Laser-induced Fluorescence Emission Research Articles

Study on quantitative generation technology of bio-fluorescence calibration particles based on inkjet generator

Accurate measurements are critical for timely early warning and effective prevention of epidemics due to the continuing impact of bioaerosols on human health. In recent years, researchers have been focused on developing and calibrating online monitoring instruments. However, there is still a lack of laboratory-generated standard aerosol samples suitable for calibration. Therefore, in this study, we utilized a self-developed Ink Jet Aerosol Generator (H-IJAG) to achieve controllable generation of monodisperse aerosol standard particles. The Aerosol Particle Size Spectrometer (APSS, TOPAS 323) was employed as the particle detector. The diameter of the droplet was calculated by measuring the projected area of the droplet in the same image using Image-J software. Experimental results demonstrated that under standardized inkjet parameters, H-IJAG exhibited good reliability and reproducibility, and generated solid particles within (0.4–15) μm. To better simulate the laser-induced fluorescence emission properties of ambient bioaerosol, tryptophan (Trp) and 7-hydroxycoumarin-4-acetic acid (7-HCA) were selected as solutes of the laboratory-generated aerosol samples, which are known bio-fluorescent materials. According to the law of propagation of uncertainty, the relative uncertainty of the volume equivalent diameter of Trp and 7-HCA solid particles by H-IJAG were 0.42 %, while the relative uncertainty of the particle number concentrations of Trp and 7-HCA solid particles generated by H-IJAG were 1.4 %. This optimized IJAG technique provides a promising solution for the accurate calibration of bioaerosol monitors.

The Effects of Ozone Sterilization on the Chemical and Mechanical Properties of 3D-Printed Biocompatible PMMA.

Since ozone is highly corrosive, it can substantially affect the mechanical and chemical properties of the materials; consequently, it could affect the applicability of those materials in medical applications. The effect of ozone sterilization on the chemical and mechanical properties of additively manufactured specimens of biocompatible poly(methyl-methacrylate) was observed. FDM 3D-printed specimens of biocompatible PMMA in groups of five were exposed to high concentrations of ozone generated by corona discharge for different durations and at different ozone concentrations inside an enclosed chamber with embedded and calibrated ozone, temperature, and humidity sensors. A novel approach using laser-induced fluorescence (LIF) and spark-discharge optical emission spectrometry (SD-OES) was used to determine an eventual change in the chemical composition of specimens. Mechanical properties were determined by testing the tensile strength and Young's modulus. A calibrated digital microscope was used to observe the eventual degradation of material on the surface of the specimens. SD-OES and LIF analysis results do not show any detectable sterilization-caused chemical degradation, and no substantial difference in mechanical properties was detected. There was no detectable surface degradation observed under the digital microscope. The results obtained suggest that ozone sterilization appears to be a suitable technique for sterilizing PMMA medical devices.

Spectroscopic detection of the gallium methylene (GaCH2 and GaCD2) free radical in the gas phase by laser-induced fluorescence and emission spectroscopy.

GaCH2, a free radical thought to play a role in the chemical vapor deposition of gallium-containing thin films and semiconductors, has been spectroscopically detected for the first time. The radical was produced in a pulsed discharge jet using a precursor mixture of trimethylgallium vapor in high pressure argon and studied by laser-induced fluorescence and wavelength resolved emission techniques. Partially rotationally resolved spectra of the hydrogenated and deuterated species were obtained, and they exhibit the nuclear statistical weight variations and subband structure expected for a 2A2-2B1 electronic transition. The measured spectroscopic quantities have been compared to our own abinitio calculations of the ground and excited state properties. The electronic spectrum of gallium methylene is similar to the corresponding spectrum of the aluminum methylene radical, which we reported in 2022.

