Integrated Fluorescence Intensity Research Articles

In Situ Formation of Ultrathin Composite Shell with Strong Water Resistance on the Surface of K2SiF6:Mn4+ via NaClO Treatment

AbstractSolving the problem of poor weather resistance of Mn4+‐doped fluoride phosphors is pivotal for their application in white‐light‐emitting diodes (WLEDs). This study introduces a one‐step synthesis strategy for the phosphor T‐KSF:Mn (KSF:M = K2SiF6:Mn4+ and T = surface‐treated with NaClO) that involves the use of a NaClO solution as a treatment agent to augment the water resistance of this phosphor. The results of transmission electron microscopy, electron diffraction tomography, and X‐ray photoelectron spectroscopy, analyses reveal the formation of an ultrathin composite shell (<5 nm) comprising K2SiF6 and KNaSiF6 on the surface of T‐KSF:Mn. The fluorescence intensity of the treated phosphor is 1.09 times that of the untreated phosphor, and its internal quantum efficiency reaches 82.72%. Even after 60 days of testing in a harsh hydrolysis environment, the fluorescence intensity of T‐KSF:Mn remains at 86.24%. At 150 and 200 °C, the integrated fluorescence intensity of T‐KSF:Mn surge to 256.84% and 292.29% of its initial value at 30 °C, respectively, demonstrating a substantial negative thermal quenching (NTQ) effect. Furthermore, the results of aging tests conducted at 85 °C and 85% relative humidity substantiate the effectiveness of the aforementioned strategy in considerably enhancing WLED stability under practical conditions.

A Ratiometric Fluorescent Probe Dye-Functionalized MOFs Integrated with Logic Gate Operation for Efficient Detection of Acetaldehyde.

Volatile organic compounds (VOCs) are a class of hazardous gases that are widely present in the atmosphere and cause great harm to human health. In this paper, a ratiometric fluorescent probe (Dye@Eu-MOFs) based on a dye-functionalized metal-organic framework was designed to detect VOCs, which showed high sensitivity and specificity for acetaldehyde solution and vapor. A linear correlation between the integrated fluorescence intensity (I510/I616) and the concentration of acetaldehyde was investigated, enabling a quantitative analysis of acetaldehyde in the ranges of 1 × 10-4~10-5 μL/mL, with a low detection limit of 8.12 × 10-4 mg/L. The selective recognition of acetaldehyde could be clearly distinguished by the naked eye under the excitation of UV light. The potential sensing mechanism was also discussed. Significantly, a molecular logic gate was constructed based on the whole system, and finally, a molecular logic network system for acetaldehyde detection connecting basic and integrated logic operations was realized. This strategy provided an effective guiding method for constructing a molecular-level logic gate for acetaldehyde detection on a simple platform.

Temporal fiber-optic fluorescence study of FAD-NADH interactions in phantoms for potential applications in rapid liquid optical biopsy procedures

Body fluids carry several biomarkers and genetic material that enable the detection of carcinogenesis and tumor metastasis. Owing to this, liquid biopsy is gaining importance and entering clinical practice as an adjunct modality to the current standard of practice in cancer detection. Liquid biopsy involving specimens such as urine is non-invasive and has biomarkers reflecting the tumor microenvironment. We investigate the normal and altered levels of cellular metabolic by-products in liquid phantoms and demonstrate their photon-induced excited-state interaction behaviour for potential diagnostic applications. Short-span temporal analysis of metabolic by-products FAD and NADH in liquid phantoms with fiber optic fluorescence spectroscopy is carried out. The mixed liquid phantom of FAD and NADH, showed excited state interactions that manifested as simultaneous inverse variation in the fluorescence emission from FAD and NADH in varying pH environments. Linear discriminant analysis of the time-varying integrated fluorescence intensity resulted in a 100% accuracy in classifying liquid samples between high and low metabolite concentrations. An extension of application of the experiment model for analysis of body fluids such as urine is also discussed.

Tuning Molecular Motion Enhances Intrinsic Fluorescence in Peptide Amphiphile Nanofibers.

