Xiaoyun Qin

Hydrothermal Treatment of Grass: A Low‐Cost, Green Route to Nitrogen‐Doped, Carbon‐Rich, Photoluminescent Polymer Nanodots as an Effective Fluorescent Sensing Platform for Label‐Free Detection of Cu(II) Ions

Increasing reaction temperature produces photoluminescent polymer nanodots (PPNDs) with decreased particle size and increased quantum yield. Such PPNDs are used as an effective fluorescent sensing platform for label-free sensitive and selective detection of Cu(II) ions with a detection limit as low as 1 nM. This method is successfully applied to determine Cu(2+) in real water samples.

Economical, Green Synthesis of Fluorescent Carbon Nanoparticles and Their Use as Probes for Sensitive and Selective Detection of Mercury(II) Ions

The present article reports on a simple, economical, and green preparative strategy toward water-soluble, fluorescent carbon nanoparticles (CPs) with a quantum yield of approximately 6.9% by hydrothermal process using low cost wastes of pomelo peel as a carbon source for the first time. We further explore the use of such CPs as probes for a fluorescent Hg(2+) detection application, which is based on Hg(2+)-induced fluorescence quenching of CPs. This sensing system exhibits excellent sensitivity and selectivity toward Hg(2+), and a detection limit as low as 0.23 nM is achieved. The practical use of this system for Hg(2+) determination in lake water samples is also demonstrated successfully.

One-pot green synthesis of Ag nanoparticles-graphene nanocomposites and their applications in SERS, H2O2, and glucose sensing

In this contribution, we demonstrate a green, cost-effective, one-pot preparative route toward Ag nanoparticles-graphene (AgNPs–G) nanocomposites in aqueous solution with the use of tannic acid (TA), an environmentally friendly and water-soluble polyphenol, as a reducing agent. Such AgNPs–G nanocomposites were synthesized through one-pot reduction of AgNO3 and GO by TA. We investigated surface enhanced Raman scattering (SERS) and electrochemical properties of the resultant AgNPs–G nanocomposites. It is found that such AgNPs–G nanocomposites show excellent SERS activity as SERS substrates and exhibit notable catalytic performance toward the reduction of H2O2. This enzymeless H2O2 sensor has a fast amperometric response time of less than 2 s. The linear range is estimated to be from 1 × 10−4 M to 0.01 M (r = 0.999) and the detection limit is estimated to be 7 × 10−6 M at a signal-to-noise ratio of 3. A glucose biosensor was further fabricated by immobilizing glucose oxidase (GOD) into chitosan–AgNPs–G nanocomposite film on the surface of a glassy carbon electrode (GCE). This sensor exhibits good response to glucose, and the linear response range is estimated to be from 2 to 10 mM (R = 0.996) at −0.5 V. The detection limit of 100 μM was achieved at a signal-to-noise ratio of 3. More importantly, we demonstrate successfully its application for glucose detection in human blood serum.

Biomolecule-Assisted, Environmentally Friendly, One-Pot Synthesis of CuS/Reduced Graphene Oxide Nanocomposites with Enhanced Photocatalytic Performance

In this work, we develop a novel environmentally friendly strategy toward one-pot synthesis of CuS nanoparticle-decorated reduced graphene oxide (CuS/rGO) nanocomposites with the use of L-cysteine, an amino acid, as a reducing agent, sulfur donor, and linker to anchor CuS nanoparticles onto the surface of rGO sheets. Upon visible light illumination (λ > 400 nm), the CuS/rGO nanocomposites show pronounced enhanced photocurrent response and improved photocatalytic activity in the degradation of methylene blue (MB) compared to pure CuS. This could be attributed to the efficient charge transport of rGO sheets and hence reduced recombination rate of excited carriers.

Synthesis of Au nanoparticles decorated graphene oxide nanosheets: Noncovalent functionalization by TWEEN 20 in situ reduction of aqueous chloroaurate ions for hydrazine detection and catalytic reduction of 4-nitrophenol

In this paper, we develop a cost-effective and simple route for the synthesis of Au nanoparticles (AuNPs) decorated graphene oxide (GO) nanosheets using polyoxyethylene sorbitol anhydride monolaurate (TWEEN 20) as a stabilizing agent for GO as well as a reducing and immobilizing agent for AuNPs. The AuNPs assemble on the surface of TWEEN-functionalized GO by the in situ reduction of HAuCl(4) aqueous solution. The morphologies of these composites were characterized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). It is found that the resultant AuNPs decorated GO nanosheets (AuNPs/TWEEN/GO) exhibit remarkable catalytic performance for hydrazine oxidation. This hydrazine sensor has a fast amperometric response time of less than 3s. The linear range is estimated to be from 5 μM to 3 mM (r=0.999), and the detection limit is estimated to be 78 nM at a signal-to-noise ratio of 3. The AuNPs/TWEEN/GO composites also exhibit good catalytic activity toward 4-nitrophenol (4-NP) reduction and the GO supports also enhance the catalytic activity via a synergistic effect.

