AgNPs Solution Research Articles

Mapping of the spatial distribution of silver nanoparticles in root tissues of Vicia faba by laser-induced breakdown spectroscopy (LIBS)

The manuscript presents a procedure for optimal sample preparation and the mapping of the spatial distribution of metal ions and nanoparticles in plant roots using laser-induced breakdown spectroscopy (LIBS) in a double-pulse configuration (DP LIBS) in orthogonal reheating mode. Two Nd:YAG lasers were used; the first one was an ablation laser (UP-266 MACRO, New Wave, USA) with a wavelength of 266nm, and the second one (Brilliant, Quantel, France), with a fundamental wavelength of 1064nm, was used to reheat the microplasma. Seedlings of Vicia faba were cultivated for 7 days in CuSO4 or AgNO3 solutions with a concentration of 10µmoll−1 or in a solution of silver nanoparticles (AgNPs) with a concentration of 10µmoll−1 of total Ag, and in distilled water as a control. The total contents of the examined metals in the roots after sample mineralization as well as changes in the concentrations of the metals in the cultivation solutions were monitored by ICP-OES. Root samples embedded in the TissueTek medium and cut into 40µm thick cross sections using the Cryo-Cut Microtome proved to be best suited for an accurate LIBS analysis with a 50µm spatial resolution. 2D raster maps of elemental distribution were created for the emission lines of Cu(I) at 324.754nm and Ag(I) at 328.068nm. The limits of detection of DP LIBS for the root cross sections were estimated to be 4pg for Cu, 18pg for Ag, and 3pg for AgNPs. The results of Ag spatial distribution mapping indicated that unlike Ag+ ions, AgNPs do not penetrate into the inner tissues of Vicia faba roots but stay in their outermost layers. The content of Ag in roots cultivated in the AgNP solution was one order of magnitude lower compared to roots cultivated in the metal ion solutions. The significantly smaller concentration of Ag in root tissues cultivated in the AgNP solution also supports the conclusion that the absorption and uptake of AgNPs by roots of Vicia faba is very slow. LIBS mapping of root sections represents a fast analytical method with sufficient precision and spatial resolution that can provide very important information for researchers, particularly in the fields of plant science and ecotoxicology.

Biosynthesis, Characterization, and Antibacterial Activity of Silver Nanoparticles Produced from Rice Straw Biomass

Silver nanoparticles (AgNPs) were synthesized from AgNO3 using rice straw biomass as the reducing agent at room temperature via light irradiation. Full wavelength scanning with UV/Vis spectrophotometer was used to study the effect of light intensity, reaction time, and concentrations of rice straw biomass and AgNO3 during AgNPs synthesis. Surface plasmon resonance (SPR) showed that the peak wavelength of synthesized silver nanoparticles arose at 425 nm, the optimal light intensity observed was 60,000 lx, and the optimal reaction time was 140 min. The optimum concentrations of the rice straw biomass and AgNO3 used were 4 mg/mL and 2 mM, respectively. The AgNPs were characterized by X-ray diffraction (XRD) analysis. The zeta potential of AgNPs reached -21.2 mV. In addition, the AgNPs synthesized by rice straw biomass revealed antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Staphyloccus aureus. The inhibition rate reached about 97.17 ± 2.01% when the concentration of AgNPs solution used was 8 μg/mL. In the detection of antimicrobial effect of AgNPs and antibiotics, the antibacterial activity was found to be superior to that of antibiotics alone.

