The biological effects associated with Terahertz (THz) radiation are not well characterized. In this study, we
investigated the cellular response of human dermal fibroblasts exposed to an optically-pumped molecular gas THz laser
(υ = 2.52 THz, irradiance = 84.8 mW/cm2, exposure duration = 5 to 80 minutes). Computational dosimetry was
conducted using finite-difference time-domain (FDTD) modeling techniques. Empirical dosimetry was conducted using
infrared cameras and thermocouples. Cellular viability was assessed 24 h post-exposure using MTT calorimetric assays.
Quantitative PCR was performed 4 h post-exposure to evaluate the transcriptional activation of genes involved in protein
and DNA damage pathways. Comparable analyses were also performed for hyperthermic and genotoxic positive control
samples. For all of the exposure durations tested, we found that greater than 95% of the cells were viable post-exposure.
In addition, the exposed cells showed only minor increases
(~3.5-fold) in heat shock protein expression. The empirical
dosimetric data showed that the temperature of the cells increased by ~3 °C during exposure. This value was consistent
with that predicted by the computational models. Interestingly, although the THz-exposed cells exhibited increases in
heat shock protein expression, the magnitude of these increases was comparable to those observed in hyperthermic
controls. In addition, none of the DNA repair genes tested were up-regulated in the THz-exposed cells, whereas 40-fold
increases were observed in the genotoxic control cells. These results suggest that the biological effects imposed by THz
radiation appear to be primarily photothermal in nature.