The application of laser‑induced fluorescence in oil spill detection

Over the past two decades, oil spills have been one of the most serious ecological disasters, causing massive damage to the aquatic and terrestrial ecosystems as well as the socio-economy. In view of this situation, several methods have been developed and utilized to analyze oil samples. Among these methods, laser-induced fluorescence (LIF) technology has been widely used in oil spill detection due to its classification method, which is based on the fluorescence characteristics of chemical material in oil. This review systematically summarized the LIF technology from the perspective of excitation wavelength selection and the application of traditional and novel machine learning algorithms to fluorescence spectrum processing, both of which are critical for qualitative and quantitative analysis of oil spills. It can be seen that an appropriate excitation wavelength is indispensable for spectral discrimination due to different kinds of polycyclic aromatic hydrocarbons' (PAHs) compounds in petroleum products. By summarizing some articles related to LIF technology, we discuss the influence of the excitation wavelength on the accuracy of the oil spill detection model and proposed several suggestions on the selection of excitation wavelength. In addition, we introduced some traditional and novel machine learning (ML) algorithms and discussed the strengths and weaknesses of these algorithms and their applicable scenarios. With an appropriate excitation wavelength and data processing algorithm, it is believed that laser-induced fluorescence technology will become an efficient technique for real-time detection and analysis of oil spills.

Wavelength-dependent photoelectrochemical response demonstrated by the determination of acetaminophen and rutin in differential molecularly imprinted polymers strategy

Herein, the excitation wavelength-dependent responses of the molecularly imprinted polymer (MIP) photoelectrochemical (PEC) sensors were investigated, using acetaminophen (AP), rutin (RT) and perfluorooctanoate (PFOA) as the model templates, pyrrole as functional monomer, CuInS2@ZnS/TiO2 NTs as the basic photoelectrode. With wavelength λ > 240 nm, the photocurrent of MIPPFOA enhanced at higher concentrations of PFOA. With increasing AP concentration, the photocurrents of MIPAP could decline with λ < 271 nm, not change at λ = 270 nm, or increase with λ > 270 nm. As RT concentration increased, the photocurrents of MIPRT could decrease (λ < 431 nm), not change (λ = 431 nm) or increase (λ > 431 nm). The PEC responses depend on the comprehensive interaction of two contrary mechanisms from the template molecules within the MIP membrane. The photocurrent is enhanced by the role of the electron donor for photo-generated holes but attenuated due to the steric hindrance effect and the excitation light intensity loss via absorption or scattering. The apparent molar absorption coefficient of AP and RT within MIP membranes are 9.1-19.4 folds of those measured from dilute solutions. By using a routine UV lamp as the light source, the photocurrents of MIPRT at 254 nm and MIPAP at 365 nm were used to determine RT and AP, with the detection limits of 5.3 and 16 nM, respectively. The interference from the non-specific adsorption of interferents on the surfaces of MIPAP and MIPRT was reduced by one order of magnitude via a differential strategy.

Confocal Raman spectroscopy at different laser wavelengths in analyzing stratum corneum and skin penetration properties of mixed PEGylated emulsifier systems

Emulsifier mixtures are widely used in cosmetics and pharmaceutics and thus, brought extensive studies for their performances on skin applications. PEG-20cetyl ether (C20) is recently proposed to induce skin irritation and is of interest to study its skin interactions when mixed with other emulsifiers. PEG-2oleyl ether (O2) and PEG-20stearyl ether (S20) are selected and in specific, 50 mM of C20, O2, S20 as well as Mix1 (50 mM C20 mixed with 50 mM O2) and Mix2 (50 mM C20 mixed with 50 mM S20) solutions were applied on skin samples. Confocal Raman spectroscopy (CRS) analyses of stratum corneum (SC) thickness and SC lipid content were performed after 4 h skin treatments. In parallel, skin penetration properties were also evaluated via CRS by applying procaine solutions with/without emulsifiers on skin samples for 24 h. In terms of the CRS measurements, two excitation wavelengths of 532 nm and 785 nm are both utilized in this study and we secondly aimed to compare their results and suitability in SC and skin analyses. Based on the experimental observations, comparable results are obtained by using both excitation wavelengths of 532 nm and 785 nm demonstrating their suitability in analyzing SC and skin samples. Thereinto, 785 nm laser wavelength shows the advantage of deeper skin penetration and allows the measurements of fluorescent skin samples; 532 nm laser wavelength enables simple measurement performance without substrate and coverslip interference. With regards to the results of emulsifier mixtures, the addition of S20 and O2 reduced the skin interactions and penetration enhancing ability of C20, giving us the hint to build milder systems with emulsifier mixtures. Besides, the CRS results of stronger skin interruption were also correlated with the higher critical micelle concentration (CMC) values of emulsifiers and their mixtures, which may provide evidence in explaining the interactions between emulsifiers and skin.

