Development of a new phosphorescence sensor based on surface molecularly imprinted Mn-doped ZnS quantum dots for detection of melamine in milk products.

This paper presents a novel room temperature phosphorescence sensor (IMIPs-ZnS QDs RTP sensor) based on inorganic surface molecularly imprinted polymers and Mn-doped ZnS quantum dots (QDs) for the rapid detection of trace melamine (MEL) in commercial milk products. The surface of Mn-ZnS QDs was modified with 3-(mercaptopropyl) trimethoxy silane (MPTS). Then, MEL, 3-aminopropyltriethoxysilane (APTES) and tetraethoxysilane (TEOS) were used as a template/target molecule, functional monomer, and cross-linker, respectively. IMIPs-ZnS QDs RTP sensor was characterized using spectrofluorimeter, UV-Vis spectrophotometer, FT-IR, transmission electron microscope (TEM), and X-ray photoelectron spectrometer (XPS). Detection time and linear range for IMIPs-ZnS QDs RTP sensor were 30 min and 4.0-79.2 µM with a correlation coefficient value of 0.9946, respectively. Furthermore, LOD and LOQ values were calculated using Stern-Volmer equation as 0.29 and 0.97 µM, respectively. Thus, IMIPs-ZnS QDs RTP sensor was successfully applied for the detection of MEL residue in milk samples. Recovery values were in the range of 88.62-90.22 % with relatively high precision values (0.57-0.92 % RSD). Our findings indicate that the developed IMIPs-ZnS QDs RTP sensor exhibits high sensitivity and selectivity towards the MEL in milk sample containing potentially relatively high number of interfering compounds.

Smartphone digital image colorimetry combined with dispersive solid-phase microextraction for the determination of boron in food samples.

Simple, inexpensive and accurate analytical methods are in high demand. Dispersive solid-phase microextraction (DSPME) was used in combination with smartphone digital image colorimetry (SDIC) to determine boron in nuts as an approach replacing existing costly alternatives. A colorimetric box was designed to capture images of standards and sample solutions. ImageJ software was used to link pixel intensity to the analyte concentration. Under optimum extraction and detection conditions, linear calibration graphs were obtained with coefficients of determination (R2) above 0.9955. Percentage relative standard deviations (%RSD) were below 6.8 %. The limits of detection (LOD) ranged between 0.07 and 0.11 µg mL-1 (1.8 to 2.8 µg g-1), which were sufficient for detection of boron in nut samples (i.e., almond, ivory, peanut and walnut), with percentage relative recoveries (%RR) between 92.0 and 106.0 %.

Switchable-hydrophilicity solvent liquid-liquid microextraction combined with smartphone digital image colorimetry for the determination of palladium in catalytic converters.

Switchable-hydrophilicity solvent liquid-liquid microextraction was coupled with smartphone digital image colorimetry for the determination of palladium as its metal chelate with N,N-diethyl-N'-benzoylthiourea. Images of the colored extract were captured in a homemade colorimetric box, which were split into their red-green-blue channels. The blue channel was used to determine the concentration of palladium. Optimum extraction conditions were achieved using 600 µL of triethylamine as the extraction solvent and 4.0 mL of 10 M sodium hydroxide as the hydrophilicity-switching trigger within 1.0 min extraction time. Optimum complexation conditions were obtained at a sample pH of 4.50, and metal/ligand mole ratio of 1:2 within 3.0 min. Optimum detection conditions were achieved at a distance of 7.0 cm between the sample solution and the detection camera, a region of interest of 175.0 px2 at a detection wavelength of 480.0 nm and 30.0% brightness of the monochromatic light source. Limits of detection and quantitation were found to be less than 0.7 and 1.8 µg g-1, respectively. A good linearity with coefficients of determination above 0.9974 was obtained. Accuracy was checked via a single-factor analysis of variance (ANOVA) test by comparing the results with the ones obtained using flame-atomic absorption spectrometry and the results were statistically in a good agreement (P > 0.05). The proposed method was applied for the determination of palladium in catalytic converters with percentage relative recoveries ranging between 95.7 and 103.7% and percentage relative standard deviations below 4.0%.

Evaluation of low-to-moderate arsenic exposure, metabolism and skin lesions in a Turkish rural population exposed through drinking water.

