A fluorescence-based multivariate method for biodiesel quantification in undiluted diesel-biodiesel blends without sample preparation.

In this work, excitation-emission matrices (EEMs) were used in association with parallel factor analysis (PARAFAC) to assess biodiesel content in undiluted diesel-biodiesel blends (DBBs) without pre-sample preparation. EEMs were decomposed using the PARAFAC (EEMs-PARAFAC), and the loading values of the PARAFAC component as a function of biodiesel content in the blends were used to build an analytical model to quantify the biodiesel content in DBBs. The proposed model presenting a limit of detection (LOD) and a limit of quantification (LOQ) of 2.5% and 11% w/w, respectively, successfully predicted the biodiesel content in the validation samples. The robustness of the model was confirmed by a close analysis of the root mean square error of prediction, standard error of prediction, relative standard deviation of prediction, and Bias. Therefore, an accurate and robust analytical model based on EEMs-PARAFAC was developed to quantify the biodiesel content in undiluted DBBs without sample preparation.

Dissolved organic matter in bovine slaughterhouse wastewater using fluorescence spectroscopy associated with CP/PARAFAC and PCA methods.

In this work, we evaluated the potential application of fluorescence spectroscopy, associated with the canonical polyadic/parallel factor analysis and principal component analysis, to monitor the dissolved organic matter (DOM) generated from a slaughterhouse industry. During the monitoring process, we analyzed the residual water at the entrance and exit sites of the slaughterhouse effluent treatment as well as downstream and upstream the effluent receiving water body of a local river. The results revealed that the fluorescence analysis was able to identify proteins, chlorophylls, and humic substances at the entrance and exit sites of the slaughterhouse treatment plant and humic substances at the river water bodies. Our data also demonstrated that the industrial effluent discharged into the river did not impact the receiving water body quality as determined by the biological and humification indices obtained by fluorescence analysis, which was confirmed by conventional physicochemical analysis. In summary, the present findings indicate that fluorescence spectroscopy, in association with multivariate analysis, can be successfully applied as an analytical tool for evaluating the quality of DOM in slaughterhouse wastewater.

Laser-Induced Breakdown Spectroscopy Associated with the Design of Experiments and Machine Learning for Discrimination of Brachiaria brizantha Seed Vigor.

Laser-induced breakdown spectroscopy (LIBS) associated with machine learning algorithms (ML) was used to evaluate the Brachiaria seed physiological quality by discriminating the high and low vigor seeds. A 23 factorial design was used to optimize the LIBS experimental parameters for spectral analysis. A total of 120 samples from two distinct cultivars of Brachiaria brizantha seeds exhibiting high vigor (HV) and low vigor (LV) in standard tests were studied. The raw LIBS spectra were normalized and submitted to outlier verification, previously to the reduction data dimensionality from principal component analysis. Supervised machine learning algorithm parameters were chosen by leave-one-out cross-validation in the test samples, and it was tested by external validation using a new set of data. The overall accuracy in external validation achieved 100% for HV and LV discrimination, regardless of the cultivar or the classification algorithm.

Metronidazole-loaded gold nanoparticles in natural rubber latex as a potential wound dressing.

Gold nanoparticles (AuNPs) have shown interesting properties and specific biofunctions, providing benefits and new opportunities for controlled release systems. In this research, we demonstrated the use of natural rubber latex (NRL) from Hevea brasiliensis as a carrier of AuNPs and the antibiotic metronidazole (MET). We prepared AuNP-MET-NRL and characterized by physicochemical, biological and in vitro release assays. The effect of AuNPs on MET release was evaluated using UV-Vis and Laser-Induced Breakdown Spectroscopy (LIBS) techniques. AuNPs synthesized by Turkevich and Frens method resulted in a spherical shape with diameters of 34.8 ± 5.5 nm. We verified that there was no emergence or disappearance of new vibrational bands. Qualitatively and quantitatively, we showed that the MET crystals dispersed throughout the NRL. The Young's modulus and elongation values at dressing rupture were in the range appropriate for human skin application. 64.70% of the AuNP-MET complex was released within 100 h, exhibiting a second-order exponential release profile. The LIBS technique allowed monitoring of the AuNP release, indicating the Au emission peak reduction at 267.57 nm over time. Moreover, the dressing displayed an excellent hemocompatibility and fibroblast cell viability. These results demonstrated that the AuNP-MET-NRL wound dressing is a promising approach for dermal applications.

