High-sensitivity NH3 gas sensor using pristine graphene doped with CuO nanoparticles.

A highly sensitive and selective NH3 gas sensor was developed based on single-layer pristine graphene doped with copper(II) oxide (CuO) nanoparticles of a specific size. High-quality single-layer graphene was grown using chemical vapor deposition. Approximately 15 nm-sized CuO colloidal nanoparticles were fabricated by a microwave-assisted thermal method using copper acetate as the precursor, and dimethylformamide as the reducing and stabilizing agent. Pristine graphene was doped with an aqueous suspension of CuO nanoparticles at a coating speed of 1500 rpm using a simple spin coater. CuO nanoparticle doping induces changes in the electronic properties of graphene; in particular, p-type doping significantly altered graphene resistivity in the presence of NH3 gas. Upon exposure of the pristine graphene surface to NH3 gas, NH3 reacted with O2-/ O-/ O2- species on the graphene surface and released electrons into graphene. This caused a change in the concentration of charge carriers in the valence channel of graphene and an increase in graphene resistivity, facilitating real-time NH3 monitoring with quick response and rapid recovery at 25 ℃ and ~ 55% relative humidity. Our results indicated that graphene doped with ~ 15 nm-sized CuO nanoparticles can sense NH3 gas selectively with a resistivity response of ~ 83%. Moreover, the sensor exhibited good reusability, fast response (~ 19 s), and rapid recovery (~ 277 s) with a detection limit of 0.041 ppm and a relative standard deviation of 0.76%.

Quantitative Detection of Thitsiol and Urushiol as Markers from the Gluta usitata Lacquer Tree Using HPLC.

Lacquer sap has been traditionally used in coatings and artwork. Suitable types of lacquer are required to preserve and restore artifacts. Recently, unsuitable cashew nut shell liquid (CNSL) has often been mixed with lacquer sap, so it is necessary to identify the characteristics of lacquer sap by the production area. However, research is still focused on urushiol and laccol. In this study, Myanmarese lacquer sap collected from Gluta usitata, which contains thitsiol as the main component, was analyzed by HPLC to quantify thitsiol using the standards 3-(10-phenyldecyl) benzene-1,2-diol (thitsiol 16) and 3-(8Z,11Z-pentadecadienyl)-benzenediol (urushiol 15:2) as markers, and calibration curves were plotted. The coefficients of determination (R2) for thitsiol 16 and urushiol 15:2 were 0.9985 and 0.9983, respectively. In addition, a blind test was conducted to confirm that accurate quantitative analysis was possible even when Myanmarese lacquer was mixed with lacquer from another production area, which contained urushiol as the main component, and CNSL, which contained cardol, a completely different catechol. Quantitative analysis of thitsiol 16 and urushiol 15:2 in Myanmarese lacquer using HPLC can be used to evaluate the quality of lacquer sap and for more sophisticated activities such as restoration by classifying differences in lacquer sap by the production area.

Computational Investigation of Conformational Properties of Short Azapeptides: Insights from DFT Study and NBO Analysis.

