Application Of Laser-induced Fluorescence Research Articles

Self-calibrated Fourier transform spectrometer for laser-induced fluorescence spectroscopy with single-photon avalanche diode detection.

Fourier transform spectrometers are commonly used in scientific and industrial settings because of their ability to record complete spectra with high signal-to-noise ratios. Using a single-photon avalanche diode as the detector improves the sensitivity but adds complications in laser-induced fluorescence applications related to detector saturation and acquisition time exceeding the typical scan time. Here, we report a spectrometer for the detection of laser-induced fluorescence signal together with the excitation light, and use the second harmonic signal from the excitation light to correct the phase and calibrate the spectrum, removing the need for a separate calibration source. We achieve a resolution of 0.4cm-1 in the wavelength range of 1140.2 nm, and demonstrate detection of signals with powers as low as 377fW, with a noise floor of 172fW/cm-1.

Applications of Laser-Induced Fluorescence in Medicine

Fluorescence is the most sensitive spectroscopic method of analysis and fluorescence methods. However, classical analysis requires sampling. There are new needs for real-time analyses of biological materials, without the need for sampling. This article presents examples of proprietary applications of laser-induced fluorescence (LIF) in medicine with such methods. A classic example is the analysis of photosensitizers using the photodynamic treatment method (PDT). The level and kinetics of accumulation and excretion of sensitizers in the body are examined, as well as the optimal exposure time after the application of compounds. The LIF method is also used to analyze endogenous fluorophores; it has been used to detect neoplasms, e.g., lung cancer or gynecological and dermatological diseases. Furthermore, it is used for the diagnosis of early stages of tooth decay or detection of fungi. The article will present the construction of sensors based on the LIF method—fiber laser spectrometers and investigated fluorescence spectra in individual applications. Examples of fluorescence imaging, e.g., dermatological, and dental diagnostics and measuring systems will be presented. The advantage of the method is it has greater sensitivity and easily detects lesions early compared to the methods used in observing the material in reflected light.

Rapid monitoring of serum albumin as a biomarker of liver and kidney diseases using femtosecond laser-induced fluorescence

Albumin is the most abundant serum protein that transports hormones, free fatty acids, bilirubin, various ions, and drugs. The current study investigated the potential application of laser-induced fluorescence (LIF) in clinical analysis of human serum albumin (HSA) as a biomarker of liver and kidney disease. The excitation wavelength and HSA concentrations were systematically varied, and the LIF spectrum was recorded, in order to construct a standard calibration curve. Over a wide range of excitation wavelengths, excitation at 350 nm showedthe maximum fluorescence emission centered at 500 nm. We compared the determination of certain concentrations of HSA using both LIF and conventional laboratory assays. The LIF technique proved to be highly accurate and efficient. It may be concluded that femtosecond LIF provides a new, easy, very sensitive, precise, and direct method of detecting albumin in various biological samples.

Fluorescence lifetime measurements applied to the characterization of the droplet temperature in sprays

Obtaining accurate droplet temperature is essential to study heat and mass transfers in a wide range of spray applications such as spray cooling and spray combustion. A novel measurement technique based on the fluorescence lifetime is developed to tackle the challenge of measuring the droplet temperature in sprays. Similarly, to the intensity of the fluorescence signal, the fluorescence lifetime can vary with the temperature for some specific organic dyes, such as rhodamine B and kiton red. In the past, applications of laser-induced fluorescence (LIF) to the measurement of the temperature in sprays have been based exclusively on the fluorescence intensity by using intensity ratios of the signal detected by two or three photodetectors (PMTs, Cameras) operating at different spectral regions. Nonetheless, this approach is not straightforward, and corrections are usually required in dense sprays to mitigate some biases, which are arising in particular from the out-of-field fluorescence and multiple light scattering by the droplets. In contrast, measuring the fluorescence lifetime makes use of only a single detection spectral band and provides an absolute measurement unlike intensity-based measurements, which are always relative. In the present study, the time-correlated single-photon counting (TCSPC) is applied for the first time to measure the lifetime of the fluorescence emitted by droplets in a spray. The measurement technique provides the mean temperature of the liquid phase. No evidence of measurement biases could be pointed out during the tests performed at different injection conditions. Besides, a very high signal-to-noise ratio could be achieved even at a relatively far distance from the injection nozzle, resulting in an absolute error on the measured temperature that typically does not exceed ± 1 °C.