Laser induced fluorescence spectroscopy of aqueous eosin Y solution

Eosin Yellow (EY) is commonly used for staining in medicine, biology, food industry, textiles, painting and cosmetics. The spectroscopic and photochemical properties of this synthetic dye have also attracted attention, making it an excellent tool for chemical identification and biosensor applications. Since EY is prone to photo-degradation upon illumination by photons at wavelengths near to the main absorption bands, special considerations should be taken into account regarding its optical characterization. In the present report, laser induced fluorescence (LIF) features of aqueous EY solution due to excitation at 405 nm and 532 nm wavelengths, under conditions with the least likelihood of photo-degradation, have been assessed by emphasizing the effect of LIF internal filters. The quantum distribution of LIF emission is demonstrated to be dependent on both the excitation wavelength and EY concentration, as well as the detection line of sight. Since the fluorescence spectrum of EY is a convolution of the monomer and dimer emissions, and those contributions change unevenly under the influence of internal filters, the corresponding spectral changeovers were investigated based on the assessment of spectral asymmetry and the use of difference spectra analysis. The inner filter effects, dimerization, and resonance energy transfer between monomers and dimers were the basis for the discussion of the results.

Laser-induced X-ray fluorescence and electron-based X-ray emission analysis of multi-layer material

Laser-induced X-ray fluorescence and electron-based X-ray emission analysis of multi-layer material

First Experimental Evidence of Anti-Stokes Laser-Induced Fluorescence Emission in Microdroplets and Microfluidic Systems Driven by Low Thermal Conductivity of Fluorocarbon Carrier Oil

With the advent of many optofluidic and droplet microfluidic applications using laser-induced fluorescence (LIF), the need for a better understanding of the heating effect induced by pump laser excitation sources and good monitoring of temperature inside such confined microsystems started to emerge. We developed a broadband highly sensitive optofluidic detection system, which enabled us to show for the first time that Rhodamine-B dye molecules can exhibit standard photoluminescence as well as blue-shifted photoluminescence. We demonstrate that this phenomenon originates from the interaction between the pump laser beam and dye molecules when surrounded by the low thermal conductive fluorocarbon oil, generally used as a carrier medium in droplet microfluidics. We also show that when the temperature is increased, both Stokes and anti-Stokes fluorescence intensities remain practically constant until a temperature transition is reached, above which the fluorescence intensity starts to decrease linearly with a thermal sensitivity of about −0.4%/°C for Stokes emission or −0.2%/°C for anti-Stokes emission. For an excitation power of 3.5 mW, the temperature transition was found to be about 25 °C, whereas for a smaller excitation power (0.5 mW), the transition temperature was found to be about 36 °C.

Barely fluorescent molecules. II. Twin-discharge jet laser-induced fluorescence spectroscopy of HSnBr and DSnBr.

HSnBr and DSnBr have been detected for the first time by a combination of laser-induced fluorescence (LIF), fluorescence hole-burning, and wavelength resolved emission spectroscopies. The transient molecules were produced in a twin-discharge jet using separate precursor streams of SnH4/SnD4 and HBr/DBr, both diluted in high pressure argon. The Ã1A″-X̃1A' spectrum of HSnBr only consists of the 00 0 and 20 1 cold bands that show clearly resolved subband structure with fluorescence lifetimes varying from 526 to 162ns. The DSnBr LIF spectrum exhibits four bands (00 0, 20 1, 20 2, and 10 1) whose fluorescence lifetimes decrease from 525ns (00) to 175ns (11). Single vibronic level emission spectra have provided extensive information on the ground state vibrations, including all the anharmonicities and the harmonic frequencies. Fluorescence hole-burning experiments have shown that a few higher HSnBr nonfluorescent levels are very short-lived but still detectable. The ab initio studies of Tarroni and Clouthier [J. Chem. Phys. 156, 064304 (2022)] show that these molecules dissociate into SnBr + H on the excited state potential surface and this is the cause of the short fluorescence lifetimes and breaking off of the LIF spectra. HSnBr is a barely fluorescent molecule in the sense that only vibrational levels less than or equal to 317cm-1 in the excited state emit detectable photons down to the ground state.

Polarization-dependent LIF/Mie ratio for sizing of micrometric ethanol droplets doped with Nile red.