Peptide amphiphiles (PAs) are highly tunable molecules that were recently found to exhibit aggregation-induced emission (AIE) when they self-assemble into nanofibers. Here, we leverage decades of molecular design and self-assembly study of PAs to strategically tune their molecular motion within nanofibers to enhance AIE, making them a highly useful platform for applications such as sensing, bioimaging, or materials property characterization. Since AIE increases when aggregated molecules are rigidly and closely packed, we altered the four most closely packed amino acids nearest to the hydrophobic core by varying the order and composition of glycine, alanine, and valine pairs. Of the six PA designs studied, C16VVAAK2 had the highest quantum yield at 0.17, which is a more than 10-fold increase from other PA designs including the very similar C16AAVVK2, highlighting the importance of precise amino acid placement to anchor rigidity closest to the core. We also altered temperature to increase AIE. C16VVAAK2 exhibited an additional 4-fold increase in maximum fluorescence intensity when the temperature was raised from 5 to 65 °C. As the temperature increased, the secondary structure transitioned from β-sheet to random coil, indicating that further packing an already aligned molecular system makes it even more readily able to transfer energy between the electron-rich amides. This work both unveils a highly fluorescent AIE PA system design and sheds insights into the molecular orientation and packing design traits that can significantly enhance AIE in self-assembling systems.

Structure and Luminescent Properties of Niobium-Modified ZnO-B2O3:Eu3+ Glass.

The effect of the addition of Nb2O5 (up to 5 mol%) on the structure and luminescent properties of ZnO-B2O3 glass doped with 0.5 mol% (1.32 × 1022) Eu2O3 was investigated by applying infrared (IR), Raman and photoluminescence (PL) spectroscopy. Through differential thermal analysis and density measurements, various physical properties such as molar volume, oxygen packing density and glass transition temperature were determined. IR and Raman spectra revealed that niobium ions enter into the base zinc borate glass structure as NbO4 tetrahedra and NbO6 octahedra. A strong red emission from the 5D0 level of Eu3+ ions was registered under near UV (392 nm) excitation using the 7F0 → 5L6 transition of Eu3+. The integrated fluorescence intensity ratio R (5D0 → 7F2/5D0 → 7F1) was calculated to estimate the degree of asymmetry around the active ion, suggesting a location of Eu3+ in non-centrosymmetric sites. The higher Eu3+ luminescence emission observed in zinc borate glasses containing 1-5 mol% Nb2O5 compared to the Nb2O5-free zinc borate glass evidences that Nb2O5 is an appropriate component for modifying the host glass structure and improving the emission intensity.

Application of chelation effect in improving the triple properties of K2SiF6Mn4+ phosphors through composite modification

Mn4+-doped fluoride phosphors are limited by their poor moisture resistance in practical applications of white light-emitting diodes (WLEDs). Herein, a new red light-emitting phosphor KSF:MnK2SiF6:Mn4+ was synthesized based on a novel strategy combining surface treatment with hexamethylene tetramine (HMTA) and coating with a matrix, hereafter referred to as P-KSF:Mn. Given the formation of the coordination bond between N and Mn4+ and the strong hydrogen bond between N and F in the shell after the protonation of HMTA, a dense and firm shell of rare Mn4+ formed on the sample surface. P-KSF:Mn showed strong emission, waterproof property and luminescent thermal stability, and its fluorescence intensity was 1.81 times that of KSF:Mn. After soaking in water for 90 d, the fluorescence intensity of P-KSF:Mn was 90.7 % of the initial value. The integrated fluorescence intensity at 200 °C was approximately 416 % of the initial value at 25 °C. The strong luminous thermal stability was supported by strong negative thermal quenching (NTQ), which is explained by the phonon induction mechanism. The WLED prototype assembled with P-KSF:Mn emitted warm white light with correlated color temperature (CCT) = 3112 K, color rendering index (CRI) = 90.7, and luminous efficiency (LE) = 119 lm/W. The results show that P-KSF:Mn is a potential candidate for applications in the field of warm WLEDs.