Laser-Plasma Spectroscopy of Hydroxyl with Applications.

This article discusses laser-induced laboratory-air plasma measurements and analysis of hydroxyl (OH) ultraviolet spectra. The computations of the OH spectra utilize line strength data that were developed previously and that are now communicated for the first time. The line strengths have been utilized extensively in interpretation of recorded molecular emission spectra and have been well-tested in laser-induced fluorescence applications for the purpose of temperature inferences from recorded data. Moreover, new experiments with Q-switched laser pulses illustrate occurrence of molecular recombination spectra for time delays of the order of several dozen of microseconds after plasma initiation. The OH signals occur due to the natural humidity in laboratory air. Centrifugal stretching of the Franck-Condon factors and r-centroids are included in the process of determining the line strengths that are communicated as a Supplementary File. Laser spectroscopy applications of detailed OH computations include laser-induced plasma and combustion analyses, to name but two applications. This work also includes literature references that address various diagnosis applications.

Correcting the effect of the detection angular on laser-induced chlorophyll fluorescence

Chlorophyll fluorescence has been widely used to monitor vegetation growth status and quantitative remote sensing monitoring of vegetation biochemical content. Therefore, it is significant to accurately measure the fluorescence information. In this study, the variation in fluorescence intensity of vivo vegetation leaf with the change in detection angle on the basis of laser-induced fluorescence technology was discussed. Experimental results demonstrated that the relationship between the emission fluorescence intensity and detection angles could be explained by the cosine expression. Then, two-step fluorescence intensity correction method was proposed. Firstly, the fluorescence intensity was corrected based on the changing of cosine expression. Secondly, the fluorescence ratio calculated based on the corrected fluorescence intensity. Results demonstrated that the effect of detection angles on fluorescence signals can be efficiently eliminated compared to the traditional spectral ratio method. Findings of this study may be valuable in promoting the applications of laser-induced fluorescence in remote sensing to achieve accurate chlorophyll fluorescence information for quantitative monitoring of plant nutrient stress.

The Use of LIF-based Instrument with 405 nm for Real-time Monitoring of Aerosolized Bio-particles

Bio-aerosols can affect public health depending on the origin of bio-particles (bacteria, virus etc.). Here, we attempted to assess the applicability of laser-induced fluorescence (LIF) instrument with 405 nm to real-time monitoring of bacteria and viruscontaining aerosols. For the purpose, the LIF-based BDS (Bio-aerosol Detection System) was used. The bio-particle monitoring of the BDS is based on fluorescence signals from two wavelength ranges [short wavelength range (SWR): 430–550 nm & long wavelength range (LWR): 500–600 nm] and the scattering signal. Firstly, auto-fluorophores (NADH, riboflavin, tyrosine, tryptophan) were tested to expect the monitoring ranges of the BDS for the auto-fluorophores. NADH and riboflavin showed fluorescence signals from two wavelength ranges, and the fluorescence efficiency of NADH was higher in the SWR than in the LWR and that of riboflavin was reversed. While tyrosine and tryptophan showed negligible fluorescence signals from two wavelength ranges as expected. Next, the lyophilized powders of Bacillus subtilis (BS), virus vaccines [ND (Newcastle Disease), IB (Infectious Bronchitis)] and the bacteriophage MS2 were tested to investigate the monitoring ranges of the BDS for the bio-particles. Individual virus and bacteriophage have been expected no fluorescence signals because of the absence of NADH and riboflavin fluorescing by 405 nm. Nonetheless, all the tested samples showed the fluorescence signals in the size range of 2 to 15 μm, generally known as bio-aerosol size. Considering that atmospheric virus particles are released through the respiratory organs of their hosts, just as virus vaccines from chicken embryo and MS2 from E. coli, it can be thought in turn that the BDS can also monitor bio-aerosols including virus as well as bacteria. Taken together, we suggests that the BDS, LIF-based instrument with 405 nm, is applicable for real-time monitoring of virus-containing aerosols as well as other bio-aerosols by counting the fluorescence particles and resolving their particle sizes.

