N-doped carbon quantum dots from osmanthus fragrans as a novel off-on fluorescent nanosensor for highly sensitive detection of quercetin and aluminium ion, and cell imaging.

In this work, fluorescent N-doped carbon quantum dots (N-CQDs) have been synthesized by simple hydrothermal heating of natural osmanthus fragrans, without any toxic ingredients or surface chemical modifications. The N-CQDs possess a high quantum yield of 21.9 %, outstanding blue fluorescence, good water dispersity, and excellent optical stability. Because the favorable inner filter effect (IFE) between N-CQDs and quercetin (QT) occurs, the addition of QT to N-CQDs can cause their fluorescence quenching. When Al3+ was added to the N-CQDs/QT system solution, it was found that the inhibition of IFE leads to the fluorescence intensity of N-CQDs/QT system enhancement by virtue of a specific binding of QT to aluminum ion (Al3+). Therefore, we used the N-CQDs as a novel off-on fluorescent nanosensor to detect QT and Al3+. Under optimal conditions, the fluorescent nanosensor can detect QT within the wide linear response in the range of 0.003-80 µmol/L with as low as 1 nmol/L detection limit. For the detection of Al3+, the N-CQDs/QT system showed linearity response toward Al3+ in a range of 0.1∼100 µmol/L and the limit of detection was found at 26 nmol/L. In addition, N-CQDs have been successfully used to efficient quantification QT in human plasma and monitor Al3+ in serum samples. Noteworthy, the N-CQDs demonstrated low toxicity toward T24 cells, which realized sensing QT and Al3+ in the living cells.

A highly efficient introduction system for single cell- ICP-MS and its application to detection of copper in single human red blood cells.

A method of simultaneous cell counting and determination of metals in single cells using time-resolved inductively coupled plasma-mass spectrometry (ICP-MS) was reported. A facile, low cost and highly efficient single-cell introduction system of time-resolved ICP-MS consists of a flow cell, a visual contrast calibration device, a customized nebulizer and a fabricated spray chamber. The flow cell includes a cell sample tube, a sheath liquid tube and a flow chamber. The visual contrast calibration device was composed of a microscope with a 16 × microscope objective (160 × total magnification). The flow chamber was used to combine a flow of red blood cell suspension (0.800 µL/min) and a flow of PBS (4.40 µL/min) into the nebulizer. The intact cells were directly introduced with the single-cell introduction system into the plasma via nebulizing, and then ion plumes corresponding to single cells were individually detected with mass spectrometer. The frequency of the spikes directly reflects the number of cells, and the intensity of spikes is proportional to the concentration of copper within one cell. The single-cell introduction system can be transported into the ICP-MS via a customized transport system with 100% efficiency. A high cell introduction efficiency into the plasma supports for a reduction of cell consumption. The Cu signal frequency was about 120 cell events per minute. This single-cell introduction system simplifies the introduction of individual and intact cells. The copper content in single red blood cell was 0.20-0.40 fg.

A Novel Carbon Quantum Dots Signal Amplification Strategy Coupled with Sandwich Electrochemiluminescence Immunosensor for the Detection of CA15-3 in Human Serum.

A sensitive sandwich electrochemiluminescence immunosensor was established by employing graphene oxide-PEI-carbon quantum dots (CQDs)-Au nanohybrid as probe to measure carbohydrate antigen 15-3 (CA15-3), a breast cancer biomarker. In this work, nanocomposites of Ag nanoparticles and polydopamine (AgNPs-PDA) were synthesized by redox reaction between dopamine and Ag+. The nanocomposite with high surface area can provide an efficient substrate for immobilizing initial antibody (Ab1). Carbon quantum dots (CQDs) are fixed on polyethylenimine-functionalized graphene oxide (PEI-GO) by amide bonds. Au nanoparticles are modified on CQDs-decorated PEI-GO substrates. The secondary antibody (Ab2) was immobilized by AuNPs/CQDs-PEI-GO composite. CQDs can be assembled onto the surface of an electrode by incorporation of CA15-3 with Ab1 and Ab2. Under the synergistic action of AgNPs, polydopamine, AuNPs, and PEI-GO, the ECL signal of CQDs is greatly amplified as an excellent conductive material to facilitate electron transfer rate and further increase electrochemical detection capability. Under optimal conditions, the fabricated immunosensor showed a linear concentration range from 0.005 to 500 U mL-1, with a detection limit of 0.0017 U mL-1 (signal-to-noise ratio of 3) for CA15-3. The designed ECL immunosensor displayed receivable accuracy, excellent stability, and high specificity. The results of the detection of human serum samples are satisfactory, revealing that the method offers a potential application for the clinical diagnosis of tumor markers.

