Reactive Tandem Ion Mobility Spectrometry with Electric Field Fragmentation of Alcohols at Ambient Pressure.

A tandem ion mobility spectrometer at ambient pressure with a reactive stage produced fragment ions by water elimination from protonated monomers of alcohols with carbon numbers three to nine. Protonated monomers of individual alcohols were mobility isolated in a first drift region and were fragmented to carbocations at 64 to 128 Td and 45 to 89°C. Precursor and fragment ions were mobility characterized in a second drift region. Enthalpies for fragmentation of ROH2+ to primary carbocations were calculated as 76 to 97 kJ/mol and enthalpies for subsequent charge migration to 2° carbocations were -49 to -58 kJ/mol. Plots of drift times for pairs of protonated monomer and fragment ions from alcohols, esters, alkanes, and aldehydes produced distinctive trend lines attributed to fragmentation paths characteristic of chemical class. Specific combinations of drift times for fragments and precursor ions provide additional chemical information for spectral interpretation in ion mobility spectrometry.

Ultrasensitive and fast fluorescent bioassay based on fluorescence enhancement of silver nanoparticles.

An ultrasensitive, fast and specific fluorescent platform for protein detection is developed. In this protocol, silver nanoparticles were conjugated with paramagnetic particles (MPs-Ag) for target capture, concentration and separation; fluorescent dyes functionalized silver nanoparticles (Tag) for generating signals. The presented method is highly sensitive and specific with a detection limit of 2.2 pM for thrombin, and no significant interference was observed for other proteins such as human serum albumin (HSA), lysozyme and IgG. This novel approach combining the magnetic separation and concentration of MPs-Ag, aptamer recognition and fluorescence enhancement of Tag, can be successfully used to enhance the sensitivity of detecting ultra-low levels of target proteins or biomolecules.

Simultaneous electrochemical measurement of metal and organic propellant constituents of gunshot residues.

The simultaneous electrochemical measurement of heavy-metal and organic propellants relevant to gunshot residues (GSRs) is demonstrated. Cyclic voltammetry (CV) and cyclic square-wave stripping voltammetry (C-SWV) are shown to detect, in a single run, common propellants, such as nitroglycerin (NG) and dinitrotoluene (DNT), along with the heavy metal constituents of GSR, antimony (Sb), lead (Pb), zinc (Zn) and barium (Ba). The voltammetric detection of the stabilizer diphenylamine (DPA) along with inorganic constituents has also been examined. The resulting electrochemical signatures combine -in a single voltammogram- the response for the various metals and organic species, based on the reduction and oxidation peaks of the constituents. Cyclic square-wave voltammetry at the glassy carbon electrode (GCE), involving an intermittent accumulation at the reversal potentials of -0.95 V (for Sb, Pb, DNT and NG) and -1.3 V (for Sb, Pb, Zn and DPA) is particularly useful to offer distinct electrochemical signatures for these constituents of GSR mixtures, compared to analogous cyclic voltammetric measurements. Simultaneous voltammetric measurements of barium (at thin-film Hg GCE) and DNT (at bare GCE) are also demonstrated in connection to intermittent accumulation at the reversal potential of -2.4 V. Such generation of unique, single-run, information-rich inorganic/organic electrochemical fingerprints holds considerable promise for 'on-the-spot' field identification of individuals firing a weapon, as desired for diverse forensic investigations.

A multiplexed screening method for agonists and antagonists of the estrogen receptor protein.

The estrogen receptor (ER) is regarded as a significant drug target because of its important physical and pathological function. In this article, we describe a novel screening method to obtain agonists and antagonists of ER. ER was immobilized onto an aldehyde-modified glass slide. The affinity of Cy3-labeled estradiol for ER protein microarrays was then determined. Two libraries, one containing 29 synthetic compounds and the other with 384 natural products that served as a model, were screened to find new ligands for ER. The IC(50) values obtained for tamoxifen and raloxifene were consistent with those found in the literature (4.85 × 10(-7) M versus 1.74~4.23 × 10(-7) M and 7.58 × 10(-8) M versus 0.89~5.84 × 10(-8) M, respectively). Finally, 65 active ligands (5 synthetic compounds and 60 natural products) of ER were identified. This novel method gave identical results to a conventional fluorescence polarization assay, thus verifying the accuracy of this simultaneous multireceptor screening method based on protein microarrays. The presented method is sensitive, accurate, and reliable, and shows great potential for use in high-throughput drug-screening research.

A novel aptasensor based on silver nanoparticle enhanced fluorescence.

