Toxic gas detection using 3-channel spark-induced plasma spectroscopy for indoor air quality monitoring.

This study explored the toxic gas detection using a set of two spark-induced plasma emission spectroscopy (SIPS) modules as an alternative to conventional chemical sensors. This opens up a new possibility for detecting toxic molecules (formaldehyde, acetaldehyde, acetic acid, toluene, and ammonia) in real-time (<3 s) at relatively high sensitivity (<5 ppm). An optimized electrical controller (Raspberry Pi), manufactured as a compact and economical 3-channel optical measuring device, was developed for handling the high-resolution time-resolved electrical signals from the plasma emissions. Subsequently, the findings of this research elucidate the usability of the 3-channel SIPS device for quantitative monitoring of toxic gases.

Accurate real-time monitoring of fine dust using a densely connected convolutional networks with measured plasma emissions.

Accurate identification and monitoring of fine dust are emerging as a primary global issue for addressing the harmful effects of fine dust on public health. Identifying the source of fine dust is indispensable for ensuring the human lifespan as well as preventing environmental disasters. Here a simple yet effective spark-induced plasma spectroscopy (SIPS) unit combined with deep learning for real-time classification is verified as a fast and precise PM (particulate matter) source identification technique. SIPS promises portable use, label-free detection, source identification, and chemical susceptibility in a single step with acceptable speed and accuracy. In particular, the densely connected convolutional networks (DenseNet) are used with measured spark-induced plasma emission datasets to identify PM sources at above 98%. The identification performance was compared with other common classification methods, and DenseNet with dropouts (30%), optimized batch size (16), and cyclic learning rate training emerged as the most promising source identification method.

A liquid breakdown driven non-invasive microjet injection system.

The purpose of this study was to develop a microjet having fully skin-penetrable jet speed, moderately small volume, and highly repeatable injection, and eventually providing a device with medical efficacy for less tissue destruction and pain. The injector allows a small volume of drug stream (0.1-1.7 µL) to flow out at a frequency of ~16 Hz, and employs two different sources of energy, namely electrical and optical, which are converted into kinetic energy of the penetrating drug solution using liquid breakdown (dielectric or laser-induced). The medical efficacy of the microjet injection was evaluated through ex-vivo and in-vivo procedures in a mouse model. Both sources of liquid breakdown generate a skin-penetrable jet speed of 200-330 m/s. These fast and repetitive jets in a small volume pass through the epidermis to exert their efficacy. The driving pressure provided by dielectric breakdown showed an extensive increase per input energy increase, which is deemed appropriate for deep skin penetration. In contrast, the laser-induced breakdown exhibited a saturation in jet speed with increasing input energy, which is indicative of a low energy conversion efficiency. The results are promising for medical procedures that require uniform drug injection over a large area, and small dosage control during intradermal procedures.

Onsite real-time detection of covid-like-virus transmission through air using spark-induced plasma spectroscopy.

In March 2020, COVID-19 was officially classified as a pandemic and as a consequence people have adopted strenuous measures to prevent infection, such as the wearing of PPE and self-quarantining, with no knowledge of when the measures will no longer be necessary. Coronavirus has long been known to be non-infectious when airborne; however, studies are starting to show that the virus can infect through airborne transmission and can remain airborne for a significant period of time. In the present study, a spark-induced plasma spectroscopy was devised to characterize the air propagation of the virus in real-time. The risk of air propagation was evaluated in terms of changes in virus concentration with respect to distance traveled and measurement time. Thus, our study provides a benchmark for performing real-time detection of virus propagation and instantaneous monitoring of coronavirus in the air.

Real-time monitoring of toxic components from fine dust air pollutant samples by utilizing spark-induced plasma spectroscopy.