Based on reduced graphene oxide-copper sulfide-carbon nitride nanosheets composite electrochemiluminescence sensor for determination of gatifloxacin in mouse plasma.

A new method for determination of gatifloxacin hydrochloride (GAT) by reduced graphene oxide-copper sulfide (rGO-CuS) composite coupled with graphite-like carbon nitride nanosheets (g-C3N4 NSs) modified glassy carbon electrode was developed. In this work, rGO-CuS composite was synthesized by one-pot hydrothermal method and used for enhancing sensitivity of GAT. g-C3N4 NSs were synthesized as radiant agent. The sensor characteristics of electrochemistry and electrochemiluminescence (ECL) were investigated. The ECL intensity has enhanced four-fold after modifying with rGO-CuS composite. The results can be ascribed to the presence of rGO-CuS composite on the electrode surface that facilitates the electron transfer rate between the electroactive center of g-C3N4 NSs and the electrode. Under the optimum experimental conditions (photomultiplier tuber for 800 V, scan rate for 0.1 V/s, 0.1 mol/L PBS (pH 7.5) and 1.0 × 10-2 mol/L K2S2O8), the linear range for GAT was from 1.0 × 10-4 to 1.0 × 10-8 mol/L (R2 = 0.9991) with detection limit of 3.5 × 10-9 mol/L (S/N = 3). RSD for ECL intensity was 4.8% (n = 10). The recoveries of GAT in mouse plasma samples were from 98.36 to 104.7%. The sensor showed the advantages of low cost, high sensitivity and wide application in drug analysis.

A novel ECL sensor based on a boronate affinity molecular imprinting technique and functionalized SiO2@CQDs/AuNPs/MPBA nanocomposites for sensitive determination of alpha-fetoprotein.

In this work, a boronate-affinity sandwich electrochemiluminescence (ECL) sensor was constructed to detect alpha-fetoprotein (AFP) based on a multiple signal amplification strategy. Gold nanoparticles (AuNPs) were utilized and modified on the surface with chitosan in order to facilitate electron transfer. The composite of the molecularly imprinted polymer (MIP) enhanced the selectivity of alpha-fetoprotein detection. 4-mercaptophenylboronic acid (MPBA) was used as the tracing tag for capture of alpha-fetoprotein. SiO2 nanoparticles carried carbon quantum dots (CQDs) labeled with gold nanoparticles and produced an ECL signal. Under the optimum experimental conditions, the linear range for alpha-fetoprotein was between 0.001 and 1000 ng/mL with a correlation coefficient of 0.9952, and the detection limit was 0.0004 ng/mL (S/N = 3). This proposed ECL sensor displayed several advantages, including outstanding selectivity, fine reproducibility, high sensitivity, low detection limit and wide linear range. Furthermore, the newly constructed boronate-affinity sandwich ECL sensor was successfully applied to the determination of alpha-fetoprotein in serum samples, indicating great potential for application in clinical diagnostics.

Ginkgo leaf-based synthesis of nitrogen-doped carbon quantum dots for highly sensitive detection of salazosulfapyridine in mouse plasma.

A simple, economical hydrothermal strategy for synthesizing nitrogen-doped carbon quantum dots (N-CQDs) was developed using Ginko leaves as a carbon source. These N-CQDs have strong blue fluorescence, excitation-relevant emissions, high monodispersity, good stability, good water solubility, and a 22.8% fluorescence quantum yield. They average 3 nm in size, and have maximum excitation and emission wavelengths of 350 and 436 nm, respectively. They are used as an effective fluorescent sensing platform for the label-free sensitive detection of salazosulfapyridine (SASP) due to the strong quenching effect of SASP. When SASP concentration is 0.1-80 µmol/L, there is a good linear relationship with a detection limit of 40 nmol/L. This method was successfully applied to detect SASP in mouse plasma. The results show that the SASP recovery range was 96%-101%. RSDs ranged from 2.6% to 3.1%.