BACKGROUND: There is no human data regarding the exposure, metabolism and potential health effects of arsenic (As) contamination in drinking water in the Central Anatolian region of Turkey. METHODS: Residents in ten villages with drinking water of total As (T-As) level >50 µg L-1 and 10-50 µg L-1 were selected as an exposed group (n = 420) and <10 µg L-1 as an unexposed group (n = 185). Time-weighted average-As (TWA-As) intake was calculated from T-As analysis of drinking water samples. Concentrations of T-As in urine and hair samples, urinary As species [i.e., As(III), As(V), MMA(V) and DMA(V], and some micronutrients in serum samples of residents of the study area were determined. Primary and secondary methylation indices (PMI and SMI, respectively) were assessed from urinary As species concentrations and the presence of skin lesion was examined. RESULTS: TWA-As intake was found as 75 µg L-1 in the exposed group. Urinary and hair T-As and urinary As species concentrations were significantly higher in the exposed group (P < 0.05). The PMI and SMI values revealed that methylation capacities of the residents were efficient and that there was no saturation in As metabolism. No significant increase was observed in the frequency of skin lesions (hyperpigmentation, hypopigmentation, keratosis) of the exposed group (P > 0.05). Only frequency of keratosis either at the hand or foot was higher in individuals with hair As concentration >1 µg g-1 (P < 0.05). CONCLUSIONS: Individuals living in the study area were chronically exposed to low-to-moderate As due to geological contamination in drinking water. No significant increase was observed in the frequency of skin lesions. Because of the controversy surrounding the health risks of low-to-moderate As exposure, it is critical to initiate long-term follow-up studies on health effects in this region.

Smartphone digital image colorimetry combined with solidification of floating organic drop-dispersive liquid-liquid microextraction for the determination of iodate in table salt.

Smartphone digital image colorimetry (SDIC), combined with solidification of floating organic drop-dispersive liquid-liquid microextraction (SFOD-DLLME), was proposed for the determination of iodate ions. A colorimetric box was designed to capture images of sample solutions. Factors affecting the efficiency of SDIC included type of phone, region of interest, position of camera, and distance between camera and sample solution. Optimum SFOD-DLLME conditions were achieved with 1-undecanol (500 µL) as the extraction solvent, ethanol (1.5 mL) as the disperser solvent within 20 s extraction time. Limit of detection (LOD) was found as 0.1 µM (0.2 µg g-1) and enrichment factors ranged between 17.4 and 25.0. Calibration graphs showed good linearity with coefficients of determination higher than 0.9954 and relative standard deviations lower than 5.6%. The proposed method was efficiently applied to determine iodate in table salt samples with percentage relative recoveries ranging between 89.3 and 109.3%.

Multiplex enumeration of Escherichia coli and Salmonella enteritidis in a passive capillary microfluidic chip.

Multiplex detection and quantification of bacteria in water by using portable devices are particularly essential in low and middle-income countries where access to clean drinking water is limited. Addressing this crucial problem, we report a highly sensitive immunoassay sensor system utilizing the fluorescence technique with magnetic nanoparticles (MNPs) to separate target bacteria and two different types of quantum dots (CdTe and Ni doped CdTe QDs) incorporated into a passive microfluidic chip to transport and to form sandwich complexes for the detection of two target bacteria, namely Escherichia coli (E. coli) and Salmonella enteritidis (S. enteritidis) in less than 60 min. The assay is carried out on a capillary driven microfluidic chip that can be operated by merely pipetting the samples and reagents, and fluorescence measurements are done by using a handheld fluorescence spectrophotometer, which renders the system portable. The linear range of the method was found to be 101 to 105 cfu mL-1 for both E. coli and S. enteritidis. The limit of detection (LOD) was calculated to be 5 and 3 cfu mL-1 for E. coli and S. enteritidis, respectively. The selectivity of the method was examined by testing Enterobacter dissolvens (E. dissolvens) and Staphylococcus aureus (S. aureus) samples, and no significant interference was observed. The method was also demonstrated to detect bacteria in tap water and lake water samples spiked with target bacteria.

Fast fluorometric enumeration of E. coli using passive chip.