Laser-induced fluorescence (LIF) as a smart method for fast environmental virological analyses: validation on Picornaviruses

Virological analysis is time-consuming and expensive. The aim of this work is to demonstrate the applicability of laser-induced fluorescence (LIF) to the classification of viruses, reducing the time for this analysis and its costs. Experimental tests were performed in which different viruses were irradiated with a UV laser emitting at 266 nm and the emitted spectra were recorded by a spectrometer. The classification techniques show the possibility of discriminating viruses. Although the application of the LIF technique to biological agents has been thoroughly studied by many researchers over the years, this work aims at validating for the first time its applicability to virological analyses. The development of a fast virological analysis may revolutionize this field, allowing fast responses to epidemiologic events, reducing their risks and improving the efficiency of monitoring environments. Moreover, a cost reduction may lead to an increase in the monitoring frequency, with an obvious enhancement of safety and prevention.

Identification of mine water inrush using laser-induced fluorescence spectroscopy combined with one-dimensional convolutional neural network.

The application of laser-induced fluorescence (LIF) combined with machine learning methods can make up for the shortcomings of traditional hydrochemical methods in the accurate and rapid identification of mine water inrush in coal mines. However, almost all of these methods require preprocessing such as principal component analysis (PCA) or drawing the spectral map as an essential step. Here, we provide our solution for the classification of mine water inrush, in which a one-dimensional convolutional neural network (1D CNN) is trained to automatically identify mine water inrush according to the LIF spectroscopy without the need for preprocessing. First, the architecture and parameters of the model were optimized and the 1D CNN model containing two convolutional blocks was determined to be the best model for the identification of mine water inrush. Then, we evaluated the performance of the 1D CNN model using the LIF spectral dataset of mine water inrush containing 540 training samples and 135 test samples, and we found that all 675 samples could be accurately identified. Finally, superior classification performance was demonstrated by comparing with a traditional machine learning algorithm (genetic algorithm-support vector machine) and a deep learning algorithm (two-dimensional convolutional neural network). The results show that LIF spectroscopy combined with 1D CNN can be used for the fast and accurate identification of mine water inrush without the need for complex pretreatments.

Application of Laser-Induced Fluorescence in Functional Studies of Photosynthetic Biofilms

Biofilms are a ubiquitous form of life for microorganisms. Photosynthetic biofilms such as microphytobenthos (MPB) and biological soil crusts (BSC) play a relevant ecological role in aquatic and terrestrial ecosystems, respectively. On the other hand, photosynthetic epilithic biofilms (PEB) are major players in the microbial-induced decay of stone structures of cultural heritage. The use of fluorescence techniques, namely, pulse-amplitude-modulated fluorometry, was crucial to understanding the photophysiology of these microbial communities, since they made it possible to measure biofilms’ photosynthetic activity without disturbing their delicate spatial organization within sediments or soils. The use of laser-induced fluorescence (LIF) added further technical advantages, enabling measurements to be made at a considerable distance from the samples, and under daylight. In this Perspective, we present state-of-the-art LIF techniques, show examples of the application of LIF to MPB and present exploratory results of LIF application to BSC, as well as to PEB colonizing stone structures of cultural heritage. Thereafter, we discuss the perspectives of LIF utilization in environmental research and monitoring, in cultural heritage conservation and assessment, and in biotechnological applications of photosynthetic biofilms.

Characterisation of estuarine intertidal macroalgae by laser-induced fluorescence

The article reports the application of laser-induced fluorescence (LIF) for the assessment of macroalgae communities of estuarine intertidal areas. The method was applied for the characterisation of fifteen intertidal macroalgae species of the Tagus estuary, Portugal, and adjacent coastal area. Three bands characterised the LIF spectra of red macroalgae with emission maxima in the ranges 577–583 nm, 621–642 nm and 705–731 nm. Green and brown macroalgae showed one emission maximum in the red region (687–690 nm) and/or one in the far-red region (726–732 nm). Characteristics of LIF emission spectra were determined by differences in the main fluorescing pigments: phycoerythrin, phycocyanin and chlorophyll a (Chl a). In the green and brown macroalgae groups, the relative significance of the two emission maxima seems to be related to the thickness of the photosynthetic layer. In thick macroalgae, like Codium tomentosum or Fucus vesiculosus, the contribution of the far-red emission fluorescence peak was more significant, most probably due to re-absorption of the emitted red Chl a fluorescence within the dense photosynthetic layer. Similarly, an increase in the number of layers of the thin-blade green macroalgae Ulva rigida caused a shift to longer wavelengths of the red emission maximum and the development of a fluorescence peak at the far-red region. Water loss from Ulva's algal tissue also led to a decrease in the red/far-red Chl fluorescence ratio (F685/F735), indicating an increase in the density of chloroplasts in the shrinking macroalgal tissue during low tide exposure.

