Colorimetric assay of lead ions in biological samples using a nanogold-based membrane

We have developed a simple paper-based colorimetric membrane for sensing lead ions (Pb(2+)) in aqueous solutions. The nitrocellulose membrane (NCM) was used to trap bovine serum albumin (BSA) modified 13.3-nm Au nanoparticles (BSA-Au NPs), leading to the preparation of a nanocomposite film of a BSA-Au NP-decorated membrane (BSA-Au NPs/NCM). The BSA-Au NPs/NCM operates on the principle that Pb(2+) ions accelerate the rate of leaching of Au NPs induced by thiosulfate (S(2)O(3)(2-)) and 2-mercaptoethanol (2-ME). The BSA-Au NPs/NCM allowed for the detection of Pb(2+) by the naked eye in nanomolar aqueous solutions in the presence of leaching agents such as S(2)O(3)(2-) and 2-ME. We employed the assistance of microwave irradiation to shorten the reaction time (<10 min) for leaching the Au NPs. Under optimal solution conditions (5 mM glycine-NaOH (pH 10), S(2)O(3)(2-) (100 mM), and 2-ME (250 mM), microwaves (450 W)), the BSA-Au NPs/NCM allowed the detection of Pb(2+) at concentrations as low as 50 pM with high selectivity (at least 100-fold over other metal ions). This cost-effective sensing system allowed for the rapid and simple determination of the concentrations of Pb(2+) ions in real samples (in this case, sea water, urine, and blood samples).     

Amplified surface plasmon resonance and electrochemical detection of Pb2+ ions using the Pb2+-dependent DNAzyme and hemin/G-quadruplex as a label

The hemin/G-quadruplex nanostructure and the Pb(2+)-dependent DNAzyme are implemented to develop sensitive surface plasmon resonance (SPR) and electrochemical sensing platforms for Pb(2+) ions. A complex consisting of the Pb(2+)-dependent DNAzyme sequence and a ribonuclease-containing nucleic acid sequence (corresponding to the substrate of the DNAzyme) linked to a G-rich domain, which is "caged" in the complex structure, is assembled on Au-coated glass surfaces or Au electrodes. In the presence of Pb(2+) ions, the Pb(2+)-dependent DNAzyme cleaves the substrate, leading to the separation of the complex and to the self-assembly of the hemin/G-quadruplex on the Au support. In one sensing platform, the Pb(2+) ions are analyzed by following the dielectric changes at the surface as a result of the formation of the hemin/G-quadruplex label using SPR. This sensing platform is further amplified by the immobilization of the sensing complex on Au NPs (13 nm) and using the electronic coupling between the NPs and the surface plasmon wave as an amplification mechanism. This method enables the sensing of Pb(2+) ions with a detection limit that corresponds to 5 fM. The second sensing platform implements the resulting hemin/G-quadruplex as an electrocatalytic label that catalyzes the electrochemical reduction of H(2)O(2). This method enables the detection of Pb(2+) with a detection limit of 1 pM. Both sensing platforms reveal selectivity toward the detection of Pb(2+) ions.     

Bifunctional fluoroionphore-ionic liquid hybrid for toxic heavy metal ions: improving its performance via the synergistic extraction strategy

Several heavy metal ions (HMIs), such as Cd(2+), Pb(2+), and Hg(2+), are highly toxic even at very low concentrations. Although a large number of fluoroionphores have been synthesized for HMIs, only a few of them show detection limits that are below the maximum contamination levels in drinking water (usually in the nM range), and few of them can simultaneously detect and remove HMIs. In this work, we report a new fluoroionphore-ionic liquid hybrid-based strategy to improve the performance of classic fluoroionphores via a synergistic extraction effect and realize simultaneous instrument-free detection and removal of HMIs. As a proof-of-concept, Hg(2+) was chosen as a model HMI, and a rhodamine thiospirolactam was chosen as a model fluoroionphore to construct bifunctional fluoroionphore-ionic liquid hybrid 1. The new sensing system could provide obviously improved sensitivity by simply increasing the aqueous-to-ionic liquid phase volume ratio to 10:1, resulting in a detection limit of 800 pM for Hg(2+), and afford extraction efficiencies larger than 99% for Hg(2+). The novel strategy provides a general platform for highly sensitive detection and removal of various HMIs in aqueous samples and holds promise for environmental and biomedical applications.     