Azapeptides have gained much attention due to their ability to enhance the stability and bioavailability of peptide drugs. Their structural preferences, essential to understanding their function and potential application in the peptide drug design, remain largely unknown. In this work, we systematically investigated the conformational preferences of three azaamino acid residues in tripeptide models, Ac-azaXaa-Pro-NHMe [Xaa = Asn (4), Asp (5), Ala (6)], using the popular DFT functionals, B3LYP and B3LYP-D3. A solvation model density (SMD) was used to mimic the solvation effect on the conformational behaviors of azapeptides in water. During the calculation, we considered the impact of the amide bond in the azapeptide models on the conformational preferences of models 4-6. We analyzed the effect of the HB between the side-chain main chain and main-chain main-chain on the conformational behaviors of azapeptides 4-6. We found that the predicted lowest energy conformation for the three models differs depending on the calculation methods. In the gas phase, B3LYP functional indicates that the conformers tttANP-1 and tttADP-1 of azapeptides 4 and 5 correspond to the type I of ß-turn, the lowest energy conformation with all-trans amide bonds. Considering the dispersion correction, B3LYP-D3 functional predicts the conformers tctANP-2 and tctADP-3 of azapeptide 4 and 5, which contain the cis amide bond preceding the Pro residue, as the lowest energy conformation in the gas phase. The results imply that azaAsx and Pro residues may involve cis-trans isomerization in the gas phase. In water, the predicted lowest energy conformer of azapeptides 4 and 5 differs from the gas phase results and depends on the calculational method. For azapeptide 6, regardless of calculation methods and phases, tttAAP-1 (ß-I turn) is predicted as the lowest energy conformer. The results imply that the effect of the side chain that can form HBs on the conformational preferences of azapeptides 4 and 5 may not be negligible. We compared the theoretical results of azaXaa-Pro models with those of Pro-azaXaa models, showing that incorporating azaamino acid residue in peptides at different positions can significantly impact the folding patterns and stability of azapeptides.

Highly sensitive colorimetric determination of nitrite based on the selective etching of concave gold nanocubes.

Concave gold nanocubes are viable optical nanoprobes for the determination of nitrite ions. Herein, a novel approach was developed, based on the measurement of localized surface plasmon resonance absorption. The addition of nitrite ions selectively induced the etching of concave gold nanocubes, abrading the sharp vertices to spherical corners, which resulted in blue-shifted absorption accompanied by a color change from sapphire blue to light violet. The mechanism of selective etching of concave gold nanocube tips was elucidated by using X-ray photoelectron spectroscopy and atom probe tomography. The optimized detection of NO2- via the concave gold nanocube-based probe occurred at pH 3.0 and in 20 mM NaCl concentration at 40 °C. The absorption ratios (A550 nm/A640 nm) were proportional to the NO2- concentrations in the range 0.0-30 µM, with a detection limit of 38 nM (limit of quantitation of 0.12 µM and precision of 2.7%) in tap water. The highly selective and sensitive colorimetric assay has been successfully applied to monitor the nitrite ion concentrations in spiked tap water, pond water, commercial ham, and sausage samples.

Investigation of Surface Properties of Fluorocarbon Films Produced Using Plasma Techniques.

Different fluorocarbon thin films were deposited on Si substrates using two different plasma polymerization methods. Fluorine-containing hydrophobic thin films were obtained using inductively coupled plasma (ICP) and capacitively coupled plasma (CCP) with a mixture of fluorocarbon precursors (C2F6, C3F8, or c-C4F8) and an unsaturated hydrocarbon (C2H2). Different process parameters for plasma polymerization (e.g., processing time) were used to generate various fluorocarbon thin films. The hydrophobic properties and mechanical properties of the new products were measured using a profilometer, water contact angle measurements, pencil hardness, and a 90° peel test. The chemical compositions of the fluorocarbon thin films were characterized using X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The water contact angle results showed that the ICP technique provides a more hydrophobic surface compared to the CCP technique. XPS and FT-IR analyses indicated that the ICP technique generated more fluorine-related functional groups (i.e., CF-CFn, CF2, and CF3) in the surface region, while the CCP technique produced fewer fluorine-containing functional groups. However, the fluorocarbon thin films produced using the CCP technique showed greater adhesive strength than did the fluorocarbon thin films produced using the ICP technique. These results are useful to establish the optimal condition for the fabrication of fluorocarbon films and to develop the device in bio-sensing applications.

Complementary Characterization of Cu(In,Ga)Se2 Thin-Film Photovoltaic Cells Using Secondary Ion Mass Spectrometry, Auger Electron Spectroscopy, and Atom Probe Tomography.

