The determination of copper ions based on sensitized chemiluminescence of silver nanoclusters

We report on the first application of novel, water-soluble and fluorescent silver nanoclusters (Ag NCs) in a chemiluminescent (CL) detection system. A method has been developed for the determination of copper(II) ion that is based on the fact that the weak CL resulting from the redox reaction between Ce(IV) ion and sulfite ion is strongly enhanced by the Ag NCs and that the main CL signals now originate from Ag NCs. UV-visible spectra, CL spectra and fluorescent (FL) spectra were acquired to investigate the enhanced CL mechanism. It is proposed that the electronic energy of the excited state intermediate SO₂* that originates from the CL reaction is transferred to Ag NCs to form an electronically excited NC whose emission is observed. In addition, it is found that copper(II) is capable of inhibiting the CL of the nanoclusters system, but not if other common metal ions are present. The detection of copper(II) is achieved indirectly by measuring the CL intensity of Ag NCs. Under the optimized experimental conditions, a linear relationship does exist between the intensity of CL and the concentrations of copper(II) in the range of 0.2?nM to 0.1?m??. The detection limit is 0.12?nM. The method is applied to the determination of copper(II) ion in tap water with satisfactory results.

Strong enhancement of the chemiluminescence of the cerium(IV)-thiosulfate reaction by carbon dots,and its application to the sensitive determination of dopamine

We show that the very weak chemiluminescence (CL) of the Ce(IV)-thiosulfate system is enhanced by a factor of ~150 in the presence of fluorescent carbon dots (C-dots). The C-dots were prepared by a solvothermal method and characterized by fluorescence spectra and transmission electron microscopy. Possible mechanisms that lead to the effect were elucidated by recording fluorescence and CL spectra. It is found that dopamine at even nanomolar levels exerts a diminishing effect on the enhancement of CL. This was exploited to design a method for the determination of dopamine in the concentration range from 2.5 nM to 20 μM, with a limit of detection (at 3 s) of 1.0 nM. Dopamine was determined by this method in spiked human plasma samples with satisfactory results.

Water-soluble homo-oligonucleotide stabilized fluorescent silver nanoclusters as fluorescent probes for mercury ion

Water–soluble fluorescent silver nanoclusters (Ag NCs) were prepared with the assistance of commercially available polyinosinic acid (PI) or polycytidylic acid (PC). The fluorescence of the Ag NCs is effectively quenched by trace mercury(II) ions, which can be applied for their detection. The response of the Ag NCs prepared with PI to Hg(II) ion is linear in the Hg(II) concentration range from 0.05 to 1.0 μM (R²?=?0.9873), and from 0.5 to 10 μM of Hg(II) (R²?=?0.9971) for Ag NCs prepared with PC. The detection limits are 3.0 nM and 9.0 nM (at an S/N of 3), respectively. The method is simple, sensitive and fairly selective.

Protein-stabilized fluorescent nanocrystals consisting of a gold core and a silver shell for detecting the total amount of cysteine and homocysteine

We report on a simple and sensitive method for the determination of the total amount of cysteine (Cys) and homocysteine (hCys), [Cys plus hCys], by exploiting the effect of Cys and hCys on the photoluminescence of human serum albumin-stabilized gold-core silver-shell nanocrystals (NCs). If Cys (or hCys) are added to these NCs, Cys (or hCys) will be adsorbed on the surface due to ligand exchange with human serum albumin, and this results in the quenching of the luminescence of the NCs. The addition of mixtures of Cys and hCys in different molar ratios also induces a decrease in luminescence whose intensity is linearly related to the concentration of [Cys plus hCys] in the range from 0.1 – 5.0 μM, with a correlation coefficient (R ²) of 0.9953 and a detection limit of 15 nM. The method is highly selective and sensitive over other α-amino acids, water-soluble thiols, and biomolecules. It has been successfully applied to the determination of the concentration of [Cys plus hCys] in spiked solutions of biomolecules and in real biological samples.

