Chemical analysis of acoustically levitated drops by Raman spectroscopy

An experimental apparatus combining Raman spectroscopy with acoustic levitation, Raman acoustic levitation spectroscopy (RALS), is investigated in the field of physical and chemical analytics. Whereas acoustic levitation enables the contactless handling of microsized samples, Raman spectroscopy offers the advantage of a noninvasive method without complex sample preparation. After carrying out some systematic tests to probe the sensitivity of the technique to drop size, shape, and position, RALS has been successfully applied in monitoring sample dilution and preconcentration, evaporation, crystallization, an acid–base reaction, and analytes in a surface-enhanced Raman spectroscopy colloidal suspension. Figure We have systematically investigated the analytical potential of Raman spectroscopy of samples in acoustically levitated drops.     

A novel approach for the detection of DNA using immobilized peptide nucleic acid (PNA) probes and signal enhancement by real-time immuno-polymerase chain reaction (RT-iPCR)

A new approach for the detection of DNA target molecules is described, using capture probes and subsequent signal enhancement by a uniform polymerase chain reaction (PCR). Peptide nucleic acid probes were immobilized in real-time PCR-compatible microtiter plates. After hybridization of biotinylated DNA targets, detection was performed by real-time immuno-PCR, a method formerly used for protein detection. We demonstrate the feasibility of this strategy for the qualitative detection of DNA oligonucleotides with a detection limit (LOD) of 6 attomol. Furthermore, the method was applied to PCR-amplified samples from genetically modified maize DNA (Mon810). A 483-bp DNA fragment was detected in mixture with 99.9% of noncomplementary DNA with a sensitivity down to the level of attomole. Figure       

Monitoring surface-assisted biomolecular assembly by means of evanescent-field-coupled waveguide-mode nanobiosensors

Biological self-assembly is a natural process that involves various biomolecules, and finding the missing partner in these interactions is crucial for a specific biological function. Previously, we showed that evanescent-field-coupled waveguide-mode sensor in conjunction with a SiO₂ waveguide, the surfaces which contain cylindrical nanometric holes produced by atomic bombardment, allowed us to detect efficiently the biomolecular interactions. In the present studies, we showed that the assembly of biomolecules can be monitored using the evanescent-field-coupled waveguide-mode biosensor and thus provide a methodology in monitoring assembly process in macromolecular machines while they are assembling. Evanescent-field-coupled waveguide-mode sensor Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Electrokinetic sample extraction and enrichment: a new method for the isolation of analytes from sludge-type matrices

Electrokinetic sample extraction and enrichment is introduced as a newly developed concept for the analysis of substances in sludge-type or paste-like matrices. It is based on electrokinetic transport phenomena as electromigration and electroosmosis occurring when an electrical field is applied to the fresh, wet samples. Problems usually associated to sample drying can be avoided, e.g., losses of volatile analytes or contamination. We have designed and built a suitable apparatus for electrokinetic sample extraction and enrichment. Appropriate operating conditions (field strength, buffer composition, concentration, and volume) were identified in experiments with an artificial sludge model and real-world lake sediments. A proof of principle of the method was provided by the electromigrative extraction and online enrichment on a solid-phase sorbent disk of an azo dye from a diatomaceous earth slurry. Electroosmotic extraction and enrichment of a cyanobacterial hepatotoxin at trace levels was finally investigated as an application example using lake sediments. Rather clean extracts were obtained even with high organic content sediment samples, as shown by high-performance liquid chromatography with diode array detection.      

Pattern recognition analysis for <Superscript>1</Superscript>H NMR spectra of plasma from hemodialysis patients

¹H NMR spectroscopic and pattern recognition-based methods (NMR-PR) were applied to the metabolic profiling studies on hemodialysis (HD). Plasma samples were collected from 37 patients before and after HD and measured by 600 MHz NMR spectroscopy. Each spectrum was data-processed and subjected to principal component analysis for pattern recognition. Spectral patterns of plasma between pre- and post-dialyses were clearly discriminated, together with significant fluctuations in the levels of creatinine, trimethylamine-N-oxide, glucose, lactate, and acetate, which were quantitated. We have first observed the significant elevation of lactate levels in post-dialysis plasma. The present study has demonstrated the high feasibility of NMR-PR method for monitoring the dialysis condition and comprehensive profiling of the change of low-molecular-weight metabolites in HD. Figure PCA for 1H NMR spectra of plasma from HD patients     

Analytical tools for the physicochemical profiling of drug candidates to predict absorption/distribution

The measurement of physicochemical properties at an early phase of drug discovery and development is crucial to reduce attrition rates due to poor biopharmaceutical properties. Among these properties, ionization, lipophilicity, solubility and permeability are mandatory to predict the pharmacokinetic behavior of NCEs (new chemical entities). Due to the high number of NCEs, the analytical tools used to measure these properties are automated and progressively adapted to high-throughput technologies. The present review is dedicated to experimental methods applied in the early drug discovery process for the determination of solubility, ionization constants, lipophilicity and permeability of small molecules. The principles and experimental conditions of the different methods are described, and important enhancements in terms of throughput are highlighted. Figure Scheme of the Drug Research Process.     

