Quantitative Determination of Iron-Siderophore Complexes in Peat by Isotope-Exchange Size-Exclusion UPLC-Electrospray Ionization High-Resolution Accurate Mass (HRAM) Mass Spectrometry.

A method was developed for the quantification of iron-siderophore complexes by electrospray high-resolution accurate mass (HRAM) mass spectrometry (MS) without the need for authentic standards. The bulk of iron-siderophore complexes was purified by solid-phase extraction (SPE) and concentrated by evaporation. The individual complexes were identified by fast size-exclusion chromatography (FastSEC)-Orbitrap MSn on the basis of the exact molecular mass (±1 ppm) and MS2 or MS3 fragmentation. Their capability to readily exchange the natural 56Fe for the added 58Fe was demonstrated by SEC with ICP MS and ESI MS detection. The method was applied to the analysis of peat sampled in the eastern part of the French Pyrenean mountains. Nineteen siderophores belonging to four different classes were identified and quantified. The results were validated using ICP MS detection of iron by matching the sum of iron complexes determined by isotope exchange-ESI MS within each peak observed by FastSEC-ICP MS.

Microfluidic paper-based analytical devices for simultaneous detection of oxidative potential and copper in aerosol samples.

The potential reach of point-of-care (POC) diagnostics into daily routines for exposure to reactive oxygen species (ROS) and Cu in aerosolized particulate matter (PM) demands that microfluidic paper-based analytical devices (µPADs) take into consideration the simple detection of these toxic PM components. Here, we propose µPADs with a dual-detection system for simultaneous ROS and Cu(II) detection. For colorimetric ROS detection, the glutathione (GSH) assay with a folding design to delay the reaction yielded complete ROS and GSH oxidation, and improved homogeneity of color development relative to using the lateral flow pattern. For electrochemical Cu(II) determination, 1,10-phenanthroline/Nafion modified graphene screen-printed electrodes showed ability to detect Cu(II) down to pg level being low enough to be applied to PM analysis. No intra- and inter-interference affecting both systems were found. The proposed µPADs obtained LODs for 1,4-naphthoquinone (1,4-NQ), used as the ROS representative, and Cu(II) of 8.3 ng and 3.6 pg, respectively and linear working ranges of 20 to 500 ng for ROS and 1 × 10-2 to 2 × 102 ng for Cu(II). Recovery of the method was between 81.4 and 108.3% for ROS and 80.5-105.3% for Cu(II). Finally, the sensors were utilized for simultaneous ROS and Cu(II) determination in PM samples and the results statistically agreed with those using the conventional methods at 95% confidence.

An electrochemical paper-based analytical sensor for one-step latex protein detection.

Exposure to natural rubber latex (NRL) can result in sensitivity to NRL protein with resulting allergic reactions. Low-cost, portable, simple, sensitive analytical tools for NRL protein measurements are needed for rapid and accurate assessments of allergenic risks at the point-of-care (POC) instead of using traditional methods that require large and expensive instruments, long-time analysis, and complex sample preparation steps. Here, an electrochemical paper-based analytical device (ePAD) is presented by combining sample preparation and electrochemical detection within a single device to offer a one-step NRL analysis. The lack of antibodies and/or enzymes against NRL makes POC analysis difficult. In this work, detection is based on electrochemical measurement of the remaining Cu after in situ protein complexation instead of more complex biological assays for the first time. Graphene screen-printed electrodes modified with 1,10-phenanthroline and Nafion were used in the ePAD to improve Cu signal 18-fold relative to unmodified carbon screen-printed electrodes. The optimum parameters including 1,10-phenanthroline concentration, reaction time between Cu and protein, and the starting Cu concentration were 5% w/v, 1 min, and 600 µg mL-1, respectively. In addition to short analysis time (4 min), the system selectivity indicated no other interfering species affecting protein detection. The proposed ePAD achieved an LOD of 3.0 mg dL-1 and a linear range of 10.0-200.0 mg dL-1. Finally, the proposed sensors were applied for NRL protein detection and the results were not significantly different from the traditional Lowry method at 95% confidence.

Dietary Intake and Milk Micronutrient Levels in Lactating Women with Full and Partial Breastfeeding.