Fluorescent detection of silver(I) and cysteine using SYBR Green I and a silver(I)-specific oligonucleotide

We report on a novel method for the determination of silver ion (Ag⁺) and cysteine (Cys) by using the probe SYBR Green I (SGI) and an Ag+-specific cytosine-rich oligonucleotide (C-DNA). The fluorescence of SGI is very weak in the absence or presence of randomly coiled C-DNA. If, however, C-DNA interacts with Ag⁺ through the formation of cytosine-Ag⁺-cytosine (C-Ag⁺-C) base pairs, the randomly coiled C-DNA undergoes a structural changes to form a hairpin-like structure, thereby increasing the fluorescence of SGI. This fluorescence turn-on process allows the detection of Ag⁺ in the 10–600?nM concentration range, with a detection limit of 4.3?nM. Upon the reaction of Ag⁺ with Cys, Cys specifically removes Ag⁺ from the C-Ag⁺-C base pairs and destroys the hairpin-like structure. This, in turn, results in a decrease in fluorescence intensity. This fluorescence turn-off process enables the determination of Cys in the 8–550?nM concentration range, with a detection limit of 4.5?nM. The method reported here for the determination of either Ag⁺ or Cys is simple, sensitive, and affordable, and may be applied to other detection systems if appropriately selected DNA sequences are available.

Silver nanoparticles plasmon resonance-based method for the determination of uric acid in human plasma and urine samples

We have developed a simple and sensitive colorimetric procedure for the quantification of trace amounts of uric acid. It is based on the finding that uric acid in a medium containing ammonia and sodium hydroxide at 65?°C can reduce silver ions to form yellow silver nanoparticles (Ag NPs). These are stabilized in solution by using poly(vinyl alcohol) as a capping agent. The yellow color of the solution that results from the localized surface plasmon resonance of Ag NPs can be observed by the bare eye. The absorbance at 415?nm is proportional to the concentration of uric acid which therefore can be determined quantitatively. The calibration curve is linear in the concentration range from 10 to 200?nM, with a limit of detection of 3.3?nM. The method was successfully applied to the determination of uric acid in human plasma and urine samples.

Anodic stripping voltammetric determination of arsenic(III) using a glassy carbon electrode modified with gold-palladium bimetallic nanoparticles

We have developed a method for the determination of the three catecholamines (CAs) epinephrine (EP), norepinephrine (NE), and dopamine (DA) at sub-nanomolar levels. It is found that the luminescence of the complexes formed between the CAs and Tb³⁺ ion is strongly enhanced in the presence of colloidal silver nanoparticles (Ag-NPs). The Ag-NPs cause a transfer of the resonance energy to the fluorophores through the interaction of the excited-state fluorophores and surface plasmon electrons in the Ag-NPs. Under the optimized condition, the luminescence intensity of the system is linearly related to the concentration of the CAs. Linearity is observed in the concentration ranges of 2.5–110?nM for EP, 2.8–240?nM for NE, and 2.4–140?nM for DA, with limits of detection as low as 0.25?nM, 0.64?nM and 0.42?nM, respectively. Relative standard deviations were determined at 10?nM concentrations (for n?=?10) and gave values of 0.98%, 1.05% and 0.96% for EP, NE and DA, respectively. Catecholamines were successfully determined in pharmaceutical preparations, and successful recovery experiments are demonstrated for urine and serum samples.