Quantitative fluorescence spectroscopy of living bacteria by optical condensation with a bubble-mimetic solid–liquid interface

Microbial interactions are closely related to human health, and secreted signal molecules from bacteria determine the gene expression of bacteria following bacterial cell density and signal molecule density. However, the conventional quantitative analysis of the number of bacteria requires several days using standard cultivation methods, and the detection of molecules secreted via microbial interactions is difficult since they are in extremely small amounts. In this study, we performed local fluorescence spectroscopy to quantitatively evaluate the density of the assembly of dispersoids (fluorescent microparticles and bacteria) under optical condensation at a solid–liquid interface on our developed bubble-mimetic substrate, which exhibits extremely low thermal damage after a few minutes of laser irradiation. The obtained results showed that the fluorescence intensity spectrum was positively correlated with the concentration of dispersoids even when only several tens of assembled microparticles were observed. Furthermore, a calibration curve was obtained by plotting the integrated fluorescence intensity by integrating the fluorescence intensity spectrum over the observed wavelength, and the concentration of living bacteria was quantitatively analyzed. The clarified mechanism of local fluorescence spectroscopy under optical condensation will pave the way for rapid and precise analysis of bacteria and their secreted biomolecules labeled with fluorescent dye.

Reductant-optimized exchange strategy to construct the water-resistant shell of Mn4+-doped phosphors

Solving the problem of poor moisture resistance of Mn4+-doped fluoride red light-emitting phosphors is the key to promoting their application in white light-emitting diodes (WLEDs). In this paper, a reductant-optimized exchange strategy is proposed, that is, treating phosphors in NH4F (40 %) solution with FeSO4 to form a Mn4+-free shell on its surface to improve the moisture resistance as well as to block energy transfer to surface defects. The thickness of the Mn4+-free shell was about 900 nm as characterized by FIB-SEM. The integrated fluorescence intensity of the treated sample (R-KTF:0.05Mn4+) was 1.07 times that of the untreated sample. The internal quantum yield (QYi) was 98 %. After testing in extreme hydrolysis environments (high temperature, high pressure, high humidity), it decreased to 93 %, which is significantly higher than the results of the in-situ passivation strategy (QYi = 28 %) and the reverse cation-exchange strategy (QYi = 37 %). Finally, aging results at 85 °C and 85 % relative humidity further confirmed that the application of this strategy resulted in a significant improvement in the operational stability of the WLEDs.

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging

An Integration Strategy to Develop Dual-State Luminophores with Tunable Spectra, Large Stokes Shift, and Activatable Fluorescence for High-Contrast Imaging

Quantifying contrast of latent fingerprints developed by fluorescent nanomaterials based on spectral analysis

Fluorescent nanoparticles (NPs) have been used to develop latent fingerprints with enhanced contrast. However, a method for quantifying the contrast is still lacking, making it impossible to achieve quantitative comparison in the contrast enhancement between different fingerprint developing agents. Here we proposed a new method to quantify the developed contrast using two indexes when fluorescent NPs were used to develop the latent fingerprint. One is the intensity index (I) defined as the ratio between the integrated fluorescence intensities of the signal and background in the fluorescence spectra of the developed fingerprint. Another is the chroma index (C) determined from the color difference between developed fingerprints and their substrates in the chromaticity graph. We defined the developed contrast as the product of the chroma index and the common logarithm of the intensity index (C·lg I), and validated this method using both down- and up-conversion fluorescent NPs and on a variety of different substrates (glass, marble, red paper and money). We showed that the developed contrast quantified by our method effectively reflected the true contrast but the intensity or chroma index alone was not always effective. This work opens up a new avenue to quantifying and enhancing the developed contrast.

A clustering of red wines based on physicochemical and optical properties

Sixty-nine samples of red wines, produced in different regions of Bulgaria, Chile and South Africa from the Merlot (42 samples) and Cabernet Sauvignon (27 samples) grape varieties are characterized by 13 physicochemical and optical properties. The physicochemical characteristics (antioxidant activity and anthocyanin content) have been obtained spectrophotometrically, while the antioxidant activity (AOA) has been measured by using both DPPH and ABTS methods. Based on a hierarchical cluster analysis with an average linkage algorithm, the studied wines from grape variety Merlot as well as the ones from grape variety Cabernet Sauvignon, according to their antioxidant activities (AOA ABTS and AOA DPPH) and anthocyanins content are grouped into three generalized groups. When integral fluorescence intensities at an excitation wavelength of 265 nm are added as a factor, for the wines from the grape variety Cabernet Sauvignon there is not any difference in their grouping, and for the ones from grape variety Merlot, the only difference is that one sample of wine passes to the first cluster. The results, obtained from the clustering procedure are presented graphically by dendrograms.

