Jinhua Zhan

Facile synthesis of N-acetyl-l-cysteine capped ZnS quantum dots as an eco-friendly fluorescence sensor for Hg2+

This paper described an investigation of a novel eco-friendly fluorescence sensor for Hg(2+) ions based on N-acetyl-l-cysteine (NAC)-capped ZnS quantum dots (QDs) in aqueous solution. By using safe and low-cost materials, ZnS QDs modified by NAC were easily synthesized in aqueous medium via a one-step method. The quantitative detection of Hg(2+) ions was developed based on fluorescence quenching of ZnS QDs with high sensitivity and selectivity. Under optimal conditions, its response was linearly proportional to the concentration of Hg(2+) ions in a range from 0 to 2.4 × 10(-6) mol L(-1) with a detection limit of 5.0 × 10(-9) mol L(-1). Most of common physiologically relevant cations and anions did not interfere with the detection of Hg(2+). The proposed method was applied to the trace determination of Hg(2+) ions in water samples. The possible quenching mechanism was also examined by fluorescence and UV-vis absorption spectra.

Cysteamine-modified silver nanoparticle aggregates for quantitative SERS sensing of pentachlorophenol with a portable Raman spectrometer.

Cysteamine-modified silver nanoparticle aggregates has been fabricated for pentachlorophenol (PCP) sensing by surface-enhanced Raman spectroscopy (SERS) using a portable Raman spectrometer. The cysteamine monolayers could preconcentrate PCP close to the substrate surface through the electrostatic interaction, which makes the SERS detection of PCP possible. Moreover, the Raman bands of cysteamine could be used as the internal spectral reference in the quantitative analysis. Qualitative detection of PCP was carried out by SERS without any sample pretreatment. Quantitative analysis of PCP was further realized based on the prepared substrate, as the log-log plot of normalized SERS intensity of PCP versus its concentrations exhibits a good linear relationship. The SERS signals collected on 20 randomly selected points show that the relative standard deviation of the normalized Raman intensity is 5.8%, which indicates the substrate had good uniformity. The PCP sensor also shows good long-term stability in the analyte solution. The substrate was cyclic immersed into PCP and methanol solution; after several cycles, the sensor still had good adsorption to PCP, which revealed the sensor has good reusability. Coupling with a portable Raman spectrometer, the cysteamine-modified silver nanoparticle aggregates have the potential to be used for in situ and routine SERS analysis of PCP in environmental samples.

A colorimetric and surface-enhanced Raman scattering dual-signal sensor for Hg2+ based on Bismuthiol II-capped gold nanoparticles

The addition of Bismuthiol II to the gold nanoparticles (AuNPs) solution led to the aggregation of AuNPs with a color change from red to blue. As a result, hot spots were formed and strong surface-enhanced Raman scattering (SERS) signal of Bismuthiol II was observed. However, the Bismuthiol II-induced aggregation of AuNPs could be reversed by Hg(2+) in the system, accompanied by a remarkable color change from blue to red. As evidenced by UV-vis and SERS spectroscopy, the variation in absorption band and SERS intensity was strongly dependent on the concentration of Hg(2+), suggesting a colorimetric and SERS dual-signal sensor for Hg(2+). The sensor had a high sensitivity, low detection limits of 2nM and 30nM could be achieved by UV-vis spectroscopy and by SERS spectroscopy, respectively. Other environmentally relevant metal ions did not interfere with the detection of Hg(2+). The method was successfully applied to detect Hg(2+) in water samples. It was simple, rapid and cost-effective without any modifying or labeling procedure.

Silver nanoparticles decorated filter paper via self-sacrificing reduction for membrane extraction surface-enhanced Raman spectroscopy detection

Silver nanoparticles (AgNPs) decorated filter papers combining solid-phase extraction (SPE) with surface enhanced Raman spectroscopy (SERS) achieved rapid collection of analytes and in situ detection. The AgNPs were fabricated by cellulose self-sacrificing reduction. Aqueous Ag(NH3)2OH was reduced by hydroxyl groups in cellulose under alkaline conditions. The AgNPs were highly uniform and firmly adhered to the microfibers. Reaction conditions were optimized by the probe molecule p-aminothiophenol (PATP) to attain the best Raman enhancement. Methylene blue trihydrate (MB) and 6-thioguanine (6-TG) were detected by flow-through method. The results exhibited outstanding SERS effect and an obvious improvement in detection limit was observed compared to common immersion methods. SERS detection was quantitative as the log-log plot of Raman intensity against MB and 6-TG concentrations showed a linear relationship. The SERS-active paper is degradable because it could be burned after analyte detection.

Synthesis of a β-cyclodextrin-modified Ag film by the galvanic displacement on copper foil for SERS detection of PCBs.

A mono-6-thio-β-cyclodextrin-modified silver film was synthesized via galvanic displacement on copper foil. The prepared silver films could enrich non-polar polychlorinated biphenyls (PCBs) molecules from hydrophilic phase using thiolate β-cyclodextrins (SH-β-CDs) as receptors. The components of as-prepared Ag-coated-Cu (Ag-Cu) film were confirmed by powder X-ray diffraction (XRD). Both surface-enhanced Raman spectroscopy (SERS) and energy dispersive X-ray spectroscopy (EDS) measurements gave strong evidences that the thiolated β-cyclodextrins (SH-β-CDs) had been immobilized on the surface of silver film. Compared to the substrates prepared in the absence of SH-β-CD, the surface morphology of the CD-modified Ag films was obviously changed. The interfacial enrichment and the capability of substrates to form inclusion complexes with PCBs molecules were tested by using PCB-15 (4,4-dichlorobiphenyl) as the probe molecules via SERS technique. The measured SERS spectra could distinguish the PCB-15 molecules at micro-molar level according to the most intense CCC bending in-plane mode of PCBs. The enhancement factor (EF) of the SERS substrates for PCB-15 was 1.2×10(5), which was comparable with a number of previous reports.

