Intracavity laser polarization spectrometer for biomolecule traces

A polarization variant of an intracavity laser spectrometer based on the competition of beams in an argon ion laser, radiating a number of narrow lines in the 275 to 529 nm spectral range, is proposed and described for the spectral analysis of liquid samples, having broad absorption bands, mainly biomolecules in solutions. By careful optimization of the operating conditions, a procedure has been established that results in a minimal measurable absorbance decreased up to 10^–5 units of optical density. The examined spectrometer provides a wide dynamic range of analysis. A determination of trace contents of amino acids in methanol were carried out.     

Computerized laser Raman spectrometer

A microprocessor computer specially designed for application in optical spectroscopy is described and the construction of a laser Raman spectrometer realized on its base is discussed. The computer exercises an active control over a high resolution double monochromator, a photon counting system and the exciting laser radiation. The spectral information can be visualized on an oscilloscope display, hardcopied on a XY recorder and stored on magnetic tape.     

Intracavity laser atomic absorption spectrometry with graphite furnace atomizer or pulsed laser sampler

An absorption intracavity laser spectrometer with two types of sample vaporization systems (graphite furnace electrothermal atomizer or laser sampler) is described that can be used for the determination of trace amounts of metals (Al, Cr, Fe and Mn) in liquid samples and at the surface of solid targets. The limits of detection for the elements tested are lower than those obtained by modern conventional spectrometers. The examined technique provides a wide dynamic range of linear standard calibration curves.     

Intracavity laser atomic absorption spectrometry with graphite furnace atomizer or pulsed laser sampler

An absorption intracavity laser spectrometer with two types of sample vaporization systems (graphite furnace electrothermal atomizer or laser sampler) is described that can be used for the determination of trace amounts of metals (Al, Cr, Fe and Mn) in liquid samples and at the surface of solid targets. The limits of detection for the elements tested are lower than those obtained by modern conventional spectrometers. The examined technique provides a wide dynamic range of linear standard calibration curves.     

Microfabricated devices for biomolecule encapsulation

Biomolecule encapsulation in droplets is important for miniaturizing biological assays to reduce reagent consumption, cost and time of analysis, and can be most effectively achieved by using microfabricated devices. Microfabricated fluidic devices can generate emulsified drops of uniform size with controlled dimensions and contents. Biological and chemical components such as cells, microgels, beads, hydrogel precursors, polymer initiators, and other droplets can be encapsulated within these drops. Encapsulated emulsions are appealing for a variety of applications since drops can be used as tiny reaction vessels to perform high-throughput reactions at fast rates, consuming minimal sample and solvent amounts due to the small size (micron diameters) of the emulsion drops. Facile mixing and droplet coalescence allow for a diversity of assays to be performed on-chip with tunable parameters. The simplicity of operation and speed of analysis with microencapsulated drops lends itself well to an array of quantitative biomolecular studies such as directed evolution, single-molecule DNA amplification, single-cell encapsulation, high-throughput sequencing, enzyme kinetics, and microfluidic cell culture. This review highlights recent advances in the field of microfabricated encapsulating devices, emphasizing the development of emulsifying encapsulations, device design, and current assays that are performed using encapsulating droplets.     

Bacteriorhodopsin--novel biomolecule for nano devices

The aim of this article is to provide insight on the use of a biological molecule--bacteriorhodopsin (bR) having all the basic properties necessary for the assembly of nanoscale electronic devices. Recent developments made during last decade supported by key references are reviewed in this contribution. Major emphasis on bR-based observations conducted in our laboratory has been elaborated. Important issues concerning structure, widely accepted photocycle of bR has been summarized. The possibility of nano-devices emanating from this biomolecule is briefly presented.     