Optical and antibacterial properties of synthesised silver nanoparticles

In the present study, tri-sodium citrate has been used as both the reducing agent and stabiliser for the synthesis of silver nanoparticles (AgNPs). Sodium borohydride (NaBH4) was used in various concentrations. The absorbance of AgNP solution was measured after the addition of NaBH4. The samples were characterised by ultraviolet-visible spectroscopy after 5, 10, 15, 25, 60 and 120 min of synthesis to investigate the stability of AgNPs for different concentrations of NaBH4. Transmission electron microscopy revealed the nanostructure of the prepared samples with average sizes as 18, 20 and 29 nm. Photoluminescence spectra of these AgNPs showed maximum emission at wavelengths 473, 470 and 469 nm, respectively, when excited at 350 nm. Further, Disk diffusion test showed that all the prepared samples are good candidates for antibacterial activity while AgNPs of average size 18 nm were found most effective against the tested Gram-positive and Gram-negative bacteria.

Antiviral properties of silver nanoparticles against norovirus surrogates and their efficacy in coated polyhydroxyalkanoates systems

Silver nanoparticles (AgNP) have strong broad-spectrum antimicrobial activity and gained increased attention for the development of AgNP based products, including medical and food applications. Initially, the efficacy of AgNP and silver nitrate (AgNO3) was evaluated for inactivating norovirus surrogates, the feline calicivirus (FCV) and the murine norovirus (MNV). These norovirus surrogates were exposed to AgNO3 and AgNP solutions for 24 h at 25 °C and then analyzed by cell-culture assays. Both AgNP and silver ions significantly decreased FCV and MNV infectivity in a dose-dependent manner between concentrations of 2.1 and 21 mg/L. Furthermore, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films were prepared by depositing a coating of thermally post-processed electrospun PHBV18/AgNP fiber mats over compression moulded PHBV3 films. After 24 h exposure at 37 °C and 100% RH, no infectious FCV were recovered when in contact with the AgNP films while MNV titers decreased by 0.86 log. The morphology of the PHBV18 and PHBV18/AgNP fibers studied by SEM showed smooth and continuous fibers in both cases and the EDAX analysis confirmed the homogeneously distribution of AgNP into the coating and onto the PHBV3/PHBV18 layer. This study showed, for the first time, the suitability of the PHBV18/AgNP electrospun coating for antiviral surfaces.

Rapid Green Synthesis of Silver Nanoparticles (AgNPs) Using (Prunus persica) Plants extract: Exploring its Antimicrobial and Catalytic Activities

Fabrication of nanoparticles by using Green synthesis is done because of its wide applications in different field such as biomedical, agriculture and food engineering. In this paper plant extract is used that contain alkaloids, flavonoids, saponins, steroid compounds, acts as reducing and stabilizing agents. The presence of AgNPs in solution was identified by UV-visible spectrophotometer. The size of AgNPs was in the range of 40-98 nm determined by Zetasizer. Spherical Shape and crystalline nature of AgNPs was confirmed by FESEM and XRD. Process Optimization was done by varying leaf extract volume, silver nitrate concentrations, pH, temperature, and time of reaction. The biosynthesized AgNPs exhibited antibacterial and catalytic activity against bacterial strains E. coli and V. cholera, and heavy metal such as Cadmium (Cd) and Palladium (Pd) in varying extents. Biosynthesized AgNPs were found to have a higher inhibitory action against E. coli and removal efficiency of Cd is higher than Pd.

The Effects of Different Ionic Liquid Coatings and the Length of Alkyl Chain on Antimicrobial and Cytotoxic Properties of Silver Nanoparticles.

