Lead (II) ion detection in surface water with pM sensitivity using aza-crown-ether-modified silver nanoparticles via dynamic light scattering

In this paper, we reported ultrasensitive lead ion detection in environmental water with pM sensitivity using aza-crown-ether-modified silver nanoparticles (ACE-Ag NPs) through dynamic light scattering (DLS). The colorimetric method based on ACE-Ag NPs is not capable of detecting Pb2+ ions over other metal ions (Fe3+, Co2+, Cu2+, Hg2+, Cd2+, Ag+, Li+, Na+, K+ and Cs+) with high sensitivity. But DLS has improved the selectivity and sensitivity of the Pb2+ detection system (50-fold or more) over colorimetric method, and its detection limit is 0.25 pM (1.03 ppt). The Pb2+ DLS assay can be applied to detect Pb2+ in the environmental water, such as in Yangtze and East Lake water samples with a detection limit of 0.20 and 0.22 pM, which is much lower than the maximum contamination level of 4.8×10(-8) M for lead in surface water defined by the national environmental quality standards of China (GB 3838-2002). Also, this method has a good performance in the determination of Pb2+ in drinking water, which is much lower than the maximum contamination level (MCL) of 72 nM for lead as defined by the US Environmental Protection Agency (EPA).     

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.     

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.     

Turn-on and near-infrared fluorescent sensing for 2,4,6-trinitrotoluene based on hybrid (gold nanorod)-(quantum dots) assembly

In this study, we design a FRET system consisting of gold nanorod (AuNR) and quantum dots (QDs) for turn-on fluorescent sensing of 2,4,6-trinitrotoluene (TNT) in near-infrared region. The amine-terminated AuNR and carboxyl-terminated QDs first form a compact hybrid assembly through amine-carboxyl attractive interaction, which leads to a high-efficiency (>92%) FRET from QDs to AuNRs and an almost complete emission quenching. Next, added TNT molecules break the preformed assembly because they can replace the QDs around AuNRs, based on the specific reaction of forming Meisenheimer complexes between TNT and primary amines. Thus, the FRET is switched off, and a more than 10 times fluorescent enhancement is obtained. The fluorescence turn-on is immediate, and the limit of detection for TNT is as low as 0.1 nM. Importantly, TNT can be well distinguished from its analogues due to their electron deficiency difference. The developed method is successfully applied to TNT sensing in real environmental samples.     

Sequence‐Specific HCV RNA Quantification Using the Size‐Dependent Nonlinear Optical Properties of Gold Nanoparticles

The hepatitis C virus (HCV) is a single‐stranded (ss) RNA virus that is responsible for chronic liver diseases, such as cirrhosis, end‐stage liver disease, and hepatocellular carcinoma. Driven by the need to detect the presence of the HCV viral sequence, herein it is demonstrated for the first time that the nonlinear optical (NLO) properties of gold nanoparticles can be used for screening and quantifying HCV RNA without any modification, with excellent detection limit (80 pM ) and selectivity (single base‐pair mismatch). The hyper‐Rayleigh scattering (HRS) intensity increases 25 times when label‐free, 145‐mer, HCV ss‐RNA is hybridized with 400 pM target RNA. The mechanism of HRS intensity change is discussed with experimental evidence for a higher multipolar contribution to the NLO response of gold nanoparticles.     

TNT detection using multiplexed liquid array displacement immunoassays

The presence of trace contamination of soil and groundwater with explosives is an ongoing concern, for which improved methods are required to facilitate their detection and quantification. This is true both for the monitoring of remediation and for site characterization. Immunosensors have been found effective for solution-phase detection of environmental contaminants. Our work utilized the Luminex100 (flow cytometer) to detect TNT in a multiplexed displacement immunoassay format. The Luminex100 can perform a multiplexed assay by discriminating between up to 100 different bead sets. We used this capability to evaluate four different TNT monoclonal antibodies, two recombinant TNT antibodies, and a control antibody simultaneously for the rapid detection of TNT and other nitroaromatics. TNT could be detected at 0.1 ppb and quantified over the range of 1.0 ppb to 10 ppm. In addition, the assay was shown to be effective in various matrixes such as lake water, seawater, and acetone extracts of soil. Seawater required dilution with two parts buffer to avoid loss of microspheres, while the acetone extracts were diluted 100-fold or more to minimize solvent affects.     