The present study deals with droplet sizing based on laser-induced fluorescence (LIF) and Mie scattering for varied polarization of the utilized laser (parallel or perpendicular). The polarization-dependent LIF/Mie ratio is studied for micrometric droplets (25-60 µm) produced with a droplet generator. The investigations were carried out with the dye Nile red dissolved in ethanol and ethanol/iso-octane mixtures. A spectral absorption and fluorescence characterization at various dye and ethanol concentrations is carried out in a cuvette in order to identify reabsorption effects. The LIF|| droplet images (index ||: parallel polarization) show a more homogeneous intensity distribution in the droplets and slightly stronger morphology-dependent resonances (MDRs) in comparison to LIF⊥ (index ⊥: perpendicular polarization). The spectral LIF emissions reveal a dependence of the MDR on the ethanol admixture. The larger the ethanol content, the lower the MDR peak, which is also shifted further to the red part of the spectrum. The Mie droplet signal images are mainly characterized by two distinct glare points, one at the entrance of the laser light (reflection) and one at the exit (first-order refraction). The Mie⊥ images show a more pronounced entrance glare point, in comparison to Mie||, where the exit glare point is more pronounced. These observations are in accordance with the theory. The calibration curve of the micro droplet signals revealed a volumetric trend of the LIF signals and a slightly higher LIF⊥ signal and sensitivity in comparison to LIF||. The signal Mie⊥ follows roughly a quadratic trend on average, while Mie|| follows a linear trend. Consequently, the calculated LIF⊥/Mie⊥ ratio shows a linear trend, whereas the LIF||/Mie|| ratio shows a quadratic trend, which confirms theoretical calculations. A numerical simulation of the Mie signal at various detection angles shows a good agreement with the experimental data at large apertures.

Creation of Non-Contact Device for Use in Metastatic Melanoma Margin Identification in ex vivo Mouse Brain.

Because contemporary intraoperative tumor detection modalities, such as intraoperative MRI, are not ubiquitously available and can disrupt surgical workflow, there is an imperative for an accessible diagnostic device that can meet the surgeon's needs in identifying tissue types. The objective of this paper is to determine the efficacy of a novel non-contact tumor detection device for metastatic melanoma boundary identification in a tissue-mimicking phantom, evaluate the identification of metastatic melanoma boundaries in ex vivo mouse brain tissue, and find the error associated with identifying this boundary. To validate the spatial and fluorescence resolution of the device, tissue-mimicking phantoms were created with modifiable optical properties. Phantom tissue provided ground truth measurements for fluorophore concentration differences with respect to spatial dimensions. Modeling metastatic disease, ex vivo melanoma brain metastases were evaluated to detect differences in fluorescence between healthy and neoplastic tissue. This analysis includes determining required-to-observe fluorescence differences in tissue. H&E staining confirmed tumor presence in mouse tissue samples. The device detected a difference in normalized average fluorescence intensity in all three phantoms. There were differences in fluorescence with the presence and absence of melanin. The estimated tumor boundary of all tissue phantoms was within 0.30 mm of the ground truth tumor boundary for all boundaries. Likewise, when applied to the melanoma-bearing brains from ex vivo mice, a difference in normalized fluorescence intensity was successfully detected. The potential prediction window for the tumor boundary location is less than 1.5 mm for all ex vivo mouse brain tumors boundaries. We present a non-contact, laser-induced fluorescence device that can identify tumor boundaries based on changes in laser-induced fluorescence emission intensity. The device can identify phantom ground truth tumor boundaries within 0.30 mm using instantaneous rate of change of normalized fluorescence emission intensity and can detect endogenous fluorescence differences in melanoma brain metastases in ex vivo mouse tissue.

