General top-down strategy for generating single-digit nanodiamonds for bioimaging.

A variety of techniques exist for synthesizing nanodiamonds. However, it is challenging to produce nanoparticles with a size smaller than 4 nm without aggregation and large volumes of colloidal solutions containing single-digit nanodiamonds. In this study, we demonstrate a facile top-down strategy for the fabrication of monodisperse colloidal fluorescent nanodiamonds with a mean size of 3.6 nm from a suspension of commercial high-pressure and high-temperature diamond microcrystals (raw industrial materials) in an ambient environment using laser ablation in liquids. The formation of colloidal nanodiamonds is ascribed to a mechanism in which diamond microcrystals are first converted into disordered carbon nanoparticles through laser ablation. Subsequently, the amorphous carbon nanoparticles as an intermediate phase are converted into the final nanodiamonds under laser irradiation. Through the in situ covalent linking of ester and ketone groups on the surfaces of the nanodiamonds, tunable, high-performance fluorescence bioimaging can be achieved. The results suggest that single-digit fluorescent nanodiamonds can be generated from colloidal solutions.

Hot Carriers and Photothermal Effects of Monolayer MoOx for Promoting Sulfite Oxidase Mimetic Activity.

Local surface plasmon resonance (LSPR)-enhanced catalysis has brought a substantial amount of opportunities across various disciplines such as photocatalysis, photodetection, and photothermal therapeutics. Plasmon-induced photothermal and hot carriers effects have also been utilized to activate the enzyme-like reactions. Compared with natural enzymes, the relatively low catalytic performance of nanozymes severely hampered the potential applications in the field of biomedicine. For these issues mentioned above, herein, we demonstrate a highly efficient sulfite oxidase (SuOx) mimetic performance of plasmonic monolayer MoOx (ML-MoOx) upon LSPR excitation. We also established that the considerable photothermal effect and the injection of hot carriers induced by LSPR are responsible for promoting the SuOx activity of ML-MoOx. The high transient local temperature on the surface of ML-MoOx generated by the photothermal effect facilitates to impact the reaction velocity and feed the SuOx-like activity, while the generation of hot carriers which are suggested as predominant effects catalyzes the oxidation of sulfite to sulfate through significantly decreasing the activation energy for the SuOx-like reaction. These investigations present a contribution to the basic understanding of plasmon-enhanced enzyme-like reaction and provided an insight into the optimization of the SuOx mimetic performance of nanomaterials.

Modified Ti3C2 nanosheets as peroxidase mimetics for use in colorimetric detection and immunoassays.

Since being discovered in 2011, a large class of two-dimensional materials, labeled MXenes, has received increased research enthusiasm both theoretically and experimentally due to the unique physical, optical and electrical properties. Here, we prepared few-layered Ti3C2 nanosheets by a facile two-step liquid exfoliation method and, for the first time, demonstrated their intrinsic peroxidase-like activity in a Ti3C2-TMB-H2O2 system. The as-produced Ti3C2 nanosheets, especially after histidine modification, were characterized with excellent water dispersibility, large specific surface area, and high stability, which contribute to their much higher affinity to both substrates when compared to HRP. We have also established the catalytic mechanism whereby Ti3C2 nanosheets, where Ti switched spontaneously from an oxidized to reduced state, promoted the electron transfer from TMB to H2O2. Given the color reaction of Ti3C2 nanosheets, we have fabricated a colorimetric paper-based sensor integrated with a smartphone to detect glucose and an immunoassay to detect IR-ß, enabling Ti3C2 nanosheets to be a powerful tool in the biodetection field.

Oxygen Vacancy-Engineered PEGylated MoO3-x Nanoparticles with Superior Sulfite Oxidase Mimetic Activity for Vitamin B1 Detection.

Sulfite oxidase (SuOx ) is a molybdenum-dependent enzyme that catalyzes the oxidation of sulfite to sulfate to maintain the intracellular levels of sulfite at an appropriate low level. The deficiency of SuOx would cause severe neurological damage and infant diseases, which makes SuOx of tremendous biomedical importance. Herein, a SuOx mimic nanozyme of PEGylated (polyethylene glycol)-MoO3-x nanoparticles (P-MoO3-x NPs) with abundant oxygen vacancies created by vacancy-engineering is reported. Their level of SuOx -like activity is 12 times higher than that of bulk-MoO3 . It is also established that the superior increased enzyme mimetic activity is due to the introduction of the oxygen vacancies acting as catalytic hotspots, which allows better sulfite capture ability. It is found that vitamin B1 (VB1) inhibits the SuOx mimic activity of P-MoO3-x NPs through the irreversible cleavage by sulfite and the electrostatic interaction with P-MoO3-x NPs. A colorimetric platform is developed for the detection of VB1 with high sensitivity (the low detection limit is 0.46 µg mL-1 ) and good selectivity. These findings pave the way for further investigating the nanozyme which possess intrinsic SuOx mimicing activity and is thus a promising candidate for biomedical detection.