In the present study, we report a novel aptasensor based on silver nanoparticle enhanced fluorescence for the detection of adenosine. First, the distance dependence nature of silver nanoparticle enhanced fluorescence was investigated through fluorescent dyes modified oligonucleotides to control the spacing distance between dyes and AgNP. The results showed that the fluorescence intensity reached the maximum value with the spacing distance of dyes about 8 nm from AgNP surface. The fluorescence intensity decreases when the spacing distance is either above or below this value. Based on this result, a fluorescence switch is constructed. In the "OFF" state, without the target molecules, there is a greater spacing distance between the Cy3 dyes and the AgNP giving comparatively lower fluorescence intensity. While in the "ON" state, in the presence of target molecules, the fluorescence signals increased for the conformation structure change of the aptamer which shorten the spacing distance between the Cy3 dyes and the AgNP to 8 nm. Using adenosine as target, the aptasensor produced a linear range from 200 nM to 200 µM with a correlation coefficient of 0.9949 and the detection limit was 48 nM estimated using 3σ. The aptasensor was also found to be specific in targeting adenosine. The presented method shows a new strategy of combining aptamer recognition and silver nanoparticle for fluorescence signal enhancement and increasing sensitivity.

Metal-enhanced fluorescent probes based on silver nanoparticles and its application in IgE detection.

In this paper, a novel metal plasmon coupled with an aptamer-nucleotide hybridized probe was fabricated and applied for protein detection. The specific aptamer and single-strand oligonucleotide were chemically bound to silver nanoparticles (AgNPs), and Cy5-labeled, complementary single-strand oligonucleotides were hybridized with the particle-bound oligonucleotides. The hybridized DNA duplexes were regarded as rigid rods that separated the fluorophore Cy5 and the surface of AgNPs to reduce the competitive quenching. Using a model system comprising human immunoglobulin E (IgE) as the analyte and goat antihuman IgE as immobilized capture antibody on glass slides, we demonstrate that the detection performance of the synthetic probe was superior to the aptamer-based fluorescent probes. The results showed a good linear correlation for human IgE in the range from 10 ng/ml to 6.25 µg/ml. The detection limit obtained was 1 ng/ml, which was 50 times lower than that using Cy5 oligonucleotide/aptamer hybrid duplex (Probe2) due to the metal-enhanced fluorescence effect. This new strategy opens the possibility for the preparation of high-sensitivity detection probes based on metal nanoparticles.

Fluorescence enhancement of silver nanoparticle hybrid probes and ultrasensitive detection of IgE.

An ultrasensitive protein assay method was developed based on silver nanoparticle (AgNP) hybrid probes and metal-enhanced fluorescence. Two aptamer based silver nanoparticles, Aptamer/Oligomer-A/Cy3-modified AgNPs (Tag-A) and Aptamer/Oligomer-B/Cy3-modified AgNPs (Tag-B) were hybridized to form a silver nanoparticle aggregate that produced a red shift and broadening of the Localized Surface Plasmon Resonance (LSPR) peak. The enhanced fluorescence resulted from the increased content of Cy3 molecules and their emission resonance coupled to the broadened localized surface plasmon (LSP) of AgNP aggregate. The separation distance between Cy3 and AgNPs was 8 nm which was the most optimal for metal enhanced fluorescence and the separation distance between adjacent AgNPs was about 16 nm and this was controlled by the lengths of oligomer-A and oligomer-B. The protein array was prepared by covalently immobilizing capture antibodies on aldehyde-coated slide. After addition of protein IgE sample, two kinds of aptamer-modified AgNPs (Tag-A and Tag-B) were employed to specifically recognize IgE and form the AgNP aggregate on the arrays based on their hybridization. The detection property of the aptamer-modified AgNP aggregate was compared to two other modified aptamer-based probes, aptamer-modified Cy3 and Tag-A. The modified AgNP hybrid probe (Tag-A and Tag-B) showed remarkable superiority in both sensitivity and detection limit due to the formed AgNP aggregate. The new hybrid probe also produced a wider linear range from 0.49 to 1000 ng/mL with the detection limit reduced to 40 pg/mL (211 fM). The presented method showed that the newly designed strategy of combining aptamer-based nanomaterials to form aggregates results in a highly sensitive optical detection method based on localized surface plasmon.

Arsenic speciation study in some spring waters of Guam, Western Pacific Ocean.

A survey of the different forms of arsenic species: inorganic arsenic (As), As(III), As(V) and organic As(III) and (V) was carried out on spring waters located along Tumon Bay in Guam. The results show that total arsenic concentrations in the spring water samples ranged from <0.3-1.2 microg/L. Inorganic arsenate, As(V), appears to be the dominant species in the spring water samples tested. The concentrations are much lower than previously reported, probably due to a much more rigorous methodological approach and requires further investigations on the status of As contamination in groundwater on the island.