BACKGROUND: Micronutrient intake and status in lactating women may impact micronutrient levels in milk. OBJECTIVES: This study aimed to determine the micronutrient intake and status in lactating women, and their association with micronutrient levels in human milk. METHODS: Lactating women were enrolled at 4-6 months postpartum. A 24h food recall was examined and nutrient intakes were analyzed using INMUCAL software. Human milk samples were collected to analyze calcium, copper, iron, and zinc levels. Plasma zinc and serum ferritin levels were determined. RESULTS: Thirty-four women participated; 19 were classified as full breastfeeding and 15 as partial breastfeeding. Mean levels of calcium, copper, iron, and zinc in human milk were 243, 0.2, 0.2, and 1.56 mg/L, respectively. The prevalence of zinc deficiency (plasma zinc < 10.7 µmol/L) was 11.8%. No lactating women had iron deficiency. Nutrient intakes were lower than the recommended amounts in 38%-70% of participants, and were not correlated with corresponding nutrient levels in human milk. Multiple linear regression showed significant association between zinc levels in human milk and plasma for lactating women with full breastfeeding (ß = 0.034, 95% confidence interval [0.003, 0.067], p = 0.040). CONCLUSIONS: Lactating women were at risk of micronutrient deficiency. There was an association between zinc levels in human milk and plasma of lactating women with full breastfeeding. As the nutritional status of lactating women influences the quality of human milk, we should encourage good nutrient intake for lactating women.

Flow field-flow fractionation for hydrodynamic diameter estimation of gold nanoparticles with various types of surface coatings.

Flow field-flow fractionation (FlFFF) with inductively coupled plasma mass spectrometric (ICP-MS) detection was applied for estimating the hydrodynamic diameter of gold nanoparticles (AuNPs). Hydrodynamic diameters of AuNPs of the same core diameter but with different surface coatings were different because the coating agents and their properties were different. The challenge of this work is due to the fact that AuNPs with various types of surface coatings exhibited different interactions in the FlFFF channel, leading to different retention behaviors. Therefore, we are interested in finding suitable FlFFF conditions for estimating the hydrodynamic diameter of AuNPs with various types of electrostatic stabilizing agents [tannic acid (TA) and citrate (CT)] and steric stabilizing agents [polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), and branched polyethylene imine (BPEI)]. Different types of carrier liquids (DI water, 0.02% FL-70, 0.05% SDS, and 30 mM Tris buffer) and membrane materials [regenerated cellulose (RC) and polyethersulfone (PES) membranes] were investigated. Generally, FlFFF was applied for size characterization of nanoparticles based on FlFFF theory but the interactions between AuNPs and membrane affected the retention and the experimentally obtained hydrodynamic diameters of AuNPs from the FlFFF system. With DI water as a carrier liquid with RC or PES membranes, the hydrodynamic diameters of negatively charged particles (TA-, CT-, PVP-, and PEG-stabilized AuNPs) from FlFFF corresponded well with the hydrodynamic diameters from dynamic light scattering (DLS). Interestingly, it was possible to estimate hydrodynamic diameters of AuNPs in the mixture by using FlFFF whereas it was not possible with the use of DLS within the size range studied. This work summarized the possible interactions between AuNPs with various coating agents and membrane materials in different carrier liquids to give guidelines on the suitable conditions of FlFFF for further applications on AuNP hydrodynamic diameter estimation.

Rapid characterization of trace aflatoxin B1 in groundnuts, wheat and maize by dispersive liquid-liquid microextraction followed by direct electrospray probe tandem mass spectrometry.

