Cold Atmospheric Plasma: An Inside Look Through Optical Diagnostics for Biomedical Applications

An emerging technology for medical applications is cold atmospheric plasma (CAP). CAP is generated using various gasses in a “pen” to create room temperature plasma and then carry the effluents and species. Success has been shown when cold atmospheric plasma is applied to oncology treatments, accelerated wound healing, pathogen disinfection, and various material-changing effects. However, the mechanisms behind these effects are still speculative. This study uses multiple diagnostic techniques including fast photography, two wavelength emission spectroscopy and optical emission spectroscopy to characterize the plasma properties and eventually further test the plasma’s interaction with biological samples. The plume dynamics are observed using fast photography methods, allowing determining visible intensity, plume length, and peak intensity, as gas flow rates and mixture are varied. A two wavelength emission spectroscopy approach is used for determination of plume temperature, using narrow band optical filters at 480 nm and 510 nm. Pixel-by-pixel, ratio of intensities is used to predict the temperature with novel image processing code. Optical emission spectroscopy is used to determine the chemical species along the plume length. The temperature of the plume is found to be slightly above room temperature at the core and then cools towards the tip. The temperature varies with intensity and peaks around 6.5lpm with pure argon and varies with gas mixture. Pure argon has the greatest intensity and plume length. The plume seems to be mostly comprised of reactive oxygen and nitrogen agents (RONS). It is likely these RONS that cause the various effects, especially in oncology

Temporal resolution of cell death signaling events induced by cold atmospheric plasma and electroporation in human cancer cells

Cancer treatment resistance and their invasive and expensive nature is propelling research towards developing alternate approaches to eradicate cancer in patients. Non-thermal, i.e., cold atmospheric plasma (CAP) and electroporation (EP) applied to the surface of cancerous tissue are new methods that are minimally invasive, safe, and selective. These approaches, both independently and synergistically, have been shown to deplete cancer cell populations, but the signaling mechanisms of death and their timelines of action are still widely unknown. To better understand the timeframe of signaling events occurring upon treatment, human cancer cell lines were treated with CAP, EP, and combined CAP with EP. The stages and incidence of apoptosis were tracked through time via flow cytometry while the activation/inactivation of the penultimate apoptotic signaling complex was examined through real-time fluorescent imaging. These treatments represent a promising new therapy in the global fight against cancer

Double-pulse Nd:YAG-CO2 LIBS Excitation for Bulk and Trace Analytes

Laser-induced breakdown spectroscopy [LIBS] is a commonly used technique for multi-element analyses for various applications such as space exploration, nuclear forensics, environmental analysis, process monitoring. The advantages of the LIBS technique include robustness, ease of use, field portability, and real-time, non-invasive multi-element analyses. However, in comparison to other lab based analytical techniques, it suffers from low precision and low sensitivity. In order to overcome these drawbacks, various approaches have been used, including double-pulse LIBS [DPLIBS]. Typically, various wavelength combinations of two Nd: yttrium aluminum garnet [YAG] lasers have been used for DPLIBS. However, the use of long wavelength (CO2) laser in combination with Nd:YAG laser has not been sufficiently studied. In this study, signal enhancement mechanisms in Nd:YAG:CO2 DPLIBS are investigated. Nd:YAG laser pulse at 1064 nm was used as pre-ablation laser while CO2 laser at 10.6 μm was used as reheating laser pulse. The results exhibit significant improvement in sensitivity of both bulk and trace analytes in the sample using DPLIBS as compared to conventional single-pulse LIBS [SPLIBS]. The bulk and trace analytes used for comparing figures of merit in the brass sample were Cu and Fe emission lines, respectively. Pre-pulse energies ranging from 20 to 120 mJ from a 1064 nm Nd: YAG laser reheated by a 10.6 μm TEA CO2 laser at constant energy of 400 mJ aligned in near collinear geometry. The observed signal intensity and signal-to-background ratio of bulk analyte as well as trace analyte increased significantly. In order to understand signal enhancement mechanisms, various experimental parameters apart from pre-pulse energy were also studied, including inter-pulse delay and ICCD gate delay. Time resolved studies showed that persistence of neutral lines increases by ~10 times for DPLIBS as compared to SPLIBS. Plasma was characterized by estimation of excitation temperature and electron density using the Boltzmann method and Stark broadening method, respectively. Plasma temperature was found to be higher for DPLIBS, which shows that reheating mechanism is dominant mechanism for signal enhancement and increased persistence in YAG:CO2 DPLIBS. The mechanisms involved in signal enhancement and persistence of neutral and ionic species from bulk and trace analyte are presented and their implications to improving figures of merit are discussed

Synergy of Cold Atmospheric Plasma and Electroporation for Treatment of Cancer Cells

