Purim Jarujamrus

Selective colorimetric sensors based on the monitoring of an unmodified silver nanoparticles (AgNPs) reduction for a simple and rapid determination of mercury.

In this work, selective colorimetric sensors for simple and rapid detection of Hg(II) ions based on the monitoring of an unmodified silver nanoparticles (AgNPs) reduction were developed. The average diameter of synthesized AgNPs was 8.3±1.4nm which was characterized by transmission electron microscopy (TEM). The abrupt change in absorbance of the unmodified AgNPs was observed which progressively decreased and slightly shifted to the blue wavelength as the concentration of Hg(II) increased, indicating the oxidation of Ag(0) to Ag(I) occurred. It appears that the AgNPs were oxidized by Hg(II), resulting in disintegration of the AgNPs into smaller particles as well as mediating the reduction of Hg(II) to Hg(0) adsorbed onto the surface of AgNPs. The adsorption of Hg(0) resulted in the lack of sufficient charges on AgNPs surfaces due to the decrease in the surface coverage of negatively charged citrate molecules, which then leaded to enlargement of AgNPs. The calibration curve of this technique was demonstrated from 0.5 to 7ppm (r(2)=0.995), the limit of detection (LOD) was 0.06ppm (SDblank/slope of calibration curve) with the precision (RSD, n=4) of 3.24-4.53. Interestingly, the results show a significant enhance in the Hg(II) analytical sensitivity when Cu(II) is doped onto the unmodified AgNPs, which improves the quantitative detection limit to 0.008ppm. In addition, greater selectivity toward Hg(II) compared with the other metal ions tested was observed. Furthermore, the percentage recoveries of spiked drinking water, tap water and SRM1641d (mercury in water) were in acceptable range with a good precision (RSD) which were in agreement with the values obtained from graphite furnace atomic absorption spectrometer (GFAAS). The technique proposed in this study provides a rapid, simple, sensitive and selective detection method for Hg(II) in water samples.

A sensitive and selective on-line amperometric sulfite biosensor using sulfite oxidase immobilized on a magnetite-gold-folate nanocomposite modified carbon-paste electrode

We describe a novel amperometric sulfite biosensor, comprising a carbon-paste electrode (Fe3O4@Au-Cys-FA/CPE) modified with immobilized sulfite oxidase (SOx) on a gold-coated magnetite nanoparticle core, encased within a conjugated folic acid (FA) cysteine (Cys) shell. The biosensor electrode was fabricated using a polydimethylsiloxane (PDMS) and mineral oil mixture as binder, which also enhances the physical stability and sensitivity of the electrode. The developed biosensor displays good electrocatalytic activity toward oxidation of H2O2, which occurs by an enzymatic reaction between SOx and sulfite. The Fe3O4@Au-Cys-FA electrode exhibits good electrocatalytic activity, and has good retention of chemisorbed SOx on the electrode because of its large surface area. Sulfite was quantified using amperometric measurements from the Fe3O4@Au-Cys-FA/CPE biosensor, and using an in-house assembled flow cell at +0.35V (vs. Ag/AgCl), with a phosphate buffer carrier (0.10M, pH 7.0) at a flow rate of 0.8mLmin(-1). The system detects sulfite over the range 0.1-200mgL(-1) (r(2)=0.998), with a detection limit of 10µgL(-1) (3σ of blank). The system exhibits acceptable precision (%R.S.D.=3.1%), rapid sample throughput (109samplesh(-1)), and good stability (2w). The developed biosensor shows satisfactory tolerance to potential interferences, such as sugars, anions, ascorbic acid, and ethanol. We applied the developed method to the determination of sulfite content in wines and pickled food extracts, and our results are in good agreement with those obtained by the standard iodometric method.