Introduction:The antibacterial efficacy and toxicity of silver nanoparticles (AgNPs) depends on their physicochemical properties including size, shape, surface charge and surface coatings. The Objectives of this study were: i) To synthesize and characterize positively charged AgNPs coated by different ionic-liquids with different alkyl chain lengths, ii) To evaluate the antimicrobial activity of these nanoparticles against Enterococcus faecalis compared to sodium hypochlorite (NaOCl) and chlorhexidine (CHX), iii) To compare the cytocompatibility of these solutions against L929 mouse fibroblasts.Methods and Materials: AgNPs with positive surface charges capped by two different ionic liquids [imidazolium (Im) and pyridinium (Py)] with two alkyl chain lengths (C12 and C18) were synthesized. Im and Py were also tested as control groups. The characterization revealed synthesis of spherical NPs in the size range of 6.7-18.5 nm with a surface charge ranging from +25 to +58 mV. To standardize the comparisons, the surface charge to radius ratio of each nanoparticle was calculated. The minimum inhibitory concentrations (MIC) of the AgNP solutions, NaOCl and CHX were determined against E. faecalis by a microdilution test. An MTT-based cytotoxicity assay evaluated the cytotoxicity of the solutions in different concentrations on L929 fibroblasts. One-way and two-way ANOVA were used for statistical analysis. Results:All tested AgNPs reached MIC90 in significantly lower concentrations compared to CHX and NaOCl. C12 Py-coated AgNPs had the lowest MIC90 value. CHX and NaOCl were more toxic on fibroblasts than all tested AgNPs. Im-coated AgNPs had better compatibility with fibroblasts than Py-coated particles; and C12 Im AgNPs had the best biocompatibility. Variations in alkyl chain length had no effects on the biocompatibility of AgNPs. Conclusion:Py improved the antibacterial efficacy of AgNPs compared to Im; however, it had a negative effect on cytocompatibility. Alkyl chain length had no effects on AgNPs’ bioactivity.

Stabilizer-free silver nanoparticles as efficient catalysts for electrochemical reduction of oxygen

In this work we demonstrated the potential of the He+5% H2+1% N2 plasma jet treatment for the synthesis of surfactant-free silver nanoparticles (Ag NPs) with narrow size distribution. The obtained colloidal solutions of electrostatically stabilized Ag NPs do not show any agglomeration for several months. Apart from an atomic thin oxide layer and the relatively weakly bound OH− ions, the surface of Ag NPs can be considered as stabilizer-free. The surface charge (characterized by the zeta potential) of Ag NPs in solution was measured by electrophoretic light scattering technique. Plasmonic band position and width in the UV/VIS extinction spectra was utilized for the assessment of Ag NPs size distribution. Highly concentrated Ag NPs were uniformly deposited on the surface of the glassy carbon (GC) electrodes by vacuum-drying technique. The deposition process was monitored with a digital camera attached to a microscope. The assemblies of Ag NPs on the electrode surface were characterized by scanning electron microscopy. The Ag NP/GC catalysts were electrochemically tested in alkaline solution using the rotating disk electrode method. The Ag NP/GC electrodes exhibited high electrocatalytic activity toward the oxygen reduction reaction (ORR) in 0.1M KOH solution, indicating their potential applicability as cathode materials for alkaline fuel cells.

4-Mercaptophenylboronic acid-induced in situ formation of silver nanoparticle aggregates as labels on an electrode surface

This work presented a general way for in situ formation of citrate-capped silver nanoparticle (AgNP) aggregates as labels on an electrode surface. When the electrode surface was functionalised with a member of the o-diphenol family, 4-mercaptophenylboronic acid (MPBA) was anchored onto the electrode surface via a boronate ester covalent bond. The anchored MPBA captured AgNPs through AgS interaction. The resulting surface-tethered AgNPs could recruit more MPBA molecules and AgNPs through the formation of an AgS bond and the covalent interaction between the α-hydroxycarboxylate of the citrate and the boronate of the MPBA. This led to in situ formation of a network of AgNPs. The complexes formed between MBPA and citrate acid, as well as dopamine (a member of the o-diphenol family), were characterized by mass spectrometry. The MBPA-induced aggregation of citrate-capped AgNPs in solution was confirmed by UV–Vis spectrophotometry and transmission electron microscopy. The network of AgNPs formed on the diphenol-covered electrode surface was characterized by scanning electron microscopy. The electrochemical signal was measured based on the solid-state Ag/AgCl reaction of the AgNPs. To demonstrate the applications and analytical merits of our design, tyrosinase and protease (thrombin) were measured as model analytes. The proposed strategy is likely to lead to the development of sensors for the detection of other biomolecules.

