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.     

Determination of trace elements in suspensions and filtrates of drinking and surface water by wavelength-dispersive X-ray fluorescence spectrometry

An X-ray fluorescence method (XRF) is presented that allowed low detection limits (at the 0.1–23 ng mL⁻¹ level) to be obtained for Cr, Mn, Fe, Ni, Zn, Sr, Pb, Bi and Br in water. The samples were prepared using a thin layer method. Trace elements were determined via the calibration curve and standard addition. Absorption effects and inhomogenities in prepared samples were checked for using the emission–transmission method and internal standards, respectively. The results from the XRF method were compared with the results from the inductively coupled plasma atomic emission spectrometry method.      

Recent advances in capillary electrophoretic analysis of individual cells

Because variability exists within populations of cells, single-cell analysis has become increasingly important for probing complex cellular environments. Capillary electrophoresis (CE) is an excellent technique for identifying and quantifying the contents of single cells owing to its small volume requirements and fast, efficient separations with highly sensitive detection. Recent progress in both whole-cell and subcellular sampling has allowed researchers to study cellular function in the areas of neuroscience, oncology, enzymology, immunology, and gene expression.      

Impedimetric genosensors for the detection of DNA hybridization

Impedance spectroscopy is proposed as the transduction principle for detecting the hybridization of DNA complementary strands. In our experiments, different DNA oligonucleotides were used as model gene substances. The gene probe is first immobilized on a graphite-epoxy composite working electrode based genosensor. Detection principle is based on changes of impedance spectra of a redox marker, the ferro/ferricyanide couple, after hybridization with target DNA. Resistance offered to the electrochemical reaction serves as the working signal, allowing for an unlabelled gene assay.      

31P NMR study on the autophosphorylation of insulin receptors in the plasma membrane

A nonradioactive ³¹P nuclear magnetic resonance (NMR) spectroscopy protocol has been developed and used to investigate in vitro autophosphorylation of insulin receptors. Optimum experimental conditions have been explored, and the effects of Mn²⁺ and phosphocreatine (PCr) on the determination of the phosphorylation reaction have been assayed. The method was used to monitor the time courses of the phosphorylation reaction in solution. The results from this NMR study were in agreement with observations of insulin receptor phosphorylation made by using Western blotting.      

Detection of bacteria by surface-enhanced Raman spectroscopy

The detection and identification of dilute bacterial samples by surface-enhanced Raman spectroscopy has been explored by mixing aqueous suspensions of bacteria with a suspension of nanocolloidal silver particles. An estimate of the detection limit of E. coli was obtained by varying the concentration of bacteria. By correcting the Raman spectra for the broad librational OH band of water, reproducible spectra were obtained for E. coli concentrations as low as approximately 10³ cfu/mL. To aid in the assignment of Raman bands, spectra for E. coli in D₂O are also reported. Figure Light scattering apparatus used to detect bacteria     

Laser-based standoff detection of explosives: a critical review

A review of standoff detection technologies for explosives has been made. The review is focused on trace detection methods (methods aiming to detect traces from handling explosives or the vapours surrounding an explosive charge due to the vapour pressure of the explosive) rather than bulk detection methods (methods aiming to detect the bulk explosive charge). The requirements for standoff detection technologies are discussed. The technologies discussed are mostly laser-based trace detection technologies, such as laser-induced-breakdown spectroscopy, Raman spectroscopy, laser-induced-fluorescence spectroscopy and IR spectroscopy but the bulk detection technologies millimetre wave imaging and terahertz spectroscopy are also discussed as a complement to the laser-based methods. The review includes novel techniques, not yet tested in realistic environments, more mature technologies which have been tested outdoors in realistic environments as well as the most mature millimetre wave imaging technique. Figure Standoff detection and identification is one of the most wanted capabilities     

Determination of the titanium content of human transferrin by inductively-coupled plasma-atomic-emission spectroscopy

We report a simple method that combines dialysis, as a purification method, with the multielement capability of ICP to determine the titanium-to-transferrin mole ratio at physiological pH, under buffer conditions. The method, by means of which titanium and transferrin are determined simultaneously, enabled us to assess the binding capacities of different titanocene complexes. Figure Titanocene dichloride     