Estimation of places of production of porcelains of unknown origins excavated at the Mietsu Naval Facility site based on differences in the solubility of trace metals during the elutriation process

More than 300 porcelains of unknown origins were excavated at the Mietsu Naval Facility site in Japan in 2009, which was designated by UNESCO as a World Heritage Site in 2015. Forty-nine representative porcelain pieces were chosen and the metals in the porcelains were identified to clarify their places of production by using the synchrotron-based X-ray fluorescence method. The metal composition of porcelains was analysed by a new method designed by the authors based on the difference in the solubility of metal ions during the elutriation process carried out during the manufacturing of porcelain. Niobium (Nb) and zirconium (Zr), which are barely soluble in water, become a part of the clay, whereas rubidium (Rb), which is highly soluble in water, easily gets discharged with the upward flow of water during elutriation. The plotting of integrated fluorescence intensity ratio of Zr/Nb vs. Rb/Nb led to the porcelains being distinguished into three groups based on their places of production: Hasami, Shida, and Arita in Hizen. X-ray diffraction (XRD) patterns of the porcelains and the XRD patterns of the powdered raw pottery stones were determined. Differences in the XRD patterns are also discussed in terms of identifying the production areas of the excavated porcelains.

Method for detecting and quantitating capture of organic molecules in hypervelocity impacts

Enceladus is a prime candidate in the solar system for in-depth astrobiological studies searching for habitability and life because it has a liquid water ocean with significant organic content and ongoing cryovolcanic activity. The presence of ice plumes that jet up through fissures in the ice crust covering the sub-surface ocean, enables remote sampling and in-situ analysis via a fly-by mission. However, capture and transport of organic materials to organic analyzers presents distinctive challenges as it is unknown whether, and to what extent, organic molecules imbedded in ice particles can be captured and survive hypervelocity impacts. This manuscript provides a fluorescence microscopic method to parametrically determine the amount of an organic fluorescent tracer dye, Pacific Blue™ (PB) deposited on a metallic surface. This method can be used to measure the capture and survival outcomes of terrestrial hypervelocity impact experiments where an ice projectile labeled with Pacific Blue impacts a soft metal surface. This work is an important step in the advancement of instruments like the Enceladus Organic Analyzer for detecting biosignatures in an Enceladus plume fly-by mission.An apparatus consisting of a substrate humidification shroud coupled with an epifluorescence microscope with CCD detector is developed to measure the intensity of quantitatively deposited Pacific Blue droplets under controlled humidity.Calibration curves are produced that relate the integrated fluorescence intensity of humidified PB droplets on metal foils to the number of PB molecules deposited.To demonstrate the utility of this method, our calibrations are used to analyze and quantitate organic capture and survival (up to 11% capture efficiency) following ice particle impacts at a velocity of 1.7 km/s on an aluminum substrate.

