A Novel Electrochemical Sensor Modified with a Computer-Simulative Magnetic Ion-Imprinted Membrane for Identification of Uranyl Ion.

In this paper, a novel ion-imprinted electrochemical sensor modified with magnetic nanomaterial Fe3O4@SiO2 was established for the high sensitivity and selectivity determination of UO22+ in the environment. Density functional theory (DFT) was employed to investigate the interaction between templates and binding ligands to screen out suitable functional binding ligand for the reasonable design of the ion imprinted sensors. The MIIP/MCPE (magnetic ion imprinted membrane/magnetic carbon paste electrode) modified with Fe3O4@SiO2 exhibited a strong response current and high sensitivity toward uranyl ion comparison with the bare carbon paste electrodes. Meanwhile, the MCPE was fabricated simultaneously under the action of strong magnetic adsorption, and the ion imprinted membrane can be adsorbed stably on the electrode surface, handling the problem that the imprinted membrane was easy to fall off during the process of experimental determination and elution. Based on the uranyl ion imprinting network, differential pulse voltammetry (DPV) was adopted for the detection technology to realize the electrochemical reduction of uranyl ions, which improved the selectivity of the sensor. Thereafter, uranyl ions were detected in the linear concentration range of 1.0 × 10-9 mol L-1 to 2.0 × 10-7 mol L-1, with the detection and quantification limit of 1.08 × 10-9 and 3.23 × 10-10 mol L-1, respectively. In addition, the sensor was successfully demonstrated for the determination of uranyl ions in uranium tailings soil samples and water samples with a recovery of 95% to 104%.

Protamine-gold nanoclusters as peroxidase mimics and the selective enhancement of their activity by mercury ions for highly sensitive colorimetric assay of Hg(II).

We certify that protamine-gold nanoclusters (PRT-AuNCs) synthesized by one-pot method exhibit peroxidase-like activity. The catalytic activity of PRT-AuNCs followed typical Michaelis-Menten kinetics and exhibited higher affinity to 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate compared to that of natural horseradish peroxidase. Meanwhile, we found that Hg(II) could dramatically and selectively enhance the peroxidase-like activity of PRT-AuNCs, and the enhanced mechanism by Hg(II) was demonstrated to be generation of the cationic Au species and the partly oxidized Au species (Auδ+) by Hg2+-Au0/Au+ interaction. Based on this finding, quantitative determinations of Hg(II) via visual observation and absorption spectra were achieved. The proposed strategy displays high selectivity that arises from the strong aurophilic interaction of mercury towards gold. Moreover, the developed method is highly sensitive with a wide linear range and low detection limit of 1.16 nM. This strategy is not only helpful to develop effective nanomaterials-based artificial enzyme mimics but also irradiative to discover new applications of artificial mimic enzymes in bio-detection, medical diagnostics, and biotechnology. Graphical abstract Protamine-gold nanoclusters (PRT-AuNCs) synthesized by one-pot method exhibit peroxidase-like activity. Hg(II) can stimulate the peroxidase-like activity of PRT-AuNCs selectively, enhancing their ability to catalyze the chromogenic reaction of TMB by H2O2.

Aggregation-induced photoluminescence enhancement of protamine-templated gold nanoclusters for 1-hydroxypyrene detection using 9-hydroxyphenanthrene as a sensitizer.

In this study, we confirmed that protamine-templated gold nanoclusters (PRT-AuNCs) exhibit aggregation-induced emission properties (AIE-PRT-AuNCs). 1-Hydroxypyrene (1-OHPy) further induced the aggregation of AIE-PRT-AuNCs via hydrogen bonding and electrostatic and hydrophobic interactions, resulting in the aggregation-induced photoluminescence enhancement of AIE-PRT-AuNCs. 9-Hydroxyphenanthrene was able to decrease the background signal, thus increasing the sensitivity of the method. Based on these findings, a cost-effective, highly sensitive and selective strategy was proposed for the quantitative detection of 1-OHPy. This method displayed a wide linear range of 0.924 - 74.1 nmol/L with a low detection limit of 0.277 nmol/L, showing great potential for the monitoring of 1-OHPy in human urine. This strategy may provide a theoretical basis for future studies of the AIE properties of metal nanoclusters and their applications in the field of chemical and biological sensing.