Direct determination of Cu, Cr, and Ni in river sediments using double pulse laser-induced breakdown spectroscopy: Ecological risk and pollution level assessment.

Double pulse laser-induced breakdown spectroscopy (DP LIBS) has attracted much attention for analyzing trace elements due to its higher sensitivity when compared to single pulse laser-induced breakdown spectroscopy (SP LIBS). However, the development of quantitative methods in LIBS for the analysis of complex samples, such as sediments, is a great challenge due to the matrix effects that are very accentuated in this technique. In this study, different spectral treatments and calibration strategies were investigated to obtain calibration models that allow determinations with satisfactory accuracy and precision of Cr, Cu, and Ni in river sediments from different hydrographic basins. The best model developed for Cr was using MMC without spectral normalization and for Cu and Ni it was using MMC with spectral normalization, and using inverse regression, an increase in the accuracy of the determinations of all analytes was obtained. These models showed limit of quantification (LOQ) of 7.87 mg kg-1, 1.62 mg kg-1, and 2.21 mg kg-1 and root mean square error of prediction (RMSEP) of 7.54 mg kg-1, 14.53 mg kg-1, and 8.29 mg kg-1 for Cr, Cu, and Ni, respectively. Therefore, the models have adequate sensitivity and precision for the quantification of the potentially toxic elements (PTEs) evaluated, since, according to Brazilian legislation, the lower concentration of threshold effect level (TEL) for Cr, Cu, and Ni is <37.3 mg kg-1, <35.7 mg kg-1, and <18 mg kg-1, respectively. The concentrations of Cr, Cu, and Ni determined by DP LIBS allowed to obtain a partial ecological risk assessment of the studied sediments. Also, the chemometric tool Kohonen self-organizing map (KSOM) were used for data interpretation.

Total phosphorus determination in eutrophic tropical river sediments by laser-induced breakdown spectroscopy techniques.

Total phosphorus (TP) in sediments is an important chemical variable in the study of the extent of eutrophication in water bodies. Two methods, based on single pulse (SP) and double pulse (DP) laser-induced breakdown spectroscopy (LIBS), were developed for determining TP in the sediment cores of Brazilian rivers upstream from the Barra Bonita reservoir. TP concentration in the sediments was determined by inductively coupled plasma optical emission spectrometry (ICP OES) on digested samples. Besides, a LIBS system operating in SP and DP modes was used to develop methods for TP quantification in sediment pellets. In LIBS, the most appropriate wavelength to measure P was 214.91 nm. The calibration curves showed correlation coefficients of 0.93 and 0.92 and limits of detection of 709 mg kg-1 and 349 mg kg-1 for SP and DP LIBS, respectively. The two proposed methods were validated and the average percentage errors were 14% and 10% for SP and DP LIBS, respectively. The ICP OES and SP and DP LIBS data showed that the most superficial layers of the Piracicaba River, all the sedimentary layers of the Tietê River, and the confluence region present a high concentration of TP, according to the Brazilian sediment quality criterion. In conclusion, SP and DP LIBS were confirmed as promising alternative tools to traditional analytical methods for monitoring the TP content in the sediments that come from different hydrographic units. The proposed method using DP LIBS proved more sensitive than SP LIBS, but the SP LIBS method demonstrated enough precision for determining TP in eutrophic river sediments.

Evaluation of rice varieties using LIBS and FTIR techniques associated with PCA and machine learning algorithms.