Critical evaluation of sample pretreatment techniques

Sample preparation before chromatographic separation is the most time-consuming and error-prone part of the analytical procedure. Therefore, selecting and optimizing an appropriate sample preparation scheme is a key factor in the final success of the analysis, and the judicious choice of an appropriate procedure greatly influences the reliability and accuracy of a given analysis. The main objective of this review is to critically evaluate the applicability, disadvantages, and advantages of various sample preparation techniques. Particular emphasis is placed on extraction techniques suitable for both liquid and solid samples. Figure Miniaturised extraction techniques allow sensitive analysis of also small sample volumes.     

Recent advances in electric analysis of cells in microfluidic systems

Microfluidics offers an ideal platform to integrate cell-based assays with electric measurements. The technological advances in microfluidics, microelectronics, electrochemistry, and electrophysiology have greatly inspired the development of microfluidic/electric devices that work with a low number of cells or single cells. The applications of these microfluidic systems range from the detecting of cell culture density to the probing of cellular functions at the single-cell level. In this review, we introduce the recent advances in the electric analysis of cells on a microfluidic platform, specifically related to the quantification and monitoring of cells in static solution, on-chip patch-clamp measurement, and examination of flowing cells. We also point out future directions and challenges in this field. Figure Different microfluidic devices applied to electrical analysis of cells     

Multiclass analysis of illicit drugs in plasma and oral fluids by LC-MS/MS

An analytical procedure for the simultaneous determination in human plasma and oral fluids of several illicit drugs belonging to different chemical and toxicological classes is presented. Amphetamine, methamphetamine, morphine, 6-monoacetylmorphine, methylenedioxyamphetamine, methylenedioxyethylamphetamine, methylenedioxymethamphetamine, cocaine, benzoylecgonine, tetrahydrocannabinol, carboxytetrahydrocannabinol, ketamine, and phencyclidine have been quantified in real samples using a very rapid sample treatment, basically a protein precipitation. The quantitative analysis was performed by liquid chromatography–tandem mass spectrometry and has been fully validated. All the analytes were detected in positive ionization mode using a TurboIonSpray source, except carboxytetrahydrocannabinol, which was detected in negative ionization mode. The use of a diverter valve between the column and the mass spectrometer allows the preservation of the ion source performances for high-throughput analysis. Figure Diverter system     

Laser desorption/ionization mass spectrometry analysis of monolayer-protected gold nanoparticles

Monolayer-protected gold nanoparticles (AuNPs) feature unique surface properties that enable numerous applications. Thus, there is a need for simple, rapid, and accurate methods to confirm the surface structures of these materials. Here, we describe how laser desorption/ionization mass spectrometry (LDI-MS) can be used to characterize AuNPs with neutral, positively, and negatively charged surface functional groups. LDI readily desorbs and ionizes the gold-bound ligands to produce both free thiols and disulfide ions in pure and complex samples. We also find that LDI-MS can provide a semi-quantitative measure of the ligand composition of mixed-monolayer AuNPs by monitoring mixed disulfide ions that are formed. Overall, the LDI-MS approach requires very little sample, provides an accurate measure of the surface ligands, and can be used to monitor AuNPs in complex mixtures.      

Electrochemical time of flight method for determination of diffusion coefficients of glucose in solutions and gels

The diffusion coefficient of glucose in different media is an important parameter in life sciences, as well as in biotechnology and microbiology. In this work a simple, fast method is proposed that is based on the electrochemical time of flight principle. In most of the earlier time of flight experiments performed, a constant flight distance was applied. In the present work a scanning electrochemical microscope (SECM) was applied as a measuring tool. With use of the SECM, the flying distance could be changed with high precision, making measurements with several flight distances more accurate and reliable values could be obtained for solutions as well as for gels. The conventional voltammetric methods are not applicable for glucose detection. In our work electrocatalytic copper oxide coated copper microelectrodes and micro-sized amperometric enzyme sensors were used as detectors, while microdroplet-ejecting pneumatically driven micropipettes were used as a source. Figure Experimental set up for SCEM-TOF diffusion coefficient measurements Presented at the 9th International Symposium on Instrumental Analysis, Pécs, Hungary, 29 July-2 August 2008     

Stripping analysis of heavy metals in tap water using the bismuth film electrode

A commercially available screen-printed carbon electrode coated with an ex situ deposited bismuth film (BiSPCE) has been applied to the determination of Pb(II) and Zn(II) ions in tap water (Barcelona water distribution network) by means of stripping voltammetry (SV) and stripping chronopotentiometry (SCP). A good reproducibility of the measurements and a satisfactory agreement between SV and SCP data were observed for both heavy metal ions. Although, in principle, the procedure could be also suited to the determination of Cd(II), this species was not detected. The results were also consistent with the routine ICP-OES measurements of the water distribution company, thus confirming the potential usefulness of such BiSPCE disposable devices for the analysis of heavy metals in natural waters.      

