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A compact tandem excitation source-in-source was designed by arranging a point discharge (PD) ignited in argon/hydrogen (Ar/H

A miniaturized optical emission spectrometer was constructed with improved point discharge microplasma as an excitation source to enhance sample introduction efficiency and excitation efficiency. By using a hollow electrode as one of the discharge electrodes, analyte-containing chemical vapor yielded via hydride generation was transported and confined into the hollow electrode and subsequently guided into the microplasma with high sample introduction efficiency. Moreover, gaseous analyte species were directly diffused from inside the electrode into the center of the microplasma, instead of traditional external diffusion into the microplasma, resulting in sufficient participation in interactions and excitation in the plasma; thus, high excitation efficiency and stability can be achieved. A 3D-printing technique was used to fabricate some components for compact integration of this spectrometer. Physical characteristics of the microplasma, 3D-printing, and experimental parameters were all investigated to better understand the excitation capability and obtain optimal analytical performance. Under optimized conditions, As, Bi, Ge, Hg, Pb, Sb, Se, and Sn were successfully detected, with detection limits of 2.5, 0.44, 1.6, 0.10, 2.8, 1.5, 31, and 0.24 μg L-1, respectively, and relative standard deviations all less than 4%. It was applied to the analysis of Certified Reference Materials (water, soil, and biological samples) and real water samples with satisfactory results. Because of its advantages of compactness, robustness, easy fabrication, and cost-effectiveness, it has a great prospect as a portable spectrometer for field analytical chemistry.

A new fluorescence method based on aptamer-target interactions has been developed for cocaine detection with target-induced strand displacement. Here we describe new probes, the hairpin-probe and the single strand-probe (ss-probe), that possess two recognition sequences of cocaine aptamer. In the presence of cocaine, both probes would associate with the target to form a tripartite complex. The conformational change in the hairpin-probe causes the opening of a hairpin structure and the hybridization to primer. With polymerase and the dNTPs, the replication of the single-stranded domain of hairpin-probe triggers the process of primer extension. When the hairpin-probe is converted into a fully double-stranded form, the ss-probe and cocaine are displaced to bind another hairpin-probe and initiate new amplification cycles. Fluorescence signal generation would be observed upon SYBR Green I intercalating into the new DNA double helix. The new protocol design permits detection of as low as 2 nM cocaine in a closed tube, offering a convenient approach for a homogeneous assay. Compared with previously reported cocaine aptameric sensors, our new method is highly sensitive, selective, and economical.

A purge-free controlled living polymerization method, activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP), is used to amplify the occurrence of protein binding events. Detection of ovalbumin is demonstrated where binding of femtomole protein is differentiable from the background using ellipsometry. Moreover, binding of subpicomole protein leads to visually distinguishable spots on the sensor surface within 15 min, which signifies its potential in future development of point-of-need devices.

A novel signal amplification strategy for electrochemical detection of DNA and proteins based on the amplification-by-polymerization concept is described. Specifically, a controlled radical polymerization reaction is triggered after the capture of target molecules on the electrode surface. Growth of long chain polymeric materials provides numerous sites for subsequent aminoferrocene coupling, which in turn significantly enhances electrochemical signal output. Activators generated electron transfer for atom transfer radical polymerization (AGET ATRP) is used in this study for its high efficiency in polymer grafting and better tolerance toward oxygen in air. 2-Hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) are examined to provide excess hydroxyl or epoxy groups for aminoferrocene coupling. A limit of detection of 15 pM and 0.07 ng/mL is demonstrated for DNA and ovalbumin, respectively. More than 7-fold signal enhancement in ovalbumin detection has been achieved comparing to the unamplified method. In addition, a more than 5 orders of magnitude of dynamic range is achieved with a linear correlation coefficient (R(2)) of 0.997 for DNA, and a more than 3 orders of magnitude with R(2) of 0.999 for ovalbumin. Together, the results show that the coupling of amplification-by-polymerization concept with electrochemical detection offers great promises in providing a sensitive and cost-effective solution for biosensing applications.