Highly fluorescent nitrogen and sulfur co-doped graphene quantum dots for an inner filter effect-based cyanide sensor

In this work, nitrogen and sulfur co-doped graphene quantum dots (N,S-GQDs), exhibiting bright blue fluorescence with an excellent quantum yield of 67%, were facilely prepared by one-pot pyrolysis of citric acid (carbon source) and cysteine (N and S sources). Compared to conventional GQDs, the doping of nitrogen/sulfur had significantly altered and uniformed the surface state, and the as-obtained N,S-GQDs displayed an excitation-independent emission behavior, where the fluorescence decay curve was nearly a single exponential. On the basis of the well-known inner filter effect of silver nanoparticles (AgNPs) and cyanide (CN−)-induced etching of AgNPs, the fluorescence of N,S-GQDs could be quenched by AgNPs, and the nonfluorescence state of the as-prepared N,S-GQD-AgNP ensemble would be switched on in the presence of CN−. Meanwhile, the addition of N,S-GQDs has almost ignorable effect on the absorption spectrum of the AgNP solution, however, the subsequent introduction of CN− would significantly decrease the absorbance value owing to the aforementioned etching behavior of CN−. Therefore, a N,S-GQD-based fluorescent and AgNP-related colorimetric dual-mode analytical system for efficacious determination of CN− has been rationally designed and successfully developed for the first time. Furthermore, the detection limits were found to be 0.52μM and 0.78μM for fluorescent and colorimetric sensors individually under the optimal experiment conditions. The proposed N,S-GQD-AgNP-based assay can be successfully utilized to the quantitative determination of CN− in spiked tap water samples.

Optical, structural and nonlinear optical properties of laser ablation synthesized Ag nanoparticles and photopolymer nanocomposites based on them

In this work Ag nanoparticles (NPs) stable colloid solution were prepared by laser ablation of chemically pure silver rod in liquid monomer isodecyl acrylate (IDA). Sizes of obtained nanoparticles were determined by scanning electron microscope and vary from 27 to 120nm. Nanocomposites films were prepared from obtained stable colloid solution of AgNPs by photocuring. For aliphatic polymer IDA long molecules cross-linking Diurethane dimethacrylate, 1,6-Hexandiol diacrylate and Tetra (ethylene glycol) diacrylate were used. Prepared nanomaterials exhibit strong third-order nonlinear optical responses, which was estimated by using z-scan technique. The third-order nonlinear optical coefficients of the studied nanocomposites were found to be up to Reχ(3)=1.31×10−5 (esu) and Imχ(3)=7.64×10−5 (esu).

Hydrothermal green synthesis of silver nanoparticles using Pelargonium/Geranium leaf extract and evaluation of their antifungal activity

Abstract Silver nanoparticles (AgNPs) were synthesized using Pelargonium/Geranium leaf extract via a hydrothermal method. The effects of the Pelargonium/Geranium leaf extract concentration (PLEC) and the amount of 1 mm AgNO3 solution on the center of the broad emission peak (λmax) and the color of the synthesized AgNP solution were investigated by using response surface methodology. The main reducing and stabilizing compounds of Pelargonium/Geranium leaf extract were identified by Fourier transform-infrared and gas chromatography. Spherical AgNPs with an average size of 29 nm were successfully fabricated at the optimal synthesis conditions using 9.8 ml of 1 mm AgNO3 solution and 0.1 ml of 0.62 g/100 ml PLEC. AgNPs were determined to have a polydispersity index value of 0.413 and a ζ potential of +0.6 mV. The antifungal activity of fabricated AgNPs was tested against Aspergillus flavus and Aspergillus terreus, and found to posses a significant inhibitory effect against these microorganisms.