RATIONALE: Aflatoxins are poisonous and cancer-related chemical compounds commonly found in crops and plants. Aflatoxin B1 is the most toxic compound among aflatoxins and has been classified as group 1 carcinogenic to humans, especially in liver cancer. Herein, an ambient mass spectrometric method was developed for rapid characterization of trace aflatoxin B1 in peanuts. METHODS: Direct electrospray probe tandem mass spectrometry (DEP-MS/MS) was used to detect aflatoxin B1 in peanuts. To avoid the matrix effect, the aflatoxin B1 in the samples was extracted and concentrated by dispersive liquid-liquid microextraction. The mass spectrometer was operated in the positive ion mode to monitor the intact molecular ion (m/z 313, MH+ ) and product ion (m/z 241) of aflatoxin B1 using multiple reaction monitoring. RESULTS: Since no clean-up procedure of the sample was required, the sampling step and the subsequent mass spectrometric detection of the aflatoxin B1 was completed in less than 5 min. The limit of detection of aflatoxin B1 is at the sub-ppb level. The results obtained by DEP-MS/MS were also validated by liquid chromatography/tandem mass spectrometry (LC/MS/MS). Recovery of aflatoxin B1 in the sample was evaluated by analyzing spiked aflatoxin B1 with LC/MS/MS to be 85% and DEP-MS/MS to be 84%. CONCLUSIONS: DEP-MS/MS combined with a simple dispersive liquid-liquid microextraction procedure was successfully used for the quantitative analysis of AFB1 in nut samples. Due to its high efficiency, it is promising in providing important toxicological information for food safety in the real world. Copyright © 2017 John Wiley & Sons, Ltd.

Application of thermospray flame furnace atomic absorption spectrometry for investigation of silver nanoparticles.

Thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was applied to investigate the time-dependent absorption peak profile of various forms of silver. The thermospray flame furnace was set up with a 10-cm-long nickel tube with six holes, each 2.0 mm in diameter, to allow the flame to enter, and this nickel tube acted as a furnace. A sample of 300 µL was introduced into this furnace by use of water as a carrier at a flow rate of 0.5 mL min-1 through the ceramic capillary (0.5-mm inner diameter and 2.0-mm outer diameter), which was inserted into the front hole of the nickel tube. The system was applied to examine atomization behaviors of silver nanoparticles (AgNPs) with particle sizes ranging from 10 to 100 nm. The atomization rate of AgNPs was faster than that of the dissolved silver ion. With increased amount of silver, the decay time observed from the time-dependent absorption peak profile was shortened in the case of dissolved silver ion, but it was increased in the case of AgNPs. With the particle size ranging from 10 to 100 nm, the detection sensitivity was indirectly proportional to the particle size, suggesting that TS-FF-AAS may offer insights into the particle size of AgNPs provided that the concentration of the silver is known. To obtain quantitative information on AgNPs, acid dissolution of the particles was performed before TS-FF-AAS analysis, and recoveries of 80-110% were obtained.

Effect of Ionic and Nonionic Carriers in Electrical Field-Flow Fractionation.

A major limitation of electrical field-flow fractionation (ElFFF) is the polarization of the electrodes that occurs when using an ionic carrier liquid. As there is great interest in using ElFFF with biological materials and biological materials typically have high ionic strengths and high osmotic concentrations, we explore the effect of concentration for phosphate buffered saline (PBS), a typical ionic medium for biological samples, and for two nonionic materials common in bioparticle analysis: isopropanol (IPA) and sucrose. Their effect on retention and separations in ElFFF for increasing concentrations was observed. The results suggest that modifying the carrier solution with PBS, sucrose, and/or IPA would enable characterization and separation of biological samples in ElFFF. Specifically, changes of elution time and electrical parameters such as current, conductivity, and bulk channel resistance were observed as functions of carrier ionic and osmotic strength for the different carrier additives. PBS can be used in the micromolar range, equivalent to about 0.1% 1× PBS (150 µM). These concentrations are far from the isotonic condition of PBS (∼ 150 mM) that is normally used with biological samples. However, the nonionic additive carriers IPA and sucrose show quality retention even when added in high concentrations. The results show that IPA could be used in ratios up to 60% and that sucrose can be used in concentrations up to 0.3 M. Concentrations of 2% IPA (0.26 M) and 0.30 M sucrose are biologically isotonic conditions (275-299 mOsm/kg), and retention was readily obtained in these conditions using both DC ElFFF and cyclical ElFFF (CyE1FFF). Carriers of this type may make it possible to use ElFFF with biological samples.

Biased cyclical electrical field-flow fractionation for separation of submicron particles.