Chromatic analysis by monitoring unmodified silver nanoparticles reduction on double layer microfluidic paper-based analytical devices for selective and sensitive determination of mercury(II)

This study demonstrates chromatic analysis based on a simple red green blue (RGB) color model for sensitive and selective determination of mercury(II). The analysis was performed by monitoring the color change of a microfluidic Paper-based Analytical Device (µPAD). The device was fabricated by using alkyl ketene dimer (AKD)-inkjet printing and doped with unmodified silver nanoparticles (AgNPs) which were disintegrated when being exposed to mercury(II). The color intensity was detected by using an apparatus consisting of a digital camera and a homemade light box generating constant light intensity. A progressive increase in color intensity of the tested area on the µPAD (3.0mm) was observed with increasing mercury(II) concentration. The developed system enabled quantification of mercury(II) at low concentration with the detection limit of 0.001mgL(-1) (3 SD blank/slope of the calibration curve) and small sample volume uptake (2µL). The linearity range of the calibration curve in this technique was demonstrated from 0.05 to 7mgL(-1) (r(2)=0.998) with good precision (RSD less than 4.1%). Greater selectivity towards mercury(II) compared with potential interference ions was also observed. Furthermore, the percentage recoveries of spiked water samples were in an acceptable range which was in agreement with the values obtained from the conventional method utilizing cold vapor atomic absorption spectrometer (CVAAS). The proposed technique allows a rapid, simple, sensitive and selective analysis of trace mercury(II) in water samples.

Selective amperometric flow-injection analysis of carbofuran using a molecularly-imprinted polymer and gold-coated-magnetite modified carbon nanotube-paste electrode

Herein, we propose a new approach for selective determination of carbofuran (CBF) in vegetables, based on a simple flow-injection system using a molecularly-imprinted amperometric sensor. The sensor design is based on a carbon-paste electrode decorated with carbon nanotubes and gold-coated magnetite (CNTs-Fe3O4@Au/CPE) coated with a molecularly-imprinted polymer (MIP) for CBF sensing. The MIP was synthesized on the electrode surface by electropolymerization using a supramolecular complex, namely 4-ter-butylcalix [8] arene-CBF (4TB[8]A-CBF), as the template. We used o-phenylenediamine as the functional monomer. Our results demonstrate that incorporation of the MIP coating improves the electrochemical catalytic properties of the electrode, increases its surface area, and increases CBF selectivity by modulating the electrical signal through elution and re-adsorption of CBF. The imprinted sensor (MIP-CNTs-Fe3O4@Au/CPE) was used in a flow-injection analysis (FIA) system. Experimental conditions were investigated in amperometric mode, with the following optimized parameters: phosphate buffer solution (0.1M, pH 8.0) as the carrier, flow rate 0.5mLmin-1, applied potential +0.50V. When used in the FIA system, the designed imprinted sensor yields a linear dynamic range for CBF from 0.1 to 100µM (r2 = 0.998) with a detection limit of 3.8nM (3Sb), and a quantification limit of 12.7nM (10Sb). The sensor exhibits acceptable precision (%RSD = 4.8%) and good selectivity toward CBF. We successfully applied the electrode to detect CBF in vegetable samples.

Development of sensitive and selective glucose colorimetric assay using glucose oxidase immobilized on magnetite–gold–folate nanoparticles

We constructed a new nanocomposite catalyst that demonstrated enzyme mimetic activity, like peroxidase, for the colorimetric detection of glucose, using glucose oxidase (GOx) immobilized by glutaraldehyde cross-linking on a gold-coated magnetite nanoparticle (Fe3O4@Au) core, encased within a conjugated cysteine (Cys) folic acid (FA) shell. The synthesized Fe3O4@Au–Cys–FA NPs were characterized using AFM, XRD, DLS and FT-IR analysis. The as-prepared Fe3O4@Au–Cys–FA–GOx nanocomposites were used to catalyze the oxidation of glucose to generate H2O2, coupled with catalyzing the oxidation of a peroxidase substrate, 2,2′-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid)-diammonium salt (ABTS), to ABTS˙+, thereby enabling the colorimetric detection of a colored oxidization product. The proposed nanocomposite exhibits good biocompatibility and provides highly efficient immobilization and retention of GOx. The designed colorimetric method provides a linear dynamic range for glucose detection from 10 μM to 1 mM (r2 = 0.998) and a detection limit of 3.8 μM (3 S.D.blank/slope) with a good reproducibility and the nanocomposite is reusable (≥6 times). Moreover, an interference study revealed that maltose, fructose and sucrose do not affect the colorimetric measurement. The developed method was successfully applied for glucose determination in energy and sports drinks. It is also expected that an expansion of the designed colorimetric method beyond this application may be possible in the future.