Gold nanoparticle-based simple colorimetric and ultrasensitive dynamic light scattering assay for the selective detection of Pb(II) from paints, plastics, and water samples

Pb (II) is a common water pollutant with high toxicity. According to the CDC, about 310,000 U.S. children of ages 1-5 have high levels of lead in their blood that it is due to the exposure to lead from plastic toys and other products. As a result, the development of ultrasensitive assays for the real-time detection of Pb(II) from plastic toys and paints is very important for water controlling, clinical toxicology and industrial processes. Driven by the need to detect trace amounts of Pb(II) from water samples, we report a label-free, highly selective and ultra sensitive glutathione modified gold nanoparticle based dynamic light scattering (DLS) probe for Pb(II) recognition in 100 ppt level from aqueous solution with excellent discrimination against other heavy metals. The sensitivity of our assay to detect Pb(II) level in water is almost 2 orders of magnitude higher than the EPA standard limit. We have also demonstrated that our DLS assay is capable of measuring the amount of Pb(II) in paint, plastic toys, and water from MS river. A possible mechanism and operating principles of our DLS assay have been discussed. Ultimately, this nanotechnology driven assay could have enormous potential applications in rapid, on-site monitoring of Pb(II) from day-to-day sample.     

Sensitive and selective detection of mercury (II) based on the aggregation of gold nanoparticles stabilized by riboflavin

Gold nanoparticles (AuNPs) can be stabilized by riboflavin against tris buffer-induced aggregation. However, in the presence of mercury (II) (Hg2+), riboflavin can be released from the AuNPs surface and the riboflavin-Hg2+ complex formed, leading to the aggregation of AuNPs in tris buffer. The aggregation extent depends on the concentration of Hg2+. Based on the aggregation extent, a simple and sensitive method of determining Hg2+ is developed. The method enables the detection of Hg2+ over the concentration range of 0.02-0.8 microM, with a detection limit (3sigma) of 14 nM, and shows excellent selectivity for Hg2+ over other metal ions (Cu2+, Co2+, Cd2+, Pb2+, Mg2+, Zn2+, Ag+, Ce3+, Ca2+, Al3+, K+). More importantly, the method avoids complicated surface modifications and tedious separation processes.     

One pot synthesis of monodispersed L-glutathione stabilized gold nanoparticles for the detection of Pb2+ ions

Direct mixture of Au³⁺ with glutathione (GSH), which act as both reduction agents and stabilizers, in aqueous solution gave rise to production of gold nanoparticles (Au NPs) with uniform sizes of around 21 nm. The GSH stabilizer Au NPs in solution show immediate aggregation after addition of 1 mol/L NaCl aqueous solution containing Pb²⁺ ions. The Pb²⁺-induced aggregation in Au NP solution is monitored by both colorimetric response and UV-vis spectroscopy. A rather broad linear range (from 0.1 to 30 μmol/L) and low detection limit (0.1 μmol/L) are explored for Au NP sensors used for detection of Pb²⁺ ions. Furthermore, the response of GSH-stabilized Au NPs toward Pb²⁺ ions is specific compared with other possible interferants (Hg²⁺, Mg²⁺, Zn²⁺, Ni²⁺, Cu²⁺, Co²⁺, Ca²⁺, Mn²⁺, Cd²⁺, and Ba²⁺).     

