Sunset Yellow (SY), which is an artificial azo dye, is preferable for its high stability and low cost. The determination of SY in foods is extremely important for human health because excessive consumption of SY has harmful effects, such as hyperactivity disorder and cancer. In this method, L-cysteine coated copper nanoclusters (CuNCs) were used as a fluorescence probe. L-cysteine has been used as both a reducing and stabilizing agent. One-step green hydrothermal synthesis of CuNCs was made. L-cysteine-coated CuNCs have been characterized using several of methods. CuNCs quenching mechanism is static and inner filter effect (IFE). The linear range is 0.65-14 μg.ml-1 at optimum conditions. LOD and LOQ values were calculated as 0.1 and 0.35 μg.ml-1, respectively. The proposed method was used for the determination of SY in different type of powder drinks. The developed nanosensor is environmentally friendly, easy, fast, reproducible, and low cost.

BACKGROUND: Fluoroquinolones (FQs) are widely used in livestock and poultry industry because of their satisfactory effects in preventing and treating bacterial infection. However, due to irrational use and poor biodegradability, FQs can easily remain in food animals and further enter the human body through the food chain. Therefore, accurate and sensitive detection of FQs residues in animal-origin food is significant. The traditional methods commonly used for FQs detection have some limitations. Ratiometric fluorescence detection technology has the advantages of fast, sensitive, self-correcting, and easy visualization. However, the reports on the use of ratiometric fluorescence probes for FQs detection are limited.
RESULTS: In this work, a novel probe was proposed for ratiometric fluorescent analysis of FQs. In this probe, the fluorescence of dithioerythritol stabilized copper nanoclusters (DTE-Cu NCs) was significantly enhanced due to the Tb3+ triggered aggregation-induced emission effect. FQs bound Tb3+ in Tb3+/DTE-Cu NCs through carboxyl and carbonyl groups, so that Tb3+ was effectively sensitized to emit green fluorescence. However, the red fluorescence of DTE-Cu NCs was not interfered. The fluorescence of the probe transformed from red to green with the increase of FQs concentration. Using norfloxacin (NOR), difloxacin (DIF), and enrofloxacin (ENR) as FQs simulants, this probe showed a sensitive linear response ranged from 0.025 to 22.5 μM, with the limits of detection of 9.6 nM, 9.3 nM, and 7.7 nM. The application potential for FQs detection was verified via a standard addition assay of egg samples with the recovery rate of 90.4 %-114.7 %.
CONCLUSIONS: The fluorescence probe based on Tb3+/DTE-Cu NCs is expected to realize the ratiometric fluorescence sensitive detection of FQs. The establishment of this simple, effective, and rapid detection platform opens up a new way for the detection of FQs residues in animal-origin foods, and also provides a new idea for the design of rapid detection platforms for other hazard factors.

To address the food safety issues caused by toxins, we established a fluorescent copper nanocluster biosensor based on magnetic aptamer for the visual and quantitative detection of ZEN. Specifically, we utilized the docking-aided rational tailoring (DART) strategy to analyze intermolecular force and interaction sites between zearalenone (ZEN) and the aptamer, and optimize the long-chain aptamer step by step to enhance the binding affinity by 3.4 times. The magnetic bead-modified aptamer underwent conformational changes when competing with complementary sequences to bind with ZEN. Then, the released complementary sequences will be amplified in template-free mode with the presence of the terminal deoxynucleotidyl transferase (TdT), and generating T-rich sequences as the core sequences for the luminescence of copper nanoclusters. The luminescence could be visualized and quantitatively detected through ultraviolet irradiation. The proposed label-free aptasensor exhibited high sensitivity and specificity, with a low limit of detection (LOD) of 0.1 ng/mL.