Morphology-dependent gas-sensing properties of ZnO nanostructures for chlorophenol.

The crystal-plane effect of ZnO nanostructures on the toxic 2-chlorophenol gas-sensing properties was examined. Three kinds of single-crystalline ZnO nanostructures including nanoawls, nanorods, and nanodisks were synthesized by using different capping agents via simple hydrothermal routes. Different crystal surfaces were expected for these ZnO nanostructures. The sensing tests results showed that ZnO nanodisks exhibited the greatest sensitivity for the detection of toxic 2-chlorophenol. The results revealed that the sensitivity of these ZnO samples was heavily dependent on their exposed surfaces. The polar (0001) planes were most reactive and could be considered as the critical factor for the gas-sensing performance. In addition, calculations using density functional theory were employed to simulate the gas-sensing reaction involving surface reconstruction and charge transfer both of which result in the change of electronic conductance of ZnO.

Magnetic nanoparticles and quantum dots co-loaded imprinted matrix for pentachlorophenol.

In this study, an imprinted silica matrix of pentachlorophenol (PCP) co-loaded with Fe(3)O(4) nanoparticles and ZnS:Mn(2+) quantum dots (QDs) was fabricated. The introduction of Fe(3)O(4) nanoparticles to the imprinted matrix provided an easy way to separate PCP under an external magnetic field. ZnS:Mn(2+) QDs offered a readout signal to monitor the amount of PCP bound to the imprinted matrix and evaluate the efficiency of imprinting. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy were used to characterize the imprinted matrix. The low angle X-ray diffraction and N(2) adsorption-desorption analysis indicated a periodic mesoporous structure. The as-synthesized imprinted matrix preferred to adsorb PCP rather than the other aromatic compounds like 2,4-dichlorophenoxy acetic acid, 2,4-dichlorophenol and phenol. The recoveries of spiked PCP in spring water and tap water with Fe(3)O(4)-ZnS:Mn(2+) co-loaded MIPs are 101% and 97%, respectively.

Facile synthesis and high formaldehyde-sensing performance of NiO–SnO2 hybrid nanospheres

A formaldehyde gas sensor with high sensitivity and superior selectivity has been fabricated successfully with NiO–SnO2 hybrid nanospheres, which consisted of n-type porous SnO2 nanospheres and p-type NiO dopants. It has been characterized by X-ray diffraction (XRD), high-resolution electron microscopy (HRTEM), Scanning Electron Microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and energy-dispersive X-ray spectroscopy (EDS). Compared with pure SnO2, the NiO-doped SnO2 nanospheres sensor exhibited significantly enhanced formaldehyde-sensing performances, including lower optimum sensing temperature (about 100 °C), lower detectable threshold (0.5 ppm), higher sensitivity (response = 26.03 to 50 ppm HCHO) and superior selectivity. Based on our experimental results, the role of the addition of NiO and a possible sensing mechanism has also been discussed.

Core–shell superparamagnetic Fe3O4@β-CD composites for host–guest adsorption of polychlorinated biphenyls (PCBs)

The effective recognition and enrichment of trace polychlorinated biphenyls (PCBs) in the environment are currently challenging issues due to human health concerns. In this paper, a surface absorptive layer coating superparamagnetic Fe3O4 nanoparticles for PCBs enrichment were prepared. This protocol involved the synthesis of Fe3O4 particles through a solvothermal reaction and the covering of a silica layer bonded β-cyclodextrin (β-CD) over Fe3O4 via a sol-gel process to construct core-shell Fe3O4@β-CD composites. β-CD was linked covalently to Fe3O4 nanoparticles to generate the binding sites, enhancing the stability of Fe3O4 nanoparticles in water. Meanwhile, superparamagnetic Fe3O4 core could be rapidly separated from matrix to simplify time-consuming washing extraction. The adsorption capacity of Fe3O4@β-CD composites to PCB28 and PCB52 in aqueous solutions was investigated. To estimate the theoretical binding site number of Fe3O4@β-CD, the obtained binding data were replotted according to Scatchard equation. The host-guest interaction between β-CD and PCBs were further examined with density functional theory (DFT) calculations. It provides theoretical evidence of β-CD as host molecule has a higher binding amount towards PCB-28 than PCB-52 on the basis of their optimized geometries and calculated complexation energies. The nanomaterial reported herein is an ideal candidate for various applications, including the recognition and removal of environmentally deleterious substances.

Surface-enhanced Raman spectroscopy detection of polybrominated diphenylethers using a portable Raman spectrometer.

Polybrominated diphenylethers (PBDEs), one of the most common brominated flame retardants, are toxic and persistent, generally detected by the chromatographic method. In this work, qualitative and quantitative detection of PBDEs were explored based on surface-enhanced Raman spectroscopy (SERS) technique using a portable Raman spectrometer. Alkanethiol modified silver nanoparticle aggregates were used as the substrate and PBDEs could be pre-concentrated close to the substrate surface through their hydrophobic interactions with alkanethiol. The effect of alkanethiols with different chain length on the SERS detection of PBDEs was evaluated. It was shown that 1-hexanethiol (HT) modified substrate has higher sensitivity, good stability and reusability. Qualitative and quantitative SERS detection of PBDEs in real sea water was accomplished, with the measured detection limits at 1.2×10(2) μg L(-1). These results illustrate SERS could be used as an effective method for the detection of PBDEs.