A fluorimetric testing strip for the visual evaluation of mercury in blood using copper nanoclusters with DMSO-enhanced fluorescence and stability

Mo(IV) Ion-Modulated BSA-Protected Gold Nanocluster Probe for Fluorescence Turn-On Detection of Trimethylamine N-Oxide (TMAO)

Trimethylamine N-oxide (TMAO), a molecule produced by the microbiota, has been associated with human health and illness. Its early discovery in body fluids may affect our understanding of the pathophysiology and treatment of many illnesses. Therefore, our knowledge of the pathophysiology and diagnostics of disorders associated with TMAO might be enhanced by the creation of dependable and fast methods for TMAO detection. Therefore, we developed a fluorescent probe for detecting TMAO utilizing an on-off-on strategy. Bovine serum albumin (BSA)@AuNCs luminescence is effectively quenched by Mo4+ because BSA@AuNCs and Mo4+ have a strong binding relationship. Mo4+ ions can substantially decrease the emission intensity of gold nanoclusters by establishing a BSA@AuNCs-Mo system. Then, the luminescence of BSA@AuNCs was restored due to the interaction between Mo4+ and TMAO. A significant linear relationship was seen between the emission intensity and TMAO concentration within the 0-201 μM range, with a detection limit of 1.532 μM. Additionally, the method can measure TMAO in blood and urine samples.

A selective colorimetric and efficient removal strategy for mercury(II) in aquatic systems using mesoporous Fe3O4-loaded silver probes

Mesoporous Fe3O4-loaded silver nanocomposites (Fe3O4@Ag) were simply fabricated as bi-functional nanozymes for the catalysis-based detection and removal of Hg2+ ions. It was found that the as-prepared magnetic Fe3O4@Ag could display peroxidase-like catalysis activity that could be rationally enhanced in the presence of Hg2+ ions. To our surprise, the shell of the Ag element may decrease the catalysis of the Fe3O4 to some degree. However, the Ag particles could serve as the probes for specifically recognizing Hg2+ ions and trigger increased catalysis through the formation of Ag-Hg alloys, with a decreased signal background. A high-throughput colorimetric analytical method was thereby developed based on the Fe3O4@Ag catalysis for probing Hg2+ ions in the muscles of fish by using 96-well plates, at linear Hg2+ concentrations ranging from 0.010 to 2.5 mg kg-1. Moreover, the developed colorimetric analytical method was applied to evaluate Hg2+ levels in muscle samples of different kinds of fish. Unexpectedly, an obvious difference of Hg2+ levels in muscles of four kinds of fish was discovered, with the order of snakehead (Ophicephalus argus) > largemouth bass (Micropterus salmoides) > crucian carp (Carassius auratus) > silver carp (Hypophthalmichthys molitrix), where the carnivorous fish showed higher Hg2+ levels than the omnivorous or plant-based ones. Moreover, the as-fabricated Fe3O4@Ag adsorbents with their large specific surface area and high environmental robustness could exhibit efficient Hg2+ adsorption with capacities of up to 397.60 mg g-1. A removal efficiency of 99.40% can also be expected for Hg2+ ions from wastewater, with the magnet-aided recycling of Fe3O4@Ag adsorbents. Such an Fe3O4@Ag-based colorimetric analysis and removal strategy for Hg2+ ions should find wide applications in the fields of aquatic food safety, environmental monitoring, and clinical diagnostics of Hg-poisoning diseases.

A sensitive and facile electrochemical paper-based sensor for glucose detection in whole blood using the Pd/CB-Ni@rGO modified electrode

We created novel Pd/CB-Ni@rGO nanomaterials for glucose detection. The as-synthesized nanomaterials were dropped on the electrode surface using the drop casting technique. The prepared electrode was then attached to a paper-based device containing the sample zone and the reaction zone, enabling plasma isolation and an enzymatic reaction for glucose detection in whole blood. The nanomaterials and surfaces of electrodes were characterized by FTIR, TEM, and SEM. The proposed approach is a disposable glucose detection method that is unaffected by protein fouling on the electrode, and it requires only one drop of human blood. Therefore, there is no need for extensive sample preparation, and there is less sample consumption. Under optimal conditions, Pd/CB-Ni@rGO can accurately measure blood glucose levels with a linear range of 7 to 7140 μM (R2 = 0.9986) and a low detection limit of 0.82 μM. Besides, the developed sensor shows excellent anti-interference capacity, stability, and satisfactory reproducibility and repeatability. Importantly, Pd/CB-Ni@rGO was successfully applied for glucose in whole blood from 4 volunteers, with results that correlated well with those obtained using an Accucheck glucometer at a 95% confidence level. Given its low cost, high accuracy, and ease of use, the blood glucose sensor holds significant potential for clinical use and broadens the area of future noninvasive sensor development.