Colorimetric and dynamic light scattering detection of DNA sequences by using positively charged gold nanospheres: a comparative study with gold nanorods

We introduce a new genosensing approach employing CTAB (cetyltrimethylammonium bromide)-coated positively charged colloidal gold nanoparticles (GNPs) to detect target DNA sequences by using absorption spectroscopy and dynamic light scattering. The approach is compared with a previously reported method employing unmodified CTAB-coated gold nanorods (GNRs). Both approaches are based on the observation that whereas the addition of probe and target ssDNA to CTAB-coated particles results in particle aggregation, no aggregation is observed after addition of probe and nontarget DNA sequences. Our goal was to compare the feasibility and sensitivity of both methods. A 21-mer ssDNA from the human immunodeficiency virus type 1 HIV-1 U5 long terminal repeat (LTR) sequence and a 23-mer ssDNA from the Bacillus anthracis cryptic protein and protective antigen precursor (pagA) genes were used as ssDNA models. In the case of GNRs, unexpectedly, the colorimetric test failed with perfect cigar-like particles but could be performed with dumbbell and dog-bone rods. By contrast, our approach with cationic CTAB-coated GNPs is easy to implement and possesses excellent feasibility with retention of comparable sensitivity--a 0.1 nM concentration of target cDNA can be detected with the naked eye and 10 pM by dynamic light scattering (DLS) measurements. The specificity of our method is illustrated by successful DLS detection of one-three base mismatches in cDNA sequences for both DNA models. These results suggest that the cationic GNPs and DLS can be used for genosensing under optimal DNA hybridization conditions without any chemical modifications of the particle surface with ssDNA molecules and signal amplification. Finally, we discuss a more than two-three-order difference in the reported estimations of the detection sensitivity of colorimetric methods (0.1 to 10-100 pM) to show that the existing aggregation models are inconsistent with the detection limits of about 0.1-1 pM DNA and that other explanations should be developed.     

Colorimetric detection of trace copper ions based on catalytic leaching of silver-coated gold nanoparticles

A colorimetric, label-free, and nonaggregation-based silver coated gold nanoparticles (Ag/Au NPs) probe has been developed for detection of trace Cu(2+) in aqueous solution, based on the fact that Cu(2+) can accelerate the leaching rate of Ag/Au NPs by thiosulfate (S(2)O(3)(2-)). The leaching of Ag/Au NPs would lead to dramatic decrease in the surface plasmon resonance (SPR) absorption as the size of Ag/Au NPs decreased. This colorimetric strategy based on size-dependence of nanoparticles during their leaching process provided a highly sensitive (1.0 nM) and selective detection toward Cu(2+), with a wide linear detection range (5-800 nM) over nearly 3 orders of magnitude. The cost-effective probe allows rapid and sensitive detection of trace Cu(2+) ions in water samples, indicating its potential applicability for the determination of copper in real samples.     

Colorimetric method for determining Pb2+ ions in water enhanced with non-precious-metal nanoparticles

Sulfur anions and their derivatives have long been recognized for their high selectivity and reactivity toward Pb(2+) ions and formation of highly absorptive yet water-insoluble compounds with both acid and base media. This phenomenon has been used for qualitative analysis of lead ions in water. We demonstrate a new method to quantitatively determine the Pb(2+) concentration in the range of 0.5-500 ppm in water using colorimetric measurement, based on forming "soluble" lead sulfide in water enhanced with non-precious-metal nanoparticles. This method has inherent high selectivity for lead over other alkali-metal and alkaline-earth-metal ions. The colorimetric measurements of the absorptive solutions provide accurate determination of the lead concentration in water comparable to that measured using inductively coupled plasma mass spectrometry. To our knowledge, this is the simplest, lowest cost, and easiest-to-use method for detecting and determining the lead concentration in water.     

高产量制备石墨烯及其优异的重金属离子检测性能

以氧化石墨的高温膨胀为基础,研发了一种简便经济的高产量制备石墨烯的工艺,考察了制备得到的石墨烯对痕量重金属离子的检测性能,检测离子包括Cu2+、Pb2+和Cd2+.所制薄层石墨烯存在部分结构缺陷和残余羟基官能团,电化学检测结果表明,这种结构的石墨烯在检测液相中重金属离子的过程中表现出了很好的性质,尤其是对铅离子的检测限...     