Cancer kills about 1500 people every day in the United States alone. Treatments for cancer patients like chemotherapy and radiation are invasive, aggressive, expensive, and can sometimes do more harm than good. There is a need for instrumentation and procedures that reduce toxicity to the human body and are more mobile and accessible to cancer and tumor patients. Electroporation and Cold Atmospheric Plasma (CAP) are two methods being explored to treat cancerous cells without affecting the healthy cells through a minimally invasive treatment. This study will focus on the optimization of parameters for both procedures for efficient apoptosis of cancer cells. This study used different cancer cells lines for both procedures in sequence and simultaneously with the goal of understanding the synergy of both techniques. The viability of cells was analyzed through the use of emission spectroscopy, fluorescence, and microscopy. Initial results show that sequential electroporation was successful at leading cells to apoptosis. These results are very encouraging and have the potential of significant advantages over current methods and techniques. Further work and studies are currently in progress to study the synergetic effect of CAP with electroporation

Exploring the Effect of Sample Properties on Spark-Induced Breakdown Spectroscopy

Optical emission spectroscopy techniques such as laser-induced breakdown spectroscopy (LIBS) and spark-induced breakdown spectroscopy (SIBS) provide portable and robust methods for elemental detection in real-time. Laser-produced emissions are then used for quantitative and qualitative analysis of a sample material with applications in explosives detection. For both techniques, the main obstacles have always been signal intensity, accuracy, and sensitivity of detection. The main advantage of the SIBS method is more safe operation, while still maintaining the portability of the technique. In this study, detailed characterization of spark induced plasma, analyte emission intensity, plasma temperature, electron density, and plasma persistence has been studied for various metallic samples with varying physical properties. Target samples, including Mg, Al, Cu, Ta, Sn, Fe, Co, W, and Mo were chosen based on their diverse set of properties, including: melting point, boiling point, first ionization potential, and conductivity. The role of sample properties on temporal evolution of SIBS signal and plasma characteristics was studied by varying the spark energy from 30 mJ to 180 mJ. Certain parameters such as the conductivity of the material greatly affect the SIBS signal intensity output. Mechanisms of SIBS plasma evolution are discussed in the context of material properties and optimal signal detection approaches are proposed. Principle component analysis is used to determine the dominant material properties that affect the SIBS signal intensity and plasma properties in order to optimize the SIBS intensity in the future

Evolution of Laser Produced Aluminum Plasma in the Presence of a Transverse Magnetic Field

Surface erosion of plasma-facing components is a very important problem in fusion reactors. In order to make fusion reactors economically viable the lifetime of plasma-facing components must be extended. My research entails using magnetic field interactions with plasma in order to determine how the plasma moves through the field, and if it can be stopped by using a certain orientation of magnetic field. A magnetic field should be able to alter the path of evolving plasma due to the interaction of the magnetic field with the charged particles in the plasma. The optimal orientation for slowing the evolution of the plasma is hypothesized to be perpendicular to the magnetic field. Also it is anticipated that the higher the magnetic field the greater the stopping of the plasma. This experiment consisted of designing a magnetic trap and creating laser produced plasma with and without a magnetic field. Intensified CCD was used to image the plasma plume expansion with and without a transverse magnetic field. An aluminum target was used to generate the plasma using laser pulse energies of 50 mJ, 100 mJ, and 150 mJ. It was found that with no magnetic field the plume expanded freely, with larger velocities for higher laser pulse energy. With magnetic field the plasma was confined and this confinement was more pronounced at higher energies. This experiment can be extended by gathering spectroscopic data in order to determine the temperature and the levels of ionization inside the plasmas at different laser energies and magnetic orientations

Collimation Effects on Magnetically Confined Laser Produced Plasmas

Tokamaks for fusion research are extremely complex and are still limited by inherent instabilities such as material erosion from plasma instabilities. Due to the lack of data and high demand of resources, simulations to portray Tokamaks are essential. A Particle-In-Cell (PIC) simulation for plasma erosion on materials within the Tokamak is to be benchmarked using the experimental data obtained in these experiments. The effects of an axial magnetic field (magnetic field lines are along the plasma propagation direction) on an expanding laser produced plasma plume are investigated. A Continuum Surelite Nd:YAG laser system at 1064 nm wavelength and 6 ns full width half max (FWHM) is used to ablate carbon, aluminum, and boron nitride surfaces in the presence of a magnetic field (~.6T) at 50 mJ, 100 mJ, and 150 mJ under vacuum. The resulting plasma plume is studied using fast photography by employing an intensified charge coupled device (ICCD). The effect of the axial magnetic field changes with the target material. Carbon plume undergoes the creation of side wings that expand perpendicular to the field and curve back into the field after the primary plume has expanded and dissipated. Both aluminum and boron nitride exhibit significant focusing at the center of the magnetic field with no evidence of wings formation. Further work using optical emission spectroscopy is in progress to obtain temperature, electron density, and ionization rate of the laser produced plasma plumes to better understand the mechanism of wing formation as well as plume focusing in different materials

Doube-pulse Laser-induced Breakdown Spectroscopy of Multi-element Sample Containing Low- And High-Z Analytes

