was quantified as 1.40 μM in the colorimetric mode and 1.71 μM in the fluorometric mode. The smartphone-enabled RGB color analysis enabled real-time monitoring of food samples and their results, and the LOD values are comparable to experimental results. The LOD was calculated as 0.434 μM (colorimetric) and 0.587 μM (fluorometric). The developed aptasensor exhibited good selectivity and practical applicability, as analysis in spiked milk and egg confirmed its potential for food safety applications.