Integrated LIBS-Raman spectroscopy: A comprehensive approach to monitor microplastics and heavy metal contamination in water resources

The increased use of plastic products and global industrial conditions have contaminated natural resources, especially water, with pollutants such as microplastics and trace elements, including heavy metals. Hence, continuous monitoring of water samples is an urgent requirement. However, the existing microplastic-heavy metal monitoring methodologies require discrete and sophisticated sampling approaches. The article proposes a multi-modal LIBS-Raman spectroscopy system for detecting microplastics and heavy metals from water resources with unified sampling and pre-processing approaches. The accomplishment of the detection process is using a single instrument by exploiting the trace element affinity of microplastics, which operates in an integrated methodology to monitor water samples for microplastic-heavy metal contamination. The polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) plastic types dominate the identified microplastics from different sampling spots: in an estuary formed by the Swarna River near Kalmadi (Malpe) in Udupi district, and from River Netravathi in Mangalore, Dakshina Kannada District, Karnataka, India. The detected trace elements from microplastic surfaces include heavy metals such as Al, Zn, Cu, Ni, Mn, and Cr and other elements counting Na, Mg, Ca, and Li. The system could record concentrations of trace elements down to 10 ppm, and comparing results with the conventional technique of Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) confirms the ability of the system to detect trace elements from microplastic surfaces. In addition, comparing results with direct LIBS analysis of water from the sampling site shows better results in microplastic-based trace element detection.

Regenerative biomineralization potential of commercially available remineralizing agents as a preventive treatment approach for tooth erosion - An in vitro laser-induced breakdown spectroscopy analysis

Context

In today's era, erosion is the most prevalent type of tooth wear. The prevention of demineralization with biomineralization is the most desired treatment.

Aim

The aim of this study is to evaluate and compare the surface remineralization potential of two remineralizing agents - self-assembling peptide P11-4 (SAP P11-4) and calcium silicate plus sodium phosphate (CSSP) salts on intact and demineralized enamel using laser-induced breakdown spectroscopy (LIBS).

Subjects and Methods

Sixteen maxillary premolars were decoronated and split into buccal and palatal halves embedded in acrylic resin with a total sample size of 32 designated into Group 1 (intact teeth) and Group 2 (demineralized teeth). Further subdivision into Groups 1a and 2a (SAP P11-4 group [n = 8]); Groups 1b and 2b (CSSP group [n = 8]), Group 2 was first exposed to Coca-Cola. Then, all groups were subjected to experimental LIBS. Groups 1a and 2a were treated with SAP P11-4 based product, i.e., CURODONT™ PROTECT gel. Groups 1b and 2b were treated with CSSP-based products regimen, i.e., REGENERATE Enamel Science™ Advanced Toothpaste and Advanced Enamel Serum. The LIBS assessment was redone for all groups to attain a change in Ca and P values.

Statistical Analysis Used

Inferential statistics were done using Wilcoxon signed-rank test (Before-After product application) and Mann-Whitney U-test (between the groups).

Results

According to the statistical evaluation there was a statistically significant difference (P < 0.05), in Ca and P values in demineralized teeth when both SAP P11-4 and CSSP groups were evaluated. Although Ca values exhibited a significant difference in intact teeth, P did not exhibit a significant difference on the application of both remineralizing agents. The remineralizing potential between the two agents, SAP P11-4 and CSSP groups. There was no statistically significant difference ( P <0.05) observed between the two agent's remineralization potential for intact and demineralized teeth.

Conclusion

SAP P11-4 and CSSP have the potential to remineralize both intact and demineralized enamel. There was increased remineralization in demineralized samples subjected to erosion.

Development of an inter-confirmatory plastic characterization system using spectroscopic techniques for waste management