An improved laser fluorimeter for the detection of traces of uranium

An improved laser fluorimeter and its application for the determination of ultratrace concentrations of uranium are described. The system developed uses a collecting lens-filter system, by which the density of laser radiation on the sample is increased greatly and the interfering stray light can be reduced to a great degree. In addition, both laser and lamp sources are joined together in the instrument. A strong green phosphor from uranium-doped sodium metaphosphate (NaPO₃: U) has been found suitable and has been used for the determination of ultratraces of uranium. A detection limit (3) of 0.36 pg of uranium (in 30 mg NaH₂PO₄ per pellet) was obtained. In the case of peak-to-background intensity ratios relative standard deviations (RSD) are 6.4% and the linear dynamic range extends from 1 pg to 10³ ng of uranium.     

Near-infrared diode laser wavelength modulation-based photoacoustic spectrometer

An inexpensive resonant photoacoustic spectrometer based on a low-power distributed feedback diode laser and wavelength modulation spectroscopy is developed. This sensor has been applied to the detection of acetylene (C2H2) using a properly designed photoacoustic cell operating on its second longitudinal mode. The minimum detectable limit of about 10 parts-per-million volume (signal to noise ratio=1) is achieved at atmospheric pressure, and the pressure and laser power linear dependence of the photoacoustic signal is also investigated. Moreover, in this paper we also describe some basic theory of gas photoacoustic spectroscopy.     

Improving precision for laser solid sampling for ICP emission with an array spectrometer

An Excimer laser operating at the wavelength of 308 nm has been used to ablate soil for bulk analysis. The ablated material has been transferred to an array ICP emission spectrometer. In order to avoid a degraded reproducibility due to imhomogeneity, repetitive firings along a sampling line have been done at a firing frequency of 3 Hz. Effects of line length, read delay and internal standardization have been studied.     

Improving precision for laser solid sampling for ICP emission with an array spectrometer

An Excimer laser operating at the wavelength of 308 nm has been used to ablate soil for bulk analysis. The ablated material has been transferred to an array ICP emission spectrometer. In order to avoid a degraded reproducibility due to imhomogeneity, repetitive firings along a sampling line have been done at a firing frequency of 3 Hz. Effects of line length, read delay and internal standardization have been studied.     

Near-infrared tunable diode laser spectrometer for the remote sensing of vehicle emissions

A near-infrared diode laser-based spectrometer has been designed and built for the remote sensing of vehicle emissions. It detects carbon monoxide and carbon dioxide absorptions around 1580 nm and can provide the ratio CO/CO(2) for vehicle exhaust studies. The system is battery powered and is designed to sit unobtrusively at the side of the road. The optics and electronics of the system is described and preliminary results are presented from field trials. Extensions to the spectrometer in terms of sensitivity by detection of the more intense first overtone of carbon monoxide around 2320 nm are described, in addition to further work on other species of interest.     

Highly resolved luminescence measurements for traces of 1,3-dibetanato europium(III) and terbium(III) complexes using a microscope laser Raman spectrometer toward the forensic discrimination.

The emission spectra of luminescent trivalent europium (Eu3+) and terbium (Tb3+) complexes were measured using a microscope laser Raman spectrometer with a doubled Nd:YAG laser (532 nm) and an Ar laser (488 nm). Excitation at 532 and 488 nm corresponded to wavelengths of the 7F1 --> 5D1 band of Eu3+ and the 7F6 --> 5D4 band of Tb3+, respectively. The Eu3+ and Tb3+ complexes were discriminated by high-resolution emission spectra more distinctly and sensitively than by fluorescence spectrometry, the usual analytical method.     

