Pinyi Ma

Determination of malachite green in environmental water using cloud point extraction coupled with surface-enhanced Raman scattering

A novel, simple and ultra-sensitive method, for rapid detection of trace malachite green (MG) in environmental water using cloud point extraction (CPE) coupled with surface-enhanced Raman scattering (SERS) is described. The colloidal gold nanoparticles (AuNPs) were synthesized by reduction of chloroauric acid (HAuCl4) with trisodium citrate and were used as SERS substrates. The SERS substrates were found to produce enhancement factors of 1.52 × 106 for MG by employing the SERS peak at 1175 cm−1. After the optimization of SERS conditions including the volumes of ethanol, colloidal AuNPs and HCl, the present method was linear for MG at 1175 cm−1 and 1618 cm−1 over the concentration range of 0.5–35.0 μg L−1 and 2.5–40.0 μg L−1, with the correlation coefficients (r) of 0.9971 and 0.9960. The limits of detection (LODs) were 0.10 μg L−1 and 0.70 μg L−1, and the intra- and inter-day relative standard deviations (RSDs) of detection were in the range of 2.0–2.5% and 1.9–3.2% at 1175 cm−1 and 1618 cm−1, respectively. Recoveries obtained by analyzing 4 spiked environmental water samples at 2 levels were between 93.1 and 106.0%.

Enhancing sensitivity of surface plasmon resonance biosensor by Ag nanocubes/chitosan composite for the detection of mouse IgG.

A novel surface plasmon resonance (SPR) biosensor based on Ag nanocubes/chitosan composite was fabricated for mouse IgG detection. Ag nanocubes (AgNCs) were successfully synthesized with sulfide-mediated protocol. They were characterized with transmission electron microscopy (TEM) and UV-vis adsorption spectrum. AgNCs were etched by 3-Mercaptopropinic acid (MPA) and simply mixed with chitosan and glutaraldehyde. The Ag nanocubes/chitosan composite was deposited on Au film by the spin-coating. The electronic coupling between the AgNCs and the surface plasmon wave leads to the amplification of the SPR response, which results in the sensitivity enhancement of SPR biosensor. Moreover, antibody can be immobilized on Au film with aldehyde groups via Schiff alkali reaction. The traditional SPR biosensor based on MPA shows a response for mouse IgG in the concentration range of 2.50-40.00 μg mL(-1). The SPR biosensor based on AgNCs/chitosan composite shows a good response for mouse IgG in the concentration range of 0.60-40.00 μg mL(-1). The limit of quantification by the biosensor based on AgNCs/chitosan composite substrate is about 4 times lower than traditional biosensor, which has proved the SPR biosensor here proposed with more sensitivity and better performance than traditional SPR biosensor.

A FRET-based fluorescent probe for mercury ions in water and living cells

On the basis of fluorescence resonance energy transfer (FRET), a new rhodamine derivative (DRh) was synthesized as a ratiometric fluorescent probe for detecting Hg(2+) in water and living cells samples. The recognition properties of the probe DRh with metal ions had been investigated in H2O/CH3CN (9:1, v/v; Tris-HCl 50mmolL(-1); pH=7.0) solution by the UV-Vis spectrophotometry and the fluorescence spectrophotometry. The results showed that the probe DRh exhibited the selective recognition of Hg(2+). Upon the addition of Hg(2+), the spirolactam ring of probe DRh was opened. The 1:1 stoichiometric structure between DRh and Hg(2+) were supported by Jobs plot, MS and DFT theoretical calculations. The linearly fluorescence intensity ratio (I582/I538) is proportional to the concentration of Hg(2+) in the range 0-30μmolL(-1). The limit of detection (LOD) of Hg(2+) is 0.008μmolL(-1) (base on S/N=3). The present probe was applied to the determination of Hg(2+) in neutral water samples and gave recoveries ranging from 104.5 to 107.9%. Furthermore, the fluorescent probe also can be applied as a bioimaging reagent for Hg(2+) detection in HeLa cells.

