A Binary Functional Substrate for Enrichment and Ultrasensitive SERS Spectroscopic Detection of Folic Acid Using Graphene Oxide/Ag Nanoparticle Hybrids

Herein graphene oxide/Ag nanoparticle hybrids (GO/PDDA/AgNPs) were fabricated according to a self-assembly procedure. Using the obtained GO/PDDA/AgNPs as SERS substrates, an ultrasensitive and label-free detection of folic acid in water and serum was demonstrated based on the inherent SERS spectra of folic acid. The modified graphene oxide exhibited strong enrichment of folic acid due to the electrostatic interaction, and the self-assembled Ag nanoparticles greatly enhanced the SERS spectra of folic acid, both of which led to an ultrahigh sensitivity. Therefore, although the SERS enhancement of p-ATP on GO/PDDA/AgNPs was weaker than that on Ag nanoparticles, the SERS signals of folic acid on GO/PDDA/AgNPs were much stronger than that on Ag nanoparticles. To improve the detection, the concentration of GO/PDDA/AgNPs was optimized to reduce background of the graphene oxide. The SERS spectra of the folic acid showed that the minimum detected concentration of folic acid in water was as low as 9 nM with a linear response range from 9 to 180 nM. To estimate the feasibility of the detection method based on GO/PDDA/AgNPs for the practical applications, diluted serum containing different concentrations of folic acid was taken as real samples. It was established that the sensitivity and the linear range for the folic acid in serum were comparable to that in water. This ultrasensitive and label-free SERS detection of folic acid based on GO/PDDA/AgNPs offers great potential for practical applications of medicine and biotechnology

Templateless, Surfactantless, Electrochemical Route to a Cuprous Oxide Microcrystal: From Octahedra to Monodisperse Colloid Spheres

Herein we report a simple electrochemical route for the controlled synthesis of a Cu2O microcrystal from perfect octahedra to monodisperse colloid spheres via control of the electrodeposition potential without the introduction of any template or surfactant. Perfect Cu2O octahedra and monodisperse colloid spheres have been obtained in high yield (∼100%)

Twenty Second Synthesis of Pd Nanourchins with High Electrochemical Activity through an Electrochemical Route

A rapid, templateless, surfactantless, electrochemical route is reported to synthesize uniform and clean Pd nanoparticles (∼350 nm in diameter) with a substructure of sharp nanospikes (∼95 nm in length). The effects of electrodeposition potential, PdCl2 concentration, and supporting electrolyte were explored for the formation of the Pd nanourchins. The systematic studies revealed that the concentration of Pd(II) greatly affects the density of the nanospikes on the Pd nanourchins in this short-time synthesis. The substructure of the nanospikes on the nanourchins was examined to be a single-crystal quadrangular pyramid. Further investigation of the Pd nanourchins by cyclic voltammetry (CV) showed their high electrochemical activity toward formic acid oxidation

Self-Assembly of Cationic Polyelectrolyte-Functionalized Graphene Nanosheets and Gold Nanoparticles: A Two-Dimensional Heterostructure for Hydrogen Peroxide Sensing

We demonstrate the use of cationic polyelectrolyte poly(diallyldimethyl ammonium chloride) (PDDA) functionalized graphene nanosheets (GNs) as the building block in the self-assembly of GNs/Au nanoparticles (NPs) heterostructure to enhance the electrochemical catalytic ability. To ensure the GNs were modified with PDDA successfully, we study the PDDA/GNs with atomic force microscopy (AFM) and zeta potential measurements on the roughness and zeta potential changes relative to those of unmodified GNs, respectively. Then, the citrate-capped Au NPs are employed as the other model particles to construct two-dimensional GNs/NPs heterostructure. Here, the use of PDDA modifiers not only alters the electrostatic charges of graphene, but also probably provides a convenient self-assembly approach to the hybridization of graphene. Furthermore, we employ the high-loading Au NPs on graphene (GN/Au-NPs) as the electrochemical enhanced material for H2O2 sensing (as the model analyte). The wide linear ranges and low detection limits are obtained using the chronoamperometry technique at the GN/Au-NPs-modified glassy carbon electrode

Interfacial Electron Regulation of Rh Atomic Layer-Decorated SnO₂ Heterostructures for Enhancing Electrocatalytic Nitrogen Reduction

Ammonia (NH3), which serves as a fertilizer supply, is struggling to satisfy the ever-growing population requirements over the world. The electrocatalytic nitrogen reduction to NH3 production is highly desired but shows the extremely poor activity and selectivity of reported electrocatalysts. In this work, we rationally design a novel Rh atomic layer-decorated SnO2 heterostructure catalyst through the interfacial engineering strategy, simultaneously achieving the highest NH3 yield rate (149 μg h–1 mgcat–1) and Faradaic efficiency (11.69%) at −0.35 V vs the reversible hydrogen electrode. This result is superior to the optimum response of previously reported SnO2- or Rh-based catalysts for electrochemical nitrogen reduction. Both X-ray absorption spectra characterization and density functional theory calculations reveal the strong electron interaction between the Rh atomic layer and the SnO2 heterostructure, which effectively regulated the interfacial electron transfer and d-band center. The downshift of the d-band center results in the greatly reduced H adsorption energy and the highly accelerated reaction kinetics for nitrogen reduction. This work endows a new insight into the interfacial electron regulation for weakening H adsorption and further enhancing the electrocatalytic N2 reduction

