We developed a sensitive and selective method for detection of 4-Nitrophenol (PNP) using Ag nanoclusters (NCs) as fluorescence probe. Bovine serum albumin (BSA) was used as the template for preparing Ag NCs via wet chemistry. The fluorescence of as-prepared Ag NCs was significantly quenched in the presence of PNP, showing excellent linear relationships between the quenching degree of the fluorescence intensity and the concentrations of PNP in the range of 0.5 μM to 60 μM. The fluorescence quenching mechanism was also investigated. Furthermore, this method was applied for the recognition of PNP in environmental samples.

A novel fluorescence method for sensitive and selective detection of phosphate was developed based on near infrared emission Ag2S QDs/ Metal − Organic Shell Composite via the deposition of metal-organic (zinc-nitrogen) coordination shell around Ag2S QDs . Under optimal conditions described, the fluorescence intensity of the composite was decreased at 685 nm in the presence of phosphate, which was linearly related to the concentration of phosphate in the range of 0. 7 to 4.2 μM and 11.2 to 88.2 μM with the relative correlation coefficient of R2 = 0.998 and 0.987 respectively and detection limit as low as 6 nM. In addition, the proposed method was successfully utilized in serum samples, tap water and Yangtze River water samples with the recoveries ranged from 94.76 to 100.86 %, which presaged more opportunities for application in related bioassay and water sample researches.

•MEF is employed to synthesize silver-carbon dot nanohybrid with NIR to blue emission tunable.•A fluorescent probe for detecting ascorbic acid in NIR window has been constructed.•An IMPLICATION logic gate based on the probe is proposed.Recently, carbon dots (CDs) have drawn extensive attention owing to their unique properties. While more and more research had been focusing on the exploration of CDs as fluorescence sensors, the blue or green fluorescence emission of CDs restricts further applications of CDs, particularly in the biology-relevant fields due to the commonly blue auto-fluorescence of biological matrix. Therefore, the preparation of CDs with strong emission at long wavelengths is highly desirable. For these situations, a facile, straightforward and extra-reductant needless method was established to fabricate silver-carbon dot nanohybrid with enhanced near-infrared fluorescence through metal-enhanced fluorescence (MEF). We applied the Ag-CD nanohybrid as a probe to detect antioxidants such as ascorbic acid in near-infrared window, and the probe possesses a linear range of 0.2–60 μM. More importantly, this sensor could not only function in aqueous solution, but also display well selective response in intricate biological fluids. In addition, an IMPLICATION logic gate was constructed based on the unique characteristics of Ag-CD nanohybrid which presages more opportunities for application in single and multiple biological sensing.

In this report, a novel one-step chemical reduction method was reported for synthesis of water-soluble and stable fluorescent glutathione-templated silver nanocluster (GSH-Ag NCs) with ascorbic acid as an environmental-friendly reducing agent. On the basis of an oxidoreduction-induced fluorescence quenching mechanism, the prepared GSH-Ag NCs found to act as a cheap, non-toxic and highly sensitive “turn-off” fluorophore for ascorbic acid (AA). Furthermore, the fluorescence of the fluorophore/AA system could be recovered through addition of arginine (Arg), which made the system function as a highly selective “turn-on” sensor for arginine. Therefore, a “turn-off-on” switch sensor was proposed for detection of AA and Arg. Under optimized conditions, the probe gives a fluorescent response that is linear in the 2–300 μM concentration range of AA, with a detection limit of 0.1 μM. The probe for Arg, in turn, has a linear range in the 10–180 μM concentration range, and the limit of detection is 0.5 μM. In addition, the developed method showed great accuracy when employed to detect AA and Arg in human urine and serum, which shows its great potential in biological molecular recognition applications.