The potential of biased cyclical electrical field-flow fractionation (BCyElFFF), which applies the positive cycle voltage longer than the negative cycle voltage, for characterization of submicron particles, was investigated. Parameters affecting separation and retention such as voltage, frequency, and duty cycle were examined. The results suggest that the separation mechanism in BCyElFFF in many cases is more related to the size of particles, as is the case with normal ElFFF, in the studied conditions, than the electrophoretic mobility, which is what the theory predicts for CyElFFF. However, better resolution was obtained when separating using BCyElFFF mode than when using normal CyElFFF. BCyElFFF was able to demonstrate simultaneous baseline separations of a mixture of 0.04-, 0.1-, and 0.2-µm particles and near separation of 0.5-µm particles. This study has shown the applicability of BCyElFFF for separation and characterization of submicron particles greater than 0.1-µm in size, which had not been demonstrated previously. The separation and retention results suggest that for particles of this size, retention is based more on particle size than on electrophoretic mobility, which is contrary to existing theory for CyElFFF.

Flow field-flow fractionation and single particle inductively coupled plasma mass spectrometry as a powerful tool for tracking and understanding the sensing mechanism of Ag-Au bimetallic nanoparticles toward cobalt ions.

BACKGROUND: Ag-Au bimetallic nanoparticles (BNPs), synthesized by using citrate reduction of Ag and Au ions, were used as sensor for detection of Co2+. In order to optimize sensing performance, it is necessary to control the particle size and size distribution of the original Ag-Au BNPs. Therefore, analytical methods based on the use of single particle inductively coupled plasma mass spectrometry (SP-ICP-MS) and flow-field flow fractionation (FlFFF)-ICP-MS were developed to track the signal of Ag and Au in bimetallic nanoparticles at each step of the procedure: BNP synthesis, aggregation and sensing in order to understand the sensing mechanism. To better understand colorimetric sensing of Co2+ using Ag-Au BNPs, various solution mixtures were analyzed by using SP-ICP-MS and FlFFF-ICP-MS. RESULTS: SP-ICP-MS provided the information on the core size, size distribution and particle number concentration, as well as the heterogeneity of the particles synthesized by using various citrate concentrations and metal ratios. FlFFF-ICP-MS offered the information on hydrodynamic size as well as the signal intensity ratio of Ag and Au in BNPs and for the understanding of the aggregation of BNPs arising from the [Co(II)(en)3]2+ complex surrounding the surface of the BNPs. Under optimum sensing condition, the use of SP-ICP-MS for BNPs assisted detection of Co2+ improved the sensitivity of Co2+ determination by 20-fold in comparison with the conventional spectrophotometric analysis. SIGNIFICANCE: The information obtained from SP-ICP-MS and FlFFF-ICP-MS can be combinedly used to understand sensing mechanism and to select the best condition for synthesis of BNPs used as sensor. This study illustrates the usefulness of SP-ICP-MS and FlFFF-ICP-MS in the nanoparticle-based sensor development research area.

Electrical field-flow fractionation for metal nanoparticle characterization.

The potential of electrical field-flow fractionation (ElFFF) for characterization of metal nanoparticles was investigated in this study. Parameters affecting separation and retention such as applied DC voltage and flow rate were examined. Nanoparticles with different types of stabilizers, including citrate and tannic acid, were investigated. Changes to the applied voltage showed a significant influence on separation in ElFFF, and varying flow rate was used to improve plate heights in the experiments. For nanoparticles of a fixed size, the separation was based primarily on electrophoretic mobility. Particles with low electrophoretic mobility elute earlier. Therefore, citrate stabilized gold nanoparticles (-2.72 × 10(-4) cm(2) V(-1) s(-1)) eluted earlier than tannic acid stabilized gold nanoparticles (-4.54 × 10(-4) cm(2) V(-1) s(-1)) of the same size. In addition, ElFFF can be used for characterization of gold nanoparticles with different particle sizes including 10, 20, and 40 nm with a fixed stabilizing agent. For a specific separation condition, the separation of 10, 20, and 40 nm gold nanoparticles was clearly based on the particle size as opposed to the electrophoretic mobility, as the elution order was in order of decreasing mobility for 10 (-4.54 × 10(-4) cm(2) V(-1) s(-1)), 20 (-3.97 × 10(-4) cm(2) V(-1) s(-1)), and 40 (-3.76 × 10(-4) cm(2) V(-1) s(-1)) nm particles, respectively.

Mechanisms of red blood cells agglutination in antibody-treated paper.