A novel heterogeneous colorimetric and spectrophotometric chemosensor for detection and adsorption of Hg0 and Hg2+

Functionalized mesoporous silica with an immobilized azobenzene-coupled receptor 1 (FMS-1) as heterogeneous "naked-eye" colorimetric and spectrophotometric chemosensor was prepared by sol-gel reaction. The optical sensing ability of FMS-1 was studied by addition of metal ions such as K+, Ca2+, Sr2+, Co2+, Cd2+, Pb2+, Zn2+, Fe3+, Cu2+ and Hg2+ in aqueous solution. Interestingly, upon the addition of Hg2+ in aqueous suspension, FMS-1 resulted in a color change from maroon to red within 10 s. On the other hand, no significant color changes were observed with the other metal ions. These findings confirm that FMS-1 can be useful as a chemosensor for selective detection of Hg2+ over a range of metal ions. Furthermore, the adsorption ability of the FMS-1 was also estimated by measuring the amount of Hg2+ and Hg0 adsorbed on the FMS-1, resulting in 95% for Hg2+ and 75% for Hg0, respectively, suggesting that the FMS-1 is potentially useful as the adsorbent for separation of Hg0 and Hg2+ in chromatography.     

Determination of lead and nickel in environmental samples by flame atomic absorption spectrometry after column solid-phase extraction on Ambersorb-572 with EDTA

Lead and nickel were preconcentrated as their ethylenediaminetetraacedic acid (EDTA) complexes from aqueous sample solutions using a column containing Ambersorb-572 and determined by flame atomic absorption spectrometry (FAAS). pH values, amount of solid phase, elution solution and flow rate of sample solution have been optimized in order to obtain quantitative recovery of the analytes. The effect of interfering ions on the recovery of the analytes has also been investigated. The recoveries of Pb and Ni under the optimum conditions were 99 +/- 2 and 97 +/- 3%, respectively, at 95% confidence level. Seventy-five-fold (using 750 mL of sample solution and 10 mL of eluent) and 50-fold (using 500 mL of sample solution and 10 mL of eluent) preconcentration was obtained for Pb and Ni, respectively. Time of analysis is about 4.5 h (for obtaining enrichment factor of 75). By applying these enrichment factors, the analytical detection limits of Pb and Ni were found as 3.65 and 1.42 ng mL(-1), respectively. The capacity of the sorbent was found as 0.17 and 0.21 mmol g(-1) for Pb and Ni, respectively. The interferences of some cations, such as Mn2+, Co2+, Fe3+, Al3+, Zn2+, Cd2+, Ca2+, Mg2+, K+ and Na+ usually present in water samples were also studied. This procedure was applied to the determination of lead and nickel in parsley, green onion, sea water and waste water samples. The accuracy of the procedure was checked by determining Pb and Ni in standard reference tea leaves sample (GBW-07605). The results demonstrated good agreement with the certified values.     

Sensitivity Tuning through Additive Heterogeneous Plasmon Coupling between 3D Assembled Plasmonic Nanoparticle and Nanocup Arrays

Plasmonic substrates have fixed sensitivity once the geometry of the structure is defined. In order to improve the sensitivity, significant research effort has been focused on designing new plasmonic structures, which involves high fabrication costs; however, a method is reported for improving sensitivity not by redesigning the structure but by simply assembling plasmonic nanoparticles (NPs) near the evanescent field of the underlying 3D plasmonic nanostructure. Here, a nanoscale Lycurgus cup array (nanoLCA) is employed as a base colorimetric plasmonic substrate and an assembly template. Compared to the nanoLCA, the NP assembled nanoLCA (NP‐nanoLCA) exhibits much higher sensitivity for both bulk refractive index sensing and biotin–streptavidin binding detection. The limit of detection of the NP‐nanoLCA is at least ten times smaller when detecting biotin–streptavidin conjugation. The numerical calculations confirm the importance of the additive plasmon coupling between the NPs and the nanoLCA for a denser and stronger electric field in the same 3D volumetric space. Tunable sensitivity is accomplished by controlling the number of NPs in each nanocup, or the number density of the hot spots. This simple yet scalable and cost‐effective method of using additive heterogeneous plasmon coupling effects will benefit various chemical, medical, and environmental plasmon‐based sensors.     