A growing modern-day concern is fine dust air pollution that contains heavy metals and ammonium ions (NH4+) from industrial and agricultural waste sources, respectively. In the current study, the development of an innovative and effective technique for real-time, quantitative monitoring of toxic fine dust components using plasma emission spectroscopy is presented as a complement to emergency preparedness plans aimed at reducing dust pollution. A novel spark-induced plasma spectroscopic (SIPS) device that can control the frequency and magnitude of plasma was developed for the toxic pollutants in this work. SIPS utilizes an electrical discharge from a high voltage at a low current to produce plasma when the applied voltage is higher than the ambient voltage surrounding the electrodes. The detection limit of this setup was enhanced by a factor of 4.3 over laser-induced plasma spectroscopy (LIPS). This compact sensing device was used in combination with a new quantitative analytical method to measure the concentration of heavy metals and ammonia molecules in fine dust air pollution. By integrating the time-resolved plasma emission signals that were based on the plasma continuum decay time of each element, quantitative measurements of the minute changes in composition of 0.1 µg/m3 were conducted. The findings of this study could inspire future research on the use of SIPS for monitoring airborne fine dust pollutants with better sensitivity in real-time via a new quantitative analytical method.

A non-calorimetric approach for investigating the moisture-induced ageing of a pyrotechnic delay material using spectroscopies.

The degradation of thermal properties due to ageing such as burning rate and exothermic heat release are unsolved issues faced during a long-term storage of the pyrotechnic substances. Accordingly, we employed various non-calorimetric methods to investigate the thermal performance of pyrotechnic delay, which is exposed to various moisture-rich conditions at extended durations. The chemical and physical changes in the compositions of a pyrotechnic delay comprised of metal fuel (Zr-Ni alloy) and oxidants (KClO4, BaCrO4) are analysed for four different relative humidity levels using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope and laser-induced breakdown spectroscopy. The calculations using the NASA Chemical Equilibrium with Applications (CEA) software indicated that the heat of reaction for the components stored under the moisture-rich conditions is reduced by more than 50%. Unlike the conventional calorimetric analysis, the present non-calorimetric approach provided the compositional changes as well as the cause and effect of the relevant ageing process of pyrotechnic delay.

Towards understanding the effects of heat and humidity on ageing of a NASA standard pyrotechnic igniter.

Ageing of pyrotechnic substance, primarily fuel oxidisation, can cause changes in composition that degrade their performance. This study investigates the effect of ageing on zirconium potassium perchlorate (ZPP), a widely used NASA Standard Initiator. Although prior studies have investigated the effects of accelerated ageing on ZPP, this is the first to conduct kinetic analyses at different relative humidity (RH) levels. Here, both thermal and kinetic analyses are conducted for a variety of hygrothermal ageing cases in order to replicate the natural ageing process. X-ray photoelectron spectroscopy (XPS) results reveal that oxidant levels drop and zirconium dioxide levels rise as ZPP ages. Lower heats of reaction and increases in activation energy were also observed under the RH conditions. Calculations using van't Hoff equation indicate that moisture shortened the lifespan of the unaged ZPP up to about 85% under extreme RH conditions, while significantly deteriorating the heat of reaction, sensitivity, and thus increased the risk of a misfire.

Two-dimensional measurement of hydrocarbon fuel concentration using multiple laser-induced plasma-forming regions.

A two-dimensional measurement of fuel distribution in a gasoline spray flow was performed using multiple laser-induced plasma-forming regions. Multiple plasma-forming regions were generated by a laser sheet with a low breakdown threshold for a two-phase flow. To observe the formation of multiple laser-induced plasma-forming regions, shadowgraphs were imaged using a high-speed camera. Hydrogen and oxygen atomic emissions from the plasma-forming regions were obtained by attaching bandpass filters to the high-speed camera, and a two-dimensional visualization of the fuel distribution in the wide plasma-forming region was obtained by dividing the hydrogen line-filtered image with the oxygen line-filtered image. The result complements a novel method for two-dimensional measurement of instantaneous fuel concentration in the reacting flow by utilizing laser-induced breakdown spectroscopy (LIBS).

Forensic Discrimination of Latent Fingerprints Using Laser-Induced Breakdown Spectroscopy (LIBS) and Chemometric Approaches.

A novel technique is reported for separating overlapping latent fingerprints using chemometric approaches that combine laser-induced breakdown spectroscopy (LIBS) and multivariate analysis. The LIBS technique provides the capability of real time analysis and high frequency scanning as well as the data regarding the chemical composition of overlapping latent fingerprints. These spectra offer valuable information for the classification and reconstruction of overlapping latent fingerprints by implementing appropriate statistical multivariate analysis. The current study employs principal component analysis and partial least square methods for the classification of latent fingerprints from the LIBS spectra. This technique was successfully demonstrated through a classification study of four distinct latent fingerprints using classification methods such as soft independent modeling of class analogy (SIMCA) and partial least squares discriminant analysis (PLS-DA). The novel method yielded an accuracy of more than 85% and was proven to be sufficiently robust. Furthermore, through laser scanning analysis at a spatial interval of 125 µm, the overlapping fingerprints were reconstructed as separate two-dimensional forms.

