Tayro E. Acosta

Near-Infrared Micro-Raman Spectroscopy for in Vitro Detection of Cervical Cancer

Near-infrared Raman spectroscopy is a powerful analytical tool for detecting critical differences in biological samples with minimum interference in the Raman spectra from the native fluorescence of the samples. The technique is often suggested as a potential screening tool for cancer. In this article we report in vitro Raman spectra of squamous cells in normal and cancerous cervical human tissue from seven patients, which have good signal-to-noise ratio and which were found to be reproducible. These preliminary results show that several Raman features in these spectra could be used to distinguish cancerous cervical squamous cells from normal cervical squamous cells. In general, the Raman spectra of cervical cancer cells show intensity differences compared to those of normal squamous cell spectra. For example, several well-defined Raman peaks of collagen in the 775 to 975 cm−1 region are observed in the case of normal squamous cells, but these are below the detection limit of normal Raman spectroscopy in the spectra of invasive cervical cancer cells. In the high frequency 2800 to 3100 cm−1 region, it is found that the peak area under the CH stretching band is lower by a factor of approximately six in the spectra of cervical cancer cells as compared with that of the normal cells. The Raman chemical maps of regions of cancer and normal cells in the cervical epithelium made from the spectral features in the 775 to 975 cm−1 and 2800 to 3100 cm−1 regions are also found to show good correlation with each other.

Single-pulse standoff Raman detection of chemicals from 120 m distance during daytime.

The capability to analyze and detect the composition of distant samples (minerals, organics, and chemicals) in real time is of interest for various fields including detecting explosives, geological surveying, and pollution mapping. For the past 10 years, the University of Hawaii has been developing standoff Raman systems suitable for measuring Raman spectra of various chemicals in daytime or nighttime. In this article we present standoff Raman spectra of various minerals and chemicals obtained from a distance of 120 m using single laser pulse excitation during daytime. The standoff Raman system utilizes an 8-inch Meade telescope as collection optics and a frequency-doubled 532 nm Nd: YAG laser with pulse energy of 100 mJ/pulse and pulse width of 10 ns. A gated intensified charge-coupled device (ICCD) detector is used to measure time-resolved Raman spectra in daytime with detection time of 100 ns. A gate delay of 800 ns (equivalent to target placed at 120 m distance) was used to minimize interference from the atmospheric gases along the laser beam path and near-field scattering. Reproducible, good quality single-shot Raman spectra of various inorganic and organic chemicals and minerals such as ammonium nitrate, potassium perchlorate, sulfur, gypsum, calcite, benzene, nitrobenzene, etc., were obtained through sealed glass vials during daytime. The data indicate that various chemicals could easily be identified from their Raman fingerprint spectra from a far standoff distance in real time using single-shot laser excitation.

Time-resolved remote Raman study of minerals under supercritical CO2 and high temperatures relevant to Venus exploration

We report time-resolved (TR) remote Raman spectra of minerals under supercritical CO2 (approx. 95 atm pressure and 423 K) and under atmospheric pressure and high temperature up to 1003 K at distances of 1.5 and 9 m, respectively. The TR Raman spectra of hydrous and anhydrous sulphates, carbonate and silicate minerals (e.g. talc, olivine, pyroxenes and feldspars) under supercritical CO2 (approx. 95 atm pressure and 423 K) clearly show the well-defined Raman fingerprints of each mineral along with the Fermi resonance doublet of CO2. Besides the CO2 doublet and the effect of the viewing window, the main differences in the Raman spectra under Venus conditions are the phase transitions, the dehydration and decarbonation of various minerals, along with a slight shift in the peak positions and an increase in line-widths. The dehydration of melanterite (FeSO4 · 7H2O) at 423 K under approximately 95 atm CO2 is detected by the presence of the Raman fingerprints of rozenite (FeSO4 · 4H2O) in the spectrum. Similarly, the high-temperature Raman spectra under ambient pressure of gypsum (CaSO4 · 2H2O) and talc (Mg3Si4O10(OH)2) indicate that gypsum dehydrates at 518 K, but talc remains stable up to 1003 K. Partial dissociation of dolomite (CaMg(CO3)2) is observed at 973 K. The TR remote Raman spectra of olivine, α-spodumene (LiAlSi2O6) and clino-enstatite (MgSiO3) pyroxenes and of albite (NaAlSi3O8) and microcline (KAlSi3O8) feldspars at high temperatures also show that the Raman lines remain sharp and well defined in the high-temperature spectra. The results of this study show that TR remote Raman spectroscopy could be a potential tool for exploring the surface mineralogy of Venus during both daytime and nighttime at short and long distances.