Laser-induced breakdown spectroscopy (LIBS) for atomic multi-elementary analyses, and Fourier transform infrared spectroscopy (FTIR) for molecular identification, are often suggested as the most versatile spectroscopic techniques. The present work aimed to evaluate the performance of both techniques, LIBS and FTIR, combined with principal component analysis (PCA) and machine learning (ML) algorithms in the detection of the composition analysis and differentiation of four different types of rice, white, brown, black, and red. The two techniques were primarily used to obtain the elemental and molecular qualitative characterization of rice samples. Then, LIBS and FTIR data sets were subjected to PCA and supervised ML analysis to investigate which main chemical features were responsible for nutritional differences for the white (milled) and colored rice samples. In particular, PCA data analysis suggested that protein, fatty acids, and magnesium were the highest contributors to the sample's differentiation. The ML analysis based on this information yielded a 100% level of accuracy, sensitivity, and specificity on sample classification. In conclusion, LIBS and FTIR coupled with multivariate analysis were confirmed as promising tools alternative to traditional analytical techniques for composition analysis and differentiation when subtle chemical variations were observed.

Soybean seed vigor discrimination by using infrared spectroscopy and machine learning algorithms.

A novel approach to distinguish soybean seed vigor based on Fourier transform infrared spectroscopy (FTIR) associated with chemometric methods is presented. Batches with high and low vigor soybean seeds were analyzed. Support vector machine (SVM), K-nearest neighbors (KNN), and discriminant analysis were applied to the raw spectral and reduced-dimensionality data from PCA (principal component analysis). Proteins, fatty acids, and amides were identified as the main molecules responsible for the discrimination of the batches. The cross-validation tests pointed out that high vigor soybean seeds were successfully discriminated from low vigor ones with an accuracy of 100%. These findings indicate FTIR spectroscopy associated with multivariate analysis as a new alternative approach to discriminate seed vigor.

Evaluating the applicability of multi-energy calibration as an alternative method for quantitative molecular spectroscopy analysis.

Multi-Energy Calibration (MEC) was recently proposed as an innovative analytical method to be used in efficient and accurate quantitative analysis based on atomic spectroscopy. Here, the applicability of the MEC method for quantifying molecular species using UV-Vis and fluorescence measurements was evaluated for the first time. UV-Vis and fluorescence spectra of the analytical solutions of methylene blue and eosin-methylene blue in two different solvents (distilled-deionized water and methanol) were collected. MEC showed high precision and sensitivity for determining the analyte concentration, providing similar limit of detection and quantification when compared with conventional analytical methods, such as external standard calibration and standard additions. Therefore, the present study has shown that MEC can be successfully applied for quantifying molecular species in a simple and efficient way accounting UV-Vis and fluorescence spectroscopy.

Determination of Pb in soils by double-pulse laser-induced breakdown spectroscopy assisted by continuum wave-diode laser-induced fluorescence.

Laser-induced breakdown spectroscopy (LIBS) has attracted a lot of attention due to its potential to rapidly identify and quantify any chemical element with minimal sample preparation. Despite continuous improvements, the sensitivity of this technique still remains a challenge. In order to increase LIBS intensity, a laser-induced fluorescence (LIF) system can be coupled with LIBS to re-excite a transition of the element in the plasma by employing very expensive optical parametric oscillators (OPO). In this work, a homemade tunable continuum wave-diode laser (CW-DL) has been developed and coupled to a double pulse (DP) LIBS system to enhance the sensitivity of Pb detection in a soil sample at the transition 6s26p2-P32→6s26p7s-P31 at 405.78 nm. Before sample analysis, the production of no scattered light by the plasma was ascertained, and the optimal temperature of 10,000 K was estimated for this transition, feasible to be achieved in DP-LIBS systems. An increase of approximately 100% for the Pb I transition at 405.78 nm was obtained by DP-LIBS-CW-DL-LIF with respect to the DP-LIBS system alone. This result opens a new promising line of research to improve LIBS sensitivity using the CW-DL approach.