Use of a Smartphone as a Colorimetric Analyzer in Paper-based Devices for Sensitive and Selective Determination of Mercury in Water Samples

A smartphone application, called CAnal, was developed as a colorimetric analyzer in paper-based devices for sensitive and selective determination of mercury(II) in water samples. Measurement on the double layer of a microfluidic paper-based analytical device (μPAD) fabricated by alkyl ketene dimer (AKD)-inkjet printing technique with special design doped with unmodified silver nanoparticles (AgNPs) onto the detection zones was performed by monitoring the gray intensity in the blue channel of AgNPs, which disintegrated when exposed to mercury(II) on μPAD. Under the optimized conditions, the developed approach showed high sensitivity, low limit of detection (0.003 mg L-1, 3SD blank/slope of the calibration curve), small sample volume uptake (two times of 2 μL), and short analysis time. The linearity range of this technique ranged from 0.01 to 10 mg L-1 (r2 = 0.993). Furthermore, practical analysis of various water samples was also demonstrated to have acceptable performance that was in agreement with the data from cold vapor atomic absorption spectrophotometry (CV-AAS), a conventional method. The proposed technique allows for a rapid, simple (instant report of the final mercury(II) concentration in water samples via smartphone display), sensitive, selective, and on-site analysis with high sample throughput (48 samples h-1, n = 3) of trace mercury(II) in water samples, which is suitable for end users who are unskilled in analyzing mercury(II) in water samples.

Complexometric and argentometric titrations using thread-based analytical devices

This work describes analytical approaches based on simple complexometric and argentometric titrations leading to the color change of a novel microfluidic thread-based analytical device (µTAD). The device was fabricated from a cotton thread (15 cm) treated with indicator solution, providing an easy-to-use platform for rapid measurement of analyte concentration in aqueous solution. The thread was immobilized onto a support, being a polypropylene sheet or box platform, to facilitate loading of liquid samples. Interaction between the deposited reagents and analytes in the samples then occurred within a few minutes. This resulted in zones of color change with different lengths along the thread depending on the analyte concentration. The interaction zones can be analyzed by human eyes based on comparison of the zone lengths with the printed scales which are correlated with the analyte concentrations. Complexometric titration using µTADs was initially investigated for Mg(II) determination in water and rubber latex samples. These devices consisted of two threads which were pretreated with Eriochrome Black T (EBT) and then treated with ethylenediaminetetraacetic acid (EDTA) in N-cyclohexyl-3-aminopropanesulfonic acid (CAPS) buffer at pH 10. Both threads were tied together with a central knot before being attached to the box platform prior to the analysis. Load of sample solution (6 µL) resulted in the length of red-violet color product on the threads being proportional to the concentration of Mg(II) in waters and rubber latex samples with the working concentration range of 25-1000 mg L-1. In addition, µTAD with a supporting polypropylene sheet consisting of several threads treated with AgNO3 and K2CrO4 indicators was applied for argentometric titration of chloride ion in water and food seasoning samples. After sample loading (3 µL), the initially red-brown threads turned into white corresponding to formation of AgCl(s) on the threads with a working concentration range of 75-600 mg L-1. Greater selectivity towards Mg(II) and chloride compared with potential interference ions was also observed. All the developed μTADs were applied for analysis of real samples which showed results being in agreement with those obtained by classical titrations.