Remote-Raman spectroscopic study of minerals under supercritical CO2 relevant to Venus exploration.

The authors have utilized a recently developed compact Raman spectrometer equipped with an 85 mm focal length (f/1.8) Nikon camera lens and a custom mini-ICCD detector at the University of Hawaii for measuring remote Raman spectra of minerals under supercritical CO(2) (Venus chamber, ∼102 atm pressure and 423 K) excited with a pulsed 532 nm laser beam of 6 mJ/pulse and 10 Hz. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10× beam expander to a 1mm spot on minerals located at 2m inside a Venus chamber, it is possible to measure the remote Raman spectra of anhydrous sulfates, carbonates, and silicate minerals relevant to Venus exploration during daytime or nighttime with 10s integration time. The remote Raman spectra of gypsum, anhydrite, barite, dolomite and siderite contain fingerprint Raman lines along with the Fermi resonance doublet of CO(2). Raman spectra of gypsum revealed dehydration of the mineral with time under supercritical CO(2) at 423 K. Fingerprint Raman lines of olivine, diopside, wollastonite and α-quartz can easily be identified in the spectra of these respective minerals under supercritical CO(2). The results of the present study show that time-resolved remote Raman spectroscopy with a compact Raman spectrometer of moderate resolution equipped with a gated intensified CCD detector and low power laser source could be a potential tool for exploring Venus surface mineralogy both during daytime and nighttime from a lander.

Raman spectroscopy of titanomagnetites: Calibration of the intensity of Raman peaks as a sensitive indicator for their Ti content

Abstract A systematic study of the Raman spectra of the titanomagnetite solid-solution series (Fe3-xTixO4) for x = ~0.0, 0.2, 0.4, and 0.6 has been conducted. The samples showed combinations of five previously predicted Raman peaks at ~190, 310, 460, 540, and 670 cm-1 that correspond to vibrational modes with T2g(1), Eg, T2g(3), T2g(2), and A1g, respectively. The calibration of Raman spectra for titanomagnetite with known values of Ti concentrations reveals a strong dependence of relative intensity for the T2g(2) and T2g(3) modes on Ti concentration. The most prominent feature is the appearance and increase in the relative intensity of a T2g(3) peak above x = ~0.2. On the other hand, the Raman peak for the T2g(2) mode gradually diminishes as Ti increases and nearly disappears at x = ~0.6. Combining the two relative intensities potentially provides a sensitive indicator of Ti content. The technique was applied to study titanomagnetite in grains from Hana Volcanics and melatroctolite from Rhode Island.

Compact time-resolved remote Raman system for detection of anhydrous and hydrous minerals and ices for planetary exploration

The University of Hawaii and NASA Langley Research Center are developing small, compact, and portable remote Raman systems with pulsed lasers for planetary exploration under the Mars Instrument Development Program. The remote Raman instruments developed previously utilized small telescopes with clear apertures of 125 mm and 100 mm diameters and were able to detect water, ice, water bearing minerals, carbon in carbonate form in calcite, magnesite, dolomite, and siderite from a distance of 10 to 50 m under daytime and nighttime conditions. Recently, we significantly reduced the size of our time-resolved (TR) remote Raman system in order to build a compact system suitable for future space missions. This compact time-resolved Raman system was developed by utilizing (i) a regular 85 mm Nikon (F/1.8) lens with a clear aperture of 50 mm as a collection optic, and (ii) a miniature Raman spectrograph that is 1/14th in volume in comparison to the commercial spectrograph used in our previous work. In this paper, we present the TR remote Raman spectra obtained during daytime from various hydrous and anhydrous minerals, water, water-ice, and CO2-ice using this new compact remote Raman system to 50 m radial distance.

