Colorimetric detection of manganese(II) ions using alginate-stabilized silver nanoparticles

Research on Chemical Intermediates - Marine algal polysaccharides have been recognized as the most effective and promising substrates for reduction and stabilization of metal nanoparticles....     

Colorimetric detection of mercury(II) in a high-salinity solution using gold nanoparticles capped with 3-mercaptopropionate acid and adenosine monophosphate

A new colorimetric sensor for sensing Hg2+ in a high-salinity solution has been developed using gold nanoparticles (AuNPs) decorated with 3-mercaptopropionate acid (MPA) and adenosine monophosphate (AMP). Because of the high negative charge density of AMP on each AuNP surface, MPA/AMP-capped AuNPs are well dispersed in a high-salt solution. In contrast, the aggregation of MPA-capped AuNPs was induced by sodium ions, which shield the negative charges of the carboxylic groups of MPA. Through the coordination between the carboxylic group of MPA and Hg2+, the selectivity of MPA/AMP-capped AuNPs for Hg2+ in a high-salt solution is remarkably high over that of the other metals without the addition of a masking agent or a change in the temperature. We have carefully investigated the effect of the AMP concentration on the stability and sensitivity of MPA/AMP-capped AuNPs. Under optimum conditions, the lowest detectable concentration of Hg2+ using this probe was 500 nM on the basis of the measurement of the ratio of absorption at 620 nm to that at 520 nm. The sensitivity to Hg2+ can be further improved by modifying the MPA/AMP-capped AuNPs with highly fluorescent rhodamine 6G (R6G). By monitoring the fluorescence enhancement, the lowest detectable concentration of Hg2+ using R6G/MPA/AMP-capped AuNPs was 50 nM.     

Colorimetric detection of kanamycin based on analyte-protected silver nanoparticles and aptamer-selective sensing mechanism

In this work, a novel colorimetric detection method for kanamycin (Kana), a widely used aminoglycoside antibiotic, has been developed using unmodified silver nanoparticles (AgNPs) as sensing probe. The method is designed based on the finding that the analyte (Kana) can protect AgNPs against salt-induced aggregation, and nucleic acid aptamers can decrease the risk of false positives through an aptamer-selective sensing mechanism. By use of the proposed method, selective quantification of Kana can be achieved over the concentration range from 0.05 to 0.6 μg mL⁻¹ within 20 min. The detection limit is estimated to be 2.6 ng mL⁻¹, which is much lower than the allowed maximum residue limit. Further studies also demonstrate the applicability of the proposed method in milk samples, revealing that the method may possess enormous potential for practical detection of Kana in the future.     

Colorimetric and bare-eye detection of alkaline earth metal ions based on the aggregation of silver nanoparticles functionalized with thioglycolic acid

We describe a simple and rapid method for colorimetric and bare-eye detection of the alkaline earth metal ions Mg(II), Ca(II), Sr(II) and Ba(II) based on the use of silver nanoparticles (AgNPs) functionalized with thioglycolic acid (TGA). The TGA ligand was self-assembled onto the AgNPs to form a probe that undergoes a color change from yellow to orange or red on exposure to the alkaline earth ions. It is presumed that the color change is a result of the aggregation of the AgNPs caused by the interaction of the bivalent ions with the carboxy groups on the AgNPs. The color change can be used for bare-eye and colorimetric determination of the alkaline earth metal ions, for example to rapidly determine water hardness.

New coordination compounds of palladium(II) with iminodiacetic acid

Summary Iminodiacetic acid (IDA) forms 1:1 or 1:2 complexes with Pdll at room temperature and pH 6.0. The solid compounds have been characterized by elemental analysis, titrimetry, magnetic measurements, i.r. spectroscopy and thermal studies. The far i.r. spectra show peaks that can be assigned to Pd-Cl, Pd-N and Pd-O vibrations. On the basis of these studies tentative structures for the isolated substances are proposed.     

Colorimetric assay for mercury (II) based on mercury-specific deoxyribonucleic acid-functionalized gold nanoparticles

A colorimetric nanoprobe-mercury-specific DNA-functionalized gold nanoparticles (Au-MSD) was developed for sensing Hg(2+). The new mercury-sensing concept relies on measuring changes in the inhibition of "non-crosslinking" aggregation of Au-MSD-induced by the folding of mercury-specific DNA strand through the thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination. In the absence of Hg(2+), a high concentration of MgCl(2) (50 mM) results in a rapid aggregation of Au-MSD because of the removal of charge repulsion. When Hg(2+) is present, the particles remain stable due to the folding of MSD functionalized on the particle surface. The assay enables the colorimetric detection of Hg(2+) in the concentration range of 0.1-10 μM Hg(2+) ions with a detection limit of 60 nM, and allows for the selective discrimination of Hg(2+) ions from the other competitive metal ions. Toward the goal for practical applications, the sensor was further evaluated by monitoring Hg(2+) in fish tissue samples.     