Recent reports on using bio-active paper and bio-active thread to determine human blood type have shown a tremendous potential of using these low-cost materials to build bio-sensors for blood diagnosis. In this work we focus on understanding the mechanisms of red blood cell agglutination in the antibody-loaded paper. We semi-quantitatively evaluate the percentage of antibody molecules that are adsorbed on cellulose fibres and can potentially immobilize red blood cells on the fibre surface, and the percentage of the molecules that can desorb from the cellulose fibre surface into the blood sample and cause haemagglutination reaction in the bulk of a blood sample. Our results show that 34 to 42% of antibody molecules in the papers treated with commercial blood grouping antibodies can desorb from the fibre surface. When specific antibody molecules are released into the blood sample via desorption, haemagglutination reaction occurs in the blood sample. The reaction bridges the red cells in the blood sample bulk to the layer of red cells immobilized on the fibre surface by the adsorbed antibody molecules. The desorbed antibody also causes agglutinated lumps of red blood cells to form. These lumps cannot pass through the pores of the filter paper. The immobilization and filtration of agglutinated red cells give reproducible identification of positive haemagglutination reaction. Results from this study provide information for designing new bio-active paper-based devices for human blood typing with improved sensitivity and specificity.

A novel sensor based on bead-counting of purple sweet potato tapioca pearl for freshness monitoring of shrimp.

A novel sensor based on bead-counting of purple sweet potato tapioca pearl for freshness monitoring of shrimp was proposed. The sensor was prepared from commercially available tapioca pearls with purple sweet potato as a natural colorant by using a similar procedure as to prepare "Thai Saku dessert". A novel concept of using five tapioca pearls stacked in a pipette tip was proposed to observe the color change of the pearls by bead counting approach. The color of the tapioca pearl changed from purple to greenish-blue upon the detection of volatile amines and then to green on prolonged exposure to volatile amines. This color change was observed from the first bead and gradually observed on the next beads according to the concept of distance-based colorimetric measurement. This work is the first to demonstrate the use of bead counting as a novel, low-cost sensor technology for estimating the freshness of shrimp.

Use of single particle inductively coupled plasma mass spectrometry for understanding the formation of bimetallic nanoparticles.

Bimetallic nanoparticles (NPs), including core-shell structure and bimetallic alloy nanoparticles, were synthesized and characterized using flow field-flow fractionation (FlFFF), single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), and transmission electron microscope (TEM) with energy-dispersive x-ray spectroscopy (EDS). For the core-shell particles, a nominal 80 nm commercial core-shell AuAg bimetallic nanoparticle was used to examine the applicability of SP-ICP-MS to determine the core size of Au and shell thickness of Ag. Then, the method was applied to estimate the core size of Au and shell thickness of Ag for the laboratory synthesized particles. The results were compared with those obtained from TEM-EDS. For the alloy nanoparticles, two synthesis protocols, based on the galvanic replacement of Ag seed particles with Au, were used. One was to prepare a hollow AgAu particle by varying the volume of dissolved Au in basic solution (K-gold) to etch some parts of AgNPs to dissolved ionic silver with the formation of AuNPs covering the remaining AgNPs, producing a hole inside the core nanoparticles. Another protocol was to prepare AgAu alloy nanoparticles. SP-ICP-MS was used in combination with FlFFF to provide information on the changes of particle size with varying volume of K-gold reagent. Hydrodynamic diameter increased with increasing K-gold, as observed by FlFFF. With SP-ICP-MS without prior FlFFF, bimodal distributions were observed in the size distribution of Au and Ag. With prior FlFFF, monomodal distributions were observed by SP-ICP-MS, which allow the use of particle concentration and size to estimate the mass concentration of elements on the fractionated bimetallic nanoparticles. This study illustrates the potential use of SP-ICP-MS for gaining information about particle transformation during the synthesis of bimetallic nanoparticles.

Particle size characterization of titanium dioxide in sunscreen products using sedimentation field-flow fractionation-inductively coupled plasma-mass spectrometry.