Trace detection and discrimination of explosives using electrochemical potentiometric gas sensors

In this article, selective and sensitive detection of trace amounts of pentaerythritol tetranitrate (PETN), 2,4,6-trinitrotoluene (TNT) and cyclotrimethylenetrinitramine (RDX) is demonstrated. The screening system is based on a sampling/concentrator front end and electrochemical potentiometric gas sensors as the detector. Preferential hydrocarbon and nitrogen oxide(s) mixed potential sensors based on lanthanum strontium chromite and Pt electrodes with yttria stabilized zirconia (YSZ) solid electrolyte were used to capture the signature of the explosives. Quantitative measurements based on hydrocarbon and nitrogen oxide sensor responses indicated that the detector sensitivity scaled proportionally with the mass of the explosives (1-3 μg). Moreover, the results showed that PETN, TNT, and RDX samples could be discriminated from each other by calculating the ratio of nitrogen oxides to hydrocarbon integrated area under the peak. Further, the use of front-end technology to collect and concentrate the high explosive (HE) vapors make intrinsically low vapor pressure of the HE less of an obstacle for detection while ensuring higher sensitivity levels. In addition, the ability to use multiple sensors each tuned to basic chemical structures (e.g., nitro, amino, peroxide, and hydrocarbon groups) in HE materials will permit the construction of low-cost detector systems for screening a wide spectrum of explosives with lower false positives than present-day technologies.     

Separation and enrichment of gold(III) from environmental samples prior to its flame atomic absorption spectrometric determination

A simple and accurate method was developed for separation and enrichment of trace levels of gold in environmental samples. The method is based on the adsorption of Au(III)-diethyldithiocarbamate complex on Amberlite XAD-2000 resin prior to the analysis of gold by flame atomic absorption spectrometry after elution with 1 molL(-1) HNO3 in acetone. Some parameters including nitric acid concentration, eluent type, matrix ions, sample volume, sample flow rate and adsorption capacity were investigated on the recovery of gold(III). The recovery values for gold(III) and detection limit of gold were greater than 95% and 16.6 microgL(-1), respectively. The preconcentration factor was 200. The relative standard deviation of the method was <6%. The adsorption capacity of the resin was 12.3 mg g(-1). The validation of the presented procedure was checked by the analysis of CRM-SA-C Sandy Soil certified reference material. The presented procedure was applied to the determination of gold in some environmental samples.     

Low Blank Preconcentration Technique for the Determination of Lead, Copper, and Cadmium in Small-Volume Seawater Samples by Isotope Dilution ICPMS

A simple low-blank method is described for the analysis of Pb, Cu, and Cd in seawater using Mg(OH)(2) coprecipitation and isotope dilution inductively coupled plasma mass spectrometry (ICPMS). Here, 20-40 μL of 9 M aqueous NH(3) is mixed into a 1.3 mL seawater sample spiked with enriched isotopes of Pb, Cu, and Cd. After centrifugation, the supernatant is discarded and the Mg(OH)(2) precipitate dissolved in 100 μL of 5% HNO(3) for ICPMS analysis. This method is simple, accurate, and precise, with detection limits of Pb = 1.3 pM, Cu = 39 pM, and Cd = 5.0 pM and blanks of Pb = 0.62 pM, Cu = 27 pM, and Cd = 6.0 pM. The method is demonstrated by oceanographically consistent profiles of these trace metals at an ocean station in the eastern North Atlantic.     

Electrochemical detectors prepared by electroless deposition for microfabricated electrophoresis chips

Microfabricated capillary electrophoresis (CE) chips with integrated electrochemical detection have been developed on glass substrates. An electroless deposition procedure was used to deposit a gold film directly onto the capillary outlet to provide high-sensitivity electrochemical detection for catechol and several nitroaromatic explosives. Scanning electron microscopy revealed that the electroless gold film contains nanoscopic gold aggregates (100-150 nm) with an average thickness of 79 nm. The electroless deposition procedure can be easily and routinely performed in any wet-chemistry laboratory, and electroless gold can be deposited onto complex and internal surfaces. Intimate coupling of electrochemical detection and CE chips obviates the need for a coupling mechanism or tedious alignment procedures. With nitroaromatic compounds as a working model, microchip capillary electrophoresis equipped with electroless gold has proven to provide high sensitivity and fast response times for sensor applications. The CE microchip system was capable of separation and determination of explosive compounds including TNT in less than 130 s with detection limits ranging from 24 to 36 microg/L, i.e., 4-fold enhancements in detection efficiency in comparison to thick-film technology.     

