Application of Carbon Quantum Dots Derived from Waste Tea for the Detection of Pesticides in Tea: A Novel Biosensor Approach

Abstract

Chemical pesticide residues have negative consequences for human health and the environment. Prioritizing a detection method that is both reliable and efficient is essential. Our innovative research explored the application of biosensors based on carbon quantum dots (CQDs) derived from waste tea to detect commonly used pesticides in tea. CQDs have been synthesized using a simple one-pot hydrothermal approach and thoroughly characterized using advanced techniques such as high-resolution transmission electron microscopy, ultraviolet-visible spectroscopy, photoluminescence (PL) spectroscopy, Raman spectroscopy, X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy. The fluorescence resonance energy transfer-based fluorescence "turn on-off" mechanism has been successfully employed to study the detection of four different pesticides, viz., quinalphos 25 EC, thiamethoxam 25 WG, propargite 57 EC, and hexaconazole 5 EC. The detection limits for quinalphos 25 EC, thiamethoxam 25 WG, and propargite 57 EC were determined to be 0.2, 1, and 10 ng/mL, respectively. Notably, these values are significantly lower than the maximum residue level for each pesticide. We achieved a strong linear correlation (R = -0.96) with a detection limit of 0.2 ng/mL for quinalphos 25 EC. The quantum yield was determined to be 40.05%. Our research demonstrates that the developed nanobiosensor reliably and accurately detects pesticides, including those present in experimental samples containing mixtures of pesticides.

Figure 1

Synthesis of CQDs from tea waste.

Figure 2

Characterization of CQDs: (a) HRTEM image depicting CQDs, (b) histogram illustrating the size distribution of CQDs, and (c) HRTEM image revealing clear lattice spacing with an interfringe distance of 0.22 nm.

Figure 3

(a) UV–vis spectroscopy analysis of CQDs. (b) Raman spectrum of CQDs.

Figure 4

(a) PL intensity of fluorescent CQDs, (b) XRD pattern of CQDs, and (c) AFM image depicting CQDs and their size distribution.

Figure 5

XPS spectra of CQDs derived from tea waste. (a) XPS survey spectrum. High-resolution spectra of (b) C 1s, (c) N 1s, and (d) O 1s.

Figure 6

Various concentrations (0.2, 1, 10, 50, 250, 1000, 2500, and 5000 ng/mL) of different pesticides, namely, (a) propargite 57 EC, (b) thiamethoxam 25 WG, (c) hexaconazole 5 EC, and (d) quinalphos 25 EC, were introduced to CQDs samples. Changes in fluorescence intensity were observed under PL and UV light conditions, and a concentration-dependent graph is presented using logarithmic values.

Figure 7

Pesticide mixture with CQDs and the corresponding graphical representation.

Figure 8

“Turn off” mechanism of fluorescence intensity due to the addition of fluorescence quenching pesticides.

Figure 9

Fluorescence intensity “turn on” mechanism triggered by the inclusion of a fluorescence-enhancing pesticide.

Figure 10

Effects of pesticide mixture on the experimental sample and the corresponding linear graphical representation.