Raman spectroscopy of melamine at high pressures

In this work, the Raman scattering of melamine was studied under high pressure up to 25 GPa. Behavior of the most intensive peaks of the Raman spectrum of melamine, 677 cm?1 and 985 cm?1 modes, and their line widths do not show any phase transition or indication of formation of sp3 bonds. Comparing behavior of the line width of the Raman peaks of graphite under pressure and that of melamine leads us to conclude that the s-triasine ring is more rigid than the C-C graphite ring.

Ultraviolet Stand-off Raman Measurements Using a Gated Spatial Heterodyne Raman Spectrometer

A spatial heterodyne Raman spectrometer (SHRS) is evaluated for stand-off Raman measurements in ambient light conditions using both ultraviolet (UV) and visible pulsed lasers with a gated ICCD detector. The wide acceptance angle of the SHRS simplifies optical coupling of the spectrometer to the telescope and does not require precise laser focusing or positioning of the laser on the sample. If the laser beam wanders or loses focus on the sample, as long as it is in the field of view of the SHRS, the Raman signal will still be collected. The SHRS is not overly susceptible to vibrations, and a vibration isolated optical table was not necessary for these measurements. The system performance was assessed by measuring stand-off UV and visible Raman spectra of a wide variety of materials at distances up to 18 m, using 266 nm and 532 nm pulsed lasers, with 12.4 in. and 3.8 in. aperture telescopes, respectively.

Compact remote Raman and LIBS system for detection of minerals, water, ices, and atmospheric gases for planetary exploration

At the University of Hawaii, we have developed a compact, portable remote Raman and Laser-Induced Breakdown Spectroscopy (LIBS) system with a 532 nm pulsed laser for planetary exploration under the Mars Instrument Development Program. The compact time-resolved remote Raman and LIBS system consists of (i) a regular 85 mm Nikon (F/1.8) camera lens with clear aperture of 50 mm as collection optics, (ii) a miniature spectrograph that occupies 1/14th the volume of a comparable commercial spectrograph from Kaiser Optical Systems Inc., (iii) a custom mini-ICCD detector, and (iv) a small frequency-doubled 532 nm Nd:YAG pulsed laser (30 mJ/pulse, 20 Hz) with a 10x beam expander. In the standoff Raman mode the system is capable of measuring various minerals, water, ices, and atmospheric gases from a 50 meter range with a 10 s integration time. At shorter distances of 10 m or less, good quality Raman spectra can be obtained within 1 s. The time-gated system is capable of detecting both the target mineral as well as the atmospheric gases before the target using their Raman fingerprints. Various materials can easily be identified through glass, plastic, and water media. The time-gating capability makes the system insensitive to window material, which is highly desirable for future missions to Venus where instruments are expected to be within the lander. The standoff LIBS range is 10 m and LIBS spectra of various minerals can be obtained with single laser pulse excitation. The standoff LIBS capability provides additional elemental verification of the targeted material.

Compact standoff Raman system for detection of homemade explosives

We present data on standoff detection of chemicals used in synthesis of homemade explosives (HME) using a compact portable standoff Raman system developed at the University of Hawaii. Data presented in this article show that good quality Raman spectra of various organic and inorganic chemicals, including hazardous chemicals such as ammonium nitrate, potassium nitrate, potassium perchlorate, sulfur, nitrobenzene, benzene, acetone, and gasoline, can be easily obtained from remote distances with a compact standoff Raman system utilizing only a regular 85 mm Nikon camera lens as collection optics. Raman spectra of various chemicals showing clear Raman fingerprints obtained from targets placed at 50 m distance in daylight with 1 to 10 second of integration time are presented in this article. A frequency-doubled mini Nd:YAG pulsed laser source (532 nm, 30 mJ/pulse, 20 Hz, pulse width 8 ns) is used in an oblique geometry to excite the target located at 50 m distance. The standoff Raman system uses a compact spectrograph of size 10 cm (length) × 8.2 cm (width) × 5.2 cm (height) with spectral coverage from 100 to 4500 cm-1 Stokes-Raman shifted from 532 nm laser excitation and is equipped with a gated thermo-electrically cooled ICCD detector. The system is capable of detecting both the target as well as the atmospheric gases before the target. Various chemicals could be easily identified through glass, plastic, and water media. Possible applications of the standoff Raman system for homeland security and environmental monitoring are discussed.