Catalytic gold nanoparticles for fluorescent detection of mercury(II) and lead(II) ions

In this study, we developed a fluorescence assay for the highly sensitive and selective detection of Hg²⁺ and Pb²⁺ ions using a gold nanoparticle (Au NP)-based probe. The Hg–Au and Pb–Au alloys that formed on the Au NP surfaces allowed the Au NPs to exhibit peroxidase-mimicking catalytic activity in the H₂O₂-mediated oxidation of Amplex UltraRed (AUR). The fluorescence of the AUR oxidation product increased upon increasing the concentration of either Hg²⁺ or Pb²⁺ ions. By controlling the pH values of 5 mM tris–acetate buffers at 7.0 and 9.0, this H₂O₂–AUR–Au NP probe detected Hg²⁺ and Pb²⁺ ions, respectively, both with limits of detection (signal-to-noise ratio: 3) of 4.0 nM. The fluorescence intensity of the AUR oxidation product was proportional to the concentrations of Hg²⁺ and Pb²⁺ ions over ranges 0.05–1 μM (R² = 0.993) and 0.05–5 μM (R² = 0.996), respectively. The H₂O₂–AUR–Au NP probe was highly selective for Hg²⁺ (>100-fold) and Pb²⁺ (>300-fold) ions in the presence of other tested metal ions. We validated the practicality of this simple, selective, and sensitive H₂O₂–AUR–Au NP probe through determination of the concentrations of Hg²⁺ and Pb²⁺ ions in a lake water sample and of Pb²⁺ ions in a blood sample. To the best of our knowledge, this system is the first example of Au NPs being used as enzyme-mimics for the fluorescence detection of Hg²⁺ and Pb²⁺ ions.     

Silver nanoparticles capped with chalcon carboxylic acid as a probe for colorimetric determination of cadmium(II)

Microchimica Acta - The authors describe a selective and sensitive method for the colorimetric determination of Cd(II) by using silver nanoparticles capped with chalcone carboxylic acid (CCA) as an...     

Surface-enhanced fluorescence of fluorescein-labeled oligonucleotides capped on silver nanoparticles

Tiopronin monolayer-protected silver nanoparticles with different core sizes (average diameter = 2, 5, 20 nm) were prepared by using different mole ratios of silver nitrate/tiopronin. Ligands on the silver particles were partially displaced by fluorescein-labeled thiolate single-stranded oligonucleotides or their complementary unlabeled oligonucleotides through ligand exchange. The fluorophores on silver particles showed a surface-enhanced fluorescence (SEF) dependent on the size of metallic cores. The particles could be coupled through hybridizations of oligonucleotides bound on the particles. The coupled particles were aggregated due to multiple displacements of oligonucleotides on each particle, resulting in stronger SEF. The dye-labeled oligonucleotides were assembled on the silver islands on the solid substrate, and the complementary oligonucleotide-displaced particles were coupled via oligonucleotide hybridization. The couplings between particles and islands resulted in an obvious fluorescence enhancement.     

Phase transfer of oleic acid capped Ni(core)Ag(shell) nanoparticles assisted by the flexibility of oleic acid on the surface of silver

The phase transfer protocols in vogue for the oleic acid capped silver nanoparticles, viz., salt-induced precipitation and redispersion or phosphoric acid-induced method, are examined and compared thoroughly. A comprehensive evaluation with respect to the mechanistic aspects involved is made and the merits and demerits of the different procedures are delineated. It is found that the salt-induced precipitation and redispersion is more versatile in that the precipitate can actually be redispersed in both aqueous and organic media. However, in terms of mechanism both the routes seem to be very similar wherein the orientational change of oleic acid on the silver surface in the two different environments-organic and aqueous-plays a crucial role in the adaptability of the system to the different environments. Subsequently, this change of orientation of oleic acid on silver surface in aqueous and organic media has been utilized to phase transfer Ni-based nanoparticulate systems. The nascent oleic acid-capped Ni nanoparticles, which were synthesized by a foam-based protocol, were dispersible in water but not in nonpolar organic media such as cyclohexane or toluene. Then, just by coating a thin shell of silver on them we could achieve complete phase transfer of the Ni(core)Ag(shell) from aqueous to organic media following similar procedures used for oleic acid-capped silver nanoparticles. Here, the phase transfer seems to be facilitated by the orientational flexibility of oleic acid on the silver surface as opposed to other metal surfaces as evidenced from the infrared and thermogravimetric analyses of oleic acid-capped Ni and Ni(core)Ag(shell) nanoparticles. This orientation-assisted phase transfer method could be generalized and can be adapted to other systems where, if the nascent nanoparticles cannot be phase transferred as is, they can be coated by a silver shell and oleic acid making them suitable for dispersion in both aqueous and organic media.     