Aptamer based test stripe for ultrasensitive detection of mercury(II) using a phenylene-ethynylene reagent on nanoporous silver as a chemiluminescence reagent

We describe a paper-based chemiluminescence (CL) test for the determination of mercury(II) ion. A single-stranded DNA aptamer was first covalently immobilized via its amino groups to the hydroxy groups on the surface of cellulosic paper. The aptamer probes can capture Hg(II) ions due to their specific interaction with thymine. The CL reagent (a caboxylated phenylene-ethynylene referred to as P-acid) was immobilized on nanoporous silver (NPS@P-acid) and used a CL label on the aptamer. The stripe is then contacted with a sample containing Hg(II) ions and CL is induced by the addition of permanganate. CL intensity depends on the concentration of Hg(II) because Hg(II) increases the quantity of the P-acid-conjugated aptamer. The highly active surface of the NPS@P-acid composites results in an 8-fold higher CL intensity compared to the use of pure P-acid. This enables Hg(II) ion to be quantified in the 20 nM to 0.5 μM concentration range, with a limit of detection as low as 1 pM. This CL aptasensor is deemed to represent a promising tool for simple, rapid, and sensitive detection of Hg(II).

Sensor for lead(II) ion based on a glassy carbon electrode modified with double-stranded DNA and ferric oxide nanoparticles

Shuttle-like Fe₂O₃ nanoparticles (NPs) were prepared by microwave-assisted synthesis and characterized by scanning electron microscopy and X-ray diffraction. The NPs were immobilized on a glassy carbon electrode and then covered with dsDNA. The resulting electrode gives a pair of well-defined redox peaks for Pb(II) at pH 6.0, with anodic and cathodic peak potentials occurring at ?0.50?V and ?0.75?V (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.12 to 40?nM, and the detection limit is 0.1?nM at a signal-to-noise ratio of 3. The sensor exhibits high selectivity and reproducibility.

Simple optical determination of silver ion in aqueous solutions using benzo crown-ether modified gold nanoparticles

We describe a method for the modification of gold nanoparticles (Au-NPs) with benzo-15-crown-5 that led to the development of a colorimetric assay for Ag(I) ion. The brown color of a solution of the modified Au-NPs turns to purple on addition of Ag(I) ion. The ratio of the UV–vis absorption at 600 nm and 525 nm is proportional to the concentration of Ag(I) ions in the range from 20 to 950 nM, and the detection limit is 12.5 nM. Other metal ions do not interfere if present in up to millimolar concentrations. The method enables a rapid determination of Ag(I) in lake and drinking water and is amenable to bare-eye readout.

Fluorescent probe for copper(II) ion based on a rhodamine spirolactame derivative, and its application to fluorescent imaging in living cells

A fluorescent probe for Cu(II) ion is presented. It is based on the rhodamine fluorophore and exhibits high selectivity and sensitivity for Cu(II) ion in aqueous methanol (2:8, v/v) at pH 7.0. The response is based on a ring opening reaction and formation of a strongly fluorescent 1:1 complex. The response is reversible and linear in the range between 50?nM and 900?nM, with a detection limit of 7.0?nM. The probe was successfully applied to fluorescent imaging of Cu(II) ions in HeLa cells.

Highly sensitive carbon paste electrode with silver-filled carbon nanotubes as a sensing element for determination of free cyanide ion in aqueous solutions

We report on newly synthesized Ag(I)-filled multiwall carbon nanotubes as a potential sensing element in ion-selective carbon paste electrodes for the determination of free cyanide in aqueous solution. The electrode was obtained by entrapping the silver-filled nanotubes into a carbon paste and displays a Nernstian response with a slope of 59.8?±?0.3?mV decade^?1, a very wide linear range (from 21.0?nM to 0.1?M of cyanide), a lower detection limit of 13.0?nM, and a response time of <2?min. The operational lifetime is up to 3?months without significant deviation in normal function.