Templated xerogels as platforms for biomolecule-less biomolecule sensors

We designed and synthesized new armed 12-oxacrown-3s bearing oxygen donor arms and forming encapsulated complexes with metal ions. The ISEs based on the single armed 12-oxacrown-3s exhibited Na⁺ ion selectivity, while the ISE based on the double armed 12-oxacrown-3 exhibited Li⁺ ion selectivity. The conformational analysis was performed on the free armed 12-oxaciown-3s and the non-encapsulated and the encapsulated armed 12-oxacrown-3 complexes using a semi-empirical method. The conformational analysis indicated that all armed 12-oxacrown-3s structurally prefer the Na⁺ ion rather than the Li⁺ ion. Further, it became apparent that the single armed 12-oxacrown-3s without a guest cation have the C_3v 12-oxaciown-3 ring and the double armed 12-oxacrown-3 without a guest cation has the bent 12-oxacrown-3 ring. The oxygens except carbonyl oxygens were directed toward the cation center in the structures of the complexes. It was clear that the ether and ester oxygens participate in the sidearm coordination.     

Tunable fiber laser and fiber amplifier based photoacoustic spectrometer for trace gas detection

A new wavelength modulated photoacoustic spectrometer based on a near-infrared tunable erbium doped fiber laser (TEDFL) and an erbium doped fiber amplifier (EDFA) is first developed for trace gas detection. This sensor has been applied to the detection of ammonia using a first longitudinal resonant photoacoustic cell with double absorption optical path (L = 20 cm) and lock-in harmonic detection technique. The minimum detectable limit of 3 parts-per-billion volume (signal-to-noise ratio = 1) and response time of approximately 1 min is achieved at room temperature and atmospheric pressure with 100 ms time constant and 500 mW optical power at the 1531.7 nm transition line.     

Variations of thermal-lens spectrophotoetry with helium-cadmium laser excitation for the determination of traces of phosphorus

Single-beam, differential single-beam and dual-beam thermal-lens measurements are compared for the determination of phosphorus traces by means of a helium-cadmium laser. Phosphate is determined as the molybdophosphate/auramine ion-pair which is extracted into 1:2 isobutanol/hexane; acetone is added to dissolve any ion-pair precipitate. In dual-beam thermal lens experiments a low-power HeNe laser is uded as the probe laser. The detection limit, restricted by variable blank measurement, is 0.6 ng cm^?3 phosphorus in all cases. The advantages and drawbacks of each measurement technique are discussed. The dual-beam system of measurement is more sensitive than the single-beam system and is appropriate for measurements on samples of small volume. The dual-beam system is applied for layer-by-layer determination of phosphorus in semiconductor silicon over the concentratin range 5 × 10^?8 ?5 × 10^?4%. The data obtained by the dual-beam method compare well with those obtained by a neutron activation method.     

Layer-by-layer-assembled microfiltration membranes for biomolecule immobilization and enzymatic catalysis

Multilayer assemblies of polyelectrolytes, for protein immobilization, have been created within the membrane pore domain. This approach was taken for two reasons: (1) the high internal membrane area can potentially increase the amount of immobilized protein, and (2) the use of convective flow allows uniform assembly of layers and eliminates diffusional limitations after immobilization. To build a stable assembly, the first polyelectrolyte layer was covalently attached to the membrane surface and inside the pore walls. Either poly(L-glutamic acid) (PLGA) or poly(L-lysine) (PLL) was used in this step. Subsequent deposition occurs by multiple electrostatic interactions between the adsorbing polyelectrolyte [poly(allylamine) hydrochloride (PAH) or poly(styrenesulfonate) (PSS)] and the oppositely charged layer. Three-layer membranes were created: PLL-PSS-PAH or PLGA-PAH-PSS, for an overall positive or negative charge, respectively. The overall charge on both the protein and membrane plays a substantial role in immobilization. When the protein and the membrane are oppositely charged, the amount immobilized and the stability within the polyelectrolyte assembly are significantly higher than for the case when both have similar charges. After protein incorporation in the multilayer assembly, the active site accessibility was comparable to that obtained in the homogeneous phase. This was tested by affinity interaction (avidin-biotin) and by carrying out two reactions (catalyzed by glucose oxidase and alkaline phosphatase). Besides simplicity and versatility, the ease of enzyme regeneration constitutes an additional benefit of this approach.     

