Laser-induced fluorescence spectroscopy of plant-based drugs: Opium and hashish provoking at 405 nm

Here, the fluorescence properties of some plant-based drug samples are characterized using a coherent excitation source at 405 nm. The laser-induced fluorescence (LIF) spectroscopy is examined to analyze opium and hashish. In order to improve traditional fluorescence methods for better analysis of optically dense materials, we have proposed five characteristic parameters based on solvent densitometry assay as the fingerprints of drugs of interest. The signal emissions are recorded in terms of various drug concentrations, such that the best fitting over experimental data determines the fluorescence extinction (α) and self-quenching (k) coefficients according to the modified Beer-Lambert formalism. The typical α value is determined to be 0.30 and 0.15 mL/(cm∙mg) for opium and hashish, respectively. Similarly, typical k is obtained 0.390 and 1.25 mL/(cm∙mg), respectively. Furthermore, the concentration at max fluorescence intensity (Cp) is determined for opium and hashish to be 1.8 and 1.3 mg/mL, respectively. Results reveal that opium and hashish benefit their own characteristic fluorescence parameters to discriminate those illicit substances promptly using the present method.

Analysis and classification of peanuts with fungal diseases based on real-time spectral processing

The study presents an approach to the analysis and classification of peanuts performed in order to detect kernels with fungi diseases, i.e. kernels prone to contamination with mycotoxigenic Aspergillus flavus (Aspergillus parasiticus). The aim of this study was to evaluate the effectiveness of luminescent spectroscopy with a violet laser (405 nm wavelength) as the excitation source of the fluorescence when applied for real-time detection of mould in peanuts performed by means of multispectral processing based on machine learning methods. We suggest a laboratory unit used to form, register, and process the luminescence spectra of peanuts in visible and near-infrared wavelength ranges in the real-time mode. The study demonstrated that contaminated peanuts have increased luminous intensity and show a redshift in the fluorescence peaks of the contaminated samples as compared to the pure ones. The difference in the fluorescence spectra of pure and contaminated kernels is compatible with the results obtained when traditional UV-light sources are used (365 nm). To classify peanuts by their spectral characteristics, neural network algorithms were used combined with dimensionality reduction methods. The paper presents the probabilities of incorrect recognition of the peanuts' type depending on the number of relevant secondary features determined when reducing the dimensionality of the initial data. When 10 spectral components were used, the error ratios were 0.7% or 0.3% depending on the method of reducing the dimensionality of the initial data.

Application of Capillary Electrophoresis with Laser-Induced Fluorescence to Immunoassays and Enzyme Assays

Capillary electrophoresis using laser-induced fluorescence detection (CE-LIF) is one of the most sensitive separation tools among electrical separation methods. The use of CE-LIF in immunoassays and enzyme assays has gained a reputation in recent years for its high detection sensitivity, short analysis time, and accurate quantification. Immunoassays are bioassay platforms that rely on binding reactions between an antigen (analyte) and a specific antibody. Enzyme assays measure enzymatic activity through quantitative analysis of substrates and products by the reaction of enzymes in purified enzyme or cell systems. These two category analyses play an important role in the context of biopharmaceutical analysis, clinical therapy, drug discovery, and diagnosis analysis. This review discusses the expanding portfolio of immune and enzyme assays using CE-LIF and focuses on the advantages and disadvantages of these methods over the ten years of existing technology since 2008.

Evaluation of a Portable Microchip Electrophoresis Fluorescence Detection System for the Analysis of Amino Acid Neurotransmitters in Brain Dialysis Samples

A portable fluorescence detection system for use with microchip electrophoresis was developed and compared to a benchtop system. Using this system, six neuroactive amines commonly found in brain dialysate (arginine, citrulline, taurine, histamine, glutamate, and aspartate) were derivatized offline with naphthalene-2,3-dicarboxaldehyde/cyanide, separated electrophoretically, and detected by fluorescence. The limits of detection for the analytes of interest were 50 - 250 nM for the benchtop system and 250 nM - 1.3 μM for the portable system, both of which were adequate for most analyte detection in brain microdialysis samples. The portable system was then demonstrated for the detection of the same six amines in a rat brain microdialysis sample.

Oral fluorescence imaging using 405-nm excitation, aiding the discrimination of cancers and precancers by identifying changes in collagen and elastic breakdown and neovascularization in the underlying stroma

BACKGROUND

Optical spectroscopy and imaging devices are being developed and tested for the screening and diagnosis of cancer and precancer in multiple organ sites.

OBJECTIVE

The aim of the study reported here is to optimize the capability of an optical imaging device to discriminate precancerous tissue from other lesions by identifying ideal excitation wavelengths.

METHODS

The studies reported here used a prototype of a direct fluorescence imaging device that uses 405-nm illumination to excite tissue.

RESULTS

There is ample evidence in the literature that 405 nm can distinguish oral cancers from normal tissue. Higher wavelengths may be necessary to differentiate potential confounding lesions, such as abrasions, burns, viral infections, inflammation, and gingivitis.