Green synthesis of silver nanoparticles using tree oyster mushroom Pleurotus ostreatus and its inhibitory activity against pathogenic bacteria

The present study reports the biological synthesis of silver nanoparticles (AgNPs) using the aqueous extract of fresh basidiocarps of the tree oyster mushroom, Pleurotus ostreatus. The AgNPs solution exhibited an absorption maximum at 440nm, corresponding to surface plasmon resonance of AgNPs. The field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) analyses revealed that the synthesised AgNPs were spherical in shape and the particle size was less than 40nm. The energy dispersive x-ray analysis (EDX) spectrum showed peaks for the presence of silver, carbon and oxygen atoms in the range of 2.8–3.2keV. Fourier transform infra-red spectroscopy (FTIR) results showed the binding properties of bio-constituents responsible for capping and stabilizing the nanoparticles. The synthesised AgNPs significantly (p<0.05) inhibited the growth of all bacterial species tested. The MIC of the tested bacterial spp. were in the range 13–27µg/mL. The results of this study indicated that the synthesised AgNPs may be developed as an effective agent against bacterial infections.

Silver nanoparticles production by two soil isolated bacteria, Bacillus thuringiensis and Enterobacter cloacae, and assessment of their cytotoxicity and wound healing effect in rats.

Production of silver nanoparticles by Bacillus thuringiensis and Enterobacter cloacae was performed and confirmed through UV-visible spectrophotometry, transmission electron microscopy (TEM), and x-ray diffraction (XRD) analyses. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay using mouse fibroblast cell line NIH-3T3 D4 was carried out and IC50s of AgNPs were obtained. The nontoxic dose of each AgNPs solution was selected for wound healing assay. Thirty-two rats were divided into four groups; two were used as the controls and two were treated by AgNPs that were produced by two bacterial strains. Results revealed that the produced AgNPs were amorphous, spherical in shapes, and had sizes under 100 nm. Histological analysis showed that AgNPs had better wound healing efficacy than the control groups. In conclusion, when the biologically produced AgNPs were used in vivo, they induced the epithelization, formation of the collagen bundles and fibroplasia and reduced the duration of completion of the epithelization and the angiogenesis.

Synthesis of antibacterial silver–chitosan-modified bionanocomposites by RAFT polymerization and chemical reduction methods

Chitosan (Cts) was first modified with 4-cyano,4-[(phenylcarbothioyl)sulfanyl]pentanoic acid to serve as reversible addition–fragmentation chain transfer (RAFT) agent, and then the controlled grafting polymerizations of acrylic acid (PAA) were performed. The resultant copolymers were used as a stabilizing agent for preparation of colloidal silver nanoparticles (Ag NPs) in the range of 2–10 nm. Afterwards, montmorillonites (MMTs) were added to the solution of colloidal Ag NPs for improving thermal stability. Proton nuclear magnetic resonance spectroscopy, Fourier transform infrared spectrometry, energy dispersive X-ray spectroscopy, X-ray diffraction analysis, and scanning electron microscopy images demonstrate the successful synthesis of the graft copolymer. Their thermal behavior was examined by differential scanning calorimetry and thermogravimetric analyses.The antibacterial activity of Ag/Cts-g-PAA and Ag/Cts-g-PAA/MMT was investigated against Staphylococcus aureus, Escherichia coli, and Candida albicans by the disc diffusion method using Mueller Hinton agar. Antimicrobial tests show that Ag/Cts-g-PAA has much higher antimicrobial activity than Ag/Cts-g-PAA/MMT. This method would enable a wide variety of molecular designs to afford novel types of tailored hybrid materials composed of natural polysaccharides and synthetic polymers. The new hybrid materials were used as a stabilizing agent for preparation of Ag bionanocomposites with good antibacterial activity.