Removal of Pb2+, Ag+, Cs+ and Sr2+ from aqueous solution by brewery's waste biomass

Heavy metal pollution is becoming a more and more serious environmental problem, posing threat to biota life. Biosorption is an alternative technology for the treatment of wastewater containing metal ions. In this paper, the removal of four metal ions, i.e., Pb2+, Ag+, Sr2+ and Cs+ by waste biomass of brewery was studied. The experimental results showed that metal uptake is a rapid process, which can be described by pseudosecond order kinetic model. The Langmuir adsorption isotherm was applied to correlate the equilibrium data and fitted quite well. The maximum biosorption capacities for four metal ions were 0.413 mmol Pb2+/g, 0.396 mmol Ag+/g, 0.091 mmol Sr2+/g and 0.076 mmol Cs+/g, respectively. The binding of metals was also discussed in term of several factors. The order of accumulated metal ions at equilibrium state on the molar basis was as follows: Pb2+>Ag+>Sr2+>Cs+, which positively correlated with their covalent index and electronegative and reversely correlated with dissociation constant.     

Determination of Lead Ions by an Optical Sensor Based on 2-Amino-Cyclopentene-1-Dithiocarboxylic Acid

A new spectrophotometric sensor for the determination of lead at trace level was developed using chemically immobilized 2-amino-cyclopentene-l-dithiocarboxylic acid (ACDA) on a triacetylcellulose. The sensor provided a wide concentration range of 1.0 x 10^-6 to 5.0 x 10^-1 M Pb(II) with a limit of detection of 6.9 X 10^-7 M Pb(II). The method also showed a reproducible result with relative standard deviation of less than 3.5% and response time of the optode was 10 min. Interference studies showed that Co(II) and Ni(II) ions interfered during the determination. The interference of potential interfering ions could be eliminated using a simple extraction procedure. The method was successfully used to determination of Pb(II) ions in reference alloy, water, and waste water samples with satisfactory results.     

A colorimetric and fluorescent chemosensor for Ni2+ based on donor-pi-acceptor charge transfer dye containing 2-cyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptor and 4-bis(pyridin-2-ylmethyl)aminobenzene donor

A new designed colorimetric and fluorescent dye chemosensor was synthesized, characterized and computationally calculated using MO theory calculation, which was based on donor-pi-acceptor electron charge transfer system. This particularly designed dye chemosensor displayed the selective Ni2+ ion chemo-sensing effects in optical properties with absorption and fluorescence emission. This dye chemosensor represented clear absorption spectra changes with Ni2+ ion and the dramatic fluorescence quenching effect with Ni2+ ion was determined. However it showed no significant optical spectra changes upon the addition of other metal ions such as Cd2+, Na2+, Mg2+, Pb2+, Fe2+, Fe3+, Ca2+, Cu2+, Hg2+, except Zn2+.     

DNAzyme-based colorimetric sensing of lead (Pb(2+)) using unmodified gold nanoparticle probes

Novel functional oligonucleotides, especially DNAzymes with RNA-cleavage activity, have been intensively studied due to their potential applications in therapeutics and sensors. Taking advantage of the high specificity of 17E DNAzyme for Pb(2+), highly sensitive and selective fluorescent, electrochemical and colorimetric sensors have been developed for Pb(2+). In this work, we report a simple, sensitive and label-free 17E DNAzyme-based sensor for Pb(2+) detection using unmodified gold nanoparticles (GNPs) based on the fact that unfolded single-stranded DNA could be adsorbed on the citrate protected GNPs while double-stranded DNA could not. By our method the substrate cleavage by the 17E DNAzyme in the presence of Pb(2+) could be monitored by color change of GNPs, thereby Pb(2+) detection was realized. The detection of Pb(2+) could be realized within 20?min, with a detection limit of 500?nM. The selectivity of our sensor has been investigated by challenging the sensing system with other divalent metal ions. Since common steps such as modification and separation could be successfully avoided, the sensor developed here could provide a simple, cost-effective yet rapid and sensitive measurement tool for Pb(2+) detection and may prove useful in the development of sensors for clinical toxicology and environmental monitoring in the future.     