[Simultaneous determination of calcium and magnesium by calculative spectrophotometric complexometric titration].

A new spectrophotometric complexometric titration method coupled with chemometrics for the determination of mixtures of metal ions has been developed. In the method described here, the titrant is a mixture of EDTA and two indicators. In the process of titration, both the volumetric addition of titrant and the progress of titration reaction can be characterized simultaneously by chemometric calculation with the absorption spectra, and then the titration curves can be obtained. With the titration curves, a matrix equation can be established, and thus the concentration of each component in the mixture of metal ions can be calculated with principal component regression. The method only needs the information of absorption spectra to obtain the analytical results, and is free of volumetric measurements. So the method is simple, convenient and precise, and has been applied to the simultaneous determination of mixtures of calcium and magnesium using malachite green and Cu-PAN as indicators with satisfactory results.

[Determination of deoxyribonucleic acids at nanograms levels with toluidine blue by a resonance light-scattering method].

Resonance light scattering (RLS) spectra of toluidine blue (TB) with DNA was studied. The RLS of TB was greatly enhanced by DNA in the range of pH 10-11. A RLS peak at 350 nm was found, and the enhanced intensity of RLS at this wavelength was proportional to the concentration of DNA. The linear range of the calibration curve was 0-900 ng x mL(-1) with the detection limit of 6.75 ng x mL(-1) for the ctDNA, and for fsDNA the linear range was 0-900 ng x mL(-1) with the detection limit of 2.99 ng x mL(-1). Precision at 500 ng x mL(-1) for the two nucleic acids was 3.7% and 5.6%, respectively. Four synthetic samples were determined satisfactorily.

A gold nanoparticles-modified aptamer beacon for urinary adenosine detection based on structure-switching/fluorescence-"turning on" mechanism.

A novel small molecule probe, aptamer beacon (AB), was introduced for adenosine (Ade) recognition and quantitative analysis. The Ade aptamer was engineered into an aptamer beacon by adding a gold nanoparticle-modified nucleotide sequence which is complementary to aptamer sequence (FDNA) at the 3'-end of FDNA. The fluorescence signal "turning on" was observed when AB was bound to Ade, which is attributed to a significant conformational change in AB from a FDNA/QDNA duplex to a FDNA-Ade complex. The Ade measurement was carried out in 20 mmol L(-1) Tris-HCl buffer solution of pH 7.4, ΔF signal linearly correlated with the concentration of Ade over the range of 2.0×10(-8) to 1.8×10(-6) mol L(-1). The limit of detection (LOD) for Ade is 6.0×10(-9) mol L(-1) with relative standard deviations (R.S.D) of 3.64-5.36%, and the recoveries were 98.6%, 100%, 102% (n=6), respectively. The present method has been successfully applied to determine Ade in human urine samples, and the obtained results were in good agreement with those obtained by the HPLC method. Our investigation shows that the unique properties of the AB could provide a promising potential for small molecules detection, and be benefit to extend the application of aptamer beacon technique.

Determination of trace formaldehyde in blood plasma by resonance fluorescence technology.

A novel method for the determination of trace formaldehyde in blood plasma has been established by using resonance fluorimetry technique. It was based on the fact that oxidation of pyronine Y by potassium bromate was catalyzed by formaldehyde in sulfuric acid. When the wavelength interval was at Δλ=0 nm, it was found that the decreased intensity (ΔF) of resonance fluorescence at 574.6 nm was proportional to the concentration of formaldehyde in the range of 1.27×10(-2) to 2.28 µg mL(-1). The limit of detection and the average recovery for formaldehyde were 3.80 ng mL(-1) and 101.6% (n=6), respectively. The present method had been applied to the determination of trace formaldehyde in blood plasma, and the obtained results were in good agreement with those obtained by the resonance light scattering method.

A wireless magnetoelastic sensor for urinary 2-naphthol detection based on the precipitation of 2-naphthol with diazonium salts.

