Pt nanoparticle (Pt NP)@UiO-66-NH2 composites were synthesized and encompassed the benefits of permanent porosity, high thermal and chemical stability of metal–organic frameworks (MOFs), together with the functional behavior of isolated Pt NPs. The PVP-stabilized Pt NPs with the average diameter of 2.48 nm were well dispersed and confined within the framework of UiO-66-NH2. Pt NPs possess highly peroxidase-like activities and make the composites oxidize 3,3′,5,5′-tetramethylbenzidine in the presence of H2O2. Moreover, the specific interaction between Hg2+ and Pt NPs leads to the effective suppression of the peroxidase-like activity of Pt NP@UiO-66-NH2, which endows excellent selectivity for Hg2+ measurement over the interfering metal ions. Based on the colorimetric sensing system, Hg2+ is linearly measured over the range from 0 to 10 nM with a detection limit of 0.35 nM. Moreover, the as-obtained Pt NP@UiO-66-NH2 nanocomposites exhibit high capacity and good selectivity for Hg2+ adsorption, which is successfully applied to treat Hg2+ in water with removal efficiency over 99%. With these findings, Pt NP@UiO-66-NH2 composites can be used to develop a simple and rapid colorimetric sensing system and are utilized as nanoadsorbents for facile removal of Hg2+. This work not only expands the scientific researches on MOFs but also provides practical application in environmental, biological, and relative fields.Keywords: adsorption; colorimetric sensor; mercury(II); peroxidase mimics; Pt nanoparticle@UiO-66-NH2 composites;

In this work, a novel ratiometric fluorescence sensor has been constructed for the selective and sensitive detection of Hg2+, which is based on the inner filter effect (IFE) of tetraphenylporphyrin tetrasulfonic acid (TPPS) toward black phosphorus quantum dots (BP QDs). Highly fluorescent BP QDs were successfully synthesized from bulk BP by sonication-assisted solvothermal method via a top-down route. In the presence of Hg2+, the IFE originating from spectral overlap between the excitation of BP QDs and the absorption of TPPS is inhibited and the fluorescence of BP QDs is restored. At the same time, the red fluorescence of TPPS is quenched due to its coordination with Mn2+. These phenomena result from the rapid coordination between Mn2+ and TPPS in the presence of Hg2+, which leads to the dramatic decrease of the absorption of TPPS. On the basis of these findings, we design a ratiometric fluorescence sensor for the detection of Hg2+. The as-constructed sensor reveals a good linear response to Hg2+ ranging from 1 to 60 nM with a detection limit of 0.39 nM. Furthermore, the sensing assay is applicable to detecting Hg2+ in real samples.Keywords: black phosphorus quantum dots; fluorescence; inner filter effect; mercury ion; ratiometric;

•Black phosphorus QDs were synthesized through sonication-assisted solvothermal method.•Green fluorescence QDs exhibit relative high quantum yield, good photostability and pH resistance.•A sensitive and label-free platform for fluorescent evaluation of the acetylcholinesterase activity was developed based on inner filter effect.In this work, a fast, sensitive and label-free fluorescence sensing platform for evaluating the acetylcholinesterase (AChE) activity was developed based on the inner filter effect (IFE) between black phosphorus quantum dots (BP QDs) and 2-nitro-5-thiobenzoate anion (TNB). BP QDs were successfully synthesized from bulk BP through a facile top-down route by sonication-assisted solvothermal method. The as-prepared QDs exhibit green fluorescence with a relative high quantum yield, good photostability and relative pH resistance. 5,5′-Dithiobis-(2-nitrobenzoic acid) (DTNB), as a well-known Ellman’s reagent, can react with thiol groups to form TNB. Based on the IFE between BP QDs and TNB, a sensitive and label-free sensing platform was developed for fluorescent measurement of thiols. As a proof-of-concept application, the platform was further applied in the evaluation of AChE activity by using acetylthiocholine as the substrate.