Gas Phase Oxygen Quenching Studies of Ketone Tracers for Laser-Induced Fluorescence Applications in Nitrogen Bath Gas

ABSTRACT In this paper we report the quantitative oxygen quenching effect on laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone at low pressures (∼700 torr) with oxygen partial pressures up to 450 torr. Nitrogen was used as a bath gas in which these molecular tracers were added in different quantities according to their vapor pressure at room temperature. These tracers were excited by using a frequency-quadrupled, Q-switched, Nd:YAG laser (266 nm). Stern–Volmer plots were found to be linear for all the tracers, suggesting that quenching is collisional in nature. Stern–Volmer coefficients (ksv) and quenching rate constants (kq) were calculated from Stern–Volmer plots. The effects of oxygen on the laser-induced fluorescence of acetone, methyl ethyl ketone, and 3-pentanone were compared with each other. Further, the Smoluchowski theory was used to calculate the quenching parameters and compared with the experimental results.

Kr II laser-induced fluorescence for measuring plasma acceleration

We present the application of laser-induced fluorescence of singly ionized krypton as a diagnostic technique for quantifying the electrostatic acceleration within the discharge of a laboratory cross-field plasma accelerator also known as a Hall effect thruster, which has heritage as spacecraft propulsion. The 728.98 nm Kr II transition from the metastable 5d(4)D(7/2) to the 5p(4)P(5/2)(∘) state was used for the measurement of laser-induced fluorescence within the plasma discharge. From these measurements, it is possible to measure velocity as krypton ions are accelerated from near rest to approximately 21 km/s (190 eV). Ion temperature and the ion velocity distributions may also be extracted from the fluorescence data since available hyperfine splitting data allow for the Kr II 5d(4)D(7/2)-5p(4)P(5/2)(∘) transition lineshape to be modeled. From the analysis, the fluorescence lineshape appears to be a reasonable estimate for the relatively broad ion velocity distributions. However, due to an apparent overlap of the ion creation and acceleration regions within the discharge, the distributed velocity distributions increase ion temperature determination uncertainty significantly. Using the most probable ion velocity as a representative, or characteristic, measure of the ion acceleration, overall propellant energy deposition, and effective electric fields may be calculated. With this diagnostic technique, it is possible to nonintrusively characterize the ion acceleration both within the discharge and in the plume.

Application of Laser Based Spectroscopic Monitoring into Soil Remediation Process of PAH-Contaminated Soil

ABSTRACT The application of Laser-Induced Fluorescence (LIF) into soil remediation process is not popular due to the difficulties of the interpretation of remediation process. The monitoring for the lab-scale surfactant enhanced electrokinetic remediation process using the LIF was performed. The variation of the fluorescence intensity and the change of the fluorescence spectral signature reflecting the nature of the surrounding environment were investigated. The diffuse reflectance correction method for the soil matrix properties on fluorescence, and the time resolution for isolation of surfactant which can be overlapped with PAHs spectra of interest were considered to provide the information of contaminants taking place during the remediation process. Eletrokinetic (EK) remediation process as control experiment was also performed and this result was compared with the surfactant-enhanced EK process especially in terms of the spectral signature of PAHs. The LIF monitoring for soil remediation process showed that the relative quantities and the state of contaminant in soil media which can be an important key to assess the feasibility of remediation process.

Qualitative Analysis of Dyed Textile Cultural Property by Laser-Induced Fluorescence

A qualitative analysis of dyed textile cultural property by spectroscopic measurement is described. An analysis by non-destructive measurement is desired in the interest of conserving of cultural property. However, the existing methods are based on destructive inspection, and a lot of time and proficiency is necessary for analysis. To improve those problems, the application of laser-induced fluorescence (LIF) as a non-destructive measurement technique is proposed in this study. We measured the LIF spectrum of a sample, and compared it with a data base. This measurement technique is non-destructive, and easy.