•An effective fluorescence “turn on-off” method based on PEI-Ag2S QDs has been constructed.•The mechanism relies on aggregation-induced emission enhancement (AIEE) and hydrolysis.•Steady-state kinetic analysis was explored to explain that the hydrolysis of heparinase I.A novel fluorescence “turn on-off” method for sensitive and selective detection of heparin and heparinase I was developed based on near infrared Polyethyleneimine Capped Ag2S Quantum Dots (PEI-Ag2S QDs). The fluorescence “turn-on” arose from aggregation-induced emission enhancement (AIEE) characteristics of PEI-Ag2SQDs induced by electrostatic interaction between PEI-Ag2SQDs and heparin. Heparinase I, which can specifically hydrolyze heparin into short fragments would de-aggregate PEI-Ag2S QDs/heparin system and lead to fluorescence “turn-off”. Under optimal conditions described, the fluorescence enhancement at 685 nm was linearly related to the concentration of heparin and heparinase I in the range of 0.069–2.275 μM and 0–103 ng mL−1 with the relative correlation coefficient of R2 = 0.997 and 0.99 and detection limit as low as 6 nM and 0.5 ng mL−1, respectively. The activity of the heparinase I was further investigated using steady-state kinetic for the reaction. In ddition, the proposed method was successfully utilized in serum samples, which presaged more opportunities for application in related biochemical and biomedical researches.

The rGO–ZnO–Fe3O4 nanocomposites were synthesized by a simple, economical and environmentally benign solvothermal method. The morphology, structure and photocatalytic activity of rGO–ZnO–Fe3O4 nanocomposites were characterized, and the effects of the preparation conditions were analyzed. The 25 mg of rGO–ZnO–Fe3O4 nanocomposites performed efficient photocatalytic activity for the degradation of 25 mL of 4.79 mg/L Rhodamine B under both ultraviolet and visible light irradiation. The nanocomposites could be easily retrieved from the wastewater by extra magnetic field due to the presence of magnetic Fe3O4 nanoparticles. After the degradation experiment was carried out five times, the degradation ratio is still close to 90% after irradiation after 5 cyclic, indicating that the rGO–ZnO–Fe3O4 nanocomposites have high stability for reuse. Therefore, the prepared rGO–ZnO–Fe3O4 nanocomposites may be a promising potential material for wastewater treatment.

The authors describe a method for increasing the peroxidase-like catalytic properties of copper nanoclusters (Cu-NCs) that are used in non-enzymatic assays. The Cu-NCs were prepared by utilizing 6-thio-β-cyclodextrin as both the template and as effective modulators for increasing the peroxidase-like properties of the Cu-NCs. The β-CD-coated Cu-NCs have an average diameter of 2 nm, are stable in aqueous solutions, display strong fluorescence with excitation/emission peak wavelengths of 360/450 nm, and possess peroxidase-like catalytic activity which makes them a useful enzyme mimic. We have applied the findings to non-enzymatic photometric determination (at 650 nm) of (a) H2O2 in the concentration range of 0.02 to 10 mM using the β-CD/Cu-NC assisted oxidation of tetramethylbenzidine by H2O2, and (b) glucose in the concentration range of 0.04 to 20 mM after addition of glucose oxidase and formation of H2O2. The detection limits (at an S/N ratio of 3) are 0.2 μM for H2O2 and 0.4 μM for glucose. The β-CD coating is found to result in a strong increase in the reaction rate, probably because the cavity of β-CD acts as a pocket for the recognition and catalysis of substrate. Hence, the binding specificity becomes similar to that of natural enzymes.

We developed a simple and sensitive room-temperature phosphorescence (RTP) method for the determination of graphene oxide (GO) in environmental water samples using amino-functionalized silica-encapsulated Mn/ZnS quantum dots (Mn/ZnS@SiO2-NH2) as a phosphorescent probe. The maximum phosphorescence excitation and emission wavelengths of the synthesized Mn/ZnS@SiO2-NH2 nanoparticles were 320 nm and 595 nm. The RTP intensity of the Mn/ZnS@SiO2-NH2 nanoparticles could be quenched in the presence of GO with a detection limit as low as 1.0 mg L−1. Good linear correlations were obtained over the concentration range from 0 to 10.0 mg L−1 with a correlation coefficient of 0.9987, and 10.0 to 25.0 mg L−1 with a correlation coefficient of 0.9979. The phosphorescence quenching mechanism was also discussed. This method was successfully applied to the determination of GO in environmental water samples which allows more opportunities for its application in biological and environmental systems.

