Bioinspired Vertically Aligned 2D ZnO Surface Nanostructures Functionalized with Carbon Quantum Dots for Electrocatalytic Monitoring of Norfloxacin

The roles of nanostructured materials are crucial for monitoring and quantifying emerging environmental contaminants that pose serious ecological and health risks. This study reports the bioinspired synthesis of 2D vertically aligned ZnO nanostructures onto fluorine-doped tin oxide glass using Sechium edule (SE) fruit extract and its functionalization with carbon quantum dots (CQDs-ZnOVANs(bio)/FTO) fabricated using carbon-rich remnant peel. The functionalized platform was tested for electrocatalytic monitoring of norfloxacin (NFX) in environmental matrices. ZnOVANs(bio)/FTO modified with CQDs at an immersion time of 1.5 min (CQDs1.5-ZnOVANs(bio)/FTO) oriented vertically with an average length of 965.3 nm and a thickness of 46.3 nm with high crystallinity. The average particle size of CQDs was 4.7 nm with an amorphous nature. CQDs1.5-ZnOVANs(bio)/FTO exhibited 2.6- and 2.7-fold enhancement in anodic current density and electroactive area (Ae), respectively, along with a 34.6% decrement in charge transfer resistance (Rp) compared to ZnOVANs(bio)/FTO. NFX monitoring at CQDs1.5-ZnOVANs(bio)/FTO took place in a two-electron and two-proton transfer process with a E0 of 1.042 V, rate constant (k0) of 0.105 s–1, and surface coverage by NFX ions (Γ*) of 2.54 × 10–11 mol cm–2. CQDs1.5-ZnOVANs(bio)/FTO exhibited a detection limit of 0.0066 μM and sensitivity of 0.1903 μA μM–1 cm–2 within 0.25–40 μM NFX. The developed electrode exhibited excellent stability with only 8.1% reduction in anodic peak current up to the 15th reuse cycle of the same sensing platform. The common antibiotics, including ciprofloxacin, phenylbutazone, sulfamethoxazole, chloramphenicol, chloroquine, and furazolidone, could not interfere with the NFX monitoring. CQDs1.5-ZnOVANs(bio)/FTO could effectively monitor and quantify NFX spiked in environmental samples, and the results are comparable to liquid chromatography.