Laser-induced fluorescence of filament-produced plasmas

Self-guided ultrafast laser filaments are a promising method for laser beam delivery and plasma generation for standoff and remote detection of elements and isotopes via filament-induced breakdown spectroscopy (FIBS). Yet, there are several challenges associated with the practical application of FIBS, including delivery of sufficient laser energy at the target for generating plasma with a copious amount of emission signals for obtaining a high signal-to-noise ratio. Here, we use laser-induced fluorescence (LIF) to boost the emission signal and reduce self-reversal in the spectral profiles. Ultrafast laser filaments were used to produce plasmas from an Al 6061 alloy target at various standoff distances from 1 to 10 m. For LIF emission enhancement, a narrow linewidth continuous-wave laser was used in resonance with a 394.40 nm Al I resonant transition, and the emission signal was monitored from the directly coupled transition at 396.15 nm. Emission signal features of Al I are significantly enhanced by resonant excitation. In addition, LIF of filament ablation plumes reduces the self-reversal features seen in the thermally excited spectral profiles. Time-resolved two-dimensional fluorescence spectroscopy was performed for evaluating the optical saturation effects, which are found to be non-negligible due to high Al atomic densities in the filament-produced plasmas.

Simultaneous imaging of two-phase velocities in particle-laden flows by two-color optical phase discrimination.

In this Letter, we present a particle image/tracking velocimetry (PIV/PTV) technique for simultaneous velocity measurement of both fluid and particle phases, adopting newly developed optical phase discrimination methods and novel optical particles. Spherical acrylic (PMMA) particles of diameter ∼O(100µm) were used as the particle phase, while fine BAM:Eu2+ phosphors of diameter ∼O(1µm) were used as the fluid tracer. Under Nd:YAG 355 nm laser excitation, both the laser-induced fluorescence (LIF) from PMMA and laser-induced phosphorescence (LIP) from BAM:Eu2+ provided sufficiently strong signals for PIV imaging with two non-intensified cameras and were clearly separable for phase discrimination using spectral filters and temporal profiles. The advantages of the PIV/PTV method include the relatively low cost of BAM:Eu2+ phosphors, high sphericity and narrow size distribution of PMMA particles with LIF emission, and direct optical discrimination eliminating artifacts, while requiring much less computational capacity for PIV/PTV processing of complex particle-laden flows.

Femtosecond laser-induced nitrogen fluorescence emission at different air pressures

In this paper, we experimentally investigate femtosecond laser-induced nitrogen fluorescence emission at different air pressures (0.1 Pa–100 kPa). The variation of nitrogen molecule (N2) and molecular nitrogen ion (N2+) characteristic fluorescence spectral lines' intensity as a function of air pressure is observed. When the air pressure is between 10 Pa and 100 kPa, the intensity of fluorescence signals from N2+ and N2 shows opposite variation as a function of air pressure. We deduce that dissociative recombination is the main pathway for the production of the C3∏u state of N2. This research helps elucidate the physical emission mechanism of femtosecond laser-induced nitrogen fluorescence emission.

Cancerous Tissue Diagnosis by LIF Spectroscopy Derived From Body-Compatible Fluorophores.

Introduction: The laser-induced fluorescence (LIF) method as molecular emission spectroscopy is used to diagnose cancerous tissues. According to the previous reports, the red-shift in the fluorescence spectrum from Rhodamine 6G (Rd6G)-stained cancerous tissues compared to healthy ones impregnated with the same dye provides the feasibility for diagnosis. In this paper, we have employed the LIF emissions as a diagnostic method to distinguish between cancerous and healthy tissues infiltrated by a body-compatible fluorophore to avoid the toxicity and hazard of Rd6G dye. Methods: Biological tissue specimens are stained with sodium fluorescein (NaFl) dye and then irradiated by the blue CW diode laser (405 nm) to examine the spectral properties that are effective in detecting cancerous tissues. Results: The spectral shift and the intensity difference of fluorescence are keys to diagnosing in vitro cancerous breast, colon, and thyroid tissues for clinical applications. The notable tubular densities in the breast and colon tissues and the space between the papillae in the thyroid ones cause the cancerous tissues to be prominently heterogeneous, providing numerous micro-cavities and thus more room for dye molecules. Conclusion: Here, we have assessed the spectral shift and intensity difference of fluorescence as a diagnostic method to distinguish between cancerous and healthy tissues for clinical applications.