Ever-accumulating amounts of plastic waste raises alarming concern over environmental and public health. A practical solution for addressing this threat is recycling, and the success of an industry-oriented plastic recycling system relies greatly on the accuracy of the waste sorting technique adapted. We propose a multi-modal spectroscopic sensor which combines laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy in a single optical platform for characterizing plastics based on elemental and molecular information to assist the plastic identification-sorting process in recycling industries. The unique geometry of the system makes it compact and cost-effective for dual spectroscopy. The performance of the system in classifying industrially important plastic classes counting PP, PC, PLA, Nylon-1 1, and PMMA is evaluated, followed by the application of the same in real-world plastics comprising PET, HDPE, and PP in different chemical-physical conditions where the system consumes less than 30 ms for acquiring LIBS-Raman signals. The evaluation of the system in characterizing commuting samples shows promising results to be applied in industrial conditions in future. The study on effect of physical-chemical conditions of plastic wastes in characterizing them using the system shows the necessity for combining multiple techniques together. The proposal is not to determine the paramount methodology to characterize and sort plastics, but to demonstrate the advantages of dual-spectroscopy sensors in such applications. The outcomes of the study suggest that the system developed herein has the potential of emerging as an industrial-level plastic waste sorting sensor.

Development of a spectroscopic technique that enables the saliva based detection of COVID-19 at safe distances

Research activities are in full swing globally to translate the use of saliva as a non-invasive and highly potential specimen for clinical diagnostics, particularly for COVID-19 detection. Being comprised of a pool of biomarkers also enriched with ACE-2 receptors, saliva can provide vital information regarding the state of the human body. Advancements in biophotonics tools for saliva investigation may offer promise for developing rapid, highly objective, optical modalities for COVID- 19 detection. This article presents concept/design study, which propose the use of Raman/laser induced fluorescence spectroscopic device that have the potential for viral detection via saliva from a safer distance. Noticeable changes of biomarkers present in saliva in response to viral infection can reflect the pathological state, thus can altogether affect the Raman spectral pattern. Monitoring these spectral patterns of saliva, which are further enhanced by using cost effective and reproducible Surface Enhanced Raman Spectroscopy substrates can be a viable option for sensitive and non-invasive viral detection. The spectral information acquired from the optical device can be processed using various multivariate statistical analytical tools, which ultimately facilitate effective viral detection in few minutes. This method doesn't demand the necessity of qualified professionals and sample processing with reagents unlike in RT-PCR test. The proposed optical device can be further modified into a portable form, which can be easily transported for field applications. The stand-off observation, contactless and highly non-invasive technique can be of paramount importance in the current context, where the safer screening of a large population for viral infection by maintaining social distances is a necessity. The proposed stand-off spectroscopic technique can also address the major concern of nosocomial viral transmission amongst healthcare workers during sample collection in a pandemic scenario.

Photonics of human saliva: potential optical methods for the screening of abnormal health conditions and infections

Human saliva can be treated as a pool of biological markers able to reflect on the state of personal health. Recent years have witnessed an increase in the use of optical devices for the analysis of body fluids. Several groups have carried out studies investigating the potential of saliva as a non-invasive and reliable clinical specimen for use in medical diagnostics. This brief review aims to highlight the optical technologies, mainly surface plasmon resonance (SPR), Raman, and Fourier transform infrared (FTIR) spectroscopy, which are being used for the probing of saliva for diverse biomedical applications. Advances in bio photonics offer the promise of unambiguous, objective and fast detection of abnormal health conditions and viral infections (such as COVID-19) from the analysis of saliva.

Thermal Energy Electrons and OH-Radicals Induce Strand Breaks in DNA in an Aqueous Environment: Some Salts Offer Protection Against Strand Breaks

Electrons and ^•OH-radicals have been generated by using low-energy laser pulses of 6 ns duration (1064 nm wavelength) to create plasma in a suspension of plasmid DNA (pUC19) in water. Upon thermalization, these particles induce single and double strand breakages in DNA along with possible base oxidation/base degradation. The time-evolution of the ensuing structural modifications has been measured; damage to DNA is seen to occur within 30 s of laser irradiation. The time-evolution is also measured upon addition of physiologically relevant concentrations of salts containing monovalent, divalent, or trivalent alkali ions. It is shown that some alkali ions can significantly inhibit strand breakages while some do not. The inhibition is due to electrostatic shielding of DNA, but significantly, the extent of such shielding is seen to depend on how each alkali ion binds to DNA. Results of experiments on strand breakages induced by thermalized particles produced upon plasma-induced photolysis of water, and their inhibition, suggest implications beyond studies of DNA; they open new vistas for utilizing simple nanosecond lasers to explore the effect of ultralow energy radiation on living matter under physiologically relevant conditions.