To enhance the conversion performance of solar cells, a quantitative and depth-resolved elemental analysis of photovoltaic thin films is required. In this study, we determined the average concentration of the major elements (Cu, In, Ga, and Se) in fabricated Cu(In,Ga)Se2 (CIGS) thin films, using inductively coupled plasma atomic emission spectroscopy, X-ray fluorescence, and wavelengthdispersive electron probe microanalysis. Depth profiling results for CIGS thin films with different cell efficiencies were obtained using secondary ion mass spectrometry and Auger electron spectroscopy to compare the atomic concentrations. Atom probe tomography, a characterization technique with sub-nanometer resolution, was used to obtain three-dimensional elemental mapping and the compositional distribution at the grain boundaries (GBs). GBs are identified by Na increment accompanied by Cu depletion and In enrichment. Segregation of Na atoms along the GB had a beneficial effect on cell performance. Comparative analyses of different CIGS absorber layers using various analytical techniques provide us with understanding of the compositional distributions and structures of high efficiency CIGS thin films in solar cells.

The disappearance rate and risk assessment of thiacloprid residues in Asian pear using liquid chromatography confirmed with tandem mass spectrometry.

This study was undertaken to quantify the residue levels and propose the dissipation kinetics of thiacloprid formulated as suspension concentrate in field-incurred Asian pears grown under two different open-field conditions. Samples were extracted with 20% distilled water in acetonitrile; partitioned with brine water and dichloromethane; and purified with a Florisil solid phase extraction cartridge. The analyte was identified with an LC ultraviolet detector, and field-incurred samples were confirmed using LC-MS/MS. The calibration curve was linear over the range 0.05-5.0 mg/L with a satisfactory coefficient of determination (R2 = 0.9994). The limits of detection and limits of quantification (LOQ) were 0.003 and 0.01 mg/kg, respectively. The recovery rate fortified to blank samples at LOQ, 10× LOQ, and the maximum residue limit (MRL) were between 73.7 and 86.2% with relative standard deviation ≤9.0%. The residual concentrations at both sites were considerably lower than the MRL (0.7 mg/kg) set by the Korean Ministry of Food Drug Safety, with biological half-lives of 5.0 and 7.4 days, for sites 1 and 2, respectively. From the pre-harvest residue limit curve, it was predicted that if the residues were <1.13 or 1.40 mg/kg 10 days before harvest, the residue level would be lower than the MRL during harvest. Risk assessment on day 0 showed an acceptable daily intake (%) of 13.0% and 11.0% for sites 1 and site 2, respectively, which indicates that the residual amounts are not hazardous to the Korean population.

Various extraction methods for detection of bistrifluron residues in Asian pear using high-performance liquid chromatography: application to dissipation patterns under open-field conditions.

The present study was carried out to develop an analytical method for the detection and quantification of bistrifluron, a benzoylphenylurea compound, in pear using high-performance liquid chromatography with UV detection. Samples were extracted using conventional, AOAC and EN quick, easy, cheap, effective, rugged and safe 'QuEChERS' methods. As expected, conventional and EN-QuEChERS methods gave higher recoveries than AOAC. In addition, interference around the analyte retention time was observed in the conventional method. Thus, the EN-QuEChERS method was selected and validated by studying various parameters, including linearity, limit of detection, limit of quantification (LOQ), recovery and precision. Linearity was excellent, with a correlation coefficient of 0.9998. Recovery rates at three spiking levels (0.05, 0.2 and 1 mg/kg) ranged from 73.76 to 98.66%. Intra- and inter-day precisions, expressed as relative standard deviations, were <6%. The LOQ of 0.05 mg/kg was considerably lower than the maximum residue limit (1 mg/kg) set by the Korean Ministry of Food and Drug Safety. The developed method was successfully applied to open-field pear samples, in which the target analyte was slowly dissipated (55% decline) over 14 days with a half-life of 10.19 days. Notably, the residue levels throughout the period of sample collection (14 days) were lower than the maximum residue limit, indicating that the residue was not hazardous for consumers. Copyright © 2016 John Wiley & Sons, Ltd.

Analysis of mandipropamid residual levels through systematic method optimization against the matrix complexity of sesame leaves using HPLC/UVD.