Angular study of laser induced fluorescence emission of hybrid media based on Stern-Volmer formalism

Here, the quenching process of Rhodamine B fluorophores coupled with Titanium dioxide (TiO2) nanoparticles (NPs) and Graphene oxide (GO) nano structures is empirically investigated during the laser induced fluorescence (LIF) events in various detection angles. According to Stern-Volmer formalism, the slope of Stern-Volmer graph is strongly dependent on the angular orientation of the detector, mainly because of the alteration in active volume. The corresponding spectral shift lucidly changes due to the anisotropy of the re-absorption events while the single and multiple scattering simultaneously take place, particularly at dense suspensions. The fluorescence Stokes shift of RdB molecules, as well as the effect of non-homogeneous population of the exited/unexcited molecules are taken into account as dominant factors during the measurements. However, the fluorescence trapping becomes more effective in dense suspension and larger detection angles.

Sub-Surface Molecular Analysis and Imaging in Turbid Media Using Time-Gated Raman Spectral Multiplexing.

Obtaining molecular information deeper within optically turbid samples is valuable in many applications. However, in many cases this is challenging, in particular when the sample elicits strong laser-induced fluorescence emission. Here, we investigated the use of time-gated and micro-spatially offset Raman spectroscopy (micro-SORS) based on spectral multiplexing detection to obtain sub-surface molecular analysis and imaging for both fluorescing and non-fluorescing samples. The multiplexed spectral detection achieved with a digital micromirror device (DMD) allowed fast acquisition of the time-gated signals to enable three-dimensional Raman mapping (raster scanning in the lateral x,y plane and using time-of-flight calibration for the axial z-direction). Sub-millimeter resolution molecular depth mapping was achieved with dwell times on the order of seconds per pixel. To suppress fluorescence backgrounds and enhance Raman bands, time-gated Raman spectroscopy was combined with micro-SORS to recover Raman signals of red pigments placed behind a layer of optically turbid material. Using a defocusing micro-SORS approach, both fluorescence and Raman signals from the surface layers were further suppressed, which enhanced the Raman signals from the deeper sublayers containing the pigment. These results demonstrate that time-gated Raman spectroscopy based on spectral multiplexed detection, and in combination with micro-SORS, is a powerful technique for sub-surface molecular analysis and imaging, which may find practical applications in medical imaging, cultural heritage, forensics, and industry.

Simultaneous measurement of CO and OH in flames using a single broadband, femtosecond laser pulse

In this short communication, we report simultaneous measurement of CO and OH in flames using a single femtosecond (fs)-duration laser source. Two-photon excitation of CO A1Π ←←X1Ʃ+(3,0), (4,0) and (5,0) bands and single-photon excitation of OH A2Ʃ+←X2Π (1,0) band are achieved simultaneously using one fs-duration laser pulse near 283 nm. Subsequently, crosstalk-free, laser-induced fluorescence (LIF) emissions are detected from the v’=3, 4 and 5 upper vibrational levels of CO in the 200–230 nm region, and (1,1) and (0,0) bands of OH near the 310-nm region. A detailed spectroscopic investigation of CO in a gas cell is followed by simultaneous detection of CO and OH in C2H4/air flames. The measured CO and OH profiles as a function of flame equivalence ratio agree well with equilibrium calculations. The present study extends the applicability of broadband fs-LIF imaging of OH in flames, and reveal an alternate method to obtain heat release rate in turbulent flames via simultaneous OH and CO measurements.

Laser-Induced Fluorescence Emission (L.I.F.E.) as Novel Non-Invasive Tool for In-Situ Measurements of Biomarkers in Cryospheric Habitats.