Surface modification using a novel type I hydrophobin HGFI

Surface wettability conversion with hydrophobins is important for its applications in biodevices. In this work, the application of a type I hydrophobin HGFI in surface wettability conversion on mica, glass, and poly(dimethylsiloxane) (PDMS) was investigated. X-ray photoelectron spectroscopy (XPS) and water-contact-angle (WCA) measurements indicated that HGFI modification could efficiently change the surface wettability. Data also showed that self-assembled HGFI had better stability than type II hydrophobin HFBI. Protein patterning and the following immunoassay illustrated that surface modification with HGFI should be a feasible strategy for biosensor device fabrication. Figure A hydrophobin HGFI has been applied into surface wettability conversion for protein immobilization Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nuclear magnetic resonance of mass-limited samples using small RF coils

Figure Schematic diagram of a typical arrangement used for hyphenating chemical microseparations (e.g. capillary HPLC, CE, or CEC) with microcoil NMR detection     

Automated extraction of direct,reactive, and vat dyes from cellulosic fibers for forensic analysis by capillary electrophoresis

Systematic designed experiments were employed to find the optimum conditions for extraction of direct, reactive, and vat dyes from cotton fibers prior to forensic characterization. Automated microextractions were coupled with measurements of extraction efficiencies on a microplate reader UV–visible spectrophotometer to enable rapid screening of extraction efficiency as a function of solvent composition. Solvent extraction conditions were also developed to be compatible with subsequent forensic characterization of extracted dyes by capillary electrophoresis with UV–visible diode array detection. The capillary electrophoresis electrolyte successfully used in this work consists of 5 mM ammonium acetate in 40:60 acetonitrile–water at pH 9.3, with the addition of sodium dithionite reducing agent to facilitate analysis of vat dyes. The ultimate goal of these research efforts is enhanced discrimination of trace fiber evidence by analysis of extracted dyes. Figure Fitted absorbance response surface for extraction of a direct dye, C. I. yellow 58, using a ternary solvent system.     

Biosensing applications of clay-modified electrodes: a review

Two-dimensional layered inorganic solids, such as cationic clays and layered double hydroxides (LDHs), also defined as anionic clays, have open structures which are favourable for interactions with enzymes and which intercalate redox mediators. This review aims to show the interest in clays and LDHs as suitable host matrices likely to immobilize enzymes onto electrode surfaces for biosensing applications. It is meant to provide an overview of the various types of electrochemical biosensors that have been developed with these 2D layered materials, along with significant advances over the last several years. The different biosensor configurations and their specific transduction procedures are discussed.      

TOF-S-SIMS molecular depth profiling of organic bilayers using mechanical wear test methodology

Recent publications on static secondary ion mass spectrometry (S-SIMS) focus on molecular depth profiling by using polyatomic or ultra-low energy monoatomic projectiles. Since their applicability depends on the relationship between the ion yield and the depth, which is hard to obtain without extensive studies, a combination of a wear test method with S-SIMS surface analysis was performed in the current study. Using this non-sputtering procedure, the relation between the signal intensity and the local concentration remains in principle the same as that at the surface (which is easy to determine). Mechanical erosion was successfully applied to expose sub-surface material from organic multilayers. Through surface analysis with S-SIMS on the gradually exposed deeper planes, molecular depth profiles could be obtained. The study was conducted on a model system relevant to offset printing, consisting of two polymer layers, containing dyes and a surfactant, cast on an Al substrate. Figure Concept of mechanical erosion followed by S-SIMS surface analysis to obtain molecular depth profiles     

Two-dimensional liquid chromatography of synthetic polymers

Two-dimensional liquid chromatography, 2D-LC of synthetic polymers is critically assessed. Similarities and differences of 2D-LC of low-molecular-mass and polymeric substances are reviewed. The rationale of application of 2D-LC to macromolecular substances is discussed. Basic information on retention mechanisms in liquid chromatography of synthetic polymers is furnished. The principles, reasons, and significance of coupling of retention mechanisms are explained. The resulting separation processes are elucidated, and the technical concepts of the corresponding experimental arrangements are described. The benefits of 2D-LC are demonstrated together with numerous problems and shortcomings of the method.