Total volatile basic nitrogen (TVB-N) is a vital indicator for assessing seafood freshness and edibility. Rapid on-site detection of volatile basic nitrogen (VBN) is of significant importance for food safety monitoring. In this study, highly luminescent self-assembled copper nanoclusters (Cu NCs@p-MBA), synthesized using p-mercaptobenzoic acid (p-MBA) as the ligand, were utilized for the sensitive detection of VBNs. Under acidic conditions, Cu NCs@p-MBA formed compact and well-organized nanosheets through noncovalent interactions, accompanied by intense orange fluorescence emission (651 nm). The benzene carboxylic acid part of Cu NCs@p-MBA provided the driving force for supramolecular assembly and exhibited a strong affinity for amines, particularly low-molecular-weight amines such as ammonia (NH3) and trimethylamine (TMA). The quantitative determination of NH3 and TMA showed the detection limits as low as 0.33 and 0.81 ppm, respectively. Cu NCs@p-MBA also demonstrated good responsiveness to putrescine and histamine. Through density functional theory (DFT) calculations and molecular dynamics (MD) simulations, the precise atomic structure, assembly structure, luminescent properties, and reaction processes of Cu NCs@p-MBA were studied, revealing the sensing mechanism of Cu NCs@p-MBA for highly sensitive detection of VBNs. Based on the self-assembled Cu NCs@p-MBA nanosheets, portable fluorescent labels were developed for semiquantitative, visual, and real-time monitoring of seafood freshness. Therefore, this study exemplified the high sensitivity of self-assembly induced emission (SAIE)-type Cu NCs@p-MBA for VBNs sensing, offering an efficient solution for on-site monitoring of seafood freshness.

A fluorescent probe based on bovine serum albumin stabilized copper nanoclusters (BSA-CuNCs) was developed for the selective and sensitive determination of ornidazole (ORN). The nanoclusters were synthesized via a one-pot hydrothermal process in basic media. The synthesized and characterized BSA-CuNCs have less than 3 nm particle size and exhibited blue emission at 405 nm when excited at 325 nm. Synthesized and characterized nanoclusters were successfully applied as a turn-off fluorescent probe for the determination of ORN in pharmaceutical dosage forms. The quenching mechanism created an was inner filter effect (IFE). The method was linear in the concentration range of 0.52-13.56 μg mL-1 with a low limit of detection (LOD) 0.01 μg mL-1. High recovery values (98.5%-102.42%) with low RSD% values (0.25%-2.73%) were obtained. The synthesized nanoclusters can be used as a turn-off probe for ORN determination with their selective, simple, rapid, and inexpensive properties.

A fluorescent probe based on bovine serum albumin stabilized copper nanoclusters (BSA-CuNCs) was developed for the selective and sensitive determination of ornidazole (ORN). The nanoclusters were synthesized via a one-pot hydrothermal process in basic media. The synthesized and characterized BSA-CuNCs have less than 3 nm particle size and exhibited blue emission at 405 nm when excited at 325 nm. Synthesized and characterized nanoclusters were successfully applied as a turn-off fluorescent probe for the determination of ORN in pharmaceutical dosage forms. The quenching mechanism created an was inner filter effect (IFE). The method was linear in the concentration range of 0.52-13.56 μg mL-1 with a low limit of detection (LOD) 0.01 μg mL-1. High recovery values (98.5%-102.42%) with low RSD% values (0.25%-2.73%) were obtained. The synthesized nanoclusters can be used as a turn-off probe for ORN determination with their selective, simple, rapid, and inexpensive properties.

Herein, a remarkable achievement in the synthesis and characterization of an atomically precise copper-hydride nanocluster, [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- via a mild one-pot reaction is presented. Through X-ray crystallography analysis, it is revealed that [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- exhibits a unique shell-core-shell structure. The inner Cu29 kernel is composed of three twisted Cu13 units, connected through Cu4 face sharing. Surrounding the metal core, two Cu6 metal shells, resembling a protective sandwich structure are observed. This arrangement, along with intracluster π···π interactions and intercluster C─H···F─C interactions, contributes to the enhanced stability of [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- . The presence, number, and location of hydrides within the nanocluster are established through a combination of experimental and density functional theory investigations. Notably, the addition of a phosphine ligand triggers a fascinating nanocluster-to-nanocluster transformation in [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- , resulting in the generation of two nanoclusters, [Cu14 (SC6 H3 F2 )3 (PPh3 )8 H10 ]+ and [Cu13 (SC6 H3 F2 )3 (P(PhF)3 )7 H10 ]0 . Furthermore, it is demonstrated that [Cu41 (SC6 H3 F2 )15 Cl3 (P(PhF)3 )6 (H)25 ]2- exhibits catalytic activity in the hydrogenation of nitroarenes. This intriguing nanocluster provides a unique opportunity to explore the assembly of M13 units, similar to other coinage metal nanoclusters, and investigate the nanocluster-to-nanocluster transformation in phosphine and thiol ligand co-protected copper nanoclusters.