CONCLUSIONS

Imaging at 405 nm could help doctors detect precancerous and cancerous oral lesions. Such imaging could be used by dentists, family practitioners, otorhinolaryngologists, general surgeons, obstetrician gynecologists, and internists, and could greatly increase the number of patients who have lesions detected in the precancerous phase.

Optoelectronic capillary sensors in microfluidic and point-of-care instrumentation

This paper presents a review, based on the published literature and on the authors' own research, of the current state of the art of fiber-optic capillary sensors and related instrumentation as well as their applications, with special emphasis on point-of-care chemical and biochemical sensors, systematizing the various types of sensors from the point of view of the principles of their construction and operation. Unlike classical fiber-optic sensors which rely on changes in light propagation inside the fiber as affected by outside conditions, optical capillary sensors rely on changes of light transmission in capillaries filled with the analyzed liquid, which opens the possibility of interesting new applications, while raising specific issues relating to the construction, materials and instrumentation of those sensors.

Determination of penicillamine in pharmaceuticals and human plasma by capillary electrophoresis with in-column fiber optics light-emitting diode induced fluorescence detection

In this paper, a capillary electrophoresis (CE) system with in-column fiber optics light-emitting diode (LED) induced fluorescence detection was developed for the determination of penicillamine (PA). The influence of buffer concentration, buffer pH, applied voltage and injection time was systematically investigated. Optimum separation conditions were obtained with 10 mM borate buffer at pH 9.1, applied voltage 20 kV and 8 s hydrodynamic injection at 30 mbar. The detection system displayed linear dynamic range from 3.2 x 10(-7) to 4.8 x 10(-5) mol L(-1) with a correlation coefficient of 0.9991 and good repeatability (R.S.D.=2.46%). The method was applied to the determination of PA in commercial tablets and human plasma, which the recoveries of standard PA added to tablets and human plasma sample were found to be in the range of 96.26-102.68 and 91.10-99.35%, respectively. The proposed method is cheap, rapid, easy, and accurate, and can be successfully applied to the formulation analysis and bioanalysis.

Enantioseparation and stacking of Cyanobenz[f]isoindole-amino acids by reverse polarity capillary electrophoresis and sulfated beta-cyclodextrin

A capillary electrophoresis method with laser-induced fluorescence detection for the chiral separation of cyanobenz[f]isoindole (CBI) derivatives of amino acids was developed and optimized. The enantioseparations are accomplished with sulfated beta-CD (S-beta-CD) as chiral selector at low pH and reverse polarity. BGE conditions were optimized for CBI-serine and then applied to other CBI-amino acids. Baseline resolution of 13 CBI-amino acids was achieved using a single BGE formulation of 2 wt % S-beta-CD in 25 mM phosphate buffer at pH 2.00 and a voltage of -30 kV. pH is the most critical BGE parameter affecting resolution. At 2 wt % S-beta-CD, CBI-serine enantiomers are baseline-resolved at pH 2.00 but no resolution is obtained at pH 3.00. l-Glutamate, l-aspartate and d-serine are simultaneously quantified in the microdialysate of an arctic ground squirrel to illustrate the application to biological samples. Dilute solutions of the CBI-amino acids in water can be stacked by hydrodynamic injection with a 100-fold improvement in signal-to-noise ratio without loss of chiral resolution. The stacking is proposed to consist of field-amplified migration, pH-mediated stacking, and sweeping by S-beta-CD. The limit of detections for CBI-dl-serine and CBI-dl-glutamate are determined as 0.20 and 0.30 nM, respectively. The stacking method was not applicable to the high ionic strength microdialysates.

Comparison of Solution Chemistries of Orthophthalaldehyde and 2,3-Naphthalenedicarboxaldehyde

Polarography was used to obtain the concentrations of the dialdehydic (10%), monohydrated acyclic (5%), and cyclic hemiacetal form (85%) of orthophthalaldehyde (OPA). For 2,3-naphthalenedicarboxaldehyde (NDA) these values were estimated to be 15, 7, and 78%. Addition of water in unbuffered solutions followed first-order kinetics with rate constants 0.0018 s-1 for OPA and 0.0012 s-1 for NDA. Dehydration to form both the dialdehyde and the monohydrate is both acid- and base-catalyzed. Both dialdehydes yield on reaction with OH- ions geminal diol anion, which is electro-oxidized to a carboxylic acid. In the most frequently used pH range for the determination of amino acids, NDA can undergo reaction with OH- ions, but OPA does not. In aqueous solutions, NDA is less strongly hydrated than OPA.

UV Light-Emitting Diode-Induced Fluorescence Detection Combined with Online Sample Concentration Techniques for Capillary Electrophoresis

The application of an ultraviolet (UV) light-emitting diode (LED) to on-line sample concentration/fluorescence detection in capillary electrophoresis (CE) is described. The utility of a UV-LED (peak emission wavelength at 380 nm, approximately 2 mW) for fluorescence detection was demonstrated by examining both a naturally fluorescent (riboflavin) compound and a nonfluorescent compound (tryptophan), respectively. The detection limit for riboflavin was determined to be 0.2 ppm by the normal MEKC mode, which was improved to 3-7 ppb when dynamic pH-junction technique was applied. On the other hand, the detection limit of the tryptophan derivative was determined to be 1.5 ppm using the MEKC mode, which was improved to 3 ppb when the sweeping-MEKC mode was applied. In an analysis of an actual sample, the concentrations of riboflavin in beer, and tryptophan in urine and milk samples were determined, respectively.