Selective and sensitive SERS sensor for detection of Hg2+ in environmental water base on rhodamine-bonded and amino group functionalized SiO2-coated Au–Ag core–shell nanorods

Here, we designed a new type of SERS sensor with high selectivity and sensitivity for the determination of Hg2+ at picomolar concentrations based on hydrolysis reactions. The Rhodamine 6G-derived Schiff base bonded and amino group functionalized SiO2-coated Au–Ag core–shell nanorods (Au@Ag@SiO2–NH2-R6G, NR-Rs), which show extraordinary enhancement factors (EF) and good stability, were employed as the SERS substrate of the sensor. The tunable ability of the chemical bonding of the substrate generates appropriate probe molecules bound to the surface of the nanorods (NRs) and improves the selectivity and sensitivity of the SERS sensor dramatically. The limit of detection (LOD) of Hg2+ obtained using the present SERS sensor was 0.33 pmol L−1. Furthermore, the proposed substrate has pH-responsive ability. The present sensor is suitable for the on-site determination of pH and Hg2+ by combining with a portable Raman spectrometer.

Determination of melamine and malachite green by surface-enhanced Raman scattering spectroscopy using starch-coated silver nanoparticles as substrates

Silver nanoparticles (AgNPs) were synthesized by a classic method. The surface-enhanced Raman scattering (SERS) activity of the as-synthesized substrates was evaluated by measuring the SERS signals of several different target analytes. The influence of starch concentration on AgNPs was studied and 1.00% (w/v) of starch was selected. The starch-coated AgNPs displayed a higher stability than the classic AgNPs. The practical application of the starch-coated SERS substrate was evaluated by determination of melamine and malachite green. Under the optimal conditions, melamine and malachite green were determined in the ranges of 2.00–50.0 μg L−1 and 0.500–35.0 μg L−1 with correlation coefficients of 0.9992 and 0.9979, and the detection limits were 0.600 μg L−1 and 0.080 μg L−1, respectively. The recoveries of melamine in spiked milk samples and malachite green in water samples were 94–104% and 96–107%, respectively. These results foresee promising application of starch-coated AgNPs as sensitive SERS substrates in both food and environmental water.

Simultaneous determination of thiocyanate ion and melamine in milk and milk powder using surface-enhanced Raman spectroscopy

In this study, a simple and efficient method based on surface-enhanced Raman spectroscopy (SERS) was developed to detect thiocyanate ion (SCN−) and melamine in milk and milk powder. Silver nanoparticles (AgNPs), sodium chloride (NaCl) and sodium hydroxide (NaOH) were used as the substrate, the aggregating agent and the alkaline adjusting agent for the SERS process, respectively. The SERS peak intensity at 445 cm−1 was measured under low NaCl concentration for determining SCN−, followed by the measurement of the SERS peak intensity at 704 cm−1 under high NaCl concentration for determining melamine. The determination conditions for SERS, including the amount of AgNPs, NaCl and NaOH, and the mixing time before measurement, were optimized. By the present method, good linear responses were obtained for SCN− and melamine in the concentration ranges of 2.00–191.00 mg L−1 and 0.01–4.80 mg L−1 respectively, with correlation coefficients higher than 0.998. The present method was successfully applied to the simultaneous determination of SCN− and melamine in four spiked milk samples and three certified milk powder samples. The recoveries of SCN− and melamine in spiked milk samples were 95.15–100.47% and 94.43–102.84%, respectively. The relative standard deviations (RSDs) for determining melamine in certified milk powder samples were lower than 1.6%.

Magnetic core/shell Fe3O4/Au nanoparticles for studies of quinolones binding to protein by fluorescence spectroscopy

Magnetic core/shell Fe3O4/Au nanoparticles were used in the determination of drug binding to bovine serum albumin (BSA) using a fluorescence spectroscopic method. The binding constants and number of binding sites for protein with drugs were calculated using the Scatchard equation. Because of their superparamagnetic and biocompatible characteristics, magnetic core/shell Fe3O4/Au nanoparticles served as carrier proteins for fixing proteins. After binding of the protein to a drug, the magnetic core/shell Fe3O4/Au nanoparticles-protein-drug complex was separated from the free drug using an applied magnetic field. The free drug concentration was obtained directly by fluorescence spectrometry and the proteins did not influence the drug determination. So, the achieved number of binding sites should be reliable. The binding constant and site number for ciprofloxacin (CPFX) binding to BSA were 2.055 × 10(5) L/mol and 31.7, and the corresponding values for norfloxacin (NOR) binding to BSA were 1.383 × 10(5) L/mol and 38.8. Based on the achieved results, a suitable method was proposed for the determination of binding constants and the site number for molecular interactions. The method was especially suitable for studies on the interactions of serum albumin with the active ingredients of Chinese medicine.

