Peeyush Sahay

Breath Analysis Using Laser Spectroscopic Techniques: Breath Biomarkers, Spectral Fingerprints, and Detection Limits

Breath analysis, a promising new field of medicine and medical instrumentation, potentially offers noninvasive, real-time, and point-of-care (POC) disease diagnostics and metabolic status monitoring. Numerous breath biomarkers have been detected and quantified so far by using the GC-MS technique. Recent advances in laser spectroscopic techniques and laser sources have driven breath analysis to new heights, moving from laboratory research to commercial reality. Laser spectroscopic detection techniques not only have high-sensitivity and high-selectivity, as equivalently offered by the MS-based techniques, but also have the advantageous features of near real-time response, low instrument costs, and POC function. Of the approximately 35 established breath biomarkers, such as acetone, ammonia, carbon dioxide, ethane, methane, and nitric oxide, 14 species in exhaled human breath have been analyzed by high-sensitivity laser spectroscopic techniques, namely, tunable diode laser absorption spectroscopy (TDLAS), cavity ringdown spectroscopy (CRDS), integrated cavity output spectroscopy (ICOS), cavity enhanced absorption spectroscopy (CEAS), cavity leak-out spectroscopy (CALOS), photoacoustic spectroscopy (PAS), quartz-enhanced photoacoustic spectroscopy (QEPAS), and optical frequency comb cavity-enhanced absorption spectroscopy (OFC-CEAS). Spectral fingerprints of the measured biomarkers span from the UV to the mid-IR spectral regions and the detection limits achieved by the laser techniques range from parts per million to parts per billion levels. Sensors using the laser spectroscopic techniques for a few breath biomarkers, e.g., carbon dioxide, nitric oxide, etc. are commercially available. This review presents an update on the latest developments in laser-based breath analysis.

Measurements of the weak UV absorptions of isoprene and acetone at 261-275 nm using cavity ringdown spectroscopy for evaluation of a potential portable ringdown breath analyzer.

The weak absorption spectra of isoprene and acetone have been measured in the wavelength range of 261–275 nm using cavity ringdown spectroscopy. The measured absorption cross-sections of isoprene in the wavelength region of 261–266 nm range from 3.65 × 10−21 cm2·molecule−1 at 261 nm to 1.42 × 10−21 cm2·molecule−1 at 266 nm; these numbers are in good agreement with the values reported in the literature. In the longer wavelength range of 270–275 nm, however, where attractive applications using a single wavelength compact diode laser operating at 274 nm is located, isoprene has been reported in the literature to have no absorption (too weak to be detected). Small absorption cross-sections of isoprene in this longer wavelength region are measured using cavity ringdown spectroscopy for the first time in this work, i.e., 6.20 × 10−23 cm2·molecule−1 at 275 nm. With the same experimental system, wavelength-dependent absorption cross-sections of acetone have also been measured. Theoretical detection limits of isoprene and comparisons of absorbance of isoprene, acetone, and healthy breath gas in this wavelength region are also discussed.

Fiber Loop Ringdown Sensor for Potential Real-Time Monitoring of Cracks in Concrete Structures: An Exploratory Study

A fiber loop ringdown (FLRD) concrete crack sensor is described for the first time. A bare single mode fiber (SMF), without using other optical components or chemical coatings, etc., was utilized to construct the sensor head, which was driven by a FLRD sensor system. The performance of the sensor was evaluated on concrete bars with dimensions 20 cm × 5 cm × 5 cm, made in our laboratory. Cracks were produced manually and the responses of the sensor were recorded in terms of ringdown times. The sensor demonstrated detection of the surface crack width (SCW) of 0.5 mm, which leads to a theoretical SCW detection limit of 31 μm. The sensors response to a cracking event is near real-time (1.5 s). A large dynamic range of crack detection ranging from a few microns (μm) to a few millimeters is expected from this sensor. With the distinct features, such as simplicity, temperature independence, near real-time response, high SCW detection sensitivity, and a large dynamic range, this FLRD crack sensor appears promising for detections of cracks when embedded in concrete.

Electron impact excitation-cavity ringdown absorption spectrometry of elemental mercury at 405 nm

We report a new method of measuring elemental mercury (Hg) at the 405 nm transition line, which corresponds to the optical transition from the metastable state 5d106s6p 3P0 to the upper state 5d106s7s 3S1. Observation of the absorption spectra and measurements of the absolute number density of Hg in the metastable state are achieved by a stepwise electron impact excitation-cavity ringdown absorption technique, in which the population of Hg atoms in the metastable state is realized through electron impact excitation by the energetic electrons (< 10 eV) generated in an atmospheric argon microwave plasma torch and the detection of Hg is achieved via cavity ringdown spectroscopy (CRDS). The major difference between this method and the previously reported detection of Hg at 254 nm using the plasma-CRDS technique is that the plasma in this method not only serves as an atomization source to generate Hg atoms from the Hg-contained compounds injected in the plasma, but also functions as an electron impact excitation source. The merit in terms of analytical instrumentation is that this new method introduces an alternative way to measure Hg using a palm-size 405 nm laser source. This can potentially lead to a portable mercury ringdown spectrometer without constraints of importability of 254 nm laser sources. Compared with the 254 nm line, the 405 nm line has no plasma-associated spectroscopic interferences, such as absorption of the OH rovibrational lines. One analytical limitation of the detection of Hg at 405 nm is the low detection sensitivity achieved in this exploratory study, 50 μg ml−1 in aqueous sample solutions, compared with the previously reported detection sensitivity of 9.1 ng ml−1 using the plasma-CRDS technique at 254 nm. Given an improved plasma excitation source-CRDS system, theoretical detection limits at 405 nm are estimated to be 50 ng ml−1 and 1.2 ppbv in aqueous samples and in gaseous samples, respectively. These sensitivities are still desirable in many applications when real-time, portable, and in-line analysis all become a major concern.