Laser-induced fluorescence detection schemes for the analysis of proteins and peptides using capillary electrophoresis

Over the past few years, a large number of studies have been prepared that describe the analysis of peptides and proteins using capillary electrophoresis (CE) and laser-induced fluorescence (LIF). These studies have focused on two general goals: (i) development of automatic, selective and quick separation and detection of mixtures of peptides or proteins; (ii) generation of new methods of quantitation for very low concentrations (nm and subnanomolar) of peptides. These two goals are attained with the use of covalent labelling reactions using a variety of dyes that can be readily excited by the radiation from a commonly available laser or via the use of noncovalent labelling (immunoassay using a labelled antibody or antigen or noncovalent dye interactions). In this review article, we summarize the works which were performed for protein and peptide analysis via CE-LIF.

Analysis of passive mixing behavior in a poly(dimethylsiloxane) microfluidic channel using confocal fluorescence and Raman microscopy

Confocal fluorescence microscopy (CFM) and confocal Raman microscopy (CRM) have been applied to monitor the laminar flow mixing behavior in a poly(dimethylsiloxane) (PDMS) microfluidic channel. Two passive PDMS micromixing devices were fabricated for this purpose: a two-dimensional round-wave channel and a three-dimensional serpentine channel. The microscale laminar flow mixing of ethanol and isopropanol was evaluated using the CFM and CRM at various flow rates. The mixing behavior of confluent streams in the microchannel was assessed by determining the degree of color change in Rhodamine 6G dye on mixing using the CFM. However, it was also possible to quantitatively evaluate the mixing process without employing a fluorescence label using the CRM. The results show a strong potential for CRM as a highly sensitive detection tool to measure fundamental fluid mixing processes and to provide detailed information on chemical changes of non-fluorescent reaction mixtures in a PDMS microfluidic channel.

Laser-based non-fluorescence detection techniques for liquid separation systems

Over the last two decades, the possibility to use lasers for detection purposes in column liquid chromatography (LC) and capillary electrophoresis (CE) received much attention in the analytical chemistry literature. Most attention has been devoted to laser-induced fluorescence. The present review covers developments on non-fluorescence techniques for LC and CE. The techniques considered are thermal lens spectrometry, photoacoustic detection, refractive index detection including refractive index backscattering, Raman spectroscopy and degenerate four-wave mixing (a special mode of transientholographic spectroscopy). The paper starts with an outline of the characteristics of lasers; it ends with an overall evaluation and a discussion of the perspectives of the techniques dealt with.

Recent advances in amino acid analysis by capillary electrophoresis

Amino acids are studied extensively using capillary electrophoresis. In this review we will report the different researchs which have been done in the literature since 1998. We will describe the developments of, detection methods, separations of enantiomers, the new medical applications, and amino acids in food and plants.

Application of semiconductor light sources for investigations of photochemical reactions

Semiconductor light sources, like laser diodes or ultrabright light emitting diodes, are widely used in optical spectroscopy. In this presentation an overview of applications in photochemistry is given. Since the beginning of the 1990s an increasing number of publications with the application of semiconductor light sources appeared. Three different techniques were used: single photon counting with short pulses, phase-modulation fluorometry using a conventional modulation spectrometer, or a lock-in amplifier. Using continuous wave laser diodes in the visible region, which are available from 690 to 630 nm (and, recently, down to 400 nm), a new compact fluorescence spectrometer was developed in our laboratory. Using the phase fluorometric method, measurements down to 100 ps are now possible. Values can be measured in steps of 10 ps with good reproducibility using a high-frequency signal generator and a GHz digital storage oscilloscope. Several investigations have been carried out applying this technique including time-resolved detection of crude oil as an example for possible practical applications.

Indirect laser-induced fluorescence detection for capillary electrophoresis using a violet diode laser

The violet (415 nm) diode laser is used for indirect laser-induced fluorescence detection in capillary electrophoretic separations of inorganic anions and chemical warfare agent degradation products. Inorganic anions were detected using 8-hydroxypyrene-1,3,6-trisulfonic acid as the indirect probe and achieved submicromolar (40-80 ppb) detection limits in a 2-min separation. The chemical warfare agent degradation products methylphosphonic acid, ethyl methylphosphonate, isopropyl methylphosphonate, and pinacolyl methylphosphonate were detected using the porphyrin tetrakis(4-sulfophenyl)porphine as the indirect probe and achieved detection limits of 0.1 microM (9 ppb), which are 1 order of magnitude better than that achieved using indirect UV detection. Baseline stability achieved with the violet diode laser was excellent, with dynamic reserve (DR) values of > 1000, which are 15 times better than that achieved using an unstabilized HeCd laser.