Based on ZnSe quantum dots labeling and single particle mode ICP-MS coupled with sandwich magnetic immunoassay for the detection of carcinoembryonic antigen in human serum.

A highly sensitive sandwich-type magnetic immunoassay based on inductively coupled plasma mass spectrometry detection in single particle mode, with ZnSe Quantum dots (QDs) serving as model tags, was proposed. The transient signals induced by the flash of ions (64Zn+) in the plasma torch from the ionization of nanoparticles tagged on antibody were recorded in a single particle mode. The frequency of transient signals is directly related to the concentration of nanoparticle tags, and the concentration of nanoparticle tagged antibodies can be quantified by the frequency of transient signals. Amino-modified magnetic nanoparticles (AMNPs) were synthesized and conjugated with primary carcinoembryonic antigen (CEA) antibody to extract the target biomarker. ZnSe QDs were synthesized as a probe to determine CEA by ICP-MS. A detection limit of 0.006 ng mL-1 was obtained for CEA after immunoreactions, and a wide linear range of 0.02-100 ng mL-1 with the relative standard deviation (RSD) was 4.4%. The method was successfully applied to human serum samples.

C18-coated stir bar sorptive extraction combined with high performance liquid chromatography-electrospray tandem mass spectrometry for the analysis of sulfonamides in milk and milk powder.

A simple, rapid, sensitive, inexpensive and less sample consuming method of C(18)-stir bar sorptive extraction (SBSE)-high performance liquid chromatography (HPLC)-tandem mass spectrometry (MS/MS) was proposed for the determination of six sulfonamides in milk and milk powder samples. C(18) silica particles coated stir bar was prepared by adhesion method, and two kinds of adhesive glue, polydimethylsiloxane (PDMS) sol and epoxy glue were tried. It was found that the C(18)-coated stir bar prepared by PDMS sol as adhesive glue is more robust than that prepared by epoxy glue when liquid desorption was employed, in terms of both lifetime and organic solvent tolerance. The preparation of C(18) stir bar was simple with good mechanic strength and the stir bar could be reused for more than 20 times. Granular coating has relatively high specific surface area and is propitious to sorptive extraction based process. Compared to conventional PDMS SBSE coating, C(18) coating shows good affinity to the target polar/weak polar sulfonamides. To achieve optimum SBSE extraction performance, several parameters including extraction and desorption time, ionic strength, sample pH and stirring speed were investigated. The detection limits of the proposed method for six sulfonamides were in the range of 0.9-10.5 µg/L for milk and 2.7-31.5 µg/kg for milk powder. Good linearities were obtained for sulfonamides with the correlation coefficients (R) above 0.9922. Finally, the proposed method was successfully applied to the determination of sulfonamides in milk and milk powder samples and satisfied recoveries of spiked target compounds in real samples were obtained.

pH-resistant titania hybrid organic-inorganic coating for stir bar sorptive extraction of drugs of abuse in urine samples followed by high performance liquid chromatography-ultraviolet visible detection.

An organic-inorganic hybrid titania-hydroxy-terminated silicone oil (titania-OH-TSO) stir bar coating was prepared by sol-gel method. The extraction performance of titania-OH-TSO coated stir bar was evaluated and compared with poly(dimethysiloxane) (PDMS), poly(dimethysiloxane)-divinylbenzene (PDMS-DVB), poly(dimethysiloxane)-ß-cyclodextrin (PDMS-ß-CD) and C(18) coated stir bar with five polar drugs of abuse including amphetamine (PA), methamphetamine (MA), 3,4-methylenedioxyamphetamine (MDA), 3,4-methylenedioxymethamphetamine (MDMA) and ketamine (Ke) as the model analytes. The experimental results revealed that the titania-OH-TSO coated stir bar exhibited highly pH-resistant ability, good preparation reproducibility, superior selectivity and high extraction efficiency for the target compounds. Based on this fact, a new method of titania-OH-TSO coated stir bar sorptive extraction (SBSE) combined with high performance liquid chromatography (HPLC)-ultraviolet visible (UV) detection was developed for the analysis of five drugs of abuse in urine samples. The factors affecting the extraction efficiency of SBSE such as sample pH, desorption solvent, sample volume, extraction time, desorption time, stirring rate and ionic strength were investigated and the optimal extraction conditions were established. Under the optimized conditions, the limits of detection (LODs) for titania-OH-TSO coated SBSE-HPLC-UV determination of five polar drugs of abuse were in the range of 2.3-9.1 µg/L with relative standard deviations (RSDs) ranging from 7.3 to 8.9% (c=300 µg/L, n=6), and all of the target compounds exhibited good linearity over a concentration range of 30-3000 µg/L. The developed method was applied to the determination of amphetamines and Ke in urine samples of drug abusers with satisfactory results.