A portable optical emission spectroscopy-cavity ringdown spectroscopy dual-mode plasma spectrometer for measurements of environmentally important trace heavy metals: Initial test with elemental Hg

A portable optical emission spectroscopy-cavity ringdown spectroscopy (OES-CRDS) dual-mode plasma spectrometer is described. A compact, low-power, atmospheric argon microwave plasma torch (MPT) is utilized as the emission source when the spectrometer is operating in the OES mode. The same MPT serves as the atomization source for ringdown measurements in the CRDS mode. Initial demonstration of the instrument is carried out by observing OES of multiple elements including mercury (Hg) in the OES mode and by measuring absolute concentrations of Hg in the metastable state 6s6p (3)P(0) in the CRDS mode, in which a palm-size diode laser operating at a single wavelength 405 nm is incorporated in the spectrometer as the light source. In the OES mode, the detection limit for Hg is determined to be 44 parts per 10(9) (ppb). A strong radiation trapping effect on emission measurements of Hg at 254 nm is observed when the Hg solution concentration is higher than 50 parts per 10(6) (ppm). The radiation trapping effect suggests that two different transition lines of Hg at 253.65 nm and 365.01 nm be selected for emission measurements in lower (<50 ppm) and higher concentration ranges (>50 ppm), respectively. In the CRDS mode, the detection limit of Hg in the metastable state 6s6p (3)P(0) is achieved to be 2.24 parts per 10(12) (ppt) when the plasma is operating at 150 W with sample gas flow rate of 480 mL min(-1); the detection limit corresponds to 50 ppm in Hg sample solution. Advantage of this novel spectrometer has two-fold, it has a large measurement dynamic range, from a few ppt to hundreds ppm and the CRDS mode can serve as calibration for the OES mode as well as high sensitivity measurements. Measurements of seven other elements, As, Cd, Mn, Ni, P, Pb, and Sr, using the OES mode are also carried out with detection limits of 1100, 33, 30, 144, 576, 94, and 2 ppb, respectively. Matrix effect in the presence of other elements on Hg measurements has been found to increase the detection limit to 131 ppb. These elements in lower concentrations can also be measured in the CRDS mode when a compact laser source is available to be integrated into the spectrometer in the future. This exploratory study demonstrates a new instrument platform using an OES-CRDS dual-mode technique for potential field applications.

Abstract 4592: MUC13 interaction with receptor tyrosine kinase HER2 drives pancreatic ductal adenocarcinoma progression

Background: Pancreatic Ductal Adenocarcinoma (PDAC) is the fourth leading cause of cancer related death in the United States and has a very poor survival rate due to late diagnosis. MUC13 is a recently identified high molecular weight glycoprotein that is upregulated in PDAC and its progression is allowed via alterations of multiple signaling pathways. MUC13 is aberrantly expressed in PDAC and generally correlates with increased expression of HER2, however, the underlying mechanism remains poorly understood. MUC13 consists of three EGF-like domains that may serve as a ligand for EGF receptors, such as HER2, and modulate EGFR signaling pathways. We sought to better characterize the interaction of MUC13 with HER2 in PDAC. Methods: MUC13 and HER2 interaction was studied using reciprocal co-immunoprecipitation, immunofluorescence, proximity ligation, Western blotting, co-capping assays in human PDAC cell lines and immunohistofluorescence techniques in human tissues. Tissue microarrays prepared from formalin-fixed, paraffin-embedded specimens of PDAC were assessed for expression of MUC13 and HER2 using our own laboratory generated anti-MUC13 mouse monoclonal antibody (MAb) through confocal immunofluorescence. The association of MUC13 and HER2 co-localization with nuclear chromatin organization was analyzed to study the stage or degree of aggressiveness of the pancreatic cancer using Dapi stained confocal images of tissues. Results: MUC13 co-localizes and interacts with HER2 in PDAC cell lines. The results from this study demonstrate that MUC13 functionally interacts and activates HER2 at Tyrp1248 in PDAC cells, leading to stimulation of HER2 signaling cascade including, ERK1/2, FAK, AKT and PAK1 as well as regulation of the growth, cytoskeleton remodeling, motility and invasion of PDAC cells - all collectively contributing to PDAC progression. The interaction between MUC13-HER2 binding resulting in their tumorigenic characteristics likely occurs at the 1st and 2nd but not the 3rd domains of MUC13 as the EGF 1 and 2 deletion mutant constructs of MUC13 failed to promote proliferation and invasion of cells. These phenotypic effects of MUC13-HER2 co-localization could be effectively compromised by depleting MUC13. MUC13-HER2 co-localization also held true in PDAC human tissues with a strong functional correlation that contributed to an increased degree of disorder and cancer aggressiveness. Conclusions: 1) MUC13 can be detected in formalin-fixed paraffin-embedded tissues using our anti-MUC13 MAb. 2) MUC13 co-localizes and activates HER2 and its downstream signaling cascade promoting PDAC progression in both cell lines and human tissue. 3) This process is reversed by depletion of MUC13. 4) This MUC13-HER2 interaction may potentially be manipulated for targeted therapeutics in patients harboring PDAC. Citation Format: Sheema Khan, Mara C. Ebeling, Mohammad Sikander, Murali M. Yallapu, Tomoko Ise, Satoshi Nagata, Stephen W. Behrman, Nadeem Zafar, Jim Y. Wan, Hemendra M. Ghimire, Peeyush Sahay, Prabhakar Pradhan, Meena Jaggi, Subhash C. Chauhan. MUC13 interaction with receptor tyrosine kinase HER2 drives pancreatic ductal adenocarcinoma progression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4592.