Laser-Assisted Tailoring of Surface Wettability - Fundamentals and Applications: A Critical Review

The control of ubiquitous wetting behavior that is determined by the surface free energy of the solid and the surface tension of the interacting liquid is an area of intense research, largely due to its applications in various sectors, ranging from healthcare to automotive industry. The failure and/or toxic nature of the conventionally employed chemical methods to engineer the surface free energy of solids paved the way for utilizing alternative techniques such as laser-based physical texturing of the surface to achieve the desired wettability behavior. This review provides insight into the implementation of lasers to engineer the surfaces of various kinds of materials and how the surface engineering manipulates their wetting characteristics based on the state of the art knowledge of the field. Various theories that explain the wetting behavior of droplets on the surfaces of homogeneous, heterogeneous, and complex structures are discussed with a special emphasis on the role of surface roughness. Further, the article focuses on the lasermatter interaction at different time scales and modification of the surfaces with different kinds of lasers (nano, pico, and femtosecond laser) and their applications. A critical analysis of the effects of experimental parameters such as laser fluence, repetition rate, laser wavelength, inter-pattern spacing on the experimentally observed wetting behavior in the recent literature is also presented. Emerging applications of laser structured surfaces in various fields, including biomedical, water harvesting, anti-bacterial, spectroscopic analysis, oil/water separation, etc. are discussed in detail.

Strong Strand Breaks in DNA Induced by Thermal Energy Particles and Their Electrostatic Inhibition by Na+ Nanostructures

Low-power laser pulses of 6 ns duration (1064 nm wavelength) have been used to create plasma in an aqueous solution of plasmid DNA (pUC19). Thermal energy electrons and ^•OH radicals in the plasma induce strand breakages in DNA, including double strand breaks and possible base oxidation/base degradation. The time evolution of these modifications shows that it takes barely 30 s for damage to DNA to occur. Addition of physiologically relevant concentrations of a salt (NaCl) significantly inhibits such damage. We rationalize such inhibition using simple electrostatic considerations. The observation that DNA damage is induced by plasma-induced photolysis of water suggests implications beyond studies of DNA and opens new vistas for using simple nanosecond lasers to probe how ultralow energy radiation may affect living matter under physiological conditions.

A hyphenated echelle LIBS-Raman system for multi-purpose applications

We have developed and standardized a novel hybrid laser-induced breakdown spectroscopy (LIBS)-Raman system using a single pulsed laser and a high-resolution intensified charge coupled device coupled echelle spectrograph. LIBS and Raman spectroscopy are highly complementary techniques which yield elemental and molecular information. Both techniques share an apparently similar instrumental configuration but need entirely different requirements like spectral range covered, resolution, and light-gathering efficiencies. There are thus many challenges to be faced in developing a combined system. In the present work, we show that an echelle spectrograph combined with a compact Q-switched Nd:YAG laser operating at 532 nm as an excitation source in a portable configuration can be efficiently used for such multi-purpose spectroscopy. Atomic and molecular emissions from the sample surface have been recorded in a gated mode using this setup. Compared to conventional spectrographs, echelle provides simultaneous broad bandpass (250-900 nm) and better spectral resolution at an extremely small fixed slit width of 10 × 50 μm without moving the dispersive elements. The echelle-based hyphenated system provides fast and reliable analysis of materials with combined atomic and molecular spectra of the same spot with better reliability. In this paper, we discuss the optimization of various instrumental parameters and optical components of this hyphenated system using a medium Raman cross section sample, CaCO₃. The feasibility of single shot LIBS-Raman measurement capabilities of echelle has also been demonstrated using the developed system.

Laser-induced breakdown spectroscopy-Raman: An effective complementary approach to analyze renal-calculi

Presence of renal-calculi (kidney stones) in human urethra is being increasingly diagnosed over the last decade and is considered as one of the most painful urological disorders. Accurate analysis of such stones plays a vital role in the evaluation of urolithiasis patients and in turn helps the clinicians toward exact etiologies. Two highly complementary laser-based analytical techniques; laser-induced breakdown spectroscopy (LIBS) and micro-Raman spectroscopy have been used to identify the chemical composition of different types of renal-calculi. LIBS explores elemental characteristics while Raman spectroscopy provides molecular details of the sample. This complete information on the sample composition might help clinicians to identify the key aspects of the formation of kidney stones, hence assist in therapeutic management and to prevent recurrence. The complementarity of both techniques has been emphasized and discussed. LIBS spectra of different types of stones suggest the probable composition of it by virtue of the major, minor and trace elements detected from the sample. However, it failed to differentiate the crystalline form of different hydrates of calcium oxalate stone. This lacuna was overcome by the use of Raman spectroscopy and these results are compared with conventional chemical analysis.

