Elucidating molecular mechanisms of rhodopsin signal transduction is crucial for understanding photo-reaction process and vision. In particular, a conformational change of retinal from 11-cis to all-trans configuration initiates a chain reaction. Earlier studies on photoinduced isomerization provided that chromophore retinal has torsional vibration modes related to the photoisomerization dynamics at very low frequency regime, including terahertz (THz) frequency. However, limited success has been made in detecting such change using low frequency electromagnetic wave, due to its extremely small absorption cross section within allowed signal-to-noise level. Here, we developed an ultrasensitive terahertz molecule sensor that allows us to detect the conformational change from 11-cis to all-trans state of retinal embedded in photoreceptor-nanovesicles. Nano-slot antenna array fabricated onto SiO2/Si substrate was used as a sensing chip for enhancing THz reflection signal change under photo excitation. In particular, THz top-down reflection system in normal geometry enabled us to measure extremely small changes in signal by dramatically reducing undesired light paths through several substrates, cover glass, and the absorptive sample itself, all of which comprise unavoidable parts in typical transmission measurement cases. Moreover, a direct monitoring of a photo-induced conformational change in photoreceptors could be performed at room temperature and in a label-free and a non-contact manner.
Bibliographical noteFunding Information:
This research was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2016R1A2B2010858 and 2018R1A2B3004498, and and the Global Frontier Program CAMM-2016M3A6B3936653) and KIST intramural grants (2E28280 and 2V05880).
© 2018 Elsevier B.V.
- Conformational change
- Terahertz spectroscopy