Fullerene-like MoS2 Nanoparticles as Cascade Catalysts Improving Lubricant and Antioxidant Abilities of Artificial Synovial Fluid.

Intraarticular injection of hyaluronic acid (HA) for viscosupplementation is a nonsurgical therapy for osteoarthritis (OA). However, HA fails to lubricate under a significant load and tends to be depolymerized by the overproduction of reactive oxygen species (ROS) in inflammation. Here, we for the first time reported that fullerene-like MoS2 (F-MoS2) nanoparticles are efficient lubricants and antioxidants for artificial synovial fluid. A model of arthrosis was built, to evaluate the tribological behavior of F-MoS2 nanoparticles. The tests showed that they significantly improve the antiwear and friction-reducing abilities of the artificial synovial fluid. More importantly, the F-MoS2 nanoparticles possess intrinsic dual-enzyme-like activity, mimicking superoxide dismutases (SOD) and catalases (CAT) under physiological conditions (pH 7.4, 25 °C). By coupling of these unique properties, a self-organized cascade catalytic system was constructed, which includes the disproportionation of superoxide radicals (O2•-) to hydrogen peroxide (H2O2) and subsequently the disproportionation of H2O2 into oxygen (O2). The effectiveness of the detox system was evaluated by human umbilical vein endothelial cells (HUVEC) models exposed to oxidative stress. After that, F-MoS2 nanoparticles were used to regulate the ROS level in artificial synovial fluid containing HA. Relative viscosity measurements showed the excellent protective effect of F-MoS2 nanoparticles against HA oxidative damage offered by O2•-. These results indicate that F-MoS2 nanoparticles are promising candidates for treatment of OA and other diseases caused by lubrication deficiency or oxidative stress.

Inorganic fullerene-like molybdenum selenide with good biocompatibility synthesized by laser ablation in liquids.

The fabrication of inorganic fullerene-like nanoparticles (IFNPs) is an attractive idea due to their unique structures and various potential applications. To date, IFNPs have been made from numerous compounds with layered two-dimensional structures, based on various synthetic methods. Here we have demonstrated for the first time that inorganic fullerene-like molybdenum selenide nanoparticles (MoSe2 IFNPs) can be synthesized by laser ablating a molybdenum selenide target in 30 vol % ethanol/water mixture at ambient temperature and pressure. The formation mechanism was proposed to elucidate the production of MoSe2 IFNPs in the process of laser ablation in liquids (LAL). The appropriate solvent facilitates the condensation of the plasma plume created by LAL to planar MoSe2. Then, laser-induced high temperature and high pressure lead to the formation of a vacancy in the planar MoSe2, causing the generation of nucleation and growth of the MoSe2 IFNPs. In addition, a CCK-8 (cell counting kit-8) assay and a cell viability assay were performed to examine the cytotoxic behavior and the effect on cell viability of MoSe2 IFNPs. The results show that MoSe2 IFNPs are reasonably nontoxic and biocompatible with the given cells, showing they have significant potential in biomedical applications.

Nanozymatic Antioxidant System Based on MoS2 Nanosheets.

The enzymatic antioxidant system (EAS) protects aerobic cells from oxidative stress. However, it is brittle and susceptible of inactivation of reactive oxygen species (ROS) immoderate production. Here, we demonstrated that MoS2 nanosheets (few-layer MoS2), as a multifunctional nanozyme, possess intrinsic activity of mimicking enzymes of superoxide dismutases (SODs), catalases (CATs), and peroxidases (PODs) under physiological conditions (pH 7.4, 25 °C). Further, MoS2 nanosheets showed POD-like activity by transferring electrons instead of generating ROS. Similar to EAS, a defense termed nanozymatic antioxidant system (NAS) was developed by MoS2 nanosheets, for regulation of oxidative stress. Surprisingly, this NAS can effectively scavenge other free radicals including hydroxyl radicals (•OH), nitrogen-centered free radicals (•DPPH), and nitric oxide (•NO). To evaluate these unique properties of MoS2-based NAS in vivo, Escherichia coli ( E. coli), Staphylococcus aureus ( S. aureus), and A549 cell models were established, respectively. These results showed MoS2 nanosheets superiorly protect bacteria and cells against oxidative injury caused by H2O2. This work makes MoS2 nanosheets promising antioxidants in the pathological processes and expands their application in biocatalysis and nano-biomedicine.

Few-layered MoSe2 nanosheets as an efficient peroxidase nanozyme for highly sensitive colorimetric detection of H2O2 and xanthine.