Colorimetric detection of D-amino acids based on anti-aggregation of gold nanoparticles

A new method has been proposed to realize the visual detection of D-amino acids(DAAs) via the antiaggregation of 4-mercaptobenzoic acid modified gold nanoparticles(AuNPs) in the presence of D-amino acid oxidase(DAAO). The negatively charged AuNPs were prepared using sodium citrate as a reducer and stabilizer. The presence of 4-mercaptobenzoic acid(4-MBA) and Cu2+induces the aggregation of AuNPs,resulting in a color change from ruby red to royal purple. However, DAAO could oxidize DAAs to generate H2O2. In the presence of H2O2, the mercapto(–SH) group in 4-mercaptobenzoic acid can be oxidized to form a disulfide(–S–S–) bond. Based on these facts, the pre-incubation of DAAs and 4-mercaptobenzoic acid with DAAO would significantly reduce the concentration of free 4-mercaptobenzoic acid molecules,thus the aggregation of AuNPs was interrupted since due to the lack of inducer. As the concentration of DAAs increases, the color of the AuNPs solution would progress from royal purple to ruby red.Consequently, DAAs could be monitored by the colorimetric response of AuNPs using a UV–vis spectrophotometer or even naked eyes. This DAAO mediated visual detection method could determine Dalanine(D-Ala) as a representative DAA with concentrations ranging from 1.5×10~(-7)mol L~(-1) to 3.0×10~(-5)mol L~(-1), and the detection limit was as low as 7.5×10~(-8)mol L~(-1). The proposed method is convenient, low-cost and free of complex equipment, making it feasible to analyze the concentration of D-Ala in real samples of b-amyloid peptide(Aβ1–42).     

Studies of the oxidation of iminodiacetic acid (IDA) and nitrilotriacetic acid (NTA) with lead dioxide suspension in nitric acid

The stoichiometry of the oxidation of IDA or NTA with lead dioxide suspension was studied by polarographic measurement and by derivative polarographic titration. One mole and two moles of Pb(IV) are reduced per mole of IDA and NTA respectively, with moderate speed at room temperature in nitric acid solutions. One mole each of carbon dioxide, formaldehyde and glycine are produced from the oxidation of 1 mole of IDA, and two moles of carbon dioxide, two moles of formaldehyde and one mole of glycine from 1 mole of NTA. The overall reaction in each case may be written as follows: Pb(IV) + IDA + H₂O → Pb(II) + CO₂ + HCHO + H₂NCH₂COOH + 2H⁺ 2Pb(IV) + NTA + 2H₂O → 2Pb(II) + 2CO₂ + 2HCHO + H₂NCH₂COOH + 4H⁺     

Titrimetric microdetermination of silver, lead and cadmium with thioglycollic acid and of mercury(II) with 2-mercaptopropanoic acid

A simple and rapid titrimetric method is described for the microdetermination of Ag(+), Cd(2+) and Pb(2+), based on their formation of mercaptides with a measured excess of 2-mercaptopropanoic acid, and similar determination of Hg(2+) with thioglycollic acid. Univalent and bivalent metal ions release one and two thiol protons respectively, which along with the carboxyl protons of the thiol reagent are titrated with standard alkali. The difference from the blank titration gives the increase in acidity which is a function of the metal-ion concentration. The proposed procedure is applicable to samples containing 0.025-0.25 mmole of these ions, the average deviation being in the range 0.2-0.5%.     