A hybrid LIBS-Raman system combined with chemometrics: an efficient tool for plastic identification and sorting

Classification of plastics is of great importance in the recycling industry as the littering of plastic wastes increases day by day as a result of its extensive use. In this paper, we demonstrate the efficacy of a combined laser-induced breakdown spectroscopy (LIBS)-Raman system for the rapid identification and classification of post-consumer plastics. The atomic information and molecular information of polyethylene terephthalate, polyethylene, polypropylene, and polystyrene were studied using plasma emission spectra and scattered signal obtained in the LIBS and Raman technique, respectively. The collected spectral features of the samples were analyzed using statistical tools (principal component analysis, Mahalanobis distance) to categorize the plastics. The analyses of the data clearly show that elemental information and molecular information obtained from these techniques are efficient for classification of plastics. In addition, the molecular information collected via Raman spectroscopy exhibits clearly distinct features for the transparent plastics (100% discrimination), whereas the LIBS technique shows better spectral feature differences for the colored samples. The study shows that the information obtained from these complementary techniques allows the complete classification of the plastic samples, irrespective of the color or additives. This work further throws some light on the fact that the potential limitations of any of these techniques for sample identification can be overcome by the complementarity of these two techniques. Graphical Abstract ᅟ.

Spectroscopic and structural study of the newly synthesized heteroligand complex of copper with creatinine and urea

Study of copper complex of creatinine and urea is very important in life science and medicine. In this paper, spectroscopic and structural study of a newly synthesized heteroligand complex of copper with creatinine and urea has been discussed. Structural studies have been carried out using DFT calculations and spectroscopic analyses were carried out by FT-IR, Raman, UV-vis absorption and fluorescence techniques. The copper complex of creatinine and the heteroligand complex were found to have much increased water solubility as compared to pure creatinine. The analysis of FT-IR and Raman spectra helps to understand the coordination properties of the two ligands and to determine the probable structure of the heteroligand complex. The LIBS spectra of the heteroligand complex reveal that the complex is free from other metal impurities. UV-visible absorption spectra and the fluorescence emission spectra of the aqueous solution of Cu-Crn-urea heteroligand complex at different solute concentrations have been analyzed and the complex is found to be rigid and stable in its monomeric form at very low concentrations.

Highly Sensitive High Performance Liquid Chromatography-Laser Induced Fluorescence for Proteomics Applications

This paper describes the sensitivity study and performance evaluation of high-performance liquid chromatography-laser-induced fluorescence detection (HPLC-LIF) system assembled in our laboratory for proteomics applications. The limits of Detection (LOD) of several serum proteins have been estimated with this instrument and are found to be much lower compared to other commonly used proteomics techniques like SELDI, MALDI, 2-D-SDS-PAGE, and so forth. Techniques for improving the LOD still further with similar setup are briefly discussed. Using the system, protein profiles of serum in normal, malignant, and premalignant conditions were recorded for different malignancy situations.

Evaluation of high-performance liquid chromatography laser-induced fluorescence for serum protein profiling for early diagnosis of oral cancer

The present work deals with the evaluation of a high-performance liquid chromatography laser-induced fluorescence (HPLC-LIF) technique developed in our laboratory for early detection of oral cancer from protein profiles of body fluids. The results show that protein profiles of serum samples from a given class of samples, say, normal, premalignant, or malignant, are statistically very close to each other, while profiles of members of any class are significantly different from other classes. The performance of the technique is evaluated by the use of sensitivity and specificity pairs, receiver operating characteristic (ROC) analysis, and Youden's Index. The technique uses protein profile differences in serum samples, registered by the HPLC-LIF technique. The study is carried out using serum samples from volunteers diagnosed as normal or premalignant clinically, and as malignant by histopathology. The specificities and sensitivities of the HPLC-LIF method at an ideal threshold (M-distance = 2) for normal, malignant, and premalignant classes are 100, 69.5, and 61.5%, and 86.5, 87.5, and 87.5% respectively.