Sequential injection for determination of gamma-aminobutyric acid based on its effect on second order light scattering of silver nanoparticles

An automated sequential injection (SI) with second order light scattering (SOS) detection for determination of gamma-aminobutyric acid (GABA) was developed. Quantitation is based on electrostatic interaction between GABA and citrate-capped silver nanoparticles (AgNPs). In acetate buffer at pH 3.8, the positively charged GABA induces the nanoparticles to aggregate. This results in a change of light scattering monitored using a spectrofluorometer. In this work, working standard solutions of GABA were prepared in-line by the SI system pumping appropriate volumes of a stock solution of GABA and acetate buffer into a holding coil. Solution of AgNPs was subsequently drawn into the coil. The reaction zone was then transferred to the spectrofluorometer, set with excitation and detection wavelengths at 300 and 600nm, respectively. Under optimised condition, the SOS intensity was proportional to the concentration of GABA. As a result, a linear curve was obtained in the range of 100–400mgL−1 GABA, with a lower limit of detection of 39.6mgL‐1. Good precision of analysis was achieved, with 0.6 and 3.3% relative standard deviation (RSD) for external calibration (n=5) and standard addition (n=3), respectively. The developed method was successfully applied for quantification of GABA in dietary supplements (2 samples) and samples of instant green tea (2 samples).

Highly selective colorimetric detection of Zn(II) ions using label-free silver nanoparticles

A simple and facile colorimetric method for the detection of zinc ions (Zn2+) using label-free silver nanoparticles (AgNPs) has been developed. Zn2+ ions induced the aggregation of label-free AgNPs in solution, resulting in a color change from yellow to forest green, which was accompanied by the appearance of a new surface plasmon absorption band at 635nm. The sensitivity of label-free AgNPs towards other metal ions was negligible, with the exception of Fe3+, which caused a modest interference. The binding site and sensing mechanism for Zn2+ ions in label-free AgNPs were characterized by Fourier Transform infrared spectroscopy, ultraviolet-visible spectroscopy, and transmission electron microscopy. The aggregation of AgNPs in the presence of Zn2+ ions was inhibited by polyvinyl alcohol, which formed a shell on the surface of AgNPs. Furthermore, Zn2+ ions coordinated with BH4− on AgNPs through a triangular sixdentate binding structure, thus inducing aggregation of AgNPs in solution.The sensor conditions were optimized with 6.0μM of sodium dodecylbenzenesulfonate (NaDDBS) and 0.23mM AgNPs at pH 6. The absorption ratios (A635/A390) of the label-free AgNPs solution exhibited a linear correlation with Zn2+ ion concentration within the range of 0.0−7.6×10−6molL−1, with a limit of detection of 0.36×10−6molL−1. This cost-effective sensing system allows rapid and facile determination of Zn2+ ions in various types of biological, mineral supplement, and environmental samples.

Green synthesis of nanosilver particles by Aspergillus terreus HA1N and Penicillium expansum HA2N and its antifungal activity against mycotoxigenic fungi.

The aim of this study was to synthesize silver nanoparticles (AgNPs) by an eco-friendly and low-cost method using the fungi Aspergillus terreus HA1N and Penicillium expansum HA2N as an alternative to chemical procedures mostly requiring drastic experimental conditions emitting toxic chemical byproducts. Also, this study has been extended to evaluate the effect of AgNPs on the growth of some mycotoxigenic fungi and ochratoxin A (OTA) produced by Aspergillus ochraceus. The AgNPs have been characterized by UV-Visible Spectrophotometer, Dynamic Light Scattering (DLS), Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscope (TEM). The TEM analysis has revealed that the size of AgNPs ranged between 14 and 25nm in the case of P.expansum and 10-18nm in the case of A.terreus. The antifungal activity of AgNP colloids has indicated that the highest inhibition zone was detected with AgNPs synthesized by A.terreus HA1N against all tested fungi. The highest inhibition zone was detected with Aspergillus niger at concentrations 3 and 6μg of AgNP solution (7·56±0·38 and 11·3±1·8mm, respectively) while, A.ochraceus showed the maximum inhibition zone (16·33±0·96mm) at the concentration 9μg of AgNPs synthesized by A.terreus. The results have also indicated that the AgNPs synthesized by A.terreus and P.expansum at the concentration 220μg/100ml media gave the highest reduction of OTA, where the percentages of reduction were 58·87 and 52·18% respectively. The smallest size AgNPs synthesized by A.terreus HA1N are better in their antifungal activity against all tested mycotoxigenic fungi than the largest one synthesized by P.expansum HA2N. This is the first study focused on using AgNPs in control of OTA production.