Colorimetric detection of lysozyme based on electrostatic interaction with human serum albumin-modified gold nanoparticles

In this study, an aqueous solution of 13-nm gold nanoparticles (AuNPs) covalently bonded with human serum albumin (HSA) was used for sensing lysozyme (Lys). HSA molecules were good stabilizing agents for AuNPs in high-salt solution and exhibited the ability to bond with Lys electrostatically. The aggregation of HSA-AuNPs was achieved upon the addition of high-pI proteins, such as Lys, alpha-chymotrypsinogen A, and conalbumin. Not the same was achieved, however, when low-pI proteins such as ovalbumin, bovine serum albumin, and alpha-lactalbumin were added. Matrix-assisted desorption/ionization mass spectrometry was used to demonstrate the interaction between HSA-AuNPs and Lys. It was found that the sensitivity of HSA-AuNPs for Lys was highly dependent on the HSA concentration. The Lys-induced aggregation of HSA-AuNPs was suggested based on the London-van der Waals attractive force. We further improved the selectivity of the probe by adjusting the pH solution to 8.0. Under the optimum conditions, the selectivity of this system for Lys over other proteins in high-salt solutions was remarkably high, even when their pI was very close to the Lys. The lowest detectable concentration of Lys in this approach was 50 nM. The applicability of the method was validated through the analyses of Lys in chicken egg white.     

Colorimetric determination of sulfide using chitosan-capped silver nanoparticles

Microchimica Acta - The article describes a simple method for the rapid photometric and visual detection of sulfide in water samples. Silver nanoparticles were capped with chitosan (chit-AgNPs) and...     

Colorimetric aggregation assay for silver(I) based on the use of aptamer modified gold nanoparticles and C-Ag(I)-C interaction

The authors describe a gold nanoparticle (AuNP) based aggregation assay for colorimetric determination of silver ions. The detection scheme is based on the release of aptamers from the surface of AuNPs that is triggered by the formation of C-Ag(I)-C links. In the absence of Ag(I) ions, the aptamers are readily adsorbed on the surface of the AuNPs. This prevents the aggregation of AuNPs and warrants the stability of the red colloidal solution at high salt concentration. In the presence of Ag(I) ions, the aptamers are released from the surface of AuNPs due to binding to Ag(I). Hence, salt-induced aggregation of AuNPs will occur which is accompanied by a gradual color change from red to blue. The color change occurs in the 1 to 500 nM Ag(I) concentration range, and the detection limit is 0.77 nM. The method was successfully applied to the determination of Ag(I) in spiked tap water samples.

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Graphical abstract Schematic of a gold nanoparticle-based aggregation assay for colorimetric determination of silver ions. Visual quantitation also is posssible due to a gradual color change from red to blue.

     

Determination of mercury(II) by surface-enhanced Raman scattering spectroscopy based on thiol-functionalized silver nanoparticles

Silver nanoparticles (Ag NPs) modified with sodium 2-mercaptoethanesulfonate (mesna) exhibit strong surface-enhanced Raman scattering (SERS). Their specific and strong interaction with heavy metal ions led to a label-free assay for Hg(II). The covalent bond formed between mercury and sulfur is stronger than the one between silver and sulfur and thus prevents the adsorption of mesna on the surface of Ag NPs. This results in a decrease of the intensity of SERS in the presence of Hg(II) ions. The Raman peak at 795?cm^?1 can be used for quantification. The effect of the concentration of mesna, the concentration of sodium chloride, incubation time and pH value on SERS were optimized. Under the optimal conditions, the intensity of SERS decreases with increasing concentration of Hg(II). The decrease is linear in the 0.01 and 2?μmol L^?1 concentration range, with a correlation coefficient (R²) of 0.996 and detection limit (S/N?=?3) is 0.0024?μmol L^?1. The method was successfully applied to the determination of the Hg(II) in spiked water samples.

Unmodified silver nanoparticles based multisensor for Ni (II) ions in real samples

This article report microwave assisted green method for the synthesis of silver nanoparticle from Brassica oleracea var. Italica (BI) extract. The synthesized silver nanoparticle (AgNP-BI) was characterized by various analytical techniques. Here we are reporting three methods for the sensing of Ni (II) from the synthesized AgNP-BI. First one is the detection of Ni (II) ion based on changes in the absorbance resulting from the complex formation of the Ni (II) ion with AgNP-BI. The second one is the fluorescent sensing of Ni (II) ion using AgNP-BI by the changes in the fluorescence intensity. The third one is the electrochemical sensing of Ni (II) ion in which silver nanoparticle attached to the platinum electrode surface. The above-mentioned methods exhibit outstanding selectivity towards Ni (II) ion. The practical application of the AgNP-BI was also carried out for the trace determination of Ni (II) ions. The limit of detection was found to be 0.932 µM using differential pulse voltammetry (DPV).