Флуоресцентные свойства гуминовых кислот почв разных условий формирования

The purpose of the study. To identify the features of humic acids of soils of different formation conditions using quantitative indicators of fluorescence spectra. Place and time of the event. The research was carried out on the territory of Siberia, where in the period 2000-2021, key areas with different natural conditions were identified in different regions. Methodology. Humic acids (HA) are considered as an independent component of the system of humus substances (SHS) of soils, the properties of which depend on the ecological conditions of formation. Soil samples were taken during the period of the most stable state of the system of humus substances in a continuous column every 5–10 cm and (or) less within the visible boundaries of genetic horizons. The HA preparations were isolated with 0.1 n NaOH after preliminary soil decalcification followed by precipitation with 2 n HCl. Additional purification from ash elements was not carried out. Fluorescence spectra of humic acid solutions with the same concentration of the substance (0.01 % HA) at pH of 13 were recorded in the wavelength range of 300–650 nm on an Agilen Cary Eclipse Fluorescence Spectrophotometer at an excitation wavelength of 330 nm. The main results. The average statistical quantitative indicators of the fluorescence spectra of humic acids of soils formed under different natural conditions were calculated: the position of the fluorescence maximum (λmax), the value of the first moment (M1), and the ratio of the integral fluorescence intensities in the areas of its maximum manifestation in the red and blue parts of the spectrum (coefficient α). The results showed that soils formed in different natural conditions have different ranges of values of all quantitative indicators of the fluorescent properties of humic acids. They differ significantly in tundra soils of plain and mountainous conditions, within the same mountainous country due to vertical zonality, within the same territory with ring zonality due to the change of humidification areas, and with other qualitative differences in the natural environment forming them. It is shown that M1 reflects the configuration features of humic acids due to the conditions of soil formation, while the coefficient α reflects the state of this soil component during the period of soil sampling depending on the local conditions of their functioning. Conclusion. The analysis of quantitative parameters of the fluorescence spectra of humic acids of soils of different conditions of formation made it possible, using emission spectra at one excitation wavelength (330 nm), to identify the specifics of the fluorescent properties of humic acids, which manifests itself in the position of the fluorescence maximum on the spectral scale, the value of the first moment and the ratio of the values of integral intensities in the long-wave and short-wave spectral regions. The data showed that the fluorescence maximum as well as the value of the first moment in mountain-tundra soils lies within very narrow limits and is among the lowest values identified in our studies. Humic acids of plain tundra soils differ significantly from their mountain analogues in all indicators of fluorescent properties. In conditions of vertical zonation in the direction from the zone of tundra soils to the zone of steppe mountain areas, a shift of the fluorescence maximum towards an increase in the wavelength is observed, however, it does not go beyond the boundaries of the blue region of the spectrum. The maximum values of these indicators are characteristic of the fluorescence of GC soils of steppe areas of intermountain basins and steppe areas of plain conditions of the Trans-Urals and Altai Region Territory. The assessment of the significance of humic acid differences in the fluorescence properties of soils of hillocks and sports of plain tundra showed that the values of λ and M differ by 10 and 7 units, respectively, and that the differences between them are significant. Differences for other objects formed in different natural conditions at the local level in the absolute majority of cases turned out to be significant. The existence of a close correlation of the values of quantitative indicators of the fluorescent properties of humic acids with the ratio of the main structure–forming elements - H:C and with climatic parameters is shown, using the example of mountain soils of Tuva and pedogenically processed deposits of the archaeological monument Grotto Obi-Rahmat, which allows us to recommend the use of these easily and quickly obtaining characteristics as an indicator for assessing the state of soils and the natural environment.

The Regenerative Potential of Donkey and Human Milk on the Redox-Sensitive and Proliferative Signaling Pathways of Skin Fibroblasts.

The influence of milk bioactive peptides on skin regenerative potential and rejuvenation is very often limited because of allergic reactions. The current study is aimed at exploring the influence of donkey colostrum and mature milk, human colostrum and mature milk, and β-casein and β-casomorphine-7, on the growth and inflammatory response of the culture of cultured skin fibroblasts exposed to these conditions for twenty-four hours. Their effects on the growth-regulatory kinases and redox-sensitive, proinflammatory transcriptional factor NF-κB were detected by using specific primary antibodies against NF-κB p65, Akt-1, phospho-Akt-1, Erk-1, phospho-Erk-1, JNK, phospho-JNK, phospho-STAT-1, and CD26, while logarithmic integrated fluorescence intensity patterns were recorded by flow cytometry. The downregulation of NF-κB p65 was observed after the exposure of skin fibroblasts to donkey milk and human colostrum, while β-casein and β-casomorphine-7 exerted the opposite effect, which suggests that noncasein bioactive peptides of donkey and human milk may be responsible for anti-inflammatory properties. The exposure to all milk species examined and β-casein leads to the activation of growth-regulatory kinases (Akt1/2/3 kinase, Erk kinase, JNK kinase, and Stat-1 kinase), especially for the p-Erk pathway, which suggests that essential amino acids of casein may be responsible for Erk-induced cell cycle activation and proliferation. The opposite effect was observed when cells were exposed to β-casomorphine-7, which may affect the skin fibroblast survival and their proliferative and regenerative potential. Donkey milk did not significantly change the CD26 antigen expression. In conclusion, our results suggest that among cell signaling molecules, the most sensitive but nonspecific downstream effector is p-Erk kinase, which may point to donkey milk usefulness in wound healing, regenerative, and aesthetic dermatology. The noncasein bioactive peptides of donkey milk may be responsible for the anti-inflammatory property of donkey milk and colostrum, which may indicate the usefulness in the treatment of inflammatory skin diseases.