In this work, a novel phenomenon was discovered that the fluorescence intensity of silver sulfide quantum dots (Ag2S QDs) could be enhanced in the presence of rare earth ions through aggregation-induced emission (AIE). Based on the strong coordination between rare earth ions and F−, a facile and label-free strategy was developed for the detection of F− in living cells. Ag2S QDs were synthesized using 3-mercaptopropionic acid as sulfur source and stabilizer in aqueous solution. The near infrared (NIR) emitting QDs exhibited excellent photostalilty, high quantum yield and low toxic. Interestingly, the fluorescence intensity of QDs was obviously enhanced upon the addition of various rare earth ions, especially in the presence of Gd3+. The AIE mechanism was proved via the TEM, zeta potential and dynamic light scattering analysis. Moreover, the coordination between rare earth ions and F− could lead to the quenching of fluorescence QDs due to the weakening the AIE. Based on these findings, we developed a highly sensitive and selective method for detection of F−. The label-free NIR fluorescence probe was successfully used for F− bioimaging in live cells.

Two-photon fluorescent (TPF) molybdenum disulfide quantum dots (MoS2 QDs) were synthesized through a facile and one-step solvothermal approach. The MoS2 QDs exhibit small size and high stability. Because of their low toxicity and TPF ability, the MoS2 QDs are successfully applied in two-photon fluorescence bio-imaging.

In this work, a bottom-up strategy is developed to synthesize water-soluble molybdenum disulfide quantum dots (MoS2 QDs) through a simple, one-step hydrothermal method using ammonium tetrathiomolybdate [(NH4)2MoS4] as the precursor and hydrazine hydrate as the reducing agent. The as-synthesized MoS2 QDs are few-layered with a narrow size distribution, and the average diameter is about 2.8 nm. The resultant QDs show excitation-dependent blue fluorescence due to the polydispersity of the QDs. Moreover, the fluorescence can be quenched by hyaluronic acid (HA)-functionalized gold nanoparticles through a photoinduced electron-transfer mechanism. Hyaluronidase (HAase), an endoglucosidase, can cleave HA into proangiogenic fragments and lead to the aggregation of gold nanoparticles. As a result, the electron transfer is blocked and fluorescence is recovered. On the basis of this principle, a novel fluorescence sensor for HAase is developed with a linear range from 1 to 50 U/mL and a detection limit of 0.7 U/mL.Keywords: biosensor; fluorescence; hyaluronidase; hydrothermal method; MoS2 quantum dots

•Rare earth metal oxide/graphene electrocatalyst with ORR activity was reported.•Electrocatalyst was synthesized by thermal treatment of Ce3+-doped GO.•Crystallization of CeO2 can be controlled through thermal treatment temperature.•CeO2/rGO nanocomposites obtained at 750 °C exhibits superior ORR activity.•Synergistic effect of CeO2 and rGO makes catalyst high performance.In this paper, a facile and simple strategy was developed for in-situ growth cerium oxide nanoparticles on reduced graphene oxide (rGO) through thermal treatment of the Ce3+-doped graphene oxide(GO) under nitrogen atmosphere. Through regulation the thermal treatment temperature, the growth of cerium oxide nanocrystals can be easily controlled in accompany with the reduction of GO. The morphology and chemical composition of the as-synthesized CeO2/rGO at different temperature are characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. The nanocomposites show electrocatalytic activity toward the oxygen reduction reaction (ORR) in alkaline solution. Especially, the cerium oxide nanoparticles/rGO nanocomposites treated at 750 °C possess excellent electrocatalytic ability with a dominating four-electron pathway, high tolerance of methanol and long-term operation stability due to the well exfoliation of graphene and perfect crystalline structure of cerium oxide. Compared to the commercial Pt/C catalyst, the synergistic effect of the fast electron transport of rGO and the high electrocatalytic activity of cerium oxide nanocrystals makes the nanocomposites as advanced, non-precious electrocatalysts for ORR.

In this work, the colloid of Au nanoparticles (AuNPs)/reduced graphene oxide (rGO) was synthesized by growth AuNPs on rGO via the reduction of HAuCl4 on graphene oxide (GO) nanosheets. The nanoarchitecture of the colloid could be controllably regulated through in-situ Pb2+-enhanced gold leaching reaction, which made the colloid be a flexible surface-enhanced Raman scattering (SERS) platform for Pb2+ detection. Upon the addition of Pb2+, the Raman signal of graphene underwent significant descent due to the decrease of the amount of the “hot spots”, which was originated from Pb2+-accelerated dissolution of AuNPs on the graphene surface in the present of thiosulfate (S2O32−). Based on the change of SERS signal through in situ regulation the nanoarchitecture of the colloid, a sensitive and selective strategy for Pb2+ measurement was developed with a linear range from 5 nM to 4 μM as well as a low detection limit of 1 nM. Furthermore, the SERS-based method was applied for the determination of Pb2+ in water samples with satisfactory results.Surface-enhanced Raman scattering method for sensitive and selective monitoring of Pb2+ was realized by in situ regulation the nanoarchitecture of gold nanoparticles/reduced graphene oxide through Pb2+-enhanced gold dissolution reaction.