Laser-induced breakdown spectroscopy (LIBS) is a portable, remote, non-invasive analytical technique which effectively distinguishes neutral and ionic species for a range of low- to high-Z elements in a multi-element target. Subsequently, LIBS holds potential in special nuclear material (SNM) sensing and nuclear forensics requiring minimal sample preparation and detecting isotopic shifts which allows for differentiation in SNM (namely U) enrichment levels. Feasible applications include not only nonproliferation and homeland security but also nuclear fuel prospecting and industrial safeguard endorsement. Elements of higher mass with complex atomic structures, such as U, however, result in crowded emission spectra with LIBS, and characteristic emission lines are challenging to discern. Preliminary research suggests double-pulse LIBS (DPLIBS) improves signal sensitivity for analytes of lower atomic mass over conventional single-pulse LIBS (SPLIBS). This study investigates signal sensitivity for low- and high-Z analytes in a glass matrix containing U (1.3%) comparing DPLIBS to SPLIBS. DPLIBS involves sequential firing of 1064 Nd: YAG (FWHM 9 ns) pre-pulse and 10.6 µm TEA CO2 (FWHM 50-100 ns) heating pulse in near collinear geometry; SPLIBS entails only the Nd:YAG laser. Optimization of experimental parameters including inter-pulse delay and energy follows identification of characteristic lines for bulk analytes Ca, Na, and Si and trace analyte U for both DPLIBS and SPLIBS. Temporally-integrated excitation temperature and electron density as well as neutral-to-ionic species ratio constitute relative figures of merit for both DPLIBS and SPLIBS plasma characterization. Temporally-resolved studies provide insight into high-Z U analyte persistence and signal enhancement with DPLIBS as compared to low-Z bulk analytes. The study predicts and discusses optimal emission conditions of U lines and relative figures of merit in both SPLIBS and DPLIBS

Femtosecond Laser Ablation: Fundamentals and Applications

Abstract Traditionally nanosecond laser pulses have been used for Laser-induced Breakdown Spectroscopy (LIBS) for quantitative and qualitative analysis of the samples. Laser produced plasmas using nanosecond laser pulses have been studied extensively since 1960s. With the advent of short and ultrashort laser pulses, there has been a growing interest in the applications of femtosecond and picosecond lasers for analysis of materials using LIBS and LA-ICP-MS. The fundamentals of laser ablation process using ultrashort laser pulses are not still fully understood. Pulse duration of femtosecond laser pulse is shorter than electron-to-ion energy transfer time and heat conduction time in the sample lattice. This results in different laser ablation and heat dissipation mechanisms as compared to nanosecond laser ablation. In this chapter, the focus will be on understanding the basics of femtosecond laser ablation processes including laser target interaction, ablation efficiency, ablation threshold, laser plasma interactions, and plume hydrodynamics. Analytical figures of merit will be discussed in contrast to nanosecond LIBS. Introduction Laser ablation (LA) and laser-produced plasmas (LPP) have been studied extensively for more than 50 years since the discovery of lasers in the 1960s. The physics involved in laser-plasma generation and subsequent evolution is very complex and contains many processes like heating, melting, vaporization, ejection of particles, and plasma creation and expansion. The laser ablation craters and plasmas produced are dependent on laser beam parameters such as pulse duration, energy, and wavelength, along with the target properties and surroundin

Total nitrogen estimation in agricultural soils via aerial multispectral imaging and LIBS

Abstract Measuring soil health indicators (SHIs), particularly soil total nitrogen (TN), is an important and challenging task that affects farmers’ decisions on timing, placement, and quantity of fertilizers applied in the farms. Most existing methods to measure SHIs are in-lab wet chemistry or spectroscopy-based methods, which require significant human input and effort, time-consuming, costly, and are low-throughput in nature. To address this challenge, we develop an artificial intelligence (AI)-driven near real-time unmanned aerial vehicle (UAV)-based multispectral sensing solution (UMS) to estimate soil TN in an agricultural farm. TN is an important macro-nutrient or SHI that directly affects the crop health. Accurate prediction of soil TN can significantly increase crop yield through informed decision making on the timing of seed planting, and fertilizer quantity and timing. The ground-truth data required to train the AI approaches is generated via laser-induced breakdown spectroscopy (LIBS), which can be readily used to characterize soil samples, providing rapid chemical analysis of the samples and their constituents (e.g., nitrogen, potassium, phosphorus, calcium). Although LIBS was previously applied for soil nutrient detection, there is no existing study on the integration of LIBS with UAV multispectral imaging and AI. We train two machine learning (ML) models including multi-layer perceptron regression and support vector regression to predict the soil nitrogen using a suite of data classes including multispectral characteristics of the soil and crops in red (R), near-infrared, and green (G) spectral bands, computed vegetation indices (NDVI), and environmental variables including air temperature and relative humidity (RH). To generate the ground-truth data or the training data for the machine learning models, we determine the N spectrum of the soil samples (collected from a farm) using LIBS and develop a calibration model using the correlation between actual TN of the soil samples and the maximum intensity of N spectrum. In addition, we extract the features from the multispectral images captured while the UAV follows an autonomous flight plan, at different growth stages of the crops. The ML model’s performance is tested on a fixed configuration space for the hyper-parameters using various hyper-parameter optimization techniques at three different wavelengths of the N spectrum