Analytical Methods to Distinguish the Positive and Negative Spectra of Mineral and Environmental Elements Using Deep Ablation Laser-Induced Breakdown Spectroscopy (LIBS).

Environments affect mineral surfaces, and the surface contamination or alteration can provide potential information to understanding their regional environments. However, when investigating mineral surfaces, mineral and environmental elements appear mixed in data. This makes it difficult to determine their atomic compositions independently. In this research, we developed four analytical methods to distinguish mineral and environmental elements into positive and negative spectra based on depth profiling data using laser-induced breakdown spectroscopy (LIBS). The principle of the methods is to utilize how intensity varied with depth for creating a new spectrum. The methods were applied to five mineral samples exposed to four environmental conditions including seawater, crude oil, sulfuric acid, and air as control. The proposed methods are then validated by applying the resultant spectra to principal component analysis and data were classified by the environmental conditions and atomic compositions of mineral. By applying the methods, the atomic information of minerals and environmental conditions were successfully inferred in the resultant spectrum.

Accuracy Enhancement of Raman Spectroscopy Using Complementary Laser-Induced Breakdown Spectroscopy (LIBS) with Geologically Mixed Samples.

Quantitative Raman analysis was carried out with geologically mixed samples that have various matrices. In order to compensate the matrix effect in Raman shift, laser-induced breakdown spectroscopy (LIBS) analysis was performed. Raman spectroscopy revealed the geological materials contained in the mixed samples. However, the analysis of a mixture containing different matrices was inaccurate due to the weak signal of the Raman shift, interference, and the strong matrix effect. On the other hand, the LIBS quantitative analysis of atomic carbon and calcium in mixed samples showed high accuracy. In the case of the calcite and gypsum mixture, the coefficient of determination of atomic carbon using LIBS was 0.99, while the signal using Raman was less than 0.9. Therefore, the geological composition of the mixed samples is first obtained using Raman and the LIBS-based quantitative analysis is then applied to the Raman outcome in order to construct highly accurate univariate calibration curves. The study also focuses on a method to overcome matrix effects through the two complementary spectroscopic techniques of Raman spectroscopy and LIBS.

Skin pre-ablation and laser assisted microjet injection for deep tissue penetration.

BACKGROUND AND AIMS: For conventional needless injection, there still remain many unresolved issues such as the potential for cross-contamination, poor reliability of targeted delivery dose, and significantly painstaking procedures. As an alternative, the use of microjets generated with Er:YAG laser for delivering small doses with controlled penetration depths has been reported. In this study, a new system with two stages is evaluated for effective transdermal drug delivery. First, the skin is pre-ablated to eliminate the hard outer layer and second, laser-driven microjet penetrates the relatively weaker and freshly exposed epidermis. Each stage of operation shares a single Er:YAG laser that is suitable for skin ablation as well as for the generation of a microjet. METHODS: In this study, pig skin is selected for quantification of the injection depth based on the two-stage procedure, namely pre-ablation and microjet injection. The three types of pre-ablation devised here consists of bulk ablation, fractional ablation, and fractional-rotational ablation. The number of laser pulses are 12, 18, and 24 for each ablation type. For fractional-rotational ablation, the fractional beams are rotated by 11.25° at each pulse. The drug permeation in the skin is evaluated using tissue marking dyes. The depth of penetration is quantified by a cross sectional view of the single spot injections. Multi-spot injections are also carried out to control the dose and spread of the drug. RESULTS: The benefits of a pre-ablation procedure prior to the actual microjet injection to the penetration is verified. The four possible combinations of injection are (a) microjet only; (b) bulk ablation and microjet injection; (c) fractional ablation and microjet injection; and (d) fractional-rotational ablation and microjet injection. Accordingly, the total depth increases with injection time for all cases. In particular, the total depth of penetration attained via fractional pre-ablation increased by 8 ∼ 11% and that of fractional-rotational pre-ablation increased by 13 ∼ 33%, when compared with the no pre-ablation or microjet only cases. A noticeable point is that the fraction-rotational pre-ablation and microjet result is comparable to the bulk ablation and microjet result of 11 ∼ 42%. The penetration depth underneath ablated stratum corneum (SC) is also measured in order to verify the pre-ablation effect. The penetration depths for each case are (a) 443 ± 104 µm; (b) 625 ± 98 µm; (c) 523 ± 95 µm; and (d) 595 ± 141 µm for microjet only, bulk ablation and microjet, fractional ablation and microjet, and fractional-rotational ablation and microjet, respectively. This is quite beneficial since any healing time associated with ablation is significantly reduced by avoiding hard-core bulk ablation. Thus the bulk pre-ablation and microjet may well be superseded by the less invasive fractiona-rotational ablation followed by the microjet injection. The density of micro-holes is 1.27 number/mm2 for fractional ablation and 4.84 number/mm2 for fractional-rotational ablation. The penetration depths measured underneath the ablated SC are 581 µm (fractional ablation and microjet) and 691 µm (fractional-rotational ablation and microjet). CONCLUSIONS: Fractional-rotational ablation increases number of micro-holes in a unit area, enabling fast reepithelialization and high drug delivery efficiency. Optimization of system parameters such as ablation time, number of ablations, and injection time will eventually ensure a macromolecule delivery technique with the potential to include vaccines, insulins, and growth hormones, all of which require deeper penetration into the skin. Lasers Surg. Med. 49:387-394, 2017. © 2016 Wiley Periodicals, Inc.