Automated stir plate (bar) sorptive extraction coupled to high-performance liquid chromatography for the determination of polycyclic aromatic hydrocarbons.

Automated methods of PDMS/beta-CD/divinylbenzene-coated stir plate sorptive extraction (SPSE) coupled to HPLC-fluorescence detector were reported for the first time. Three automation modes, static SPSE, circular flow SPSE and continuous flow SPSE, were evaluated and critically compared with stir bar sorptive extraction by using six polycyclic aromatic hydrocarbons as model analytes. It was found that the operable sample volume for circular flow SPSE and continuous flow SPSE was larger than that for static SPSE. Under the same extraction conditions, continuous flow SPSE exhibited the highest extraction efficiencies in all automated modes and manual stir bar sorptive extraction for the target compounds. Compared with the manual operation (approximately 5-10 min), automated SPSE required a relatively short time (117-180 s) to finish sampling, washing and sample loading. Besides being labor-saving and time-saving, automated SPSE has other advantages, such as no time limit and non-attended operation. The proposed continuous flow PDMS/beta-CD/divinylbenzene-coated SPSE-HPLC-fluorescence detector was successfully applied to environmental water analysis.

Preparation of polydimethylsiloxane/beta-cyclodextrin/divinylbenzene coated "dumbbell-shaped" stir bar and its application to the analysis of polycyclic aromatic hydrocarbons and polycyclic aromatic sulfur heterocycles compounds in lake water and soil by high performance liquid chromatography.

A "dumbbell-shaped" stir bar was proposed to prevent the friction loss of coating during the stirring process, and thus prolonged the lifetime of stir bars. The effects of the coating components, including polydimethylsiloxane (PDMS), beta-cyclodextrin (beta-CD) and divinylbenzene (DVB) were investigated according to an orthogonal experimental design, using three polycyclic aromatic hydrocarbons (PAHs) and four polycyclic aromatic sulfur heterocycles (PASHs) as model analytes. Four kinds of stir bars coated with PDMS, PDMS/beta-CD, PDMS/DVB and PDMS/beta-CD/DVB were prepared and their extraction efficiencies for the target compounds were compared. It was demonstrated that PDMS/beta-CD/DVB-coated stir bar showed the best affinity to the studied compounds. The preparation reproducibility of PDMS/beta-CD/DVB-coated stir bar ranged from 3.2% to 15.2% (n = 6) in one batch, and 5.2% to 13.4% (n = 6) among batches. The "dumbbell-shaped" stir bar could be used for about 40 times, which were 10 extractions more than a normal stir bar. The prepared PDMS/beta-CD/DVB-coated "dumbbell-shaped" stir bar was used for stir bar sorptive extraction (SBSE) of PAHs and PASHs and the desorbed solution was introduced into HPLC-UV for subsequent analysis. The limits of detection of the proposed method for seven target analytes ranged from 0.007 to 0.103 microg L(-1), the relative standard deviations were in the range of 6.3-12.9% (n = 6, c = 40 microg L(-1)), and the enrichment factors were 19-86. The proposed method was successfully applied to the analysis of seven target analytes in lake water and soil samples.

Sol-gel polydimethylsiloxane/poly(vinylalcohol)-coated stir bar sorptive extraction of organophosphorus pesticides in honey and their determination by large volume injection GC.

