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A portable surface-enhanced Raman scattering (SERS) sensor is developed and applied to simultaneous detection of aniline and phenol derivatives in a label-free way with an electrostatic preconcentration technique to amplify the signals. A SERS-active substrate, silver-electrodeposited screen-printed electrodes (Ag-SPEs), is used for qualification and quantification of polar organic pollutants. Observation of SERS spectra at different potentials indicates that polar pollutants are selectively adsorbed on the Ag-SPEs at a given potential, suggesting that Ag-SPEs could selectively attract polar pollutants to an oppositely charged electrode at different potentials. Optimum SERS-active substrate was obtained when a potential of-0.15 V vs Ag/AgC1 was applied on the SPEs in 0.1 M AgN[O.sub.3] solution for 10 min. Moreover, the effects of experimental variables such as the electrodeposition time and potential of Ag and preconcentration time of polar molecules on the SERS signals are presented. Under optimum conditions and with a 785 nm laser, the method is effective over a wide range of concentration (1 nM to 1 [micro]M) for aniline and phenol derivatives. The novel method described herein presents a new detection regime for environmental pollutant analysis and also demonstrates simultaneous multiplexed detection of polar organic pollutants using convenient Ag-SPEs. 10.1021/ac101812x

The cystamine conjugate [[(BocNH)Fc(CO)CSA].sub.2] was prepared by coupling cystamine with the N-protected ferrocene amino acid derivative BocHN-Fc-COOH and was fully characterized by spectroscopic methods and by single-crystal X-ray diffraction. The cystamine conjugate forms films on gold substrates, which upon deprotection of the amino group, react with chemical warfare agent (CWA) mimics, upon which the redox properties of the Fc group are affected significantly. Cyclic voltammetry shows 50(5) mV anodic shifts of the Fc redox potentials after exposure to EtSC[H.sub.2]C[H.sub.2]Cl, a simulant for sulfur mustard HD (MA), and (NC)[(EtO).sub.2]P(O), a simulant for nerve agent Tabun (NA). Exposure to MA and NA causes an increase in 2.3 and 4.5 ng mass, respectively, in QCM which indicates ca. 70% efficiency in Boc-deprotection. Ellipsometry measured a film thickness increase from 6([+ or -]1) [Angstrom] for the deprotected film to 10([+ or -]4) [Angstrom] for the film modified with MA and to 7([+ or -]2) [Angstrom] for the film modified with NA. AFM measurements show changes in the thickness and morphology of the film after reaction with MA and NA. The surfaces were analyzed by X-ray photoelectron spectroscopy (XPS) and clearly show the attachment of the cystamine conjugate on the surface and its reaction with CWA mimics.

The detection of a single-nucleotide mismatch in unlabeled duplex DNA by electrochemical methods is presented. Impedance spectroscopy is used to characterize a perfect duplex monolayer and three DNA monolayers differing in the position of the mismatch. The monolayers were studied as B-DNA (normal duplex DNA) and after conversion to M-DNA (a metalated duplex). Modeling of the impedance data to an equivalent circuit provides parameters that are useful in discriminating the four monolayer configurations. The resistance to charge transfer, [R.sub.CT], was lower for all duplexes after conversion to M-DNA. Contrary to expectations, [R.sub.CT] was also found to decrease for duplexes containing a mismatch. However, [R.sub.CT] was found to be diagnostic for mismatch detection. In particular, the difference in [R.sub.CT] between B- and M-DNA ([DELTA][R.sub.CT]) decreased from 190(22) [OMEGA]x[cm.sup.2] for a perfectly matched duplex to 95(20), 30(20), and 85(20) [OMEGA]x[cm.sup.2] for a mismatch at the top (distal), middle, and bottom (proximal) positions of the monolayer with respect to the gold surface. Further, a method to form loosely packed single-stranded (ss)-DNA monolayers by duplex dehybridization that is able to rehybridize to target strands is presented. Rehybridization efficiencies were in the range of 40-70%. Under incomplete hybridization conditions, the [R.sub.CT] was the same for matched and mismatched duplexes under B-DNA conditions. However, [DELTA][R.sub.CT] between B- and M-DNA, under incomplete hybridization, still provided a distinction. The [DELTA][R.sub.CT] for a perfect duplex was 76(12) [OMEGA]x[cm.sup.2], whereas a mismatch in the middle of the sequence yielded a [DELTA][R.sub.CT] value of 30(15) [OMEGA]x[cm.sup.2]. The detection limit was measured and the impedance methodology reliably detected single DNA base pair mismatches at concentrations as low as 100 pM.