A table‐top PXI based low‐field spectrometer for solution dynamic nuclear polarization

We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of ¹H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced ¹H signal at 288 kHz was constructed with Litz wire. The largest observed ¹H enhancements (ε) at 6.7 mT for ¹⁴N‐CTPO radical in air saturated aqueous solution was ε~65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi‐frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards.     

Ultra-rapid laser protein micropatterning: screening for directed polarization of single neurons

Protein micropatterning is a powerful tool for studying the effects of extracellular signals on cell development and regeneration. Laser micropatterning of proteins is the most flexible method for patterning many different geometries, protein densities, and concentration gradients. Despite these advantages, laser micropatterning remains prohibitively slow for most applications. Here, we take advantage of the rapid multi-photon induced photobleaching of fluorophores to generate sub-micron resolution patterns of full-length proteins on polymer monolayers, with sub-microsecond exposure times, i.e. one to five orders of magnitude faster than all previous laser micropatterning methods. We screened a range of different PEG monolayer coupling chemistries, chain-lengths and functional caps, and found that long-chain acrylated PEG monolayers are effective at resisting non-specific protein adhesion, while permitting efficient cross-linking of biotin-4-fluorescein to the PEG monolayers upon exposure to femtosecond laser pulses. We find evidence that the dominant photopatterning chemistry switches from a two-photon process to three- and four-photon absorption processes as the laser intensity increases, generating increasingly volatile excited triplet-state fluorophores, leading to faster patterning. Using this technology, we were able to generate over a hundred thousand protein patterns with varying geometries and protein densities to direct the polarization of hippocampal neurons with single-cell precision. We found that certain arrays of patterned triangles as small as neurite growth cones can direct polarization by impeding the elongation of reverse-projecting neurites, while permitting elongation of forward-projecting neurites. The ability to rapidly generate and screen such protein micropatterns can enable discovery of conditions necessary to create in vitro neural networks with single-neuron precision for basic discovery, drug screening, as well as for tissue scaffolding in therapeutics.     

Matrix-assisted laser desorption ionization with a magnetic mass spectrometer.

Matrix-assisted laser desorption ionization has been carried out with a high mass double-focusing magnetic mass spectrometer. The pulsed ion signal, generated by irradiation of the sample (substance P, ubiquitin, and cytochrome c) embedded in 2,5-dihydroxybenzoic acid with a XeF excimer laser (353 nm, 12 ns pulse, 10-160 Hz), was recorded with an integrating array detector. Good resolution of 2600 (full width at half maximum) and high sensitivity (a few pmol) were obtained. The loss of small neutral fragments was observed, supporting the notion that the peak broadening observed in the time-of-flight mass spectrometers commonly used for this ionization mode is due to such metastable decomposition.     

Ion optics of the LAMAS-10 laser time-of-flight mass spectrometer

In laser time-of-flight mass spectrometers, satisfactory resolution by weight is achieved for a fixed initial kinetic energy acquired by the ions in the plasma. The integration of mass spectra in a wide energy range intended for obtaining satisfactory results of analysis leads to a 3–5-fold reduction of the resolving capacity. In the case of the LAMAS-10 device, the resolution for W = 50–300 eV energy dispersion of the ions varies from R ∼ 1000 (for W = 300 eV) to R ∼ 150 (for W = 50 eV), such values being insufficient for quantitative elemental analysis. It has been demonstrated that the main reason for the differences in the resolution values for LAMAS-10 are time aberrations by energies in the laser plasma drift space. The modification of the ion optics theory for LAMAS-10 allows the determination of the principles of the influence of the initial ion energies generated in the laser plasma on the resolution. The dependence of the conditions of the time focusing of ions by energies has been determined in a wide range of the initial values. This dependence provides software-controlled readjustment of the time focusing before the registration of the mass spectra for each initial ion energy. When time focusing of the ions was performed in a wide range of the initial energies, the resolution increased to R = 1300 at W = 50 eV, such parameters providing the quantitative analysis of solid bodies and powders.