Standoff Detection of Geological Samples of Metal, Rock, and Soil at Low Pressures Using Laser-Induced Breakdown Spectroscopy.

Categorized certified reference materials simulating metal, rock, soils, or dusts are used to demonstrate the standoff detection capability of laser-induced breakdown spectroscopy (LIBS) at severely low pressure conditions. A Q-switched Nd:YAG laser operating at 1064 nm with 17.2-50 mJ energy per pulse was used to obtain sample signals from a distance of 5.5 m; the detection sensitivity at pressures down to 0.01 torr was also analyzed. The signal intensity response to pressure changes is explained by the ionization energy and electronegativity of elements, and from the estimated full width half-maximum (FWHM) and electron density, the decrease in both background noise and line broadening makes it suitable for low pressure detection using the current standoff LIBS configuration. The univariate analyses further showed high correlation coefficients for geological samples. Therefore, the present work has extended the current state-of-the-art of standoff LIBS aimed at harsh environment detection.

Novel control of plasma expansion direction aimed at very low pressure laser-induced plasma spectroscopy.

A plasma confinement approach has been applied to enhance the signal intensity of laser-induced plasma in low pressure conditions down to 10(-2) torr. Detection of plasma emission spectrum is a daunting task at low pressure due to the low electron density and the short persistence time of plasma that undergoes a rapid expansion. Here we devised a spatial confinement setup that increases the electron density at various range of low pressures. A confining window is placed above the sample surface to control the direction of the expanding plasma aimed at optimizing the efficiency of the low pressure detection. More ions, atoms, and molecules can reach the detector by a direction-controlled confinement of an otherwise freely expanding plasma. The spectral intensities of neutral atoms increased up to 4 times with a single laser pulse by the proposed confining method at 1 torr. The signal of doubly ionized carbon atom which was detectable only at low pressure is also enhanced 4 times. The results of this study provide an important guideline for strengthening the otherwise weak signals at low pressure by controlling the plasma expansion direction.

Laser-induced microjet injection into preablated skin for more effective transdermal drug delivery.

A breakthrough in the efficient transdermal delivery of drug via the laser-driven microjet is reported. A single source of laser beam is split into two: one beam ablates a targeted spot on a skin and another beam drives the injector for fast microjet ejection into a preablated spot. This combined ablation and microjet injection scheme using a beam splitter utilizes laser energy sharing between generation of the microhole via ablation and the microjet which is generated using the Er:YAG laser beam at a 2940-nm wavelength and pulse duration. A careful analysis of the injection mechanism is carried out by studying the response of the elastic membrane that separates a driving water unit for bubble expansion from a drug unit for a microjet ejection. The efficiency of the present delivery scheme is evaluated by the abdominal porcine skin test using the fluorescein isothiocyanate staining and the confocal microscopy for quantitative delivery confirmation. The depth of penetration and the injected volume of the drug are also confirmed by polyacrylamide gel tests.