Global warming affects microbial communities in a variety of ecosystems, especially cryospheric habitats. However, little is known about microbial-mediated carbon fluxes in extreme environments. Hence, the methodology of sample acquisition described in the very few studies available implies two major problems: A) high resolution data require a large number of samples, which is difficult to obtain in remote areas; B) unavoidable sample manipulation such as cutting, sawing, and melting of ice cores that leads to a misunderstanding of in situ conditions. In this study, a prototype device that requires neither sample preparation nor sample destruction is presented. The device can be used for in situ measurements with a high spectral and spatial resolution in terrestrial and ice ecosystems and is based on the Laser-Induced Fluorescence Emission (L.I.F.E.) technique. Photoautotrophic supraglacial communities can be identified by the detection of L.I.F.E. signatures in photopigments. The L.I.F.E. instrument calibration for the porphyrin derivates chlorophylla (chla) (405 nm laser excitation) and B-phycoerythrin (B-PE) (532 nm laser excitation) is demonstrated. For the validation of this methodology, L.I.F.E. data were ratified by a conventional method for chla quantification that involved pigment extraction and subsequent absorption spectroscopy. The prototype applicability in the field was proven in extreme polar environments. Further testing on terrestrial habitats took place during Mars analog simulations in the Moroccan dessert and on an Austrian rock glacier. The L.I.F.E. instrument enables high resolution scans of large areas with acceptable operation logistics and contributes to a better understanding of the ecological potential of supraglacial communities in the context of global change.

Laser-Induced Fluorescence Emission (L.I.F.E.) as Novel Non-Invasive Tool for In-Situ Measurements of Biomarkers in Cryospheric Habitats

Laser-Induced Fluorescence Emission (L.I.F.E.) as Novel Non-Invasive Tool for In-Situ Measurements of Biomarkers in Cryospheric Habitats

Characteristics of the deposited fuel liquid film when GDI spray impacts viscous oil film

Quantitative two-dimensional characteristics of the deposited fuel film on a surface with pre-existing thin oil film after the impingement of a GDI (gasoline direct injection) spray were investigated with laser induced fluorescence (LIF) technique. Since the oil and the incident test fuel could mix during impingement, we examined the theory of the LIF technique and found it could no longer provide information on the mixture thickness but could still help us measuring the mass of the deposited fuel. Mixture of isooctane and 3-pentanone was chosen as the test fuel and silicone oil of different viscosity was selected as the surrogate liquid for the oil to eliminate disturbing LIF emission. The sprays with injection pressure from 7 to 15 MPa, injected mass from 2.9 to 6.4 mg were tested, the pre-existing oil film with viscosity of 10 and 100 cSt and thickness between 10 and 50 μm were studied. A lower fuel mass deposited ratio was found under higher injection pressure and thinner oil film, while the effects of the injected mass and viscosity of oil viscosity were found to be more complicated and were analysed with the help of single drop experiments from literature.

Real-space laser-induced fluorescence imaging applied to gas-liquid interfacial scattering

We describe the real-space imaging of the products of molecular scattering, applied to collisions of hydroxyl radicals with low-vapor-pressure-liquid surfaces. A pulsed molecular beam of OD (for technical reasons) with a mean laboratory-frame kinetic energy of 29.5 kJ mol−1 was directed at continually refreshed surfaces of the representative liquids perfluoropolyether, squalane, and squalene. Laser-induced fluorescence (LIF) was excited by pulsed laser light shaped into a planar sheet, tuned to selected rovibronic transitions in the OD A–X band. The LIF emission was imaged and intensified before being captured by an external camera. Sequences of images allowed the evolution of the incident packet and scattered plumes of OD molecules to be observed. The results confirm previous observations of the internal-state distributions of the scattered OD and its differential survival probability on different liquid surfaces. New measurements of the angular distributions found them all to be broad and approximately symmetric, independent of the angle of incidence. This is interpreted as implying a high degree of atomic-scale roughness, rather than a predominant trapping-desorption mechanism, because of the other observed signatures of impulsive scattering; these include the degree of OD rotational excitation, superthermal speeds, and the correlation of speed with scattering angle. This approach has considerable potential to be applied in related gas-surface scattering experiments. It is immune from the difficulties of some other imaging methods that involve charged-particle detection and allows a spatially extended region of the scattering plane perpendicular to the surface to be imaged.