An analytical method was developed to detect mandipropamid residues in sesame leaves using high-performance liquid chromatography-ultraviolet detection. Samples were extracted with acetonitrile and were prepurified using a solid-phase extraction (SPE) cartridge with an additional dispersive-SPE (d-SPE) sorbent application. The method was validated using an external calibration curve prepared using pure solvent. The linearity was excellent with determination coefficient = 1. The limits of detection and quantification were 0.003 and 0.01 mg/kg, respectively. Recoveries at three spiking levels - 0.1, 0.5, and 1.0 mg/kg - were in the range 80.3-90.7% with relative standard deviations <2%. This method was applied to field-treated samples collected from two different areas, Gwangju and Muan, in the Republic of Korea and the half-lives were similar, 5.10 and 5.41 days, respectively. The pre-harvest residue limit was also predicted for both sites. The proposed method is sensitive and able to quantify trace amounts of mandipropamid in leafy vegetables. The combination of SPE and d-SPE effectively removed the matrix components in sesame leaves. Copyright © 2015 John Wiley & Sons, Ltd.

A colorimetric probe to determine Pb(2+) using functionalized silver nanoparticles.

A simple and sensitive colorimetric method for the determination of Pb(2+) ions in aqueous samples was developed using 1-(2-mercaptoethyl)-1,3,5-triazinane-2,4,6-trione (MTT) functionalized silver nanoparticles (MTT-AgNPs). The Pb(2+) ion acted as the metal center of the coordination complex, which formed N-Pb(2+)-O coordination bonds with the MTT-AgNPs, shortening the interparticle distance, and inducing aggregation of the MTT-AgNPs. This aggregation resulted in a dramatic color change from yellow to dark blue. Using this methodology, the concentration of Pb(2+) ions in environmental samples could be quantitatively detected with the naked eye or by using UV-vis spectrometry. Also, we found that the selectivity and sensitivity of detection were noticeably improved in the pH range of 7-8, at which a more obvious color change was observed. The absorption ratios (A625/A395) of the modified AgNP solution exhibited a linear correlation with Pb(2+) ion concentrations within the linear range of 0.1-0.6 µg mL(-1), and the limits of detection in tap and pond water were 0.02 and 0.06 µg mL(-1), respectively. This cost-effective sensing system allows for the rapid and facile determination of Pb(2+) ions in aqueous samples.

A combination of solid-phase extraction and dispersive solid-phase extraction effectively reduces the matrix interference in liquid chromatography-ultraviolet detection during pyraclostrobin analysis in perilla leaves.

Perilla leaves contain many interfering substances; thus, it is difficult to protect the analytes during identification and integration. Furthermore, increasing the amount of sample to lower the detection limit worsens the situation. To overcome this problem, we established a new method using a combination of solid-phase extraction and dispersive solid-phase extraction to analyze pyraclostrobin in perilla leaves by liquid chromatography with ultraviolet absorbance detection. The target compound was quantitated by external calibration with a good determination coefficient (R(2) = 0.997). The method was validated (in triplicate) with three fortification levels, and 79.06- 89.10% of the target compound was recovered with a relative standard deviation <4. The limits of detection and quantification were 0.0033 and 0.01 mg/kg, respectively. The method was successfully applied to field samples collected from two different areas at Gwangju and Muan. The decline in the resiudue concentrations was best ascribed to a first-order kinetic model with half-lives of 5.7 and 4.6 days. The variation between the patterns was attributed to humidity.

Novel H2S sensing mechanism derived from the formation of oligomeric sulfide capping the surface of gold nanourchins.