Soil organic matter in podzol horizons of the Amazon region: Humification, recalcitrance, and dating.

Characteristics of soil organic matter (SOM) are important, especially in the Amazon region, which represents one of the world's most relevant carbon reservoirs. In this work, the concentrations of carbon and differences in its composition (humification indexes) were evaluated and compared for several horizons (0 to 390cm) of three typical Amazonian podzol profiles. Fluorescence spectroscopy was used to investigate the humic acid (HA) fractions of SOM isolated from the different samples. Simple and labile carbon structures appeared to be accumulated in surface horizons, while more complex humified compounds were leached and accumulated in intermediate and deeper Bh horizons. The results suggested that the humic acids originated from lignin and its derivatives, and that lignin could accumulate in some Bh horizons. The HA present in deeper Bh horizons appeared to originate from different formation pathways, since these horizons showed different compositions. There were significant compositional changes of HA with depth, with four types of organic matter: recalcitrant, humified, and old dating; labile and young dating; humified and young dating; and little humified and old dating. Therefore, the humification process had no direct relation with the age of the organic matter in the Amazonian podzols.

Fluorescence lifetime evaluation of whole soils from the Amazon rainforest.

Time-resolved fluorescence spectroscopy (TRFS) is a new tool that can be used to investigate processes of interaction between metal ions and organic matter (OM) in soils, providing a specific analysis of the structure and dynamics of macromolecules. To the best of our knowledge, there are no studies in the literature reporting the use of this technique applied to whole/non-fractionated soil samples, making it a potential method for use in future studies. This work describes the use of TRFS to evaluate the fluorescence lifetimes of OM of whole soils from the Amazon region. Analysis was made of pellets of soils from an oxisol-spodosol system, collected in São Gabriel da Cachoeira (Amazonas, Brazil). The fluorescence lifetimes in the oxisol-spodosol system were attributed to two different fluorophores. One was related to complexation of an OM fraction with metals, resulting in a shorter fluorophore lifetime. A short fluorescence lifetime (2-12 ns) could be associated with simpler structures of the OM, while a long lifetime (19-66 ns) was associated with more complex OM structures. This new TRFS technique for analysis of the fluorescence lifetime in whole soil samples complies with the principles of green chemistry.

Semiquantitative analysis of mercury in landfill leachates using double-pulse laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS) is showing to be a promising, quick, accurate, and practical technique to detect and measure metal contaminants and nutrients in urban wastes and landfill leachates. Although conventional LIBS presents some limitations, such as low sensitivity, when used in the single pulse configuration if compared to other spectroscopic techniques, the use of the double-pulse (DP) configuration represents an adequate alternative. In this work DP LIBS has been applied to the qualitative and quantitative analysis of mercury (Hg) in landfill leachates. The correlation analysis performed between each intensified charge-coupled device pixel and the Hg concentration allowed us to choose the most appropriate Hg emission line to be used for its measure. The normalization process applied to LIBS spectra to correct physical matrix effects and small fluctuations increased from 0.82 to 0.98 the linear correlation of the calibration curve between LIBS and the reference data. The limit of detection for Hg estimated using DP LIBS was 76 mg Kg-1. The cross validation (leave-one-out) analysis yielded an absolute average error of about 21%. These values showed that the calibration models were close to the optimization limit and satisfactory for Hg quantification in landfill leachate.

Double pulse laser induced breakdown spectroscopy: A potential tool for the analysis of contaminants and macro/micronutrients in organic mineral fertilizers.