Molybdenum-containing and selenium-containing enzymes are generally prevalent in the biosphere, and the active sites of these involve molybdenum and selenium respectively. Herein, we for the first time demonstrated that few-layered molybdenum selenide (MoSe2) nanosheets possess intrinsic peroxidase-like activity. The few-layered MoSe2 nanosheets were prepared by a simple liquid exfoliation method. The catalytic process of the MoSe2 nanosheets accords with the Michaelis-Menten behavior and they have a higher affinity to both TMB and H2O2 compared to HRP. In addition, we established that the MoSe2 nanosheets catalyze the oxidation of TMB by promoting the electron transfer process from TMB to H2O2. More importantly, we applied the MoSe2 nanosheets to the field of biological detection by developing a highly sensitive and selective colorimetric detection of H2O2 and xanthine concentration. With these advantages, the few-layered MoSe2 nanosheets have critical potential in the diagnostics and biomedical fields.

2,6-Disubstituted pyrazines and related analogs as NR2B site antagonists of the NMDA receptor with anti-depressant activity.

Herein we describe the discovery of compounds that are competitive antagonists of the CP101-606 binding site within the NR2B subtype of the NMDA receptor. The compounds identified do not possess phenolic functional groups such as those in ifenprodil and related analogs. Initial identification of hits in this series focused on a basic, secondary amine side chain which led to good potency, but also presented a hERG liability. Further modifications led to examples of non-basic replacements which demonstrated much less liability in this regard. Finally, one compound in the series, 6a, was tested in the mouse forced swim depression assay and found to show activity (s.c. 60 mg/kg).

Discovery and pharmacological characterization of a small-molecule antagonist at neuromedin U receptor NMUR2.

Neuromedin U (NMU), through its cognate receptor NMUR2 in the central nervous system, regulates several important physiological functions, including energy balance, stress response, and nociception. By random screening of our corporate compound collection with a ligand binding assay, we discovered (R)-5'-(phenylaminocarbonylamino)spiro[1-azabicyclo[2.2.2]octane-3,2'(3'H)-furo[2,3-b]pyridine] (R-PSOP), a highly potent and selective NMUR2 antagonist. R-PSOP is a nonpeptidic small-molecule with the chemical composition C(20)N(4)O(2)H(22). In competition binding experiments, this compound was found to bind to NMUR2 with high affinity; the K(i) values were determined to be 52 and 32 nM for the human and rat NMUR2, respectively. Moreover, in functional assays measuring phosphoinositide turnover or intracellular calcium mobilization, R-PSOP strongly inhibited the responses stimulated by peptide agonists NMU-25, NMU-23, and NMU-8 in human embryonic kidney 293 cells expressing NMUR2. From Schild analyses, the functional K(b) values for R-PSOP were determined to be 92 and 155 nM at human and rat NMUR2, respectively. Highly selective for NMUR2, R-PSOP exhibited low affinity to the other subtype of NMU receptor, NMUR1, with a K(i) value >10 microM. R-PSOP in vivo attenuated NMU-23-evoked nociceptive responses in a rat spinal reflex preparation. To our knowledge, this is the first antagonist ever reported for NMU receptors. This compound could serve as a valuable tool for further understanding the physiological and pathophysiological roles of NMU system, while providing a chemical starting point that may lead to development of new therapeutics for treatment of eating disorders, obesity, pain, and stress-related disorders.

A high-throughput functional assay for characterization of gamma-aminobutyric acid(A) channel modulators using cryopreserved transiently transfected cells.

The ionotropic -aminobutyric acid (GABA)A receptors are an important family of drug targets for a variety of neurological and psychiatric disorders. Selective modulation of certain subtypes of the receptor could lead to novel or improved therapies. However, the discovery of subtype-selective compounds has been hampered by the lack of a high-throughput functional assay and the difficulty in establishing stable cell lines expressing GABAA receptor in a proper subunit composition. To meet drug discovery need we developed a fluorescent imaging plate reader(FLIPR)-based membrane potential assay with sufficient robustness and reproducibility for use in a high-throughput format. Two major subtypes of GABAA receptor were used: GABAA1 and GABAA2, which are composed of (alpha1)2(beta2)2gama2 and (alpha1)2(beta3)2gama2, respectively. We expressed the receptors by transiently co-transfecting cells with the three subunit DNAs in separate constructs, and by controlling the ratio of the DNA amount for each subunit transfected we forced the cells to express GABAA receptors in a pharmacologically relevant form. A large batch of transfected human embryonic kidney 293 cells were cryopreserved and used to screen and evaluate GABAA modulators.In these cells, agonist activation of GABAA receptor resulted in Cl- efflux and membrane depolarization, which was detected by FLIPR as an increase in fluorescence signal. Based on our characterization of several known GABAA modulators and a test set of compounds known to bind to the GABAA benzodiazepine site, we have demonstrated the validity and utility of this assay for discovery of novel pharmacological agents acting at GABAA receptors.