Non-destructive analysis of museum objects by fibre-optic Raman spectroscopy

Raman spectroscopy is a versatile technique that has frequently been applied for the investigation of art objects. By using mobile Raman instrumentation it is possible to investigate the artworks without the need for sampling. This work evaluates the use of a dedicated mobile spectrometer for the investigation of a range of museum objects in museums in Scotland, including antique Egyptian sarcophagi, a panel painting, painted surfaces on paper and textile, and the painted lid and soundboard of an early keyboard instrument. The investigations of these artefacts illustrate some analytical challenges that arise when analysing museum objects, including fluorescing varnish layers, ambient sunlight, large dimensions of artefacts and the need to handle fragile objects with care. Analysis of the musical instrument (the Mar virginals) was undertaken in the exhibition gallery, while on display, which meant that interaction with the public and health and safety issues had to be taken into account. Experimental set-up for the non-destructive Raman spectroscopic investigation of a textile banner in the National Museums of Scotland     

Cation identity dependence of crown ether photonic crystal Pb<Superscript>2+</Superscript> sensing

We quantitatively modeled the volume phase transition of a hydrogel containing a crystalline colloidal array with a crown ether ligand which binds Pb²⁺. The hydrogel volume response and the wavelength diffracted depend on the Pb²⁺ concentration and on both the ionic strength and the valence of the nonbinding ionic species. We successfully modeled the response of this hydrogel Pb²⁺ sensor to ionic strength and the cation valence of the added salts. Figure Cation identity dependence of crown ether photonic crystal Pb⁺ sensing     

Study of the dynamics of surface molecules by time-resolved sum-frequency generation spectroscopy

Sum-frequency generation (SFG) is a nonlinear laser-spectroscopy technique suitable for analysis of adsorbed molecules. The sub-monolayer sensitivity of SFG spectroscopy enables vibrational spectra to be obtained with high specificity for a variety of molecules on a range of surfaces, including metals, oxides, and semiconductors. The use of ultra-short laser pulses on time-scales of picoseconds also makes time-resolved measurements possible; this can reveal ultrafast transient changes in molecular arrangements. This article reviews recent time-resolved SFG spectroscopy studies revealing site-hopping of adsorbed CO on metal surfaces and the dynamics of energy relaxation at water/metal interfaces. Time-resolved sum frequency generation spectroscopy at surfaces with non-resonant laser pulse irradiation     

Modì: a new mobile instrument for in situ double-pulse LIBS analysis

Laser-induced breakdown spectroscopy (LIBS) is a promising technique for in situ elemental analysis. A new mobile instrument for LIBS analysis, developed in a collaboration between Marwan Technology s.r.l. and the Applied Laser Spectroscopy Laboratory in Pisa, is presented, and some applications of it and results from it are outlined. The innovative experimental set-up, based on the use of two suitably retarded laser pulses and a standardless analysis procedure, which overcomes problems related to matrix effects, greatly improves the potential of this technique for accurate quantitative analysis.      

Raman spectroscopic investigation of cocaine hydrochloride on human nail in a forensic context

This study describes the application of Raman spectroscopy to the detection of drugs of abuse and noncontrolled substances used in the adulteration of drugs of abuse on human nail. Contamination of the nail may result from handling or abusing these substances. Raman spectra of pure cocaine hydrochloride, a seized street sample of cocaine hydrochloride (77%), and paracetamol could be acquired from drug crystals on the surface of the nail. An added difficulty in the analytical procedure is afforded by the presence of a nail varnish coating the nail fragment. By using confocal Raman spectroscopy, spectra of the drugs under nail varnish could be acquired. Spectra of the drugs could be readily obtained nondestructively within three minutes with little or no sample preparation. Raman spectra could be acquired from drug particles with an average size of 5–20 μm. Acquisition of Raman point maps of crystals from both pure and street samples of cocaine hydrochloride under nail varnish is also reported. Figure Raman spectrum and point Raman map of cocaine HCI     