Amine-capped ZnS-Mn2+ nanocrystals for fluorescence detection of trace TNT explosive

Mn2+-doped ZnS nanocrystals with an amine-capping layer have been synthesized and used for the fluorescence detection of ultratrace 2,4,6-trinitrotoluene (TNT) by quenching the strong orange Mn2+ photoluminescence. The organic amine-capped nanocrystals can bind TNT species from solution and atmosphere by the acid-base pairing interaction between electron-rich amino ligands and electron-deficient aromatic rings. The resultant TNT anions bound onto the amino monolayer can efficiently quench the Mn2+ photoluminescence through the electron transfer from the conductive band of ZnS to the lowest unoccupied molecular orbital (LUMO) of TNT anions. The amino ligands provide an amplified response to the binding events of nitroaromatic compounds by the 2- to approximately 5-fold increase in quenching constants. Moreover, a large difference in quenching efficiency was observed for different types of nitroaromatic analytes, dependent on the affinity of nitro analytes to the amino monolayer and their electron-accepting abilities. The amine-capped nanocrystals can sensitively detect down to 1 nM TNT in solution or several parts-per-billion of TNT vapor in atmosphere. The ion-doped nanocrystal sensors reported here show a remarkable air/solution stability, high quantum yield, and strong analyte affinity and, therefore, are well-suited for detecting the ultratrace TNT and distinguishing different nitro compounds.     

Immunochemical approaches for purification and detection of TNT traces by antibodies entrapped in a sol-gel matrix

A highly sensitive immunochemical method for immunoaffinity purification (IAP) and detection of trace amounts of TNT was developed on the basis of antibodies (Abs) in a ceramic matrix (sol-gel). The study resulted in: (i) a highly sensitive and reproducible TNT ELISA (I50 and I20 values of 0.4 +/- 0.09 ppb and 0.12 +/- 0.03 ppb, respectively; n = 12), which is highly specific to TNT; and (ii) successful entrapment of the Abs that bound free analyte from solution. Binding was found to be highly reproducible, dose dependent, and only slightly (1.2-1.8-fold) lower than that in solution. The entrapped Abs did not leach from the matrix and were tolerant of absolute ethanol, acetone, and acetonitrile. Bound analytes could be easily eluted from the sol-gel matrix at high recoveries. The sol-gel-based IAP method described above introduces a simple one-step procedure that has a high potential to serve as a suitable and convenient immunochromatographic device for cleanup and concentration of TNT from "real field" samples in a manner that complies with both chemical and immunochemical residue analysis methods.     

Single-nucleotide polymorphism genotyping by nanoparticle-enhanced surface plasmon resonance imaging measurements of surface ligation reactions

A sensitive method for the analysis of single nucleotide polymorphisms (SNPs) in genomic DNA that utilizes nanoparticle-enhanced surface plasmon resonance imaging (SPRI) measurements of surface enzymatic ligation reactions on DNA microarrays is demonstrated. SNP identification was achieved by using sequence-specific surface reactions of the enzyme Taq DNA ligase, and the presence of ligation products on the DNA microarray elements was detected using SPRI through the hybridization adsorption of complementary oligonucleotides attached to gold nanoparticles. The use of gold nanoparticles increases the sensitivity of the SPRI so that single bases in oligonucleotides can be successfully identified at a concentration of 1 pM. This sensitivity is amply sufficient for performing multiplexed SNP genotyping by using multiple PCR amplicons and should also allow for the direct detection and identification of SNP sequences from 1 pM unamplified genomic DNA samples with this array-based and label-free SPRI methodology. As a first example of SNP genotyping, three different human genomic DNA samples were screened for a possible point mutation in the BRCA1 gene that is associated with breast cancer.     

