A highly sensitive and selective method, using isotope-dilution liquid chromatography with tandem mass spectrometry (LC/MS/MS), for quantification of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), an important biomarker of oxidative stress, was developed and compared with a method using an enzyme-linked immunosorbent assay (ELISA). The synthesis of (15)N(5)-8-OHdG is described. In this study, 140 urine samples were collected from workers in a coke oven plant, including samples from 49 control workers and 91 workers who had been occupationally exposed to polyaromatic hydrocarbons (PAHs). The major urinary metabolite of PAHs, 1-hydroxypyrene (1-OHP), was measured for the exposed workers. Results from the present study showed a significant correlation between these two measurements for determination of 8-OHdG (p < 0.05, r(2) = 0.70). However, only the LC/MS/MS measurements of urinary levels of 8-OHdG showed a significant difference between the exposed and the control subjects (p < 0.05). The ELISA method failed to demonstrate this difference. Furthermore, only by using the LC/MS/MS method was a significant correlation observed between the urinary levels of 1-OHP and 8-OHdG. These findings suggest that a highly specific and sensitive analytical method such as isotope-dilution LC/MS/MS is extremely important and necessary for accurate measurement and a comprehensive study of oxidative stress in human subjects.

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The purposes of the present study were: (i) to investigate the potential use of several biomarkers as quantitative indicators of the in vivo conversion of ethylene (ET) to ethylene oxide (EO); (ii) to produce molecular dosimetry data that might improve assessment of human risk from exogenous ET exposures. Groups (n = 7/group) of male F344 rats and B6C3F1 mice were exposed by inhalation to 0 and 3000 p. p.m. ET for 1, 2 or 4 weeks (6 h/day, 5 days/week) or to 0, 40, 1000 and 3000 p.p.m. ET for 4 weeks. N:-(2-hydroxyethyl)valine (HEV), N:7-(2-hydroxyethyl) guanine (N7-HEG) and HPRT: mutant frequencies were assessed as potential biomarkers for determining the molecular dose of EO resulting from exogenous ET exposures of rats and mice, compared with background biomarker values. N7-HEG was quantified by gas chromatography coupled with high resolution mass spectrometry (GC-HRMS), HEV was determined by Edman degradation and GC-HRMS and HPRT: mutant frequencies were measured by the T cell cloning assay. N7-HEG accumulated in DNA with repeated exposure of rodents to 3000 p.p.m. ET, reaching steady-state concentrations around 1 week of exposure in most tissues evaluated (brain, liver, lung and spleen). The dose-response curves for N7-HEG and HEV were supralinear in exposed rats and mice, indicating that metabolic activation of ET was saturated at exposures >/=1000 p.p.m. ET. Exposures of mice and rats to 200 p.p.m. EO for 4 weeks (as positive treatment controls) led to significant increases in HPRT: mutant frequencies over background in splenic T cells from exposed rats and mice, however, no significant mutagenic response was observed in the HPRT: gene of ET-exposed animals. Comparisons between the biomarker data for both unexposed and ET-exposed animals, the dose-response curves for the same biomarkers in EO-exposed rats and mice and the results of the rodent carcinogenicity studies of ET and EO suggest that too little EO arises from exogenous ET exposure to produce a significant mutagenic response or a carcinogenic response under standard bioassay conditions.

THz radiation is generated from topological insulators using femtosecond laser pulses. Two‐channel free carrier absorption with bulk and surface carriers is indispensable to explaining the strong dependence of THz emission power on the carrier concentration. The characteristics of THz emission provide valuable information regarding the fundamental properties of Dirac fermions.

The recent focus on topological insulators is due to the scientific interest in the new state of quantum matter as well as the technology potential for a new generation of THz optoelectronics, spintronics and quantum computations. It is important to elucidate the dynamics of the Dirac fermions in the topologically protected surface state. Hence we utilized a novel ultrafast optical pump mid-infrared probe to explore the dynamics of Dirac fermions near the Dirac point. The femtosecond snapshots of the relaxation process were revealed by the ultrafast optics. Specifically, the Dirac fermion-phonon coupling strength in the Dirac cone was found to increase from 0.08 to 0.19 while Dirac fermions were away from the Dirac point into higher energy states. Further, the energy-resolved transient reflectivity spectra disclosed the energy loss rate of Dirac fermions at room temperature was about 1 meV/ps. These results are crucial to the design of Dirac fermion devices.