Sedimentation field-flow fractionation-inductively coupled plasma-mass spectrometry (SdFFF-ICP-MS) was successfully applied to investigate particle size distribution of titanium dioxide (TiO(2)) in sunscreen samples after hexane extraction to remove organic components from the samples. Three brands of sunscreen products of various sun protection factor (SPF) value were used as samples. Different particle size distribution profiles were observed for sunscreen samples of various brands and SPF values; however, the particle size distributions of titanium dioxide in most sunscreen samples investigated in this work were larger than 100 nm. The titanium dioxide concentrations were higher for the products of higher SPF values. By comparing the results obtained from online SdFFF-ICP-MS and those from the off-line ICP-MS determination of titanium after acid digestion, ICP-MS was found to effectively atomize and ionize the titanium dioxide particle without the need for acid digestion of the samples. Therefore, the online coupling between SdFFF and ICP-MS could be effectively used to provide quantitative information of titanium dioxide concentrations across particle size distribution profiles.

Use of electrical field-flow fractionation for gold nanoparticles after improving separation efficiency by carrier liquid optimization.

Electrical field-flow fractionation (ElFFF) is a useful separation technique for nanoparticles, however, it has been limited by polarization/electrical double layer formation which reduces an effective field for separation. With an appropriate direct current (DC) applied voltage, sodium carbonate, FL-70, Triton X-100 and acetonitrile were explored as additive substances for preparation of carrier liquid used in normal ElFFF to enhance an amplitude of effective field by their ionic redox-active species, ionic and nonionic surfactant and wide electrochemical potential window nonionic organic solvent properties, respectively. Effective field was indirectly measured in each carrier liquid by investigating retention behavior of polystyrene latex nanoparticles and gold nanoparticles. Effective field improvement was observed in all carrier liquid types (except FL-70) by which the highest effective field existed in 16 µM sodium carbonate at 1.70 V and 0.01% (V/V) Triton X-100 and 50% (V/V) acetonitrile at 1.90 V as compared to deionized water at 1.90 V. In addition, those carrier liquids were applied for separation of 5 nm and 15 nm gold nanoparticles mixture by which Triton X-100 exhibited the best separation resolution (Rs = 1.11).

Flow field-flow fractionation: a versatile approach for size characterization of alpha-tocopherol-induced enlargement of gold nanoparticles.

Flow field-flow fractionation (FlFFF) was used for size characterization of gold nanoparticles. The measured particle sizes obtained from FlFFF for the commercial 10 nm gold nanoparticle standard and the gold nanoparticles synthesized in the laboratory were in good agreement with those measured by transmission electron microscopy (TEM). Further, the capability of alpha-tocopherol to induce enlargement of gold nanoparticles by catalysis of the reduction of AuCl(4)(-) by citrate was observed by monitoring the changes in particle size of gold nanoparticles using FlFFF. The effects of alpha-tocopherol and incubation time on enlargement of the gold nanoparticles were examined. Higher concentrations of alpha-tocopherol resulted in larger nanoparticles. At fixed alpha-tocopherol concentration, larger nanoparticles were formed at longer incubation times.

Use of flow field-flow fractionation and single particle inductively coupled plasma mass spectrometry for size determination of selenium nanoparticles in a mixture.

Various analytical techniques have been used for size analysis of selenium nanoparticles (SeNPs). These include flow field-flow fractionation (FlFFF), single particle inductively coupled plasma mass spectrometry (SP-ICP-MS), dynamic light scattering (DLS) and transmission electron microscopy (TEM). For hydrodynamic diameter estimation, the FlFFF technique was used and the results were compared with those analyzed by DLS. For core diameter estimation, the results obtained from SP-ICP-MS were compared with those from TEM. Two types of FlFFF channel were employed, i.e., symmetrical FlFFF (Sy-FlFFF) and asymmetrical FlFFF (Asy-FlFFF). Considering the use of FlFFF, optimization was performed on a Sy-FlFFF channel to select the most appropriate carrier liquid and membrane in order to minimize problems due to particle membrane interaction. The use of FL-70 and 10 kDa RC provided an acceptable compromise peak quality and size accuracy for all samples of SeNPs which were coated by proteins (positively charged SeNPs) and sodium dodecyl sulfate (negatively charged SeNPs). FlFFF always yielded the lower estimate of the hydrodynamic size than DLS as a reference method. The results obtained by SP-ICP-MS were consistent with the TEM method for the core diameter estimation. The results from FlFFF and the DLS reference method were significantly different as confirmed by paired t-test analysis, while the results provided by SP-ICP-MS and the TEM reference method were not significantly different. Furthermore, consecutive size analysis by SP-ICP-MS for the fractions collected from FlFFF was proposed for sizing of SeNP mixtures. The combined technique helps to improve the size analysis in the complex samples and shows more advantages than using only SP-ICP-MS.