Catalytic activity of noble metal ions for the degradation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine in the presence of oxidizing agent, and its application to the determination of ultra trace amounts of ruthenium

Trace quantities of ruthenium(II) ion catalyze the oxidation of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine (TPPS) by potassium bromate. This reaction can be used for the determination of ultra trace amounts of ruthenium using the water-soluble porphyrin with its high molar absorbance. The scope of the reaction was investigated in terms of the reaction conditions and selectivity with respect to other noble metal ions. The effect of pH, concentration of bromate, the reaction time, and the type of metalloporphyrin were studied so as to optimize the method for the determination of trace amounts of Ru(III). The apparent reaction rate constant for the disappearance of TPPS (or metal-TPPS) is proportional to the root of the concentration of bromate, and directly related to that of Ru(III). The limit of detection is 0.11?nM (equal to 10.7?pg?mL^?1) at pH?4.25, where the turnover number is 201. The reproducibility for five measurements at 2.7?nM of Ru(III) was 2.9%.

Sensitive immunoassay for porcine pseudorabies antibody based on fluorescence signal amplification induced by cation exchange in CdSe nanocrystals

We report on a novel immunoassay for porcine pseudorabies virus (PRV) antibody that is based on fluorescence signal amplification induced by silver(I) ion exchange in CdSe nanocrystals. An antigen-antibody-secondary antibody sandwich structure was first formed from PRV, PRV antibody, and CdSe-labeled rabbit anti-pig antibody. Then, the Cd(II) ions in the CdSe labels were released by a cation exchange reaction with Ag(I). Released Cd(II) was finally quantified using the sensitive fluorescent probe Rhodamine 5 N. Due to this signal amplification, the sensitivity and linear range of the immunoassay were largely improved (compared to the traditional ELISA) in having a limit of detection as low as 1.2 ng?mL^?1 of PRV antibody and a linear range from 2.44 to 312 ng?mL^?1. The successful determination of PRV antibody in pig serum samples is proof for the utility of the method.

Surface molecular imprinting for chemiluminescence detection of the organophosphate pesticide chlorpyrifos

We report on a surface molecular imprinting strategy for synthesizing core-shell particles whose shell is imprinted with chlorpyrifos (CPF). The particles were prepared by copolymerization of the methacryloyl groups on the surface of silica particles modified with 3-methacryloxypropyl trimethoxysilane a functional monomer and a cross-linking agent. The imprinted particles exhibit larger binding capacity, faster binding kinetics, and higher recognition selectivity for CPF. Combined with highly sensitive chemiluminescence assay, the method was applied to the determination of CPF with a detection limit of 0.92?nM which is about 2 orders of magnitude lower than that by conventional CL method. The method also displays repeatability for more than 200 times.

Ligation-triggered fluorescent silver nanoclusters system for the detection of nicotinamide adenine dinucleotide

Herein, we demonstrate a novel silver nanocluster-based fluorescent system for the detection of nicotinamide adenine dinucleotide (NAD⁺), an important biological small molecule involved in a wide range of biological processes. A single-stranded dumbbell DNA probe was designed and used for the assay, which contained a nick in the stem, a poly-cytosine nucleotide loop close to 5′ end as the template for the formation of highly fluorescent silver nanoclusters (Ag NCs) and another loop close to 3′ end. Only in the presence of NAD⁺, the probe was linked at 5′ and 3′ ends by Escherichia coli DNA ligase, which blocked the DNA polymerase-based extension reaction, ensuring the formation of fluorescent Ag NCs. This technique provided a logarithmic linear relationship in the range of 1 pM–500 nM with a detection limit of as low as 1 pM NAD⁺, and exhibited high selectivity against its analogues, and was then successfully used for the detection of NAD⁺ level in four kinds of cell homogenates. In addition, this new approach was conducted in an isothermal and homogeneous condition without the need of any thermal cycling, washing, and separation steps, making it very simple. Overall, this label-free protocol offers a promising alternative for the detection of NAD⁺, taking advantage of specificity, sensitivity, cost-efficiency, and simplicity.