Tip-enhanced Raman spectroscopy for nanoscale strain characterization

Tip-enhanced Raman spectroscopy (TERS), which utilizes the strong localized optical field generated at the apex of a metallic tip when illuminated, has been shown to successfully probe the vibrational spectrum of today’s and tomorrow’s state-of-the-art silicon and next-generation semiconductor devices, such as quantum dots. Collecting and analyzing the vibrational spectrum not only aids in material identification but also provides insight into strain distributions in semiconductors. Here, the potential of TERS for nanoscale characterization of strain in silicon devices is reviewed. Emphasis will be placed on the key challenges of obtaining spectroscopic images of strain in actual strained silicon devices. Figure Figure Concept of Tip Enhanced Raman Spectroscopy (TERS), which utilizes the strong localized optical field generated at the apex of a metallic tip when illuminated. TERS has been demonstrated to successfully probe the vibrational spectrum of today’s and tomorrow’s state-of-the-art silicon and next generation semiconductor devices     

Application of anodized aluminum in fluorescence detection of biological species

Thin nanoporous alumina obtained by anodization of aluminum films offers promising advantages for application in fluorescence-based biological sensors including convenient preparation, increased density of binding sites, and improved collection efficiency of fluorescence. These advantages are illustrated in the detection of streptavidin using biotin covalently bound to the surface of alumina nanopores. Fluorescence intensity enhancement as high as 7 times is observed in nanopores in comparison to flat glass surface.      

Neutron activation analysis and X-ray Rayleigh and Raman scattering of hair and nail clippings as noninvasive bioindicators for Cu liver status in Labrador Retrievers

The heritability of chronic hepatitis in the Labrador Retriever is studied with the aim of identifying the related gene mutation. Identification of cases and controls is largely based on instrumental neutron activation analysis (INAA) Cu determination in liver biopsies. The burden for these companion animals may be reduced if nail clippings and hair (fur) could serve as a noninvasive indicator for the hepatic Cu concentrations. No correlation was found between hepatic Cu concentrations and Cu concentrations in hair and nail samples. However, hair and nail samples were also analyzed by X-ray tube excitation, taking advantage of the X-ray Compton, Rayleigh, and Raman scattering which reflects the organic components such as the type of melanin. Principal component analysis provided first indications that some differentiation between healthy and sick dogs could indeed be obtained from hair and nail analysis. Figure Principal component analysis of scattered region of x-ray fluorescence spectra of Labrador dog nails, demonstrating the differentiation towards dogs with high and low Cu liver levels (respectively positive and negative PC2 values) reflecting hepatitis, as well as gender (PC1: negative values for female and positive values for males)     

Chemiluminescent detection of DNA hybridization using gold nanoparticles as labels

A chemiluminescent (CL) detection method has been developed for DNA hybridization. The assay relies on a sandwich-type DNA hybridization in which gold nanoparticles modified with alkylthiol-capped oligonucleotide strands are used as probes to monitor the presence of the specific target DNA. The , which is the dissolving product of the gold nanoparticles anchored on the DNA hybrids, serves as an analyte in the H₂O₂–luminol– CL reaction for the indirect measurement of the target DNA. The combination of the remarkable sensitivity of the CL analysis with the large number of released from each DNA hybrid allows a detection limit at levels as low as 0.1 pM of the target DNA. Moreover, with a further silver amplification step, the detection limit will be pushed down to the femtomolar domain.      

Colorimetric detection of immunoglobulin G by use of functionalized gold nanoparticles on polyethylenimine film

A method based on use of functionalized gold nanoparticles on polyethylenimine film has been developed for colorimetric detection of immunoglobulin G (IgG). The immunogold nanoparticles were immobilized on quartz slides by recognition between antibody and antigen, with the antigen chemically adsorbed on the polyethylenimine film. By measurement of the UV–visible spectra of the immobilized immunogold, detection of h-IgG was achieved. The detection limit for h-IgG by use of this method can be as low as 0.01 μg mL⁻¹. This method is quite promising for numerous applications in immunoassay. Figure     

Arsine and selenium hydride trapping in a novel quartz device for atomic-absorption spectrometry

A novel quartz device has been designed to trap arsine and selenium hydride and subsequently to volatilize the collected analyte and atomize it for atomic-absorption spectrometric detection. The device is actually the multiple microflame quartz-tube atomizer (multiatomizer) with inlet arm modified to serve as the trap and to accommodate the oxygen-delivery capillary used to combust hydrogen during the trapping step. The effect of relevant experimental conditions (trap temperature during trapping and hydrogen flow rate and trap temperature during volatilization) on collection and volatilization efficiency was investigated. Under the optimum conditions collection and volatilization efficiency for arsenic and selenium were 50 and 70%, respectively.