Research On The Synthesis Of Metal Nanoclusters And Their Detection In Tetracycline Antibiotics

Metal nanoclusters are emerging as a novel class of fluorescent nanomaterials that bridge the size gap between metal nanoparticles and metal atoms.Typically composed of a specialized outer layer of molecules and internal metal atoms,these nanoclusters exhibit a unique feature.Their size closely approximates the Fermi wavelength,leading to energy level splitting and enabling the production of vibrant fluorescence upon excitation by ultraviolet light.In comparison to conventional organic dyes and semiconductor quantum dots used in fluorescence applications,metal nanoclusters offer several advantages.They demonstrate remarkable optical stability,possess a significant Stokes shift,and exhibit low toxicity towards the environment.Consequently,they have found widespread utilization as fluorescent probes across diverse domains such as biochemical sensing,biological labeling,and bioimaging.Tetracycline antibiotics,discovered in the 20th century and produced by actinomycetes,have emerged as a powerful class of antibiotics that exert their antibacterial effects by inhibiting protein synthesis within bacteria.With their broad-spectrum antimicrobial activity and growth-promoting properties in animals,tetracycline antibiotics have found widespread applications in medical and livestock industries.However,their excessive use,resulting from improper practices among healthcare and livestock personnel,has led to the presence of tetracycline residues in animal products such as milk and meat.This,in turn,poses a risk to consumers,potentially causing harm to human organs upon ingestion.Consequently,there is a crucial need for rapid and efficient pre-market testing of animal products to prevent the circulation of tetracycline residues.The current national standard detection method for tetracycline is liquid chromatography-mass spectrometry.While this method ensures accuracy,its complex sample preparation,slow detection speed,and expensive equipment make it ill-suited for the demands of rapid tetracycline testing.In recent years,fluorescence detection methods have garnered significant attention due to their rapidity,high selectivity,and the portability of the required equipment.These methods typically employ fluorescent materials as probes,allowing for interaction with the target substances and enabling quantitative detection based on changes in fluorescence intensity.Metal nanoclusters,a novel class of fluorescent materials,possess exceptional fluorescence properties.Compared to traditional fluorescent dyes,they exhibit improved biocompatibility and resistance to photobleaching.As such,metal nanoclusters hold tremendous potential as fluorescent probes for quantitative detection.In light of the issue of tetracycline antibiotic residues in the environment,this study focuses on the design and development of two specific types of metal nanoclusters for the detection of tetracycline antibiotics.Leveraging the superior fluorescence properties and specific recognition capabilities of these nanoclusters,the study aims to achieve convenient,sensitive,and rapid detection of tetracycline antibiotics.The specific research objectives and details are outlined below:（1）In this system,silver nanoclusters were synthesized using the UV reduction method,employing Polymethacrylic acid terminated with Pentaerythritol Tetra（3-mercaptopropionate）as the ligand and silver nitrate as the metal precursor.The resulting clusters displayed a vibrant orange fluorescence when exposed to UV lamp irradiation,with an optimal excitation wavelength of 330 nm and an optimal emission wavelength of 630 nm.The clusters exhibited a fluorescence lifetime of 67.7μs and a fluorescence quantum yield of 6.72%.Transmission electron microscopy measurements revealed the clusters’particle size to be 2.1±0.3 nm.Investigations showed that the fluorescence intensity of the silver nanoclusters decreased gradually with increasing concentrations of tetracycline and oxytetracycline.Within the concentration ranges of 0-80μM for tetracycline and 0-20μM for oxytetracycline,the fluorescence intensity demonstrated a robust linear relationship with the concentrations of these two antibiotics.The detection limits were determined to be0.192μM for tetracycline and 0.223μM for oxytetracycline.Moreover,selective testing confirmed that the synthesized Ag NCs@PTMP-PMAA exhibited excellent selectivity for the detection of tetracycline and oxytetracycline.（2）Due to the presence of chloride ions（Cl^-）in water,Ag⁺ions easily form AgCl precipitates.In System 1,the Ag nanoclusters synthesized contained some Ag⁺ions,leading to potential interference during detection.Moreover,the high cost of the silver nitrate metal precursor poses a challenge.Therefore,System 2 opted for Cu²⁺ions as the metal precursor and carboxymethyl chitosan（CMCS）as the protective ligand to synthesize copper nanoclusters under hydrothermal conditions.By optimizing the preparation conditions,blue-emitting copper nanoclusters were successfully obtained.The synthesized clusters exhibited an optimal excitation wavelength of 360 nm and an optimal emission wavelength of 470 nm.They displayed a fluorescence lifetime of3.2 ns and a fluorescence quantum yield of 2.73%.The clusters demonstrated good temporal stability,oxidative stability,and stability in salt solutions.Even in 1 mol/L H2O2 and NaCl solutions,the clusters maintained their fluorescence properties.Transmission electron microscopy analysis revealed a particle size of 2.6±0.5 nm for the clusters.Using Cu NCs@CMCS as the fluorescent probe,the detection of tetracycline antibiotics in aqueous solutions was achieved.The detection limits were determined to be 0.166μM（tetracycline）,0.273μM（oxytetracycline）,0.198μM（chlortetracycline hydrochloride）,and 0.279μM（streptomycin hydrochloride）.Upon interaction between the cluster solution and antibiotic solution,the solution’s color under UV light transitioned from blue to white as the antibiotic concentration increased.