An effective fluorescence method for the selective and rapid determination of trace-level Hg2+ in a wide pH range had been proposed based on the glutathione-protected Ag nanoclusters (NCs). Factors affecting the fluorescence intensity of GSH–Ag NCs were investigated. We found that the fluorescence intensity of Ag NCs remained high and stable under pH from 4 to 10, which benefits the monitoring of Hg2+ under different pH conditions in real samples. The fluorescence quenching mechanism is also discussed. The fluorescence of Ag NCs could be quenched in the presence of Hg2+ with a detection limit as low as 1 nM. Good linear correlations were obtained over the concentration range from 0 to 2.5 μM under different pH values (pH = 7, pH = 4 and pH = 9). In addition, this method was successfully applied to the determination of Hg2+ in real samples.

We show that copper nanoclusters coated with bovine serum albumin are viable probes for fluorometric determination of Cu(II) ion. The effect is attributed to the paramagnetic nature of Cu(II) bound to BSA. The ions Hg(II) and Fe(III) also give a strong effect but can be discerned by addition of EDTA. The probe can be regenerated by adding an excess of EDTA. The method is capable of detecting Cu(II) in the 0.02–34 μM, and the limit of detection is 1nM. The method was applied to the determination of Cu(II) in spiked water samples. It is rapid, simple, and fairly sensitive. The method may also be applied to detect Hg(II) and Fe(III) if Cu(II) is absent.

•An effective dual-emission fluorescent Ag NCs-based probe has been constructed.•Reversible phase transfer method is employed to synthesize Ag NCs with tunable dual-emission.•This established probe can avoid the interference of the autofluorescence of the biosystems.An effective dual-emission fluorescent Ag nanoclusters (NCs)-based probe have been constructed for rapid and selective detection of cysteine (Cys) with tunable sensitivity. Electrostatically induced reversible phase transfer method is employed to synthesize Ag nanoclusters with tunable emission intensity at 430 nm and 630 nm by controlling molar ratio between Ag and glutathione. The fluorescence of the Ag nanoclusters could be selectively quenched in the presence of Cys with a detection limit as low as 10 nM. Good linear correlations are obtained over the concentration range from 0.5 to 55 μM (quenched emission at 630 nm), 55 to 120 μM and 120 to 220 μM (enhanced emission at 555 nm) and 120 to 200 μM (quenched emission at 430 nm), respectively. The long-wavelength emission of the Ag nanoclusters can avoid the interference of the autofluorescence of the biosystems, which facilitated their applications in monitoring Cys in urine.

We employed 3-aminopropyltriethoxysilane to assist the synthesis of Ag NCs using polyethyleneimine as the template for detecting Hg2+ by localized surface plasmon resonance light-scattering technology. The developed selective and sensitive method presaged more opportunities for application in environmental systems.

A graphical abstract is available for this content

A graphical abstract is available for this content

We developed a simple and sensitive room-temperature phosphorescence (RTP) method for the determination of graphene oxide (GO) in environmental water samples using amino-functionalized silica-encapsulated Mn/ZnS quantum dots (Mn/ZnS@SiO2-NH2) as a phosphorescent probe. The maximum phosphorescence excitation and emission wavelengths of the synthesized Mn/ZnS@SiO2-NH2 nanoparticles were 320 nm and 595 nm. The RTP intensity of the Mn/ZnS@SiO2-NH2 nanoparticles could be quenched in the presence of GO with a detection limit as low as 1.0 mg L−1. Good linear correlations were obtained over the concentration range from 0 to 10.0 mg L−1 with a correlation coefficient of 0.9987, and 10.0 to 25.0 mg L−1 with a correlation coefficient of 0.9979. The phosphorescence quenching mechanism was also discussed. This method was successfully applied to the determination of GO in environmental water samples which allows more opportunities for its application in biological and environmental systems.