A gold nanourchin (AuNU) probe with a novel sensing mechanism for monitoring H2S was developed as a feasible colorimetric sensor. In this study, AuNUs that are selectively responsive to H2S were fabricated in the presence of trisodium citrate and 1,4-hydroquinone using a seed-mediated approach. Upon exposure of the AuNU solution to H2S, the hydrosulfide ions (HS-) in the solution are converted into oligomeric sulfides by 1,4-hydroquinone used as a reducing agent during the synthesis of AuNUs. The oligomeric sulfides formed in the AuNU solution upon the addition of H2S were found to coat the surface of the AuNUs, introducing a blue shift in absorption accompanied by a color change in the solution from sky blue to light green. This colorimetric alteration by the capping of oligomeric sulfides on the surface of AuNUs is unique compared to well-known color change mechanisms, such as aggregation, etching, or growth of nanoparticles. The novel H2S sensing mechanism of the AuNUs was characterized using UV-Vis spectroscopy, high-resolution transmission microscopy, X-ray photoelectron spectroscopy, surface-enhanced Raman spectroscopy, secondary ion mass spectroscopy, liquid chromatography-tandem mass spectrometry, and atom probe tomography. H2S was reliably monitored with two calibration curves comprising two sections with different slopes according to the low (0.3-15 µM) and high (15.0-300 µM) concentration range using the optimized AuNU probe, and a detection limit of 0.29 µM was obtained in tap water.

Surface Analysis of Fermented Wheat and Rice Starch Used for Coating Traditional Korean Textiles.

Wheat and rice starches, traditionally used to stiffen fabric, become less contaminated and more antiseptic after fermentation for several years, thus enhancing their functional activity. In the present study, analytical techniques using particle size analysis, a gloss meter and a colorimeter were used to measure the physical properties of wheat and rice starches that had been fermented for 5 and 7 years, respectively. Their chemical contents and composition were determined by nutrient measurements and time-of-flight secondary ion mass spectrometry (ToF-SIMS). The ToF-SIMS spectra and ion images showed that fermented starch contained more carbohydrate and less lipid than fresh starch. The surface morphologies of the fermented starch granules and starch-coated textiles were examined by scanning electron microscopy and compared with the surface morphologies of fresh starch granules. The fermented wheat and rice starch granules were smaller and more rounded with a lower level of N-containing compounds (proteins) and exhibited more antiseptic properties than fresh starch granules. The results showed that physical measurements and chemical analysis were simple and complementary techniques for investigating traditional Korean starch materials and textiles.

Prostate cancer biomarker citrate detection using triaminoguanidinium carbon dots, its applications in live cells and human urine samples.

Citrate is a tricarboxylate, plays vital role in prostate cancer (PC) and the level of citrate is an indicator for PC identification. Herein, triaminoguanidine carbon dots (TAG-CDs) prepared by one step hydrothermal method and used as a citrate receptor. Notably the TAG-CDs without alkaline treatment were highly fluorescent at pH 7 with high quantum yield (11.3%). TAG-CDs were characterized through TEM, XRD, FT-IR, UV-vis and spectrofluorimetry. It is noted that the average size was of 2.8 nm, the presence of highly disordered carbon, retain the functionality of TAG. The absorbance maxima obtained at 294 nm and good emitting response observed at 396 nm. The Y-aromaticity of receptor guanidinium moiety acts as Lewis acid and have peculiar interaction with Lewis base citrate via electrostatic interaction and also protons in the TAG participate hydrogen bonds with citrate, which causes quenching of TAG-CDs. From the obtained linear quenching equation the LOD was found to be 4 nM. The probe expressed high selectivity, high interference tolerance (500 - fold), fast response in 15 mins and good biocompatible. Finally, TAG-CDs utilized for the intracellular imaging of citrate in live MCF-7 cells, it showed good cytotoxicity and delivered contrast images in presence, absence of citrate. TAG-CDs detected the citrate level in human urine samples, the obtained results are validated with HPLC method.

A new recognition moiety diphenylborinate in the detection of pyruvate via Lewis acid/base sensing pathway and its bioimaging applications.