Amplification-by-Polymerization reportedly offers a sensitive and detector-free approach for DNA detection. However, the requirement for an oxygen-free environment when classic radical polymerization reactions are used in signal amplification significantly limits the mobility of this approach for point-of-need applications. We report here the employment of a purge-free controlled/"living" polymerization reaction, activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP), to achieve signal amplification upon DNA hybridization. Its aptitude in simplifying assay procedure and shortening assay turn-around has been demonstrated in this report, which substantiates the feasibility of using Amplification-by-Polymerization for high throughput or portable screening of genetic mutations. In addition, employment of water-soluble ascorbic acid as the reducing agent has overcome the hurdles encountered by heterogeneous AGET ATRP reactions. Optimization of AGET ATRP in the presence of oligonucleotides has been conducted where tris[(2-pyridyl)methyl]amine (TPMA) was selected as the catalyst ligand for its mild reaction rate. Effective polymer growth has been achieved when the concentration of the Cu(II) catalyst was controlled at 20 mM and ascorbic acid at 18 mM. The propagation and termination reaction constants have been derived, purporting the speculated controlled growth kinetics during polymer grafting. A linear relationship between the grafted polymer film thickness and the amount of captured DNA target sequences has been established, which provides the quantification basis during DNA detection. Detection of DNA sequences with single-point mutations has been successful regardless of the mutation site.

Development of novel tools to image spatial distribution of small molecules in biological samples is essential in disease diagnosis and biomarker discovery. To simplify sample preparation and reduce background noise in the low-mass region, we describe here the use of a matrix-free mass spectrometric imaging method, i.e., desorption/ionization on silicon (DIOS), for biological surface analysis. The imaging parameters, such as the laser beam diameter and the translation stage movement, were studied and optimized to improve imaging performance. The use of DIOS imaging to map small molecules on mouse liver tissues was demonstrated. In addition, phosphatidylcholine (PC) and propidium iodide (PI) were used as the cell membrane and nucleus markers, respectively, to "visualize" the presence of HEK 293 cells. The reconstructed ion maps of PC and PI were compared with the optical images collected from the same sample using bright-field and fluorescence microscopy. A good correlation of the spatial distribution of cells confirmed the validity of this DIOS imaging approach.

Schizophrenia is a relatively common psychiatric syndrome that affects virtually all brain functions. We investigated the plasma proteome of 22 schizophrenia male patients and 20 healthy male controls using two-dimensional gel electrophoresis and mass spectrometry. In total, we have identified 66 protein spots in human plasma and found that seven of them showed altered changes in schizophrenia patients, as compared to healthy controls, which mainly were acute phase proteins (APPs). Among these APPs, haptoglobin alpha2 chain (p0.001), haptoglobin beta chain (p0.001), alpha1-antitrypsin (p = 0.001), and complement factor B precursor (p = 0.022) showed overexpression in schizophrenia patients, whereas apolipoprotein A-I (p = 0.034) and transthyretin (p = 0.035) were found to be significantly decreased in patients. In addition, the expression of apolipoprotein A-IV (p = 0.018) was significantly up-regulated in schizophrenia patients, as compared to controls. We also found these APP genes, which were differentially expressed in this study, overlap in the schizophrenia susceptibility loci. Our findings further support the hypothesis that the inflammatory response system is linked to the pathophysiology of schizophrenia.

In this report, we systematically investigated DNA immobilization at gold surfaces with electrochemical techniques. Comparative cyclic voltammetric and chronocoulometric studies suggested that DNA monolayers immobilized at gold surfaces were not homogeneous. Nonspecific Au-DNA interactions existed even with the treatment of mercaptohexanol, which was known to competitively remove loosely bound DNA at gold surfaces. While both thiolated and nonthiolated DNA formed monolayers on gold surfaces, their hybridization abilities were distinctly different. In contrast to thiolated DNA probes, nonthiolated DNA probes immobilized at gold surfaces were essentially nonhybridizable. The experimental results presented here might be useful for the design of high-performance electrochemical DNA sensors.

A laminar flow nebulizer was developed for use with aerosol matrix-assisted laser desorption/ionization mass spectrometry. The nebulizer consists of a glass pneumatic nebulizer combined with a laminar flow tube. Particles formed at the pneumatic nebulizer are entrained in an auxiliary gas stream that dries the particles in the laminar flow tube. The mass range of the reflectron time-of-flight mass spectrometer has been extended to greater than 5000 Da: a mass spectrum of bovine insulin is reported at a mass resolution of 100. Mass spectra of bovine insulin and the peptides bradykinin and angiotensin II contain features resulting from prompt analyte dissociation prior to ion acceleration.