A wireless magnetoelastic sensor has been developed for the determination of 2-naphthol (2-NAP) in human urine. This method is based on the precipitation of 2-NAP with diazonium salts produced by the diazo-reaction of sulfamethoxazole (SMZ) with nitrite under a weak alkaline condition, resulting in a descending of the resonance frequency of a wireless magnetoelastic sensor. The frequence shift values (ΔF) of the sensor were directly proportional to the concentration in the range of 1.13 - 139 µmol L(-1) for 2-NAP with a correlation coefficient of 0.997 and a detection limit of 0.340 µmol L(-1). The relative standard deviations were 2.38, 2.40 and 2.44%, and the average recovery was 107% (n = 6). The proposed method has additional advantages of being less time-consuming, low cost and remote query, and can be applied for real-time and in situ monitoring of 2-NAP in human urine. It would be a benefit to extend the scope of applications of magnetoelastic sensing techniques.

Rapid simultaneous analysis of 1-hydroxypyrene, 2-hydroxyfluorene, 9-hydroxyphenanthrene, 1- and 2-naphthol in urine by first derivative synchronous fluorescence spectrometry using Tween-20 as a sensitizer.

A novel method of first derivative synchronous fluorescence was developed for the rapid simultaneous analysis of trace 1-hydroxypyrene (1-OHP), 1-naphthol (1-NAP), 2-naphthol (2-NAP), 9-hydroxyphenanthrene (9-OHPe) and 2-hydroxyfluorene (2-OHFlu) in human urine. Only one single scan was needed for quantitative determination of five compounds simultaneously when Deltalambda=10 nm was chosen. In the optimal experimental conditions, there was a linear relationship between the fluorescence intensity and the concentration of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in the range of 1.75 x 10(-9) to 4.50 x 10(-6) mol L(-1), 3.64 x 10(-8) to 2.20 x 10(-4) mol L(-1), 8.18 x 10(-9) to 1.20 x 10(-4) mol L(-1), 3.26 x 10(-9) to 8.50 x 10(-5) mol L(-1) and 4.88 x 10(-9) to 5.50 x 10(-6) mol L(-1), respectively. The limits of detection (LOD) were found to be 5.25 x 10(-10) mol L(-1) for 1-OHP, 1.10 x 10(-8) mol L(-1) for 1-NAP, 2.46 x 10(-9) mol L(-1) for 2-NAP, 9.77 x 10(-10) mol L(-1) for 9-OHPe and 1.46 x 10(-9) mol L(-1) for 2-OHFlu. The proposed method is reliable, selective and sensitive, and has been used successfully in the determination of traces of 1-OHP, 1-NAP, 2-NAP, 9-OHPe and 2-OHFlu in human urine samples, whose results were in good agreement with those gained by the HPLC method.

Synchronous fluorescence determination of urinary 1-hydroxypyrene, beta-naphthol and 9-hydroxyphenanthrene based on the sensitizing effect of beta-cyclodextrin.

A novel method for the simultaneous determination of 1-hydroxypyrene (1-OHP), beta-naphthol (beta-NAP) and 9-hydroxyphenanthrene (9-OHPe) in human urine has been established by using synchronous fluorescence spectrometry. It was based on the fact that synchronous fluorescence spectrometry can resolve the broad-band overlapping of conventional fluorescence spectra, which arise from their similar molecular structures. Only one single scan is needed for quantitative determination of three compounds simultaneously when Deltalambda=15nm is chosen. The signals detected at these three wavelengths, 369.6, 330.0 and 358.0nm, vary linearly when the concentration of 1-OHP, beta-NAP and 9-OHPe is in the range of 2.16x10(-8)-1.50x10(-5)molL(-1), 1.20x10(-7)-1.10x10(-5)molL(-1) and 1.07x10(-7)-3.50x10(-5)molL(-1), respectively. The correlation coefficients for the standard calibration graphs were 0.994, 0.999 and 0.997 (n=7) for 1-OHP, beta-NAP and 9-OHPe, respectively. The limits of detection (LOD) for 1-OHP, beta-NAP and 9-OHPe were 6.47x10(-9)molL(-1), 3.60x10(-8)molL(-1) and 3.02x10(-8)molL(-1)with relative standard deviations (R.S.D.) of 4.70-6.40%, 2.80-4.20%, 3.10-4.90% (n=6), respectively. The method described here had been applied to determine traces of 1-OHP, beta-NAP and 9-OHPe in human urine, and the obtained results were in good agreement with those obtained by the HPLC method. In addition, the interaction modes between beta-cyclodextrin (beta-CD) and 1-OHP, beta-NAP or 9-OHPe, as well as the mechanism of the fluorescence enhancement were also discussed.