A PDMS/poly(vinylalcohol) (PDMS/PVA) film prepared through a sol-gel process was coated on stir bars for sorptive extraction, followed by liquid desorption and large volume injection-GC-flame photometric detector (LVI-GC-FPD) for the determination of five organophosphorus pesticides (OPPs) (phorate, fenitrothion, malathion, parathion, and quinalphos) in honey. The preparation reproducibility of PDMS/PVA-coated stir bar ranged from 4.3 to 13.4% (n = 4) in one batch, and from 6.0 to 12.6% (n = 4) in batch to batch. And one prepared stir bar can be used for more than 50 times without apparent coating loss. The significant parameters affecting stir bar sorptive extraction (SBSE) were investigated and optimized. The LODs for five OPPs ranged from 0.013 (parathion) to 0.081 microg/L (phorate) with the RSDs ranging from 5.3 to 14.2% (c = 1 microg/L, n = 6). The proposed method was successfully applied to the analysis of five OPPs in honey.

Preparation of sol-gel polyethylene glycol-polydimethylsiloxane-poly(vinyl alcohol)-coated sorptive bar for the determination of organic sulfur compounds in water.

A novel headspace sorptive extraction (HSSE) using a glass bar coated with carbowax (polyethylene glycol)-polydimethylsiloxane-poly(vinyl alcohol) (CW/PDMS/PVA) prepared by sol-gel technology method was proposed for the determination of volatile organic sulfur compounds (VOSs) in water. After the extraction, the sorptive bar was desorbed with 60 microL of ethanol and 30 microL of the extract was analysed by large volume injection (LVI) into a gas chromatography-flame photometric detector (GC-FPD). The parameters affecting the headspace sorptive extraction of VOSs such as extraction and desorption time, extraction temperature, stirring speed, desorption solvent, headspace phase ratio, salt and pH were carefully investigated and the optimized experimental conditions were established. The limits of detection (LODs) for the studied VOSs ranged from 0.04 to 4.8 microg/L with the relative standard deviations (RSDs) ranging from 4.5 to 10.2% (n=6). The reproducibility for the preparation of CW/PDMS/PVA-coated sorptive bar ranged from 3.2 to 9.2% in one batch, and from 2.8 to 18.5% in batch-to-batch, and more than 50 extractions can be achieved without apparent loss. The proposed method was compared with polydimethylsiloxane-HSSE and carboxen/PDMS-headspace-solid phase microextraction (CAR/PDMS-HS-SPME) under their optimum conditions, CW/PDMS/PVA-HSSE shows the highest adsorption capacity (larger surface area and more active sites), the highest sensitivity (about 10 times) and the best polarity matching for VOSs.

Comparison of dual solvent-stir bars microextraction and U-shaped hollow fiber-liquid phase microextraction for the analysis of Sudan dyes in food samples by high-performance liquid chromatography-ultraviolet/mass spectrometry.

Two sample preparation methods, dual solvent-stir bars microextraction (DSSBME) and U-shaped hollow fiber-liquid phase microextraction (U-shaped HF-LPME), are proposed and critically compared for high-performance liquid chromatography (HPLC)-ultraviolet (UV)/mass spectrometry (MS) analysis of Sudan dyes in this paper. In DSSBME, the organic solvent was confined to a pair of hollow fiber membrane fixed on a stir bar, which can stir by itself, while the hollow fiber in U-shaped HF-LPME was fixed by two microsyringes. The significant factors affecting the microextraction of Sudan dyes in both microextraction techniques have been examined and no obvious difference in the effect of extraction solvent, pH and salt concentration on the extraction efficiency of Sudan dyes was observed except extraction time and stirring speed. Both microextraction techniques were similar in terms of analytical performance from aqueous solutions (LODs ranged from 0.09 to 0.95 microgL(-1) by HPLC-UV and 2.5-6.2 microgL(-1) by HPLC-MS; the absolute LODs ranged from 0.9 to 11.25 pg by HPLC-UV and 5-21.2 pg by HPLC-MS), however, DSSBME was more stable (lower stirring speed required), less sample consuming and much shorter time required to reach extraction equilibrium; while U-shaped HF-LPME was easier to operate and no more special device required. The two microextraction techniques combined with HPLC-UV/MS were successfully applied to the analysis of real samples including strawberry sauce, capsicum oil, salted egg, and two kinds of chilli sauce. Although the LODs of HPLC-UV are lower than that of HPLC-MS by a factor of 10 in this work, the absolute LODs for both HPLC-UV and HPLC-MS are comparable. HPLC-UV cannot identify the suspicious peaks at the same retention time as that of Sudan II and III in salted egg, while HPLC-MS can give exact information of Sudan I-IV in real sample analysis and is more reliable. The sensitivity of HPLC-MS is enough for real sample analysis.