Novel paper-based colorimetric immunoassay (PCI) for sensitive and specific detection of salbutamol residues in flesh of swine and urine using Ag3 PO4 /Ag nanocomposite as label.

Salbutamol (SAL) can cause potential hazards to human health and its use as a growth promoter in meat-producing animals is illegal. This work reports a novel approach for competitive paper-based colorimetric immunoassay (PCI) using the Ag3 PO4 /Ag nanocomposite as label for sensitive and specific determination of SAL in flesh of swine and urine. The Ag3 PO4 /Ag nanocomposite was synthesized by a one-step chemical bath method, which could instantly oxidize a chromogenic substrate for the color development under acidic conditions without the participation of H2 O2 . This approach provides high affinity between the Ag3 PO4 /Ag nanocomposite and the substrate (with the Michaelis-Menten constant of 0.44 mM). In addition, the fabrication process of the PCI was simple and cost-effective. Particularly, the novel PCI also exhibits simplicity and cost-effectiveness of the fabrication process through a simple wax screen-printing, which requires inexpensive equipment and material including a screen, wax, a squeegee, and a hair dryer. Under optimal conditions, the competitive PCI exhibited a linearity range of 0.025 to 1.00 µg/L. The developed approach offers advantages over the conventional ELISA for the purpose of routine use because it requires a shorter incubation time (<1 hr), significantly small volumes of reagents and samples (<100 µL each), and an inexpensive consumer-grade digital camera coupled with a simple gray-scale transformation of the RGB (Red Green Blue) color image for the purpose of quantification of the detection. PRACTICAL APPLICATION: Salbutamol (SAL) can cause potential hazards to human health and the use of which as growth promoter in meat-producing animals is illegal. This work introduces a novel approach for competitive immunoassay on paper-based colorimetric immunoassay using the Ag3 PO4 /Ag nanocomposite as the label (instead of using natural enzyme) for low-cost, sensitive, and specific determination of SAL residues at low level in flesh of swine and urine samples. The proposed approach offers advantages over the conventional ELISA for the purpose of routine use.

Exploring the applicability of nano-selenium for capture of mercury vapor: Paper based sorbent and a chemical modifier in graphite furnace atomic absorption spectrometry.

The ability of the selenium nanoparticles (SeNPs) to capture mercury (Hg) is a subject of interest as this concept can be applied to reduce mercury poisoning cases to certain extent. In this work, SeNPs were fabricated on a paper and used as sorbent for capturing mercury vapor. The formation of the stable HgSe on the paper sorbent after the sequestration was visible to the naked eye for mercury concentration of higher than 200 µg L-1, corresponding with the discoloration of the paper sorbent from dark orange to gray color. The gray color was more intense with increasing Hg concentrations from 200 to 300, 500, and 1000 µg L-1. Therefore, color analysis software was used as a semi-quantitative technique for mercury analysis. The mercury captured was also analyzed with the inductively coupled plasma mass spectrometry (ICP-MS). After confirming that SeNPs helps capture mercury, it was further applied as a chemical modifier in graphite furnace atomic absorption spectrometry (GFAAS) for mercury determination. The SeNPs (410 mg L-1) allowed the use of pyrolysis temperature up to 300 °C with adequate sensitivity. Calibration curve was constructed from 100 to 500 µg L-1 with good linearity (R2 = 0.9968). With the use of SeNPs, 15 times sensitivity improvement was obtained compared to that without the use of any chemical modifier. The detection limit (N = 10 at 3σ) was calculated at 2 µg L-1 for the Hg standard. The proposed modifier was used for analyzing mercury in the saliva sample. Apart from minimizing extensive sample pretreatment process, the recovery percentage of Hg from the spiked sample was found to be approximately 90% (RSD 0-2%) with the help of the SeNPs modifier. This work exhibits multi-dimensional applications of SeNPs towards mercury analysis.