CdTe-CdSe nanocrystals capped with dimethylaminoethanethiol as ultrasensitive fluorescent probes for chromium(VI)

We report on the synthesis of water-soluble luminescent colloidal CdTe nanocrystals capped with various stabilizers (mercaptopropanol, thioglycolic acid, mercaptosuccinic acid, mercaptopropionic acid, L-cysteine, reduced L-glutathione, mercaptoethanol and dimethylaminoethanethiol), and their use as fluorescent probes for chromium(VI) ions. The results show that Cr(VI) ions can be ultrasensitively detected with CdTe NCs capped with dimethylaminoethanethiol (DMAET), with high selectivity over Cr(III) and other ions. Synchronous fluorescence spectroscopy was applied to quantify trace levels of Cr(VI) ions with this probe in the 3.0 nM to 0.2 μM concentration range, with a detection limit as low as 0.57 nM. The interaction between the nanocrystals and Cr(VI) ions was investigated in a study on the zeta potentials, UV-Vis absorption spectroscopy and time-resolved luminescence spectroscopy. Electron transfer process occurred and the decay times of the probe remain constant (about 14 ns). This simple and ultrasensitive analytical method was successfully applied to the direct determination of Cr(VI) in spiked samples of environmental waters.

Iodide-induced adsorption of lead(II) ion on a glassy carbon electrode modified with ferroferric oxide nanoparticles

Spherical Fe₃O₄ nanoparticles (NPs) were prepared by hydrothermal synthesis and characterized by scanning electron microscopy and X-ray diffraction. A glassy carbon electrode was modified with such NPs to result in a sensor for Pb(II) that is based on the strong inducing adsorption ability of iodide. The electrode gives a pair of well-defined redox peaks for Pb(II) in pH 5.0 buffer containing 10 mM concentrations of potassium iodide, with anodic and cathodic peak potentials at ?487 mV and ?622 mV (vs. Ag/AgCl), respectively. The amperometric response to Pb(II) is linear in the range from 0.10 to 44 nM, and the detection limit is 40 pM at an SNR of 3. The sensor exhibits high selectivity and reproducibility.

Synthesis and characterization of an ion-imprinted polymer for selective solid phase extraction of thorium(IV)

A new surface ion-imprinted composite polymer containing 3-methyl-1-phenyl ?4-(cis-acylbutenoic acid)-2-pyrazolin-5-one as the functional reagent is presented that is capable of extracting and preconcentrating traces of Th(IV) ion prior to its photometric determination. Parameters affecting the recovery of Th(IV) such as acidity, shaking time, initial concentration of Th(IV), elution condition, sample flow rate, and influence of potentially interfering ions were investigated. The maximum uptake capacity of this material and that of the non-imprinted polymer at pH 4.5 are 56.8 and 26.3?mg?g^?1, respectively. Recovery exceeds 95% and is complete within 5?min. A Langmuir isotherm fits the experimental data. The relative selectivity factor for Th(IV)/U(VI), Th(IV)/La(III), and Th(IV)/Ce(III) are 50.8, 78.3, and 82.6, respectively. The relative standard deviation is <2.5%, the detection limit is 0.54???g?L^?1 (3??). The imprinted polymer was coupled to spectrophotometry to separate and determine trace levels of Th(IV) in a soil standard material with satisfactory results.

Anodic stripping voltammetric determination of silver ion at a carbon paste electrode modified with carbon nanotubes

A carbon paste electrode (CPE) was modified with multi-wall carbon nanotubes and successfully applied to the determination of silver ion by differential pulse anodic stripping voltammetry. Compared to a conventional CPE, a remarkably improved peak current response and sensitivity is observed. The analytical procedure consisted of an open circuit accumulation step for 2?min in ?0.4?V, this followed by an anodic potential scan between +0.2 and?+?0.6?V to obtain the voltammetric peak. The oxidation peak current is proportional to the concentration of silver ion in the range from 1.0?×?10^?8 to 1.0?×?10^?5?mol?L^?1, with a detection limit of 1.8?×?10^?9?mol?L^?1 after an accumulation time of 120?s. The relative standard deviation for 7 successive determinations of Ag(I) at 0.1???M concentration is 1.99%. The procedure was validated by determining Ag(I) in natural waters.