In this report, a passive microfluidic chip design was developed for fast and sensitive fluorometric determination of Escherichia coli (E. coli) based on sandwich immunoassay. Initially, magnetic nanoparticles (MNPs) and chitosan modified mercaptopropionic acid capped cadmium telluride (CdTe) quantum dots (QDs) were functionalized with E.coli specific antibody to form a sandwich immunoassay with the E. coli. The magnetic separation and preconcentration of the E.coli from the sample solution was performed in the vial. Conjugation of QDs to the magnetically captured E. coli and washing were performed using a passive type of microchip. The microfluidic chip consists of four microchambers connected to each other by microchannels which act as capillary valves. Signal measurement was performed at the last chamber by using a hand-held spectrofluorometer equipped with a fiber optic reflection probe. The selectivity of the method was tested with Enterobacter aerogenes (E. aerogenes) and Salmonella enteritidis (S. enteritidis), it was observed that these bacteria have no interference effect on E.coli determination. The calibration curve was found to be linear in the range of 101-105 cfu/mL with a correlation coefficient higher than 0.99. The limit of detection was calculated as 5 cfu/mL. The method was successfully applied to spiked tap and lake water samples. The results suggest that the developed method is applicable for on-site E. coli detection and offers several advantages such as large dynamic range, high sensitivity, high selectivity and short analysis time.

Use of Water Soluble and Phosphorescent MPA-capped CdTe Quantum Dots for the Detection of Urea.

OBJECTIVES: To describe a method for the determination of urea in blood serum using urease enzyme and 3-MPA-capped CdTe quantum dots. MATERIALS AND METHODS: The method is based on the increase in pH of the solution as a result of the reaction between urea and urease, which causes an increase in the phosphorescence signal of MPA-CdTe quantum dots in the pH range of 2.5-5.0. Under the optimum conditions, the linear range of urea was 0.016-0.16 mM (1-10 mg/L) and the limit of detection based on 3 s/b was calculated as 0.003 mM (0.17 mg/L). The relative standard deviation was calculated as 3.4% at 4 mg/L urea concentration (n=7). RESULTS: The method was applied to human serum samples. The same samples were analyzed by an independent laboratory and the results were not statistically different, at 95% confidence level (F test). CONCLUSION: The proposed method does not need sample pretreatment, is simple, selective, and cost-effective for the determination of urea in serum samples.

Effects of heat treatment parameters on liquid whole egg proteins.

The aim of this study was to analyse the effect of heat treatment parameters on liquid whole egg (LWE) proteins by using ultraviolet-visible (UV-VIS) spectroscopy and capillary electrophoresis (CE). Heat treatment (at 60-68°C for 1-5min) was applied to LWE. Treated LWE was centrifuged and supernatant was taken for measurement of UV-VIS spectroscopy and CE. The change in UV absorbance showed loss of protein solubility depending on heat treatments parameters. Electropherograms of samples demonstrated the effect of treatment parameters on composition of LWE proteins. It was found that conalbumin and lysozyme were influenced by the treatment, while ovalbumin and ovomucoid were not affected. CE combined with principal component analysis (PCA) was used for classification of samples untreated or treated and treated at different treatment parameters. The results of the study revealed that the extent of heat treatment in LWE samples could be determined with PCA of the CE measurements.

Polyethyleneimine brushes effectively inhibit encrustation on polyurethane ureteral stents both in dynamic bioreactor and in vivo.

Polyurethane (PU) ureteral stents have been widely used as biomedical devices to aid the flow of the urine. Due to the biofilm formation and encrustation complications it has been hindered their long term clinical usage. To overcome these complications, in this study, cationic polyethyleneimine (PEI) brushes grafted on PU stents and their performances were tested both in a dynamic biofilm reactor system (in vitro) and in a rat model (in vivo). Thus, we hypothesized that PEI brushes inhibit bacterial adhesion owing to the dynamic motion of brushes in liquid environment. In addition, cationic structure of PEI disrupts the membrane and so kills the bacteria on time of contact. Cationic PEI brushes decreased the biofilm formation up to 2 orders of magnitude and approximately 50% of encrustation amount in respect to unmodified PU, in vitro. In addition, according to Atomic Absorption Spectroscopy (AAS) results, approximately 90% of encrustation was inhibited on in vivo animal models. Decrease in encrustation was clearly observed on the stents obtained from rat model, by Scanning Electron Microscopy (SEM). Also, histological evaluations showed that; PEI brush grafting decreased host tissue inflammation in close relation to decrease in biofilm formation and encrustation. As a results; dual effect of anti-adhesive and contact-killing antibacterial strategy showed high efficiency on PEI brushes grafted PU stents both in vitro and in vivo.