LIF diagnostics for selective and quantitative measurement of PAHs in laminar premixed flames

Laser-induced fluorescence (LIF) technique has been widely applied in PAH measurement in sooting flames, but it is still a big challenge to quantitatively identify the specific PAH species due to the complexities of spectral characteristics and calibration method. In this study, we aimed at developing a spectral-resolved LIF analytic model that can obtain PAH mole fractions in flames. A comprehensive LIF spectrum database in the wide temperature and concentration ranges was firstly established by the LIF experiments of gas-phase PAHs in an optical cell. Then, a spectral-resolved LIF analytic model was presented based on linear superposition regulation and an optimization fitting algorithm, and the LIF spectra of PAH components can be decomposed from the LIF spectra of the flame using this model. Finally, the integral fluorescence intensities of each PAH component were calibrated to their mole fractions by the calibration factors at corresponding temperatures. In this way, we can measure the mole fractions of several PAHs. Subsequently, the presented LIF method was applied to investigate the PAH formation characteristics at different flame temperatures. The experimental results showed that the mole fractions of each PAH except naphthalene decreased around 60% to 70% when the temperature increased from 1186 K to 1483 K, while the mole fraction of naphthalene kept nearly constant. The mole fractions simulated by a chemical kinetic model well reproduce the experimental results. According to the chemical kinetic analysis, C2H2 oxidation reaction was promoted and the C2H2-addition reactions were suppressed by increasing temperatures, which suppressed the PAH formation.

Preconcentration with Chlorella vulgaris combined with energy dispersive X-ray fluorescence spectrometry for rapid determination of Cd in water.

Freshwater green algae Chlorella vulgaris was selected as an adsorbent, and a simple, rapid, economical and environmentally friendly method for the detection of heavy metal Cd in water samples based on preconcentration with C. vulgaris combined with energy dispersive X-ray fluorescence (EDXRF) spectrometry was proposed. Chlorella vulgaris could directly and rapidly adsorb Cd2+ without any pretreatment, and the maximum adsorption efficiency could be obtained when the contact time was 1 min with an optimal pH of 10. The obtained Cd-enriched thin samples after preconcentration with C. vulgaris by suction filtration of reaction solution had very good uniformity, which could be directly measured by EDXRF spectrometry, and the net integral fluorescence intensity of Cd Kα characteristic peak had a very good linear relationship with the initial concentration of Cd in the range of 0.703–74.957 µg ml−1 with a correlation coefficient of 0.9979. When the Cd thin samples with a Cd-enriched region of 15.1 mm in diameter were formed by the developed preconcentration method with suction filtration of 10 ml reaction solution, the detection limit of this method was 0.0654 µg ml−1, which was lower than the maximum allowable discharge concentration of Cd in various industrial wastewaters. The proposed method was simple to operate, and could effectively remove the influence of matrix effect of water samples and effectively improve the sensitivity and stability of EDXRF spectrometry directly detecting heavy metals in water samples, which was successfully applied to detect Cd in real water samples with satisfactory results, and the recoveries ranged from 94.80% to 116.94%. Moreover, this method can be applied to the rapid detection and early warning of excessive Cd in discharged industrial wastewaters. This work will provide a methodological basis for the development of rapid and online monitoring technology and instrument of heavy metal pollutants in water.