Developing new reaction based recognizing units can enhance the specificity of target analyte molecules in practical applications of real samples and biosystems. Therefore, introducing a recognizing moiety diphenylborinate was encountered for the detection of pyruvate biomolecule through Lewis acid-base reaction based sensing strategy. The construction of the Schiff-base back bone between quinoline and N-(diethylamino)salicylaldehyde-diphenylborinate (QSB) were expressed the red shift from blue emission of quinoline in to green as that of dative bond developed between Schiff base nitrogen and boron atoms. The new sensing approach was involved such a way that fluorophore QSB is a Lewis acid while pyruvate acts as Lewis base, where the elimination of Lewis pair produced a weak green fluorescence including the formation of quinoline, N-(diethylamino)salicylaldehyde (QS). The switching products were witnessed through 1H NMR titration, HR-MS and FT-IR studies. The good selectivity and interference ability were achieved in presence of 1000-fold excess of possible interferences with LOD of 16 nM. Moreover, the tracking ability of the probe was employed towards pyruvate in live HeLa cell imaging for evaluating an exogenous and endogenous signals producing ability and its mitochondria targeting property was investigated successfully. Further, the practical utility of the probe was tested with milk samples and obtained good recovery results.

Quantitative Hg2+ detection via forming three coordination complexes using a lysosome targeting quinoline - Fisher aldehyde fluorophore.

This work describes (Z)-N-((Z)-2-(1,3,3-trimethylindolin-2ylidene)ethylidene)quinoline-8-amine (LYSO-QF), a high-performing and biocompatible dye comprised of quinoline and Fisher aldehyde moieties linked via an imine vinyl backbone with lysosome targeting ability that can be used to quantitatively detect the mercury ion (Hg2+) in biosystems and the natural environment. This is achieved by forming three different tetrameric, trimeric and dimeric complexes between Hg2+ and LYSO-QF with the limit of detection (LOD) of 11 nm. The complexes formed were analyzed with the aid of time-dependent density functional theory (TD-DFT) calculations. The concentration dependence of the Hg2+ complex fluorescence emission changes from grey-green to jade green and then to red as the different types of complex are formed. The favorable sensor properties of the LYSO-QF probe are demonstrated by monitoring different Hg2+ concentrations in buffer solutions, HeLa cells, zebrafish model samples and several different types of water sample. Experiments with Whatman paper strips demonstrate that the cost-effective LYSO-QF also has considerable potential for use in on-site Hg2+ detection with the naked eye.

Improved Measurements of the Physical Properties of Oriental Lacquers Using Atomic Force Microscopy and a Nanoindenter.

Researchers have widely investigated Oriental lacquers to identify the chemical composition and have elucidated corresponding polymerization mechanisms using rigorous analytical techniques. However, researchers generally test the physical properties of Oriental lacquers by conventional methods that are perhaps overly simplistic. Here, we propose accurate and quantitative methods for evaluating the physical properties of Korean, Vietnamese, and Myanmarese lacquer films using atomic force microscopy (AFM), a nanoindenter, and a 90° peel tester. We obtained surface images of the lacquers in accordance with drying time using scanning electron microscopy and AFM. The Korean lacquer film exhibited fast hardening speed, enhanced hardness, and strong adhesion strength compared with the other lacquers, although the Myanmarese lacquer film had a smoother surface than the Korean lacquer film. We used our characterization approach for evaluating a mixed Korean/Myanmarese (50/50 w/w) lacquer. Our proposed measurement techniques for Oriental lacquer films provided results that agreed with qualitative results from conventional tests. Force-distance curves in AFM and force-displacement with nanoindenter for Oriental lacquer films showed more accurate and quantitative data on the mechanical properties. Thus, researchers will find our approach useful when they optimize the chemical compositions and improve the physical properties of Oriental lacquer films for industrial applications.

Successive Detection of Zinc Ion and Citrate Using a Schiff Base Chemosensor for Enhanced Prostate Cancer Diagnosis in Biosystems.

