Laser induced breakdown spectroscopy for the rapid detection of SARS-CoV-2 immune response in plasma.

As the SARS-CoV-2 pandemic persists, methods that can quickly and reliably confirm infection and immune status is extremely urgently and critically needed. In this contribution we show that combining laser induced breakdown spectroscopy (LIBS) with machine learning can distinguish plasma of donors who previously tested positive for SARS-CoV-2 by RT-PCR from those who did not, with up to 95% accuracy. The samples were also analyzed by LIBS-ICP-MS in tandem mode, implicating a depletion of Zn and Ba in samples of SARS-CoV-2 positive subjects that inversely correlate with CN lines in the LIBS spectra.

Detection and classification of live and dead Escherichia coli by laser-induced breakdown spectroscopy.

A common goal for astrobiology is to detect organic materials that may indicate the presence of life. However, organic materials alone may not be representative of currently living systems. Thus, it would be valuable to have a method with which to determine the health of living materials. Here, we present progress toward this goal by reporting on the application of laser-induced breakdown spectroscopy (LIBS) to study characteristics of live and dead cells using Escherichia coli (E. coli) strain K12 cells as a model organism since its growth and death in the laboratory are well understood. Our goal is to determine whether LIBS, in its femto- and/or nanosecond forms, could ascertain the state of a living organism. E. coli strain K12 cells were grown, collected, and exposed to one of two types of inactivation treatments: autoclaving and sonication. Cells were also kept alive as a control. We found that LIBS yields key information that allows for the discrimination of live and dead E. coli bacteria based on ionic shifts reflective of cell membrane integrity.

Soil diversity and hydration as observed by ChemCam at Gale crater, Mars.

The ChemCam instrument, which provides insight into martian soil chemistry at the submillimeter scale, identified two principal soil types along the Curiosity rover traverse: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic soil component is representative of widespread martian soils and is similar in composition to the martian dust. It possesses a ubiquitous hydrogen signature in ChemCam spectra, corresponding to the hydration of the amorphous phases found in the soil by the CheMin instrument. This hydration likely accounts for an important fraction of the global hydration of the surface seen by previous orbital measurements. ChemCam analyses did not reveal any significant exchange of water vapor between the regolith and the atmosphere. These observations provide constraints on the nature of the amorphous phases and their hydration.

Continuous wave achromatic thermal lens spectroscopy.

We present a mode-mismatched continuous wave (cw) achromatic thermal lens experiment in which the pump beam is focused in the presence of a collimated probe beam. This scheme presents a distinct advantage over mode-matched thermal lens experimental methods in that it considerably reduces chromatic aberrations. Further, using the proposed method, we measure the near infrared spectrum of distilled water. The results are in good agreement with previous transmission measurements.

Absorption spectra of dye solutions measured using a white light thermal lens spectrophotometer.

We describe a two-beam thermal lens spectrophotometer that uses a xenon lamp as the excitation source and a low power diode pumped Nd-YAG laser as the probe light. The white light from the xenon source is filtered using a variable interference filter producing a partial monochromatic light within the spectral range 400-700 nm and with a spectral resolution of 10 nm. We measure the thermal lens spectrum of a nonfluorescent dye (Malachite Green) and show that this spectrum reproduces its absorbance spectra measured by the usual transmission method. A comparison of the thermal lens and the absorbance spectra of a fluorescent dye (Rhodamine B) reveals substantial differences. These differences can yield important applications of the device for the characterization of fluorescent materials.

The effect of irradiation wavelength bandwidth and spot size on the scraping depth and temperature rise in composite exposed to an argon laser or a conventional quartz-tungsten-halogen source.

OBJECTIVES: The purpose of this study was to investigate the effect of the spectral distribution of the curing irradiation near the maximum excitation wavelength of the photo-initiator and the effect of the irradiation spot size on the scraping depth-of-cure and temperature rise in a resin composite for both an argon laser and a quartz-tungsten-halogen lamp. METHODS: Using bandpass filters, the spectral outputs of an argon laser and a quartz-tungsten-halogen lamp were restricted to pass selected wavelengths on to a commercial camphorquinone-based resin composite and the depth-of-cure, using scraping methods, was measured. The temperature rise in composite was measured for some of the above-mentioned sources. The spot sizes for both sources were varied and the scraping depth was measured. Lateral curing or the extent of curing away from the focused spot was also measured. RESULTS: For constant power density and exposure time, an irradiation spectral distribution closer to the photo-initiator excitation peak yielded a higher scraping depth than a broadband spectral distribution for both sources. Under similar conditions, the argon laser resulted in a lower temperature rise in the composite than the lamp. For the same total energy imparted to the resin composite, the scraping depth increased with reducing spot size of the curing irradiation. Furthermore lateral curing of the composite well beyond the irradiation spot size was observed. SIGNIFICANCE: The spectral and spatial characteristics of the curing irradiation need to be carefully considered as these affect the scraping depth-of-cure and temperature rise in a resin composite.

Chirp-free nanosecond laser amplifier for precision spectroscopy.

We describe a simple method for greatly reducing optical phase perturbations in a nanosecond pulsed dye amplifier. The laser dye mix is tailored to produce a susceptibility near zero at the operating wavelength. Frequency shifts are reduced to less than 3 MHz, and frequency chirping to less than 10 MHz, without significant loss of amplified power. This technique has been used to improve the accuracy of precision far-UV wavelength measurements in H(2) to ~7 parts in 10(9).

Generation of vacuum ultraviolet radiation for precision laser spectroscopy.

We report on the generation of tunable nanosecond pulsed VUV radiation near 120 nm using difference-frequency mixing in H(2). Our scheme uses two dye lasers, one fixed at 606 nm and the other tunable in the red. These convenient wavelengths simplify the metrology needed for accurate VUV laser spectroscopy. Efficient VUV generation is attained with modest Nd:YAG pump laser energies (approximately 160 mJ at 532 nm), making the scheme attractive even when narrow bandwidths are not essential.

Frequency-modulation spectroscopy with transform-limited nanosecond laser pulses.

We demonstrate high-quality FM spectra with nanosecond laser pulses. Transform-limited pulses with FM sidebands are produced by pulsed amplification of a phase-modulated cw laser. The pulses can be shifted to the UV by nonlinear mixing. We report both initial experiments on I(2) and what is to our knowledge the first observation of a far-UV transition by FM spectroscopy, at 214.5 nm. Major advantages of this method include (1) spectral resolution of the order of 0.001 cm(-1), (2) better-defined optical phase, and (3) a much smaller and more easily detected modulation frequency, ~500 MHz. The absorption sensitivity is ~10(-4), and considerable further improvement is expected.