High sensitivity of in vivo detection of gold nanorods using a laser optoacoustic imaging system

The development of a contrast agent for a laser optoacoustic imaging system (LOIS) can significantly widen preclinical and clinical applications of this imaging modality for early detection of cancerous tumors. Gold nanorods were engineered to enhance the contrast for optoacoustic imaging. Under in vivo conditions, 25 microL of gold nanorods solution at a concentration of 1.25 pM were injected into nude mice and detected using a single-channel acoustic transducer. LOIS was used to visualize the distribution of gold nanoparticles at a concentration of 125 pM in vivo when 100 microL of solution of gold nanoparticles was delivered subcutaneously. Our results suggest that LOIS can be used for in vivo detection of gold nanorods at low concentrations and the nanoparticles can be engineered to enhance the diagnostic power of optoacoustic imaging.     

Metallic nanoparticle-carbon nanotube composites for electrochemical determination of explosive nitroaromatic compounds

Metal nanoparticles (Pt, Au, or Cu) together with multiwalled and single-walled carbon nanotubes (MWCNT and SWCNT) solubilized in Nafion have been used to form nanocomposites for electrochemical detection of trinitrotoluene (TNT) and several other nitroaromatics. Electrochemical and surface characterization by cyclic voltammetry, AFM, TEM, SEM, and Raman spectroscopy confirmed the presence of metal nanoparticles on CNTs. Among various combinations tested, the most synergistic signal effect was observed for the nanocomposite modified glassy carbon electrode (GC) containing Cu nanoparticles and SWCNT solubilized in Nafion. This combination provided the best sensitivity for detecting TNT and other nitroaromatic compounds. Adsorptive stripping voltammetry for TNT resulted in a detection limit of 1 ppb, with linearity up to 3 orders of magnitude. Selectivity toward the number and position of the nitro groups in different nitroaromatics was very reproducible and distinct. Reproducibility of the TNT signal was within 7% (n = 8) from one electrode preparation to another, and the response signal was stable (+/-3.8% at 95% confidence interval) for 40 repeated analyses with 10 min of preconditioning. The Cu-SWCNT-modified GC electrode was demonstrated for analysis of TNT in tap water, river water, and contaminated soil.     

On-chip enzyme immunoassay of a cardiac marker using a microfluidic device combined with a portable surface plasmon resonance system

This paper reports a miniaturized immunosensor designed to determine a trace level cardiac marker, B-type natriuretic peptide (BNP), using a microfluidic device combined with a portable surface plasmon resonance (SPR) sensor system. Sample BNP solution was introduced into the microchannel after an immunoreaction with acetylcholine esterase-labeled antibody (conjugate), and only unbound conjugate was trapped on the BNP-immobilized surface in the flow channel. Then, the thiol compound generated by the enzymatic reaction with the trapped conjugate was accumulated on a gold thin film located downstream in the microchannel to monitor the real-time SPR angle shift. We achieved a detectable concentration range of 5 pg/mL-100 ng/mL by monitoring the SPR angle shift, which covers the required detection range for the BNP concentrations found in blood. This success resulted from the use of a T-shaped microfluidic device structure, which prevents the sample solution from flowing over the gold film used for SPR detection. We were able to measure trace levels of BNP peptide (15 fg) within 30 min since the procedure with our immunosensor is simpler than a multistep immunoassay through the simultaneous use of a labeled enzymatic reaction and the real-time monitoring of enzymatic product accumulation in the microfluidic device. We employed the procedure to detect serum BNP by using spiked samples in human serum and achieved satisfactory recovery for heat-treated samples to denature the esterase in the serum before the immunoreaction.     