Sensitive and quantitative detection of prostate cancer (PC) requires a chemosensor with an applicable sensing strategy. A star-shaped Schiff base triaminoguanidine-integrated thiophene fluorophore TAT was rationally designed with nitrogen and sulfur atoms to coordinate with Zn2+ as the initial step and to chelate with citrate as the following step. Formation of the complex TAT-Zn2+ induced an intramolecular charge transfer and caused a red-shifted, Zn2+ concentration-dependent fluorescence at 507 nm. Chelation of TAT-Zn2+ with citrate led to an emission band at 692 nm upon an aggregation-induced emission mechanism. The distinctive fluorescence emissions of Zn2+ and citrate biomarkers were demonstrated first in on-site paper-based test strips showing gradually enhanced colors at yellow and red channels and second in both in vitro and in vivo by using PC3 cells and BALB/c nude mouse animal models, respectively. The in vitro test confirmed the mitochondria organelle-targeting property of TAT, and the in vivo performance manifested the successful application of the probe in recognizing the prostate cancer. This is the first applicable chemosensor that could be in continuous recognition of dual PC biomarkers Zn2+ and citrate in cancer diagnosis with a mitochondria organelle-targeting ability.

A dual colorimetric probe for rapid environmental monitoring of Hg2+ and As3+ using gold nanoparticles functionalized with d-penicillamine.

A highly sensitive and selective colorimetric assay for the dual detection of Hg2+ and As3+ using gold nanoparticles (AuNPs) conjugated with d-penicillamine (DPL) was developed. When Hg2+ and As3+ ions coordinate with AuNP-bound DPLs, the interparticle distance decreases, inducing aggregation; this results in a significant color change from wine red to dark midnight blue. The Hg4f and As3d signals in the X-ray photoelectron spectra of Hg2+ (As3+)-DPL-AuNPs presented binding energies indicative of Hg2+-N(O) and As3+-N(O) bonds, and the molecular fragment observed in time-of-flight secondary ion mass spectra confirmed that Hg2+ and As3+ coordinated with two oxygen and two nitrogen atoms in DPL. The detection of Hg2+ and As3+ can be accomplished by observing the color change with the naked eye or by photometric methods, and this was optimized to provide optimal probe sensitivity. The assay method can be applied for environmental monitoring by first selectively quantifying Hg2+ in water samples at pH 6, then estimating the As3+ concentration at pH 4.5. The efficiency of the DPL-AuNP probe was evaluated for the sequential quantification of Hg2+ and As3+ in tap, pond, waste, and river water samples, and absorbance ratios (A 730/A 525) were correlated with Hg2+ and As3+ concentrations in the linear range of 0-1.4 µM. The limits of detection in water samples were found to be 0.5 and 0.7 nM for Hg2+ and As3+, respectively. This novel probe can be utilized for the dual determination of Hg2+ and As3+, even in the presence of interfering substances in environmental samples.

Tetraphenylethene-based fluorescent probe with aggregation-induced emission behavior for Hg2+ detection and its application.

A tetraphenylethene (TPE) derivative was designed and synthesized upon conjugation with bis(thiophen-2-ylmethyl) amine (BTA) containing a mercury-binding moiety and further characterized by using Nuclear magnetic resonance (NMR), LC-MS, UV-Vis, and fluorescence spectroscopic methods. The resulting TPE-BTA exhibited comprehensive aggregation-induced emission while expressing a high quantum yield and emission intensity at 70% water fraction. The probe exhibited a good photochromic effect with a Stokes shift of 178 nm, and the emission intensity at 550 nm increased considerably with the color turning from dark green to bright green under a UV lamp upon the addition of 5 µM Hg2+. The lowest-energy conformation of the probe showed that two thiophene rings were perpendicular to the phenyl ring, while two BTA molecules were situated in a staggered form to each other. The sulfur and nitrogen atoms present in TPE-BTA were coordinated to the Hg2+ ion, and these binding sites were confirmed by the NMR parameters, X-ray photoelectron spectroscopy signals, and structural calculations. The binding of Hg2+ to TPE-BTA was believed to restrict the intramolecular motion of TPE-BTA, thus inducing it to shine brighter according to the unique aggregation-induced emission effect. The concentration of Hg2+ was determined based on the enhancement of the emission intensity, and the present probe showed an extremely high sensitivity with a limit of detection of 10.5 nM. Furthermore, TPE-BTA enabled selective detection of Hg2+ even in the presence of a 1000-fold excess of other interfering metal ions. The proposed method was successfully employed to determine Hg2+ in living HeLa cells and real water samples.