Organic fertilizers are obtained from waste of plant or animal origin. One of the advantages of organic fertilizers is that, from the composting, it recycles waste-organic of urban and agriculture origin, whose disposal would cause environmental impacts. Fast and accurate analysis of both major and minor/trace elements contained in organic mineral and inorganic fertilizers of new generation have promoted the application of modern analytical techniques. In particular, laser induced breakdown spectroscopy (LIBS) is showing to be a very promising, quick and practical technique to detect and measure contaminants and nutrients in fertilizers. Although, this technique presents some limitations, such as a low sensitivity, if compared to other spectroscopic techniques, the use of double pulse (DP) LIBS is an alternative to the conventional LIBS in single pulse (SP). The macronutrients (Ca, Mg, K, P), micronutrients (Cu, Fe, Na, Mn, Zn) and contaminant (Cr) in fertilizer using LIBS in SP and DP configurations were evaluated. A comparative study for both configurations was performed using optimized key parameters for improving LIBS performance. The limit of detection (LOD) values obtained by DP LIBS increased up to seven times as compared to SP LIBS. In general, the marked improvement obtained when using DP system in the simultaneous LIBS quantitative determination for fertilizers analysis could be ascribed to the larger ablated mass of the sample. The results presented in this study show the promising potential of the DP LIBS technique for a qualitative analysis in fertilizers, without requiring sample preparation with chemical reagents.

The importance of humin in soil characterisation: A study on Amazonian soils using different fluorescence techniques.

Soil organic matter (SOM) is a complex mixture of molecules with different physicochemical properties, with humic substances (HS) being the main component as it represents around 20-50% of SOM structure. Soil of the Amazon region is considered one of the larger carbon pools of the world; thus, studies of the humic fractions are important for understanding the dynamics of organic matter (OM) in these soils. The aim of this study was to use laser-induced fluorescence spectroscopy (LIFS) and a combination of excitation-emission matrix (EEM) fluorescence with Parallel Factor Analysis (CP/PARAFAC) to assess the characteristics of humin (HU) extracted from Amazonian soils. The results obtained using LIFS showed that there was an increasing gradient of humification degree with depth, the deeper horizon presenting a higher amount of aromatic groups in the structure of HU. From the EEM, the contribution of two fluorophores with similar behaviour in the structures of HU and whole soil was assessed. Additionally, the results showed that the HU fraction might represent a larger fraction of SOM than previously thought: about 80-93% of some Amazon soils. Therefore, HU is an important humic fraction, thus indicating its role in environmental analysis, mainly in soil analysis.

Quantification of total carbon in soil using laser-induced breakdown spectroscopy: a method to correct interference lines.

The C cycle in the Brazilian forests is very important, mainly for issues addressed to climate changes and soil management. Assessing and understanding C dynamics in Amazonian soils can help scientists to improve models and anticipate scenarios. New methods that allow soil C measurements in situ are a crucial approach for this kind of region, due to the costs for collecting and sending soil samples from the rainforest to the laboratory. Laser-induced breakdown spectroscopy (LIBS) is a multielemental atomic emission spectroscopy technique that employs a highly energetic laser pulse for plasma production and requires neither sample preparation nor the use of reagents. As LIBS takes less than 10 s per sample measurement, it is considered a promising technique for in situ soil analyses. One of the limitations of portable LIBS systems, however, is the common overlap of the emission lines that cannot be spectrally resolved. In this study a method was developed capable of separating the Al interference from the C emission line in LIBS measurements. Two typical forest Brazilian soils rich in Al were investigated: a spodosol (Amazon Forest) and an oxisol (Atlantic Forest). Fifty-three samples were collected and analyzed using a low-resolution LIBS apparatus to measure the intensities of C lines. In particular, two C lines were evaluated, at 193.03 and 247.86 nm. The line at 247.86 nm showed very strong interference with Fe and Si lines, which made quantitative analysis difficult. The line at 193.03 nm showed interference with atomic and ionic Al emission lines, but this problem could be solved by applying a correction method that was proposed and tested in this work. The line at 247.86 was used to assess the proposed model. The strong correlation (Pearson's coefficient R=0.91) found between the LIBS values and those obtained by a reference technique (dry combustion by an elemental analyzer) supported the validity of the proposed method.

Effect of photodynamic therapy on the skin using the ultrashort laser ablation.