Novel combined stir bar sorptive extraction coupled with ultrasonic assisted extraction for the determination of brominated flame retardants in environmental samples using high performance liquid chromatography.

A combined stir bar coated with poly (dimethysiloxane)-beta-cyclodextrin (PDMS-beta-CD) on single side has been prepared for the first time by sol-gel method and was coupled with ultrasonic assisted extraction (UAE) for the determination of some brominated flame-retardant compounds (BFRs) in soil and dust samples by high performance liquid chromatography (HPLC). Four different kinds of coatings including PDMS-beta-CD, PDMS, carbowax (CW)-PDMS-poly (vinyl alcohol) (PVA) and PDMS-PVA were evaluated for stir bar sorptive extraction of BFRs by orthogonal experiment design. The experimental results reveal that the PDMS-beta-CD combined stir bar exhibited the best extraction efficiency for the target analytes. The reproducibility for the preparation of PDMS-beta-CD combined stir bar ranged from 1.3% to 15.7% in one batch, and 7.2% to 15.1% among batches. Extraction time, desorption solvent, concentration of methanol and NaCl in the matrix, pH, temperature and stirring speed were optimized. The combined stir bar can avoid direct friction of the coating with the bottom of the vessel, and could be used for more than 100 times. Linearity (>0.993), repeatability (<10.5%), reproducibility (<16.5%), recovery (56-118%) and detection limits (2.9-4.2 microg L(-1)) were proper to determine the seven BFRs. The developed method was applied to the determination of BFRs in soil and dust with satisfactory results.

Comparison of headspace and direct single-drop microextraction and headspace solid-phase microextraction for the measurement of volatile sulfur compounds in beer and beverage by gas chromatography with flame photometric detection.

Three approaches based on headspace single-drop microextraction (HS-SDME), direct single-drop microextraction (Direct-SDME), and headspace solid-phase microextraction (HS-SPME), have been compared for analyzing volatile sulphur compounds (VSCs) in beer and beverage. Procedures and performance of the three methods have been contrasted through the determination of extraction efficiencies, precision, linearity and limits of detection. The overall process of HS-SDME and HS-SPME was applied to GC-FPD determination of five VSCs in beer and beverage.

Optimization of a single-drop microextraction procedure for the determination of organophosphorus pesticides in water and fruit juice with gas chromatography-flame photometric detection.

A single-drop microextraction (SDME) procedure was developed for the analysis of organophosphorus pesticides (OPPs) in water and fruit juice by gas chromatography (GC) with flame photometric detection (GC-FPD). The significant parameters affecting the SDME performance such as selection of microextraction solvent, solvent volume, extraction time, stirring rate, sample pH and temperature, and ionic strength were studied and optimized. Two types of SDME mode, static and cycle-flow SDME, were evaluated. The static SDME procedure provided more sensitive analysis of the target analytes. Therefore, static SDME with tributyl phosphate (TBP) as internal standard was selected for the real sample analysis. The limits of detection (LODs) in water for the six studied compounds were between 0.21 and 0.56ng/mL with the relative standard deviations ranging from 1.7 to 10.0%. Linear response data was obtained in the concentration range of 0.5-50ng/mL (except for dichlorvos 1.0-50ng/mL) with correlation coefficients from 0.9995 to 0.9999. Environmental water sample collected from East Lake and fruit juice samples were successfully analyzed using the proposed method, but none of the analytes in both lake water and fruit juice were detected. The recoveries for the spiked water and juice samples were from 77.7 to 113.6%. Compared with the conventional methods, the proposed method enabled a rapid and simple determination of organophosphorus pesticides in water and fruit juice with minimal solvent consumption and a higher concentration capability.