Investigation on the Flame Front and Flow Field in Acoustically Excited Swirling Flames with and without Confinement

ABSTRACT Open and confined dimethyl ether/air swirling flames were investigated with an acoustically excited swirling burner. Simultaneous particle-image velocimetry and formaldehyde planar laser-induced fluorescence were measured using a high repetition rate burst-mode laser at 20 kHz. Time-averaged velocity field, vorticity and flame brush cloud were compared under different confinements and acoustic excitation conditions. The integrated fluorescence intensities are similar while the open flame has dramatically large fluorescence areas. Time-resolved velocity field and flame brush were measured to investigate the continuous evolution of swirling flame front and acoustically induced vortex. The flame brush was found to be much dispersed in the open flame due to the mixing effect from the surrounding air. Flame root and flame angle were extracted and analyzed statistically using the fluorescence images. Different stages of acoustically induced vortex were observed in both confined and open cases. The vortex trajectory along the outer shear layer determines that the flame tip can perceive the vortex instead of the flame base. The flame regions affected and unaffected by acoustically induced vortex indicate different perturbation mechanisms for the heat release.

Fluorescence photo-bleaching of urine and its applicability in oral cancer diagnosis.

Photo-stability of urine is of crucial importance for the applicability of fluorescence spectroscopy of urine samples for diagnosis of cancer. We report the results of a detailed study on fluorescence photo-bleaching of human urine samples. We also present the results of a preliminary investigation on evaluation of the applicability of photo-bleaching characteristics of urine for discriminating patients with oral cancer from healthy volunteers. The time-lapse fluorescence induced by continuous shining of 405 nm radiation from a diode laser was recorded from the urine samples obtained from 18 patients with oral cancer as well as from 22 healthy volunteers with history of no known major illness in the past two months. The integrated fluorescence intensity (ΣI), calculated for each spectrum, was found to decrease with time till a point after which no further decrease was observed. Further, while significant differences were observed in the spectra of cancerous patients and healthy volunteers, these differences were found to be varying with time till the intensities of the observed fluorescence spectra corresponding to the two categories of urine samples became stable. The curve, generated by plotting ΣI vs. time, was found to be best fitted (R2 > 0.95) with a double-exponential decay function. The photo-bleaching constants, obtained from curve-fitting, were found to have statistically significant differences corresponding to the urine samples of cancerous patients and healthy volunteers. A classification algorithm developed based on nearest-mean classifier (NMC) and applied on the photo-bleaching constants in leave-one-subject-out cross-validation mode was found to provide a sensitivity and specificity of up to ∼ 86% in discriminating the two categories of urine samples.

Investigation on the LIF spectrum superposition of gas-phase PAH mixtures at elevated temperatures: potential for the analysis of PAH LIF spectra in sooting flames

Laser-induced fluorescence (LIF) technique has been widely used to measure the polycyclic aromatic hydrocarbons (PAHs) in sooting flames, but the assignment of the LIF signals measured in flames to specific PAH species is hard to obtain. Investigation on the LIF spectra of gas-phase PAH mixtures could be helpful to analyze LIF spectra measured in flames for more detailed PAH information. In this study, the LIF spectra of gas-phase PAH mixtures containing naphthalene, phenanthrene, pyrene, fluoranthene were experimentally investigated in an optical cell at 673 K and 1073 K. The experimental results indicated that the integral fluorescence intensity of each PAH was in direct proportion to its mole fraction. Moreover, the LIF spectra of PAH mixtures were linearly superposed from the spectra of their components weighted using mole fractions. The component concentrations of the PAH mixtures were able to be fitted from the LIF spectra using multiple linear regression method, and most of the relative errors were less than 5%. In the light of these results from gas-phase PAHs, the LIF spectra of flame-formed PAHs measured in a laminar premixed ethylene flame were discussed. Considering the temperature effects on LIF spectra and simulated PAH concentrations in the flame, the lighter PAHs will contribute to the fluorescence signals shorter than 450 nm measured in the flame. Using the multiple linear regression method established in this study, the relative ratios of naphthalene, phenanthrene and pyrene can be fitted from the LIF spectrum of the flame. In this way, more selective information of these lighter PAHs can be obtained from the LIF spectrum measured in flames. On the other hand, fluorescence signals in the flame longer than 450 nm are possibly emitted from the PAHs with five-membered-ring structures or (and) nanoparticles and nascent soot particles, which are still ambiguous and needs to be further investigated in future works.