Ag nanoparticles decorated polyaniline nanofibers: synthesis, characterization, and applications toward catalytic reduction of 4-nitrophenol and electrochemical detection of H2O2 and glucose

Polyaniline nanofibers (PANINFs) have been facilely prepared by electrochemical polymerization of aniline monomers in acidic aqueous media without using any templates and surfactants. The subsequent treatment of such nanofibers with a AgNO3 aqueous solution leads to in situ chemical reduction of Ag+ on them to form Ag nanoparticles decorated PANINFs (AgNPs/PANINFs) nanocomposites. We investigated the catalytic activity and electrochemical properties of these nanocomposites. It is found that such nanocomposites exhibit excellent catalytic activity toward reduction of 4-nitrophenol to 4-aminophenol by NaBH4 and exhibit remarkable catalytic performance for H2O2 reduction. The enzymeless H2O2 sensor constructed using the nanocomposites shows a fast amperometric response time of less than 3 s. The linear range and detection limit are estimated to be from 0.1 mM to 60 mM (r = 0.998) and 1.7 μΜ at a signal-to-noise ratio of 3, respectively. We have fabricated a glucose biosensor by immobilizing glucose oxidase into the AgNPs/PANINFs-modified glassy carbon electrode for glucose detection. This sensor exhibits good response to glucose. The linear response range is estimated to be from 1 mM to 12 mM (r = 0.997) at −0.58 V. The detection limit is estimated to be 0.25 mM at a signal-to-noise ratio of 3.

Green, low-cost synthesis of photoluminescent carbon dots by hydrothermal treatment of willow bark and their application as an effective photocatalyst for fabricating Au nanoparticles–reduced graphene oxide nanocomposites for glucose detection

In this study, we demonstrate that hydrothermal carbonization of low-cost wastes of willow bark leads to water-soluble, photoluminescent carbon dots (CDs) with diameters ranging from 1 to 4 nm and a quantum yield of approximately 6.0%. We further demonstrate the proof of concept that such CDs can be used as an effective photocatalyst for the simultaneous reduction of Au(III) complex and graphene oxide to form Au nanoparticles decorated reduced graphene oxide (AuNPs–rGO) nanocomposites by UV irradiation of a mixture of GO and HAuCl4 aqueous solution in the presence of CDs. It is found that the resultant AuNPs–rGO nanocomposites exhibit notable catalytic performance for H2O2 reduction and oxidation. Furthermore, we fabricate a glucose biosensor by immobilizing glucose oxidase on the AuNPs–rGO-modified glassy carbon electrode for glucose detection. The linear response range and detection limit are estimated to be from 2 mM to 18 mM (r: 0.995) and 45 μM, respectively. The application of this glucose sensor in human blood serum has also been demonstrated successfully.

A simple route for preparation of highly stable CuO nanoparticles for nonenzymatic glucose detection

Highly stable CuO nanoparticles about 2–4 nm in diameter have been successfully prepared by heating aqueous Cu(OAc)2 and urea solution in the presence of poly[(2-ethyldimethylammonioethyl methacrylate ethyl sulfate)-co-(1-vinylpyrrolidone)] (PQ11). Direct placing of the resultant dispersion on a glassy carbon electrode (GCE) without the use of an immobilization support matrix leads to very stable CuO nanoparticle-containing films with remarkable catalytic performance toward the oxidation of glucose. This sensor shows good response to glucose in comparison to other normally co-existing electroactive species (such as dopamine, ascorbic acid and uric acid). The linear detection range is estimated to be from 5 μM to 2.3 mM (r = 0.994), and the detection limit is estimated to be 0.5 μM at a signal-to-noise ratio of 3. More importantly, it suggests that this glucose sensor can be used for the glucose detection in human blood serum.

High-yield, large-scale production of few-layer graphene flakes within seconds: using chlorosulfonic acid and H2O2 as exfoliating agents

The present communication reports on a rapid exfoliation method for high-yield production of few-layer graphene flakes on a large scale from graphite within seconds with the use of chlorosulfonic acid and H2O2 as exfoliating agents.

Ag@poly(m-phenylenediamine)-Ag core–shell nanoparticles: one-step preparation, characterization, and their application for H2O2 detection

We have recently found that the direct mixing of m-phenylenediamine (MPD) and AgNO3 aqueous solutions at room temperature leads to Ag@poly(m-phenylenediamine) (Ag@PMPD) core–shell nanoparticles (Langmuir, 2011, 27, 2170). In this study, we characterize such core–shell nanoparticles in more detail by X-ray diffraction and IR techniques and further demonstrate that the size of the core and whole particle as well as the ratio of the shell thickness to the core size can be tuned by the molar ratio of MPD to Ag. Furthermore, the PMPD shell can be further used as a reductant to reduce Ag+ into small Ag nanoparticles (AgNPs) which are embedded in the PMPD matrix, leading to nanoparticles with a Ag core and a small AgNP-embedded PMPD shell (Ag@PMPD–Ag core–shell nanoparticles). The Ag core, although buried in the central part of the resultant nanoparticle, can still catalyze the reduction of H2O2, but the embedded AgNPs in the PMPD matrix exhibit superior catalytic performance. With these Ag@PMPD–Ag core–shell nanoparticles, we constructed an enzymeless H2O2 sensor with a fast amperometric response time of less than 2 s, a linear range of 0.1 to 170 mM and a detection limit of 2.5 μM at a signal-to-noise ratio of 3.