Voltammetric detection of mercury and copper in seawater using a gold microwire electrode

A procedure is presented by which mercury and copper are determined simultaneously in seawater and dilute acid (0.01 M HCl) by anodic stripping voltammetry using gold microwire electrodes. It was found that anion (halide) adsorption is the cause for a gradual decrease in the height and potential of the mercury peak. The effect is eliminated by including an anion desorption step in the analysis at -0.8 V prior to each scan. This step was found to greatly improve the stability of the scans and enabled the use of background subtraction. Advantages of the microwire electrodes were a low roughness of the surface, without a need for pretreatment, and a very small diffusion layer (2 microm with stirring). Under the optimized voltammetric conditions, the detection limits were 6 pM mercury and 25 pM copper using 300-s deposition. These values are well below those reported previously for other electrodes including rotating disk electrodes. Measurements of the influence of the major anions I-, Br-, Cl-, SO4(2-), F-, HCO3-, and B(OH)4 on the response for mercury showed that bromide and chloride are predominantly responsible for the underpotential deposition mechanism of mercury in seawater. The method was applied to coastal water samples from Liverpool Bay.     

Amplified voltammetric detection of DNA hybridization via oxidation of ferrocene caps on gold nanoparticle/streptavidin conjugates

Gold nanoparticle/streptavidin conjugates covered with 6-ferrocenylhexanethiol were attached onto a biotinylated DNA detection probe of a sandwich DNA complex. Due to the elasticity of the DNA strands, the ferrocene caps on gold nanoparticle/streptavidin conjugates are positioned in close proximity to the underlying electrode modified with a mixed DNA capture probe/hexanethiol self-assembled monolayer and can undergo reversible electron-transfer reactions. A detection level, down to 2.0 pM (10 amol for the 5 microL of sample needed) for oligodeoxynucleotide samples was obtained. The amplification of the voltammetric signals was attributed to the attachment of a large number of redox (ferrocene) markers per DNA duplex formed. The ferrocene oxidation current increased with the target concentration and began to level off at a target concentration of 10 nM. An Excellent linearity was found within the range between 6.9 and 150.0 pM and reasonable relative standard deviations (between 3.0 and 13.0%) were obtained. The amenability of this method to the analyses of polynucleotides (i.e., PCR products of the pre-S gene of hepatitis B virus in serum samples) was also demonstrated. The method is shown to be simple, selective, reproducible, and cost-effective and does not require labeling of the DNA targets.     

2,4,6-Trinitrotoluene detection by laser-photofragmentation-laser-induced fluorescence

Photofragmentation (PF) and subsequent nitric oxide (NO) laser-induced fluorescence (LIF) is being developed to measure the concentration of energetic materials (EM's) in soil and other media. Laser radiation near 226 nm photodissociates gas-phase EM to NO(2), which predissociates into NO that gives an intense luminescence. The EM concentration is inferred from the intensity of the NO fluorescence. We have studied the factors that affect the PF-LIF signal intensity, including the effect of buffer gas on the LIF spectrum of pure NO, the effect of 2,4,6-trinitrotoluene (TNT) pressure on the PF-LIF spectrum, the effect of buffer-gas pressure on the PF-LIF signal intensity of pure TNT, and the effect of temperature on the PF-LIF spectra of pure TNT and of TNT in simulated soil. Heating of the TNT sample above 343 K was found to increase the magnitude of the PF-LIF signal intensity significantly, but also was found to cause physical and chemical changes in the TNT sample. The effects of heating and evacuating on the TNT sample were investigated. TNT concentration calibration curves were obtained for TNT in simulated soil mixtures. The limit of detection of TNT in soil was estimated to be 40 parts in 10(9).     

Functionalized mesoporous silica for microgravimetric sensing of trace chemical vapors

Featuring a huge surface-to-volume ratio, synthesized SBA-15 mesoporous silica is functionalized by inner-channel-wall modification of sensing groups for highly specific chemical-vapor detection at trace level. With the developed sensing material loaded on resonant microcantilevers, the specifically adsorbed chemical-vapor molecules act as an added mass to shift the cantilever resonant frequency for gravimetric sensing signal readout. Two kinds of sensing materials for trinitrotoluene (TNT) and ammonia/amine are respectively prepared by inner-wall layer-by-layer grafting functionalization. By using hexafluoro-2-propanol-functionalized mesoporous silica (HFMS), experimental results show highly specific and rapid detection of TNT vapor, with a ppt-level detection limit; functionalized with a carboxyl (COOH) group, the mesoporous silica is loaded onto the cantilever resonating sensor that experimentally exhibits an ultrafine detection limit of tens of ppb to ammonia/amine gases.