Hydrogen evolution reaction (HER) catalyzed by molybdenum sulfide quantum dots (MoS 2 QDs) has attracted extensive attention in the energy field. Monitoring HER catalyzed by MoS 2 QDs based on a glass nanopore with an electrochemically confined effect was proposed for the first time. MoS 2 QDs inside the glass nanopore is driven toward the orifice of the nanopore and bonded with the Ag nanoparticles (Ag NPs) to form a single nanocomposite. When enough voltage is applied across the orifice, the single Ag NP acts as a single nanoparticle electrode to conduct the electrochemically bipolar reaction on its two extremities. In the process, HER is catalyzed by MoS 2 QDs, and Ag NPs are oxidized at the same time. The appearance of blockages on the elevated ionic current is attributed to the generation of a H 2 bubble. Furthermore, by analyzing the modulations in the ionic current oscillation, the frequency of hydrogen bubble generation that is related to the catalytic efficiency of MoS 2 QDs could be estimated. The results reveal the capability of the glass nanopore for the real-time monitoring electrocatalytic behavior, which makes the glass nanopore an ideal candidate to further reveal the heterogeneity of catalytic capability at the single particle level.

Lipids are the main component of the cell membrane. They not only provide structural support of cells but also directly participate in complex cellular metabolic processes. Lipid signaling is an important part of cell signaling. Evidence showed that abnormal cellular metabolism may induce lipids changes. Besides, owing to single cell heterogeneity, it is necessary to distinguish different behaviors of individual cells. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is a sensitive surface analysis technique with high spatial resolution, which is useful in single cell surface analysis. Herein, we used ToF-SIMS to investigate silver nanoparticle induced lipids changes on the surface of single macrophage cells. Delayed extraction mode of ToF-SIMS was used to simultaneously obtain high mass resolution of mass spectra and high spatial resolution of single cell chemical imaging. Principle component analysis (PCA) results showed good agreement with the cytotoxicity assay results. Clear distinctions were observed between the cell groups treated with high or low dose of silver nanoparticles. The loadings plots revealed that the separation was mainly due to changes of cholesterol and diacylglycerol (DAG) as well as monoacylglycerol (MAG). Meanwhile, the chemical mapping of single cell components showed that cholesterol and DAG tend to migrate to the surrounding of the cells after high dose silver nanoparticles (Ag NPs) treatment. Our results demonstrated the feasibility of ToF-SIMS for characterizing the changes of the lipids on a single cell surface, providing a better understanding of the mechanism of cell-nanoparticle interactions at the molecular level.

A novel surface-enhanced Raman scattering (SERS) nanosensor was developed by modifying oxidized cytochrome c (Cyt c) on gold nanoparticles (Au NPs) for the sensitive and selective determination of intracellular superoxide anion radical (O2(•-)). On the basis of the differences in the SERS spectra between the oxidized and reduced form of Cyt c, this nanosensor could be employed to investigate O2(•-) concentration by measuring the SERS spectra of the reduced Cyt c. Using this SERS nanosensor, a detection limit of 1.0 × 10(-8) M for O2(•-) could be attained. Additionally, the selectivity of the SERS nanosensor for O2(•-) was examined, showing that other reactive oxygen species (ROS) and biologically relevant species did not influence the detection of O2(•-). More importantly, the nanosensor could be delivered to the living HeLa and normal human liver cells and permitted the concentration of O2(•-) to be monitored in real time and in a noninvasive manner, which indicates that this nanosensor will be suitable for the qualitative and quantitative analysis of O2(•-) in biosystems, thus leading to a greater understanding of oxidative-stress-related diseases at a cellular level.