Towards clinical use of a laser-induced microjet system aimed at reliable and safe drug delivery.

An Er:YAG laser with 2940-nm wavelength and 250-µs pulse duration is used to generate a microjet that is ejected at ∼50 m/s in air. The strength of the microjet depends on the bubble dynamics from the beam-water interaction within the driving chamber as well as the discharging of the drug solution underneath the elastic membrane that separates the drug from the driving liquid. The jet characteristics, such as velocity, volume, and level of atomization, are obtained by high-speed camera images taken at 42,000 fps. The enhancements in jet volume (dosage) and repeated jet generation, which are aimed at making the injector suitable for general clinical applications, are achieved. The generation of repeated microjets is achieved with the help of a stepping motor that provides a uniform pressure within the drug reservoir before an ejection occurs through a micro nozzle. Also, two types of human growth hormones are used for monitoring any potential thermal damage to the drug solution due to a repeated laser ablation when driving the microjet. We provide strong evidence to support that the drugs, as they are injected to porcine skins, are free of the damage associated with the present delivery method.

Er:YAG laser pulse for small-dose splashback-free microjet transdermal drug delivery.

The microjet injector system accelerates drugs and delivers them without a needle, which is shown to overcome the weaknesses of existing jet injectors. A significant increase in the delivered dose of drugs is reported with multiple pulses of laser beam at lower laser energy than was previously used in a Nd:YAG system. The new injection scheme uses the beam wavelength best absorbable by water at a longer pulse mode for elongated microjet penetration into a skin target. A 2.9 µm Er:YAG laser at 250 µs pulse duration is used for fluorescent staining of guinea pig skin and for injection controllability study. Hydrodynamic theory confirms the nozzle exit jet velocity obtained by the present microjet system.

Laser-induced plasma peculiarity at low pressures from the elemental lifetime perspective.

The Laser-Induced Breakdown Spectroscopy (LIBS) plasma characteristics are known to strongly dependent on the surrounding pressure. Six different samples (C, Ni, Cu, Sn, Al, Zn) are used to support the existence of a `soft spot' in the vicinity of 1 torr where the maxima in plasma lifetime is observed. With pressure decrease, the elemental lifetimes of samples except for carbon increased until 1 torr and started to decline with continued pressure drop. The boiling point and electronegativity of the samples are amongst the physicochemical properties that are used to explain this peculiarity.

Effective laser-induced breakdown spectroscopy (LIBS) detection using double pulse at optimum configuration.

A short laser pulse is irradiated on a sample to create a highly energetic plasma that emits light of a specific peak wavelength according to the material. By identifying different peaks for the analyzed samples, their chemical composition can be rapidly determined. The characteristics of the laser-induced breakdown spectroscopy (LIBS) plasma are strongly dependent on the ambient conditions. Research aimed at enhancing LIBS intensity is of great benefit in advancing LIBS for the exploration of harsh environments. By using double-pulse LIBS, the signal intensity of Al and Ca lines was enhanced by five times compared to the single-pulse signal. Also, the angles of the target and detector are adjusted to simulate samples of arbitrary shape. We verified that there exists an optimal angle at which specific elements of a test sample may be detected with stronger signal intensity. We provide several optimum configurations for the LIBS system for maximizing the signal intensity for the analysis of a nonstandard aluminum sample.

Biolistic injection of microparticles with high-power Nd:YAG laser.

Irradiation of a high-power laser pulse (above 10(9)W/cm(2)) on thin metal foil causes ablation, which is characterized by a strong plasma-shock formation followed by a rapid expulsion of surface matter. The shock propagates through the foil and reverberates on the rear side causing instant deformation of the metal foil, whose surface is treated with microparticles prior to ablation. Based on this principle of microparticle ejection, we develop a laser-based injector that features controllability and stability. We also perform characterization of the penetration depths at varying confinements and energy levels. The confinement media include glass (BK7), water, and ultrasound gel. Biological tissue was replicated by a gelatin-water solution at a 3% weight ratio. Present data show that the confinement effect results in a significant enhancement of penetration depth reached by 5 microm cobalt microparticles. Also, there exists an optimal thickness at each energy level when using liquid confinement for enhanced particle delivery.