Magnetic solid-phase extraction of triazine herbicides from rice using metal-organic framework MIL-101(Cr) functionalized magnetic particles

The metal-organic framework (MOF) functionalized magnetic graphene oxide/mesoporous silica composites (Fe3O4@SiO2-GO/MIL-101(Cr)) were synthesized and utilized as magnetic solid-phase extraction (MSPE) adsorbent for the extraction of seven triazine herbicides (terbuthylazine, secbumeton, terbumeton, atraton, atrazine, prometon and trietazine) in rice samples. Several experimental parameters, including type and volume of extraction solvent, amount of MIL-101(Cr), extraction time, volume of desorption solvent and desorption time were investigated and optimized. The limits of detection (LODs) of seven triazine herbicides obtained by using the proposed MSPE method combined with high performance liquid chromatography (HPLC) were in the range of 0.010-0.080µgkg-1. The recoveries of the triazine herbicides in spiked rice samples ranged from of 83.9-103.5% with the relative standard deviations lower than 8.7%. The intra and inter-day (n = 6) precisions for all triazine herbicides at the spiked level of 100.0µgkg-1 were 1.4-5.9% and 2.6-7.8%, respectively.

A novel surface plasmon resonance biosensor based on the PDA-AgNPs-PDA-Au film sensing platform for horse IgG detection

Herein we report a novel polydopamine-silver nanoparticle-polydopamine-gold (PDA-AgNPs-PDA-Au) film based surface plasmon resonance (SPR) biosensor for horse IgG detection. The PDA-AgNPs-PDA-Au film sensing platform was built on Au-film via layer-by-layer self-assembly. Ag ion was reduced in situ to AgNPs in presence of PDA. The top PDA layer can prevent AgNPs from being oxidized and connect with antibody via Schiff alkali reaction directly. The morphology and thickness of the modified gold film were characterized using scanning electron microscope and Talystep. Experimental results show that the PDA-AgNPs-PDA-Au film sensing platform is stable, regenerative and sensitive for horse IgG detection. The detection limit of horse IgG obtained with the present biosensor is 0.625μgmL-1, which is 2-fold and 4-fold lower than that obtained with biosensor based on PDA modified Au film and conventional biosensor based on MPA, respectively. Furthermore, when challenged to real serum samples, our sensor exhibited excellent specificity to horse IgG, suggesting its potential for industrial application.

Rapid aqueous synthesis of CuInS/ZnS quantum dots as sensor probe for alkaline phosphatase detection and targeted imaging in cancer cells

Early diagnosis of chronic, critical diseases improves clinical outcomes, and biomarkers play an important role as an indicator of severity or presence of a disease. Alkaline phosphatase (ALP) is one such vital biomarker in the diagnosis of several diseases. Herein we introduce a facile, sensitive fluorescent assay, based on the inner filter effect (IFE), for ALP activity determination in serum and in living cells. It is well known that the key to maximize the sensitivity of an IFE-based fluorescence assays is to broaden the overlap between the absorption of an absorber and the excitation/emission of a fluorophore. We employed CuInS/ZnS quantum dots (CIS/ZnS QDs) and p-nitrophenylphosphate (PNPP) as the fluorescent indicator and the substrate, respectively, for ALP activity assessment. Due to the CIS/ZnS QDs have an efficient excitation at 405 nm, meanwhile with a large Stokes shift emission at 588 nm, p-nitrophenol (PNP) with absorption peak at 405 nm, the hydrolyzed produce of PNPP and ALP, can act as a competitive absorber to absorb the excitation light of CIS/ZnS QDs, resulting in noticeable quenching of CIS/ZnS QDs. The proposed sensor detects ALP activity in human serum samples (sample consumption: 20 μL) with detection limit of 0.01 U L-1. Excellent biocompatibility of CIS/ZnS QDs enables the sensor to monitor endogenous ALP in living cells. Furthermore, because the surface modification or the linking between the receptor and the fluorophore is no longer required, this fluorescent sensing system has the potential to simplify ALP clinical measurement, thereby improving diagnostics of relevant diseases.