Effect of Ag containing (nano)particles on reactive adsorption of mustard gas surrogate on iron oxyhydroxide/graphite oxide composites under visible light irradiation

Iron oxyhydroxide and graphite oxide (GO) composites with either 1 or 10% of GO were modified with Ag (1 or 5% of AgNP solution) using a single step in situ procedure. The synthesized samples were tested as reactive adsorbents of chloroethyl ethyl sulfide vapors (CEES). The composites had large surface areas that were slightly affected by the Ag addition. Three different kinds of Ag particles were identified: AgCl, Ag2O and Ag0. The amount of silver in the precursor solution affects the amount of deposited AgCl and its particle size. Potentiometric titration and FTIR results indicated the interactions of the Ag species with bridge and terminal hydroxyl groups on the iron oxyhydroxide and with oxygen groups of the GO surface. Energy band gaps of all materials were estimated to be in the visible light range. The composites exhibit high capacities for CEES adsorption. Ethyl vinyl sulfide and 1,2-bis(ethylthio)ethane were identified as the main reaction products of the CEES reactive adsorption. The analysis of the extracts showed the presence of oxidation products and disulfides. The Ag species had a marked catalytic effect on the formation of oxidation products and thiyl radicals.

Molecular assembly of 3-mercaptopropinonic acid and guanidine acetic acid on silver nanoparticles for selective colorimetric detection of triazophos in water and food samples

In this work, a novel colorimetric nanosensor was developed for the selective detection of triazophos in environmental water and food samples using bifunctionalized silver nanoparticles (Ag NPs) as a probe. The Ag NPs were bifunctionalized with 3-mercaptopropinonic acid (MPA) and guanidineacetic acid (GAA) and used as a colorimetric probe for the selective sensing of triazophos via hydrogen bonding. The addition of triazophos into the bifunctionalized Ag NPs solution triggers the aggregation of bifunctionalized Ag NPs, inducing a color change from yellow to dark orange, which yields a red-shift in the surface plasmon resonance (SPR) peak of GAA-MPA-Au NPs. Results showed that the absorbance ratio (A550/A400) was linear with the logarithm of triazophos concentration in the range of 0.5–500μM and the detection limit (3σ) obtained by UV–visible spectra were 0.10 and 0.08μM using Tris-HCl pH 5.0 and sodium acetate pH 10.0 with addition of NaCl (0.4mM). The sensitivity of method was improved ∼85-fold using 0.4mM of NaCl as an ionic strength. This method was successfully applied to detect triazophos in water (tap, canal and river) and food (rice and apple) samples.

Spectrophotometric determination of l-cysteine by using polyvinylpyrrolidone-stabilized silver nanoparticles in the presence of barium ions

In this article a simple and selective colorimetric probe for cysteine determination using silver nano particles (AgNPS) is described. The determination process was based upon the surface plasmon resonance properties of polyvinylpyrrolidone-stabilized AgNPS. Interaction of AgNPS with cysteine molecules in the presence of barium ions induced a red shift in the surface plasmon resonance (SPR) maximum of AgNPs, as a result of nanoparticle aggregation. Consequently, yellow color of AgNP solution was changed to pink. The linear range for the determination of cysteine was 3.2–8.2μM (R=0.9965) with a limit of detection equal to 2.8μM (3σ). The proposed method was successfully applied to the determination of cysteine in human plasma samples. Acceptable recovery results of the spiked samples confirmed the validity of the proposed method.