Coal humus acid functionalized high stability fluorescent copper nanoclusters for tumor identification by sequential off-on-off monitoring tryptophan and Hg2

The abnormalities of Tryptophan (Trp) and mercury ions (Hg²⁺) not only easily activate diseases, including mental illness and cancer, but also seriously affect human wellbeing. Fluorescent sensors are profoundly attractive options for identifying amino acids and ions; however, most sensors remain challenging due to the multipliable cost and deviation from the asynchronous quenching detection. In particular, fluorescent copper nanoclusters with high stability that quantitatively monitoring Trp and Hg²⁺ successively have seldom been reported. Herein, we employ coal humus acid (CHA) as a protective ligand and successfully construct weak cyan fluorescent copper nanoclusters (CHA-CuNCs) by a rapid, environmentally benign and cost-effective method. Significantly, the fluorescence of CHA-CuNCs is obviously improved by introducing Trp, because the indole group of Trp enhances the radiative recombination and aggregation-induced emissions. Interestingly, CHA-CuNCs not only realizes the highly selective and specific detection of Trp with a linear range of 25-200 μM and a detection limit of 0.043 μM based on the turn-on fluorescence strategy, but also quickly achieves the consecutive turn-off detection of Hg²⁺ due to the chelation interaction between Hg²⁺ and pyrrole heterocycle in Trp. Moreover, this method is successfully applied in the analysis of Trp and Hg²⁺ in real samples. Furthermore, the confocal fluorescent imaging of tumor cells demonstrates that CHA-CuNCs can be used for bioimaging and cancer cell recognition with Trp and Hg²⁺ abnormalities. These findings provide new guidance for the eco-friendly synthesis of CuNCs with eminent sequential off-on-off optical sensing property, indicating good prospects in biosensing and clinical medicine applications.

Simultaneous fluorescence sensing of vitamin B2 and sulfur ions based on fluorescent copper nanoparticles

In this study, the F-CuNPs were synthesized by a modified liquid-phase chemical reduction method. Throughout the preparation process, anhydrous copper sulfate was used as the copper source, and ascorbic acid in the NaOH solution served as the reducing and protective agent. Förster resonance energy transfer (FRET) may exist between F-CuNPs and vitamin B2 due to the large spectral overlap between the fluorescence emission spectra of F-CuNPs and the UV-vis absorption spectra of vitamin B2. Therefore, the detection of vitamin B2 was designed based on a FRET system between F-CuNPs and vitamin B2. With S^2- into the F-CuNPs&VB2 system, the fluorescence intensity of vitamin B2 was quenched, while the fluorescence intensity of F-CuNPs was almost unchanged. There may be a specific reaction between S^2- and vitamin B2. Therefore, the research system can be further used to detect S^2- based on ratiometric fluorescent probe. The research findings show that the linear range of vitamin B2 was 0.51 nM-34.64 nM with a detection limit of 0.25 nM (S/N = 3), the linear range of S^2- was 0.64 μM-60.00 μM with a detection limit of 0.32 μM (S/N = 3). Furthermore, the simultaneous fluorescent sensing system has high sensitivity and selectivity. Therefore, this system was designed and successfully used to detect the content of vitamin B2 and S^2- in actual samples to find a new effective method to detect analytes.

Selective and ratiometric fluorescence sensing of bisphenol A in canned food based on portable fluorescent test strips

In this study, a conversion method and molecular imprinting technology were used to design molecularly imprinted polymers (MIP)-based ratiometric fluorescence test papers. The ZnO quantum dots (ZnO QDs) acted as the background quantum dots and ZIF-8 raw material. Carbon dots (CDs) were used as the identification signals. The imprinting layer achieved a selective function. Therefore, a ZnO@ZIF-8/CDs@MIPs sensor was designed for the detection of Bisphenol A (BPA). The sensor exhibited a fast response time for BPA detection. In addition, the sensor demonstrated that effective detection of BPA can still be achieved in complex environments. The detection limit of this sensor was 0.778 nM with a linear range of 0-60 nM. The corresponding test solutions exhibited clear changes from blue to yellow. The selectivity experiments results demonstrated that ZnO@ZIF-8/CDs@MIPs only exhibit excellent selective recognition effect for BPA. ZnO@ZIF-8/CDs@MIPs-2 was used for the detection of BPA in canned food and compared with the results of HPLC detection of BPA. The two spiked recovery ranges were 96.58-102.04% and 97.43-103.82%, respectively. In addition, the prepared ZnO@ZIF-8/CDs@MIPs-2 test paper visually recognized BPA under ultraviolet light. This study provides guidelines for the design and application of fluorescent test papers for quick detection in practical applications.