Greigite magnetic nanoparticles (Fe3S4-MNPs) were prepared and reveal a peroxidase-like activity. Kinetic studies revealed a pseudo-enzymatic activity that is much higher than that of other magnetic nanomaterial-based enzyme mimetics. This finding was exploited to design a photometric enzymatic glucose assay based on the formation of H2O2 during enzymatic oxidation of glucose by glucose oxidase, and the formation of a blue product from an enzyme substrate that is catalytically oxidized by H2O2 in the presence of Fe3S4-MNPs. Glucose can be detected in the 2 to 100 μM concentration range, and the low detection limit is 0.16 μM. The method was applied to quantify glucose in human serum. In our perception, this enzyme mimetic has a large potential in that it may be used in other oxidase based assays, but also in ELISAs.

•MoS2/Nitrogen-doped graphene (NG) composites were obtained by physically mixing method.•MoS2 sheets deposited NG could be used as effective electrocatalyst for ORR.•Enhanced electrocatalytic activity is due to the synergistic effect of MoS2 and NG.•The ORR is a four-electron process based on Koutecky-Levich equation.A simple yet effective strategy was developed to generate a non-precious oxygen electrode electrocatalyst of MoS2/nitrogen-doped graphene (NG) by physical mixing MoS2 sheets with NG. The micrometer-sized MoS2 sheets were obtained through ultrasonication exfoliation of the bulk MoS2, only showing little oxygen reduction reaction (ORR) activity. MoS2/NG hybrid was obtained by loading MoS2 sheets onto NG through ultrasonication, and the resulting nanocomposites exhibited improved electrocatalytic activity for ORR with dominant 4 electron pathway in alkaline solutions. The exposed active edges as well as the synergistic effect and reduced resistance connection jointly make the MoS2/NG composite a highly competitive ORR catalyst.A simple yet effective method was developed for generating an electrocatalyst for oxygen reduction reaction by deposited MoS2 sheets on nitrogen-doped graphene (NG). Due to the synergistic effect of MoS2 and NG, enhancement of electrocatalytic oxygen-reduction was realized.

In this work, we developed a novel, label-free, colorimetric sensor for Pb2+ detection based on the acceleration of gold leaching by graphene oxide (GO) at room temperature. Gold nanoparticles (AuNPs) can be dissolved in a thiosulfate (S2O32−) aqueous environment in the presence of oxygen; however, the leaching rate is very slow due to the high activation energy (27.99 kJ mol−1). In order to enhance the reaction rate, some accelerators should be added. In comparison with the traditional accelerators (metal ions or middle ligands), we found that GO could efficiently accelerate the gold leaching reaction. Kinetic data demonstrate that the dissolution rate of gold in the Pb2+–S2O32−–GO system is 5 times faster than that without GO at room temperature. In addition, the effects of surface modification and the nanoparticle size on the etching of AuNPs were investigated. Based on the GO-accelerated concentration-dependent colour changes of AuNPs, a colorimetric sensor for Pb2+ detection was developed with a linear range from 0.1 to 20 μM and the limit of detection (LOD) was evaluated to be 0.05 μM. This colorimetric assay is simple, low-cost, label-free, and has numerous potential applications in the field of environmental chemistry.

•Surface charge could affect the peroxidase-like activity of MoS2 NPs.•SDS–MoS2 NPs possess highly-efficient peroxidase-like activity.•Catalytic kinetics of SDS–MoS2 NPs show a ping–pong mechanism.•Colorimetric detection of H2O2 and glucose was realized.In this work, we find that the peroxidase-like activity of MoS2 nanoparticles (NPs) is dependent on the surface charge. Negatively charged sodium dodecyl sulfate modified MoS2 nanoparticles (SDS–MoS2 NPs) possess highly-efficient peroxidase-like activity. MoS2 NPs with intrinsic peroxidase-like activity were synthesized through a simple one-pot hydrothermal route. The peroxidase-like activities of different surfactants modified MoS2 NPs were discussed. Compared with bare MoS2 NPs and positively charged cetyltrimethyl ammonium bromide modified MoS2 NPs, SDS–MoS2 NPs have the best peroxidase-like activity. SDS–MoS2 NPs can efficiently catalyze the oxidation of 3,3,5,5-tetramethylbenzidine (TMB) in the presence of H2O2 to generate a blue product. On basis of this, we have successfully established a novel platform for colorimetric detection of H2O2, and the detection limit is 0.32 μM. Furthermore, the SDS–MoS2 NPs based platform can also be used for high sensitivity and selectivity detection of glucose with a wide linear range of 5.0–500 μM by controlling the generation of H2O2 in the presence of glucose oxidase.Sodium dodecyl sulphate modified MoS2 nanoparticles show highly-efficient peroxidase-like activity and can be used for the colorimetric detection of H2O2 and glucose.