Reversibly Electroswitched Quantum Dot Luminescence in Aqueous Solution

In this study, we fabricated a novel hybrid film system, in which reversible electroswitching quantum dot (QD) luminescence was realized in aqueous solution for the first time. On the basis of an electrochromic material, poly(methylene blue) (PMB), QD luminescence could be switched effectively in a narrow potential range of −0.4 to 0 V via the corresponding luminescence quenching effect. The luminescence switching operation was reversible and reproducible, and no noticeable changes in both “on” and “off” luminescence intensities were observed in 20 cycles. This simple system not only effectively overcame the harsh operation environment that generally existed in previous reports but also provided an easy method for the design and fabrication of other novel QD electroswitchable hybrid components

Deep Eutectic Solvent with Prussian Blue and Tungsten Oxide for Green and Low-Cost Electrochromic Devices

Deep eutectic solvents (DESs), as a class of green and sustainable solvents, are the valuable alternative media for various applications. Here choline chloride (ChCl)-urea DES was used as the electrolyte for electrochromic reactions of two inorganic electrochromic materials (Prussian blue (PB) and tungsten trioxide (WO3)). Starting from the evaluations of thermal and electrochemical properties of ChCl-urea DES, we found the DES electrolyte can be used in the electrochromic experiments at a wide temperature range (from 25 to 100 °C) and potential range (from −0.8 to 1.0 V vs Ag). And as the temperature increased, both coloring and bleaching time dramatically decreased but efficiency decreased little. A complementary electrochromic device with PB-DES-WO3 was also fabricated to demonstrate the feasibility for electrochromic applications with the combination of green and cheap DES and inorganic electrochromic materials

Easy Synthesis and Imaging Applications of Cross-Linked Green Fluorescent Hollow Carbon Nanoparticles

We propose an ingenious method for synthesizing cross-linked hollow fluorescent carbon nanoparticles (HFCNs) with green emission by simply mixing acetic acid, water, and diphosphorus pentoxide. This is an automatic method without external heat treatment to rapidly produce large quantities of HFCNs, in contrast to other syntheses of fluorescent carbon nanoparticles that required high temperature, complicated operations, or long reaction times. Characterizations of HFCNs through high-resolution transmission electron microscopy, infrared/Raman spectroscopy, and X-ray diffraction indicate that abundant small oxygenous graphite domains existed and endowed the HFCNs with fluorescent properties. After simple post-treatments, the cross-linked HFCNs can be used for cell-imaging applications. Compared with traditional dyes and CdTe quantum dots, HFCNs are the superior fluorescent bioimaging agent according to their low toxicity, stability, and resistance to photobleaching. The HFCNs were also applied to watermark ink and fluorescent powder, showing their promising potentials for further wide usage

Specific Nanodrug for Diabetic Chronic Wounds Based on Antioxidase-Mimicking MOF-818 Nanozymes

Chronic wound is a common complication for diabetic patients, which entails substantial inconvenience, persistent pain, and significant economic burden to patients. However, current clinical treatments for diabetic chronic wounds remain unsatisfactory. A prolonged but ineffective inflammation phase in chronic wounds is the primary difference between diabetic chronic wounds and normal wounds. Herein, we present an effective antioxidative system (MOF/Gel) for chronic wound healing of diabetic rats through integrating a metal organic framework (MOF) nanozyme with antioxidant enzyme-like activity with a hydrogel (Gel). MOF/Gel can continuously scavenge reactive oxygen species to modulate the oxidative stress microenvironment in diabetic chronic wounds, which leads to a natural transition from the inflammation phase to the proliferation phase. Impressively, the efficacy of one-time-applied MOF/Gel was comparable to that of the human epidermal growth factor Gel, a widely used clinical drug for various wound treatments. Such an effective, safe, and convenient MOF/Gel system can meet complex clinical demands

Specific Nanodrug for Diabetic Chronic Wounds Based on Antioxidase-Mimicking MOF-818 Nanozymes

Chronic wound is a common complication for diabetic patients, which entails substantial inconvenience, persistent pain, and significant economic burden to patients. However, current clinical treatments for diabetic chronic wounds remain unsatisfactory. A prolonged but ineffective inflammation phase in chronic wounds is the primary difference between diabetic chronic wounds and normal wounds. Herein, we present an effective antioxidative system (MOF/Gel) for chronic wound healing of diabetic rats through integrating a metal organic framework (MOF) nanozyme with antioxidant enzyme-like activity with a hydrogel (Gel). MOF/Gel can continuously scavenge reactive oxygen species to modulate the oxidative stress microenvironment in diabetic chronic wounds, which leads to a natural transition from the inflammation phase to the proliferation phase. Impressively, the efficacy of one-time-applied MOF/Gel was comparable to that of the human epidermal growth factor Gel, a widely used clinical drug for various wound treatments. Such an effective, safe, and convenient MOF/Gel system can meet complex clinical demands