Morphology and Enzyme-Mimicking Activity of Copper Nanoassemblies Regulated by Peptide: Mechanism, Ultrasensitive Assaying of Trypsin, and Screening of Trypsin Inhibitors

To regulate nanostructure synthesis is of crucial importance for developing various applications, including catalysis, bioanalysis, and optical devices. Herein, the morphology and peroxidase (POD)-mimicking activity of peptide-templated copper nanoassemblies (Cu NAs) are regulable with peptide types. The Cu NAs templated with peptide containing single cysteine are uniform nanoclusters with strong POD-like activity. However, the Cu NAs templated with peptide containing two cysteines are fusiform-like with very weak POD-like activity. Unexpectedly, the POD-like activity of Cu NAs templated with peptide containing two cysteines with lysine between the cysteines is significantly enhanced when trypsin is incubated, which is unchanged for the Cu NAs templated with peptide containing two cysteines without lysine between the cysteines. The remarkably enhanced POD-mimicking activity originates from trypsin specifically shearing the peptide bond on the lysine, thereby allowing the aggregated Cu NAs to unravel into individual nanoclusters. Therefore, a robust colorimetric sensing platform was constructed for sensitive and selective detection of trypsin, which showed a linear concentration range of 3-1000 nM and a detection limit of 0.82 nM (S/N = 3). More interestingly, featured by trypsin inhibitor restraining trypsin activity, it enabled us to screen trypsin inhibitors as well. Subsequently, the developed assay was applied to detect trypsin in serum samples with good accuracy and reproducibility. Thus, this strategy shows great potential application in the clinic for diagnosis of trypsin-indicating diseases as well as the screening of trypsin inhibitor-based anti-cancer drugs.

Copper nanocluster composites for analytical (bio)-sensing and imaging: a review

As an ideal substitute for traditional organic fluorescent dyes or up-conversion nanomaterials, copper nanoclusters (CuNCs) have developed rapidly and have been involved in exciting achievements in versatile applications. The emergence of novel CuNCs composites improves the poor stability and fluorescence intensity of CuNCs. With this in mind, great efforts have been made to develop a wide variety of CuNCs composites, and impressive progress has been made in the past few years. In this review, we systematically summarize absorption, fluorescence, electrochemiluminescence, and catalytic properties and focus on the multiple factors that affect the fluorescence properties of CuNCs. The fluorescence properties of CuNCs are discussed from the point of view of core size, surface ligands, self-assembly, metal defects, pH, solvent, ions, metal doping, and confinement effect. Especially, we illustrate the research progress and representative applications of CuNCs composites in bio-related fields, which have received considerable interests in the past years. Additionally, the sensing mechanism of CuNCs composites is highlighted. Finally, we summarize current challenges and look forward to the future development of CuNCs composites. Schematic diagram of the categories, possible sensing mechanisms, and bio-related applications of copper nanoclusters composites.

Ultrasensitive and turn-on homogeneous Hg2+ sensing based on a target-triggered isothermal cycling reaction and dsDNA-templated copper nanoparticles

In this work, an ultrasensitive and turn-on sensor for homogeneous Hg2+ detection has been constructed based on a target-triggered isothermal cycling reaction and rapid label-free signal output with dsDNA-templated copper nanoparticles (CuNPs). As the key component of the sensor, a hairpin DNA without any labels was designed to contain different functional sequence segments and to resist digestion by exonuclease due to the protruding 3'-terminus. In the presence of Hg2+, the formation of a T-Hg2+-T structure turned the protruding 3'-terminus of the hairpin DNA to a blunt end that could be efficiently digested by Exo III, accompanied by Hg2+ release, followed by another digestion cycle. Hence, the Hg2+-triggered isothermal cycling reaction accumulated numerous dsDNA templates that facilitated fluorescent CuNP generation and finally output an amplified signal used to identify the target. This protocol is capable of Hg2+ sensing in a concentration range of 5 orders of magnitude with a detection limit down to 3.9 pM. The as-constructed sensor also revealed high selectivity, as well as satisfactory results in recovery experiments of Hg2+ detection in real water samples.

Dual-Emission Fluorescence Probe Based on CdTe Quantum Dots and Rhodamine B for Visual Detection of Mercury and Its Logic Gate Behavior

It is urgent that a convenient and sensitive technique of detecting Hg2+ be developed because of its toxicity. Conventional fluorescence analysis works with a single fluorescence probe, and it often suffers from signal fluctuations which are influenced by external factors. In this research, a novel dual-emission probe assembled through utilizing CdTe quantum dots (QDs) and rhodamine B was designed to detect Hg2+ visually. Only the emission of CdTe QDs was quenched after adding Hg2+ in the dual-emission probe, which caused an intensity ratio change of the two different emission wavelengths and hence facilitated the visual detection of Hg2+. Compared to single emission QDs-based probe, a better linear relationship was shown between the variation of fluorescence intensity and the concentration of Hg2+, and the limit of detection (LOD) was found to be11.4 nM in the range of 0-2.6 μM. Interestingly, the intensity of the probe containing Hg2+ could be recovered in presence of glutathione (GSH) due to the stronger binding affinity of Hg2+ towards GSH than that towards CdTe QDs. Based on this phenomenon, an IMPLICATION logic gate using Hg2+/GSH as inputs and the fluorescence signal of QDs as an output was constructed.