In this work, L-Histidine-protected copper nanoclusters synthesized by changing the pH levels of precursor solution have been shown to display different emission wavelengths and intensities. As determined by mass spectrometry, nanoclusters Cu3L2 synthesized at acidic pH have 3 atoms in their core and emit in the greenish-yellow region, and nanoclusters Cu2L2, synthesized in the basic conditions have 2 atoms in their core and emit in the blue-green region. They are expected to have coordination through the carboxylate group and nitrogen of the imidazole ring of histidine ligand, respectively. Metal ions Mg2+, Mn2+, Zn2+, and Pb2+ selectively enhance the interaction between carboxylate - copper metal core and increase the emission intensity of Cu3L2. These metal ions weaken the interaction between imidazole nitrogen and copper metal core and quench the emission intensity of Cu2L2. As synthesized, nanoclusters exhibit good water solubility and photostability, they can act as fluorescent probes to sense the metal ions, therefore, they were utilized for the optical sensing of the mentioned metal ions. Fluorescent nanoclusters were found to sense even a very low concentration of metal ions with a limit of detection (3 σ/slope) in nanomolar range.

Fluorescent probes with on-site visual detection function have received extensive attention in the detection of chlortetracycline (CTC), which was widely used in aquaculture and animal husbandry. Copper nanoclusters (Cu NCs) with excellent optical properties were prepared using bovine serum albumin (BSA) as a template, and a multicolor fluorescence strategy based on BSA-stabilized Cu NCs (BSA-Cu NCs) for detecting CTC was proposed. BSA-Cu NCs had a red emission at 640 nm. After the addition of CTC, the red emission of BSA-Cu NCs gradually decreased for internal filtering effect, while the green emission of CTC was significantly enhanced under the sensitization of BSA. This simple sensing process can be achieved in real time by directly mixing the target sample with BSA-Cu NCs, and the detection limit (LOD) of the system for CTC was 12.01 nM. Based on this sensing strategy, a fluorescence film sensing detection platform was constructed to achieve ultra-fast detection of CTC within 30 s. This work provided a fluorescent film sensor with the advantages of portability, ultra-fast and low cost, which provided a feasible alternative for on-site ultra-fast screening of CTC.

Conceptually mimicking biomolecules\' ability to construct multiple-helical aggregates with emergent properties and functions remains a long-standing challenge. Here we report an atom-precise 18-copper nanocluster (NC), Cu18 H(PET)14 (TPP)6 (NCS)3 (Cu18 H) which contains a pseudo D3 -symmetrical triple-helical Cu15 core. Structurally, Cu18 H may be also viewed as sandwich type of sulfur-bridged chiral copper cluster units [Cu6 -Cu6 -Cu6 ], endowing three-layered 3D chirality. More importantly, the chiral NCs are aggregated into an infinite double-stranded helix supported by intra-strand homonuclear C-H⋅⋅⋅H-C dihydrogen contacts and inter-strand C-H/π and C-H/S interactions. The unique multi-layered 3D chirality and the double-helical assembly of Cu18 H are evocative of DNA. Moreover, the collective behaviours of the aggregated NCs not only exhibit crystallization-induced emission enhancement (CIEE) and aggregation-induced emission enhancement (AIEE) effects in the deep-red region, but also efficiently catalyze electron transfer (ET) reaction. This study thus presents that hierarchical assemblies of atomically defined copper NCs could be intricate as observed for important biomolecules like DNA with emergent properties arising from aggregated behaviours.