Adsorption of chromium(III), mercury(II) and lead(II) ions onto 4-aminoantipyrine immobilized bentonite

In this work, the immobilization of 4-aminoantipyrine onto bentonite was carried out and it was then used to investigate the adsorption behavior of Cr(III), Hg(II) and Pb(II) ions from aqueous solutions. The separation and preconcentration conditions of analytes were investigated, including effects of pH, the shaking time, the sample flow rate and volume, the elution condition and the interfering ions. Under optimum pH value (pH 4.0), the maximum static adsorption capacity of the sorbent was found to be 38.8, 52.9 and 55.5 mg g(-1) for Cr(III), Hg(II) and Pb(II), respectively. 2.0 mL of 2% thiourea in 1.0 M HCl solution effectively eluted the adsorbed metal ions. The detection limit (3σ) of this method defined by IUPAC was found to be 0.12, 0.09 and 0.23 ng mL(-1) for Cr(III), Hg(II) and Pb(II), respectively. The relative standard deviation (RSD) was lower 3.0% (n=8). The developed method has been validated by analyzing certified reference materials and successfully applied to the determination of trace Cr(III), Hg(II) and Pb(II) in water samples with satisfactory results.     

Graphene-DNAzyme based biosensor for amplified fluorescence "turn-on" detection of Pb2+ with a high selectivity

On the basis of the remarkable difference in affinity of graphene (GO) with ssDNA containing a different number of bases in length, we for the first time report a GO-DNAzyme based biosensor for amplified fluorescence "turn-on" detection of Pb(2+). A FAM-labeled DNAzyme-substrate hybrid acted as both a molecular recognition module and signal reporter and GO as a superquencher. By taking advantage of the super fluorescence quenching efficiency of GO, our proposed biosensor exhibits a high sensitivity toward the target with a detection limit of 300 pM for Pb(2+), which is lower than previously reported for catalytic beacons. Moreover, with the choice of a classic Pb(2+)-dependent GR-5 DNAzyme instead of 8-17 DNAzyme as the catalytic unit, the newly designed sensing system also shows an obviously improved selectivity than previously reported methods. Moreover, the sensing system was used for the determination of Pb(2+) in river water samples with satisfying results.     

Synthesis of biosurfactant‐coated magnesium oxide nanoparticles for methylene blue removal and selective Pb2+ sensing

Dyes and lead (Pb²⁺) are toxic compounds that can contaminant water. In this study, magnesium oxide (MgO) nanoparticles (NPs) prepared using clove, i.e. Syzygium aromaticum extract [clove extract (CE)] were used for methylene blue (MB) removal and Pb²⁺ ion sensing in aqueous solution. Maximum 90% MB removal was achieved using MgO NPs. The MB adsorption on MgO NPs surface followed second‐order kinetics and Langmuir isotherm. MB dye was adsorbed as a monolayer on the surface of MgO NPs with maximum adsorption capacity, 5555 mg g⁻¹. MgO NPs were also able to selectively detect lead (Pb²⁺) in 1 nM–200 µM range with 24 µM (3σ) limit of detection. So, CE prepared MgO NPs are useful for MB dye adsorption and metal ion sensing applications.Inspec keywords: magnesium compounds, nanoparticles, dyes, lead, chemical sensors, adsorptionOther keywords: biosurfactant‐coated magnesium oxide nanoparticles, methylene blue removal, selective lead sensing, dyes, toxic compounds, Syzygium aromaticum extract, clove extract, MB adsorption, second‐order kinetics, Langmuir isotherm, maximum adsorption capacity, MgO, Pb²⁺