Determination of antazoline and tetrahydrozoline in ophthalmic solutions by capillary electrophoresis and stability-indicating HPLC methods.

Capillary electrophoretic (CE) and high performance liquid chromatographic (HPLC) methods were developed and optimized for the determination of antazoline (ANT) and tetrahydrozoline (TET) in ophthalmic formulations. Optimum electrophoretic conditions were achieved using a background electrolyte of 20mM phosphate buffer at pH 7.0, a capillary temperature of 25°C, a separation voltage of 22 kV and a pressure injection of the sample at 50 mbar for 17s. HPLC analysis was performed with Kinetex (150 × 4.6mm ID × 5 µm) (Phenomenex, USA) analytical column with 1 mL min(-1) flow rate of mobile phase which consisted of 0.05% TFA in bidistilled water (pH adjusted to 3.0 with 5M NaOH) and acetonitrile/buffer in the ratio of 63:37 (v/v) at room temperature. Injection volume of the samples was 10 µL and the wavelength of the detector was set at 215 nm for monitoring both analytes. Calibration graphs showed a good linearity with a coefficient of determination (R(2)) of at least 0.998 for both methods. Intraday and interday precision (expressed as RSD%) were lower than 2.8% for CE and 0.92% for HPLC. The developed methods were demonstrated to be simple and rapid for the determination of ANT and TET in ophthalmic solutions providing recoveries in the range between 97.9 and 102.70% for CE and HPLC.

L-Cysteine capped Mn-doped ZnS quantum dots as a room temperature phosphorescence sensor for in-vitro binding assay of idarubicin and DNA.

L-cysteine capped Mn doped ZnS quantum dots/ Idarubicin (IDA) nanohybrids were used as novel room temperature phosphorescence (RTP) sensor to detect double stranded deoxyribonucleic acid (ds-DNA)/drug interaction. IDA, anthracycline derivative anticancer drug, was adsorbed on the surface of the QDs as an electron acceptor to quench the RTP emission. The RTP intensity of QDs was quenched quickly upon addition of quencher and the reaction reached equilibrium within 2 min. The quenching mechanism of phosphorescence of Mn-doped ZnS QDs by IDA is a combined dynamic and static quenching. The static and dynamic quenching constants were found as 1.1×10(5) M(-1) and 8.7×10(4) M(-1), respectively. The addition of ds-DNA caused formation of ds-DNA/IDA complex and recovered the RTP signal of Mn-doped ZnS QDs, which allowed qualitative analysis. Under optimal conditions, RTP intensity of QDs/IDA nanohybrids increased linearly with the concentration of ds-DNA from 1.2 to 6.0 µM. This method is simple, low cost and avoids from interferences.

Determination of parabens in human milk and other food samples by capillary electrophoresis after dispersive liquid-liquid microextraction with back-extraction.

Dispersive liquid-liquid microextraction (DLLME) with back-extraction was used prior to capillary electrophoresis (CE) for the extraction of four parabens. Optimum extraction conditions were: 200 µL chloroform (extraction solvent), 1.0 mL acetonitrile (disperser solvent) and 1 min extraction time. Back-extraction of parabens from chloroform into a 50mM sodium hydroxide solution within 10s facilitated their direct injection into CE. The analytes were separated at 12°C and 25 kV with a background electrolyte of 25 mM borate buffer containing 5.0% (v/v) acetonitrile. Enrichment factors were in the range of 4.3-10.7 and limits of detection ranged from 0.1 to 0.2 µg mL(-1). Calibration graphs showed good linearity with coefficients of determination (R(2)) higher than 0.9957 and relative standard deviations (%RSDs) lower than 3.5%. DLLME-CE was demonstrated to be a simple and rapid method for the determination of parabens in human milk and food with relative recoveries in the range of 86.7-103.3%.