Photodynamic Therapy (PDT) with 5-aminolevulinic acid (ALA) is known to be limited for applications in tumours of large volume mainly due to the limited penetration of topical photosensitization. The results show that micro-holes created using a femtosecond laser before PDT significantly increased the depth of PDT effect in the healthy tissue. The combination of ultrashort laser ablation technique with PDT showed an important scientific breakthrough related to transportation and delivery of drugs into the deeper regions of the tissue.

Influence of the hydration state on the ultrashort laser ablation of dental hard tissues.

Since about 40 years, laser-based surgical tools have been used in medicine and dentistry to improve clinical protocols. In dentistry, femtosecond lasers have been claimed to be a potential ablation tool. It would, however, be good to perform a more fundamental investigation to understand ablation interaction mechanisms and possible side effects, depending on different specific components of the target tissue. The goal of this study is to show the changes of ablation characteristics in the femtosecond regime at different levels of structural water within dental hard tissues. Thirty human teeth samples were split into three hydration groups and subdivided into dentin and enamel groups (n = 5). The specimens were irradiated using a 70-fs Ti:sapphire laser (with a 1-kHz repetition rate and a 801-nm wavelength output). Ablation was performed using five different power levels and three exposure times. The results clearly show an inversely proportional dependence of the ablation threshold to the hydration level of the tissues. A known mathematical model was adapted in order to include the influence of the changes on the relative fractional composition of dental hard tissues. This analysis was consistent with the experimental results regarding the ablation threshold. High thermal and mechanical damages were observed as a high repetition rate had been applied. Macroscopic images and scanning electron microscopy images were used to preliminarily analyze both the thermal and mechanical damage thresholds, and their variations according to the hydration level present. By manipulating the hydration states, the modifications in the proportions of the molecules that build dental hard tissues clearly shift, and therefore, the characteristics of a plasma-induced ablation change.

Influence of effective number of pulses on the morphological structure of teeth and bovine femur after femtosecond laser ablation.

Femtosecond lasers have been widely used in laser surgery as an instrument for contact-free tissue removal of hard dental, restorative materials, and osseous tissues, complementing conventional drilling or cutting tools. In order to obtain a laser system that provides an ablation efficiency comparable to mechanical instruments, the laser pulse rate must be maximal without causing thermal damage. The aim of this study was to compare the different morphological characteristics of the hard tissue after exposure to lasers operating in the femtosecond pulse regime. Two different kinds of samples were irradiated: dentin from human extracted teeth and bovine femur samples. Different procedures were applied, while paying special care to preserving the structures. The incubation factor S was calculated to be 0.788±0.004 for the bovine femur bone. These results indicate that the incubation effect is still substantial during the femtosecond laser ablation of hard tissues. The plasma-induced ablation has reduced side effects, i.e., we observe less thermal and mechanical damage when using a superficial femtosecond laser irradiation close to the threshold conditions. In the femtosecond regime, the morphology characteristics of the cavity were strongly influenced by the change of the effective number of pulses.

Evidence of 5-aminolevulinic acid (ALA) penetration increase due to microdrilling in soft tissue using femtosecond laser ablation.

Photodynamic therapy (PDT) is a therapeutic technique mainly applied to the treatment of malignant and pre-malignant lesions, which induces cell death by the combined effect of a photosensitizer, irradiation in a proper wavelength, and molecular oxygen. One of the main limitations of PDT using 5-aminolevulinic acid (ALA) is the superficial volume of treatment, mainly due to the limited penetration of topical photosensitization. In this context, the present study investigates if a laser micromachining producing microchannels on the tissue surface could improve ALA penetration and result in an increase in the treatment depth. The laser micromachining under femtosecond regime was performed on the tissue surface of rat livers. Conventional PDT was applied and the induced depth of necrosis with or without laser micromachining was compared. The results showed an increase of more than 20% in the depth of necrosis when the femtosecond laser micromachining was performed before the treatment with the PDT.