Fluorescence spectroscopy method for estimation of Ivabradine in bulk and the tablet dosage form

A simple and sensitive spectrofluorimetric method has been developed for the estimation of Ivabradine HCl in bulk and the tablet dosage form. Ivabradine HCl in methanol produces fluorescence at 325 nm (λem) with excitation at 287 nm (λex). The linearity range was found to be 100-500 ng/ml with a correlation coefficient of 0.999. The limit of detection (LOD) and limit of quantitation (LOQ) for the developed method were found to be 8.38 and 25.39 ng/ml, respectively. The developed method was found to be specific, sensitive, accurate, and precise. It was successfully used for the estimation of Ivabradine HCl in its tablet dosage form. The content of Ivabradine HCl in marketed formulations was found to be 101.25 ± 1.16 % of label claims.

Spectroscopic and Photo-Physical Properties of Near-IR Laser Dye in Novel Benign Green Solvents

IR-792 as near IR (NIR) laser dye was dissolved with different concentrations in two types of ionic liquids (ILs) of different anion and cation, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI) & 1-Butyl-3-methylimidazolium tetrafluoroborate (BMIM BF₄), as the benign green solvent and in methanol (MeOH) as a standard solvent. The behavior of fluorescence of IR-792 dye was studied. The fluorescence of IR-792 dissolved in the ILs was heavily compared to organic solvent. Some photo-physical parameters of IR-792 were calculated. Mainly, IR-792 had a very low quantum yield of fluorescence with high intersystem crossing rate & fluorescence lifetime in picosecond range. Optical absorption and behavior of fluorescence for the rigorously the purified imidazolium ILs in the neat condition and effect of IR-792 on their fluorescence have been examined. The emission behavior of IR-792 in green solvents was independent upon the wavelength of excitation, while the emission behavior of green solvents dependent upon the wavelength of excitation whether in pure state or with NIR laser dye. At most, the intensity of fluorescence of ILs is dependent upon dye concentration.

Absolute luminescence quantum yield for nanosized carbon particles in water as a function of excitation wavelength

The absolute luminescence quantum yield Q as a function of excitation wavelength λ_ex in a wide spectral range 270-470 nm was measured for the first time for the group of carbon nanoparticles dispersed in water: carbon dots (CD), detonation nanodiamonds (DND), as well as detonation nanodiamonds decorated with carbon dots (CD-DND). The luminescence quantum yield for DND increased after functionalization; the CD-decorated DND demonstrated significantly higher Q values in the UV region of excitation. We found that the quantum yield for CD luminescence is 4-8 times higher than that for CD-DND luminescence, and 20 times higher than that for DND luminescence. Roughly three spectral regions can be distinguished within the Q(λ_ex): below 330 nm, 330-390 nm and 390-470 nm. Conclusions are drawn about the number of chromophores of the studied nanoparticles and transfer of photoexcitation energy in the systems under consideration.

A practical fluorometric assay method to measure lysosomal acid lipase activity in dried blood spots for the screening of cholesteryl ester storage disease and Wolman disease

Fluorometric measurements of 4-methylumbelliferone (4-MU) are generally used to screen lysosomal storage diseases (LSDs) using dried blood spots (DBSs). However, in DBS, it is difficult to measure lysosomal acid lipase (LAL) activity due to the influence of other lipases in whole blood. Recently, Hamilton used a fluorometric enzyme assay with 4-MU derivatives to measure the LAL activity in DBS. This method requires mercury chloride as stopping reagent, and the fluorescence intensity of 4-MU was measured at an acidic pH. We report a revised method to measure the LAL activity without using toxic mercury chloride and to measure the fluorescence intensity of 4-MU at a basic pH. For this measurement, we established a more practical method that does not require mercury chloride. The LAL activity in DBS was measured in 51 normal controls, seven obligate carriers and seven patients with CESD. The average LAL activities ± SD in the DBS from the normal, obligate carriers and CESD patients were 0.68 ± 0.2 (range: 0.3-1.08), 0.21 ± 0.1 (range: 0.11-0.41) and 0.02 ± 0.02 (range: 0-0.06) nmol/punch/h, respectively. There was a significant difference between the normal and the CESD. Our method does not require toxic mercury chloride and is an appropriate revised enzyme assay using DBS for screening patients with CESD.