Dispersive liquid-liquid microextraction combined with field-amplified sample stacking in capillary electrophoresis for the determination of non-steroidal anti-inflammatory drugs in milk and dairy products.

Dispersive liquid-liquid microextraction (DLLME) was coupled with field-amplified sample stacking in capillary electrophoresis (FASS) for the determination of five non-steroidal anti-inflammatory drugs (NSAIDs) in bovine milk and dairy products. After extraction, the enriched analytes were back-extracted into a basic aqueous solution for injection into CE. Under optimum conditions, enrichment factors were in the range 46-229. Limits of detection of the analytes ranged from 3.0 to 13.1 µg kg(-1) for all matrices analysed. Calibration graphs showed good linearity with coefficients of determination (R(2))≥ 0.9915 and relative standard deviations (RSD%) of the analyses in the range of 0.6-6.2% (n=5). Recoveries of all NSAIDs from bottled milk, raw milk, yogurt and white cheese samples were in the ranges of 86.6-109.3%, 84.3-100.5%, 77.4-107.3%, and 90.9-101.6%, respectively. DLLME-FASS-CE was demonstrated to be a rapid and convenient method for the determination of NSAIDs in milk and dairy products.

Dispersive liquid-liquid microextraction based on solidification of floating organic drop combined with field-amplified sample injection in capillary electrophoresis for the determination of beta(2)-agonists in bovine urine.

Dispersive liquid-liquid microextraction based on solidification of floating organic drop (DLLME-SFO) was for the first time combined with field-amplified sample injection (FASI) in CE to determine four ß(2)-agonists (cimbuterol, clenbuterol, mabuterol, and mapenterol) in bovine urine. Optimum BGE consisted of 20 mM borate buffer and 0.1 mM SDS. Using salting-out extraction, ß(2)-agonists were extracted into ACN that was then used as the disperser solvent in DLLME-SFO. Optimum DLLME-SFO conditions were: 1.0 mL ACN, 50 µL 1-undecanol (extraction solvent), total extraction time 1.5 min, no salt addition. Back extraction into an aqueous solution (pH 2.0) facilitated direct injection of ß(2)-agonists into CE. Compared to conventional CZE, DLLME-SFO-FASI-CE achieved sensitivity enhancement factors of 41-1046 resulting in LODs in the range of 1.80-37.0 µg L(-1). Linear dynamic ranges of 0.15-10.0 mg L(-1) for cimbuterol and 15-1000 µg L(-1) for the other analytes were obtained with coefficients of determination (R(2)) ≥ 0.9901 and RSD% ≤5.5 (n = 5). Finally, the applicability of the proposed method was successfully confirmed by determination of the four ß(2)-agonists in spiked bovine urine samples and accuracy higher than 96.0% was obtained.

Ultrasound-assisted emulsification microextraction for the determination of ephedrines in human urine by capillary electrophoresis with direct injection. Comparison with dispersive liquid-liquid microextraction.

Ultrasound-assisted emulsification microextraction and dispersive liquid-liquid microextraction were compared for extraction of ephedrine, norephedrine, and pseudoephedrine from human urine samples prior to their determination by capillary electrophoresis. Formation of a microemulsion of the organic extract with an aqueous solution (at pH 3.2) containing 10% methanol facilitated the direct injection of the final extract into the capillary. Influential parameters affecting extraction efficiency were systematically studied and optimized. In order to enhance the sensitivity further, field-amplified sample injection was applied. Under optimum extraction and stacking conditions, enrichment factors of up to 140 and 1750 as compared to conventional capillary zone electrophoresis were obtained resulting in limits of detection of 12-33 µg/L and 1.0-2.8 µg/L with dispersive liquid-liquid microextraction and ultrasound-assisted emulsification microextraction when combined with field-amplified sample injection. Calibration graphs showed good linearity for urine samples by both methods with coefficients of determination higher than 0.9973 and percent relative standard deviations of the analyses in the range of 3.4-8.2% for (n = 5). The results showed that the use of ultrasound to assist microextraction provided higher extraction efficiencies than disperser solvents, regarding the hydrophilic nature of the investigated analytes.

Determination of tin by in situ trapping of stannane on a resistively heated iridium treated tungsten coil surface and interference studies.