We describe an electrochemical sensor for melamine based on a glassy carbon electrode (GCE) modified with reduced graphene oxide that was decorated with gold nanoparticles (AuNP/rGO). The AuNPs/rGO nanocomposite was synthesized by co-reduction of Au(III) and graphene oxide and characterized by transmission electron microscopy, Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The response of the modified GCE to melamine was investigated by using hexacyanoferrate as an electrochemical reporter. It is found that the electrochemical response to hexacyanoferrate is increasingly suppressed by increasing concentration of melamine. This is attributed to competitive adsorption of melamine at the AuNP/rGO composite through the interaction between the amino groups of melamine and the AuNPs. The presence of rGO, in turn, provides a platform for a more uniform distribution of the AuNPs and enhances the electron transfer rate of the redox reaction. The findings were used to develop a sensitive method for the determination of melamine. Under optimized conditions, the redox peak current of hexacyanoferrate at a working voltage of 171 mV (vs. SCE) is linearly related to the concentration of melamine in 5.0 to 50 nM range. The method was successfully applied to the determination of melamine in food contact materials.

•The stable and cadmium-free DNA functionalized ZnS:Mn2+ QDs were successfully synthesized through a facile one-step route.•We constructed a novel FRET system based on one-step synthesized DNA-ZnS:Mn2+ QDs (donor) and WS2 nanosheets (acceptor).•The FRET-based strategy was applied for the detection of streptavidin and folate receptor by combining TPSMLD and Exo III.DNA functionalized quantum dots (QDs) are promising nanoprobes for the fluorescence resonance energy transfer (FRET)-based biosensing. Herein, cadmium-free DNA functionalized Mn-doped ZnS (DNA-ZnS:Mn2+) QDs were successfully synthesized by one-step route. As-synthesized QDs show excellent photo-stability with the help of PAA and DNA. Then, we constructed a novel FRET model based on the QDs and WS2 nanosheets as the energy donor-acceptor pairs, which was successfully applied for the protein detection through the terminal protection of small molecule-linked DNA assay. This work not only explores the potential bioapplication of the DNA-ZnS:Mn2+ QDs, but also provides a platform for the investigation of small molecule-protein interaction.

In this work, we developed a novel, label-free, colorimetric sensor for Pb2+ detection based on the acceleration of gold leaching by graphene oxide (GO) at room temperature. Gold nanoparticles (AuNPs) can be dissolved in a thiosulfate (S2O32−) aqueous environment in the presence of oxygen; however, the leaching rate is very slow due to the high activation energy (27.99 kJ mol−1). In order to enhance the reaction rate, some accelerators should be added. In comparison with the traditional accelerators (metal ions or middle ligands), we found that GO could efficiently accelerate the gold leaching reaction. Kinetic data demonstrate that the dissolution rate of gold in the Pb2+–S2O32−–GO system is 5 times faster than that without GO at room temperature. In addition, the effects of surface modification and the nanoparticle size on the etching of AuNPs were investigated. Based on the GO-accelerated concentration-dependent colour changes of AuNPs, a colorimetric sensor for Pb2+ detection was developed with a linear range from 0.1 to 20 μM and the limit of detection (LOD) was evaluated to be 0.05 μM. This colorimetric assay is simple, low-cost, label-free, and has numerous potential applications in the field of environmental chemistry.

Two-photon fluorescent (TPF) molybdenum disulfide quantum dots (MoS2 QDs) were synthesized through a facile and one-step solvothermal approach. The MoS2 QDs exhibit small size and high stability. Because of their low toxicity and TPF ability, the MoS2 QDs are successfully applied in two-photon fluorescence bio-imaging.