Reversible addition-fragmentation chain transfer polymerization is employed here to allow detector-free visualization of specific DNA sequences for which dynamic polymer growth is used in signal amplification. In particular, surface-initiated polymer growth was regulated by the immobilization of chain transfer agents on the Au surface where DNA hybridization occurred. A linear polymer growth was observed as a function of the reaction time, characteristic of "living" polymer reactions. Significant improvement in assay sensitivity was realized in comparison to the previously reported polymerization-based sensing method by enhancing polymer growth rate and reducing background noises caused by nonspecific adsorption. Direct visualization of fewer than 2,000 copies of a short oligonucleotide sequence was demonstrated in a detector-free fashion.

We report here a new DNA detection method in which polymer growth in atom transfer radical polymerization (ATRP) is used as a means to amplify detection signals. In this method, DNA hybridization and ligation reactions led to the attachment of ATRP initiators on a solid surface where specific DNA sequences were located. These initiators subsequently triggered the growth of poly(hydroxyethyl methacrylate) (PHEMA) at the end of immobilized DNA molecules and formed polymer brushes. The formation of PHEMA altered substrate opacity, rendering the corresponding spots readily distinguishable to the naked eye. A second ATRP reaction to form branched polymers on the surface drastically improved the visibility of DNA hybridization and significantly shortened the detection time. The resulting polymer film was characterized using infrared spectroscopy, ellipsometry, contact angle measurements, and atomic force microscopy. Direct visualization of 1 fmol of target DNA molecules of interest was demonstrated. A proof-of-principle experiment to detect DNA point mutation was conducted. The perfectly matched DNA targets were distinctively differentiated from those with mutations. The demonstrated capability to detect DNA mutation with direct visualization laid the groundwork for the future development of detector-free testing kits in single-nucleotide polymorphism screenings.

We report here a simple method to generate ordered nanocavity arrays on a Si wafer and use it in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). A close-packed SiO2 nanosphere array was first deposited on a low-resistivity Si wafer using a convective self-assembly method. The nanoparticle array was then used as a mask in a reactive ion etching (RIE) process to selectively remove portions of the Si surface. Subsequent sonication removed those physically adsorbed SiO2 nanoparticles and exposed an ordered nanocavity array underneath. The importance of this approach is its capability of systematically varying surface geometries to achieve desired features, which makes detailed studies of the impacts of surface features on the desorption/ionization mechanism feasible. We demonstrated that the in-plane width and out-of-plane depth of the cavities were adjustable by varying etching times, and the intercavity spacing was controllable by varying the number of particle layers deposited. MS detection of small peptides on these substrates showed comparable sensitivity to conventional porous Si substrates (DIOS, desorption/ ionization on porous silicon). The desorption and ionization efficiency of these roughened surfaces exhibited a nonmonotonic relationship to the increased total surface area. Several possible factors contributing to the observed phenomenon are speculated upon. The application of this arrayed surface in metabolite detection of Arabidopsis thaliana root extracts is also demonstrated.

In this report, we present data demonstrating that cylindrical metallic particles, with various submicrometer striping patterns, may be readily distinguished in an optical microscope. Accurate particle identification is discussed relative to synthesis reproducibility and the limitations of optical microscopes. Results from a library of these particles, of which over 100 different striping patterns have been produced, are presented. For these particles, made with Au and Ag stripes, more than 70 patterns may be identified with greater than 90% accuracy. The ability to chemically modify the surface of these particles, making them useful for bioanalytical measurements, is also demonstrated. Finally, we discuss improvements in our manufacturing and identification processes that will lead to both larger numbers of striping patterns and improved identification accuracy.

A new approach to detecting capillary electrophoresis (CE) eluent components by interfacing CE with a surface-enhanced Raman scattering (SERS) system is described. In this approach, CE-based separation of a mixture of trans-1,2-bis(4-pyridyl)ethylene and N,N-dimethyl-4-nitrosoaniline has been detected by SERS in a postcolumn geometry. The retention time obtained from SERS corresponds well with that from conventional UV−visible detection. Meanwhile, CE eluants are identified by their characteristic vibrational spectra, demonstrating the validity of SERS as a structure-specific detection method for CE. In addition, the ability to monitor SERS intensity changes at molecule-specific frequencies makes selective detection of individual analytes possible, even when separation is incomplete. Finally, CE-SERS is evaluated for separation of amino acids (tyrosine and tryptophan) and environmental pollutants (chlorophenol mixtures).

The familiar concept of the barcode for tracking may be coming to a chemical reaction near you in the form of coded microparticles.