Evaluation of the irising effect of a slow-gating intensified charge-coupled device on laser-induced incandescence measurements of soot

Intensified charge-coupled devices (ICCDs) are used extensively in many scientific and engineering environments to image weak or temporally short optical events. To optimize the quantum efficiency of light collection, many of these devices are chosen to have characteristic intensifier gate times that are relatively slow, on the order of tens of nanoseconds. For many measurements associated with nanosecond laser sources, such as scattering-based diagnostics and most laser-induced fluorescence applications, the signals rise and decay sufficiently fast during and after the laser pulse that the intensifier gate may be set to close after the cessation of the signal and still effectively reject interferences associated with longer time scales. However, the relatively long time scale and complex temporal response of laser-induced incandescence (LII) of nanometer-sized particles (such as soot) offer a difficult challenge to the use of slow-gating ICCDs for quantitative measurements. In this paper, ultraviolet Rayleigh scattering imaging is used to quantify the irising effect of a slow-gating scientific ICCD camera, and an analysis is conducted of LII image data collected with this camera as a function of intensifier gate width. The results demonstrate that relatively prompt LII detection, generally desirable to minimize the influences of particle size and local gas pressure and temperature on measurements of the soot volume fraction, is strongly influenced by the irising effect of slow-gating ICCDs.

Fluorescence spectroscopy to diagnose hepatic steatosis in a rat model of fatty liver

Steatosis is diagnosed on the basis of the macroscopic aspect of the liver evaluated by the surgeon at the time of organ extraction or by means of a frozen biopsy. In the present study, the applicability of laser-induced fluorescence (LIF) spectroscopy was investigated as a method for the diagnosis of different degrees of steatosis experimentally induced in rats. Rats received a high-lipid diet for different periods of time. The animals were divided into groups according to the degree of induced steatosis diagnosis by histology. The concentration of fat in the liver was correlated with LIF by means of the steatosis fluorescence factor (SFF). The histology classification, according to liver fat concentration was, Severe Steatosis, Moderate Steatosis, Mild Steatosis and Control (no liver steatosis). Fluorescence intensity could be directly correlated with fat content. It was possible to estimate an average of fluorescence intensity variable by means of different confidence intervals (P=95%) for each steatosis group. SFF was significantly higher in the Severe Steatosis group (P<0.001) compared with the Moderate Steatosis, Mild Steatosis and Control groups. The various degrees of steatosis could be directly correlated with SFF. LIF spectroscopy proved to be a method capable of identifying the degree of hepatic steatosis in this animal model, and has the potential of clinical application for non-invasive evaluation of the degree of steatosis.

Simultaneous laser-induced fluorescence and sub-Doppler polarization spectroscopy of the CH radical

The first application of polarization spectroscopy (PS) to the CH radical is demonstrated. In particular, we report on the simultaneous application of laser-induced fluorescence (LIF) and sub-Doppler PS to CH. The conventional experimental setup for PS was supplemented with a second detection system in order to collect the LIF emission. At the same time a Fabry–Perot etalon and molecular iodine were utilized to obtain a precise relative and absolute frequency scale, respectively. CH was investigated in a low pressure methane–oxygen flame. The R2(5) transition of the B–X (0,0) band corresponding to a wavelength around 387.3nm was scanned while fluorescence emission was collected in the spectral region around 431nm from the B–X (0,1), A–X (1,1) and A–X (0,0) bands. The saturation behavior of both techniques is investigated as well as line broadening effects due to the pump laser pulse energy or rather fluence. Saturation fluence for LIF was found to be more than one order of magnitude higher as compared to PS.

Application of laser-induced fluorescence for remote sensing of vegetation

The possibilities of applying a fluorescent lidar based on the second harmonic of a Nd:YAG laser to study vegetation under natural conditions are analyzed. The dynamics of development has been studied for several species of arboreous plants grown in West Siberia in a five-year measurement cycle. The fluorescent lidar developed has been used for identification of plant species and for investigation of fading caused by an adverse environment. It is shown that the fluorescent signal can be used for remote detection of plant stresses at earlier stages, when there are no visible symptoms. For the first time, the quantitative relations are established between the intensity of red nanosecond fluorescence and the chlorophyll concentration in needles and leaves of the most typical representatives of West Siberian arboreous plants. Fluorescent data were checked using the traditional spectrophotometric method. The spectrophotometric data and lidar measurements were used to calibrate the lidar, and this calibration has allowed the chlorophyll concentration in arboreous plants to be determined from the ratio of signals of laser-induced fluorescence.

Mini-conference on laser-induced fluorescence in plasmas

A mini-conference on laser-induced fluorescence in plasmas was held on 29 October 2003 as part of the 45th meeting of the Division of Plasma Physics of the American Physical Society. This paper summarizes material discussed in the talks presented as part of the mini-conference. The mini-conference was also an occasion to honor Raul Stern on his 75th birthday and to recognize his many contributions to plasma physics and to the applications of laser-induced fluorescence.