A novel method was developed for the in situ trapping of stannane on an iridium-coated tungsten coil. Coating the tungsten coil with iridium has significantly improved the sensitivity. The tungsten coil can either be used as an on-line atomizer or as a trapping surface. The interference effect of some hydride-forming elements such as, As(III), Se(IV), Te(IV), Sb(III) was investigated. The interference effect of Sb(III) and Se(IV) could not be completely eliminated using in situ trapping mode but the magnitude of their interferences was reduced significantly when compared to quartz T-tube atomizer. The limit of detection with iridium-coated tungsten coil for a 60s trapping period (sample volume 6 ml) was found to be 0.065 ng ml(-1) and the calibration was linear over the range of 0.5-4.0 ng ml(-1). The precision of the analytical method was determined to be 2.2% RSD (n=11) for 1.0 ng ml(-1) Sn concentration. Analytical performance of the proposed method was checked by analyzing tap water, spring water and mineral water samples for Sn. The accuracy of the method was tested with two different certified reference materials; fortified water TMDA 61 (NWRI) and Dogfish Liver DOLT-3 (NRC). The results were in a good agreement with the certified values at 95% confidence level.

Determination of 7-ethoxyresorufin-o-deethylase (EROD) induction in leaping mullet (Liza saliens) from the highly contaminated Aliaga Bay, Turkey.

Pollution of the aquatic environment is a global concern owing to the devastating effects of contaminants whose levels are growing at an alarming rate, and it has become a major threat for marine organisms, as well as to humans as consumers. This study has been carried out on leaping mullet obtained from Aliaga Bay, which is located on the west coast of the Aegean Sea near Izmir and hosts the world's fifth largest shipyard, plus a broad range of industrial activities, including an oil refinery and a paper factory. The waste from these industries, combined with municipal sewer discharges, is the main cause of pollution in this region. There is no national documentation or research on the determination of pollution resulting from the industrial activities in this area. In the present study, the degree of induction of CYP4501A-associated 7-ethoxyresorufin O-deethylase (EROD) activity and immunochemical detection of CYP1A1 in the liver of leaping mullet (Lisa saliens) were used as biomarkers for the assessment of polycyclic aromatic hydrocarbon (PAH)-type organic pollutants in Aliaga Bay. Mullet caught from different locations of the bay had approximately 52 times more EROD activity than the feral fish sampled from a clean reference site near Foca, Izmir. The results of this study indicate that Aliaga Bay is highly contaminated with PAH-type organic pollutants.

Mercury exposure in dental practice.

Since elemental mercury is absorbed by dental professionals through direct skin contact or inhalation, the use of mercury in dental amalgam continues to be a controversial issue. In this study, the authors address the possible health risk of occupational exposure to mercury vapor in the dental office. The cytogenetic examination of leukocytes with alkaline comet assay and blood mercury levels with Atomic Absorption Spectrometer of dentists exposed to mercury vapor below 0.1mg/m(3) concentrations failed to find cytogenetic damage and related correlation. However, higher cytogenetic damage and blood mercury levels evaluated in controls from mercury intake by seafood consumption justifies additional study.

Direct-write fabrication of functional protein matrixes using a low-cost Q-switched laser.

We report the use of an inexpensive, small, and "turn-key" Q-switched 532-nm Nd:YAG laser as a source for nonlinear, direct-write protein microfabrication. In this approach, microJoule pulses (pulse widths, approximately 600 ps) are focused using high numerical aperture optics to submicrometer focal spots, creating instantaneous intensities great enough to promote multiphoton excitation of a photosensitizer and subsequent intermolecular cross-linking of protein molecules. By scanning the femtoliter focal volume through reagent solution, extended protein-based structures can be fabricated with precise, three-dimensional topographies. As with earlier studies using a femtosecond titanium:sapphire laser costing more than 100K, physically robust and chemically responsive microstructures can be fashioned rapidly with feature sizes smaller than 0.5 microm, and cross-linking can be achieved using both biologically benign sensitizers (e.g., flavins) and by using the proteins themselves to sensitize cross-linking. We demonstrate in situ fabrication to corral neurite outgrowth and show the ability to functionalize avidin structures with biotinylated reagents, an approach that enables chemical sensing to be performed in specified microenvironments. Characterization of this inexpensive, low-power source will greatly broaden access to direct-write protein microfabrication.