Johannes Kepler University, Biophysics Institute, Gruberstr. 40, 4020 Linz, Austria.
Nanoscale. 2019 Mar 7;11(10):4303-4309. doi: 10.1039/c8nr05880f.
We investigate the nearfield dipole mobility of protein membranes in a wide frequency range from 3 kHz to 10 GHz. The results of our nanoscale dielectric images and spectra of bacteriorhodopsin (bR) reveal Debye relaxations with time constants of τ ∼ 2 ns and τ ∼ 100 ns being characteristic of the dipole moments of the bR retinal and α-helices, respectively. However, the dipole mobility and therefore the protein biophysical function depend critically on the amount of surface water surrounding the protein, and the characteristic mobility in the secondary structure is only observed for humidity levels <30%. Our results have been achieved by adding the frequency as a second fundamental dimension to quantitative dielectric microscopy. The key elements for the success of this advanced technique are the employed heterodyne detection scheme, the broadband electrical signal source, a high frequency optimized cabling, development of calibration procedures and precise finite element modelling. Our study demonstrates the exciting possibilities of broadband dielectric microscopy for the investigation of dynamic processes in cell bioelectricity at the individual molecular level. Furthermore, the technique may shed light on local dynamic processes in related materials science applications like semiconductor research or nano-electronics.
我们研究了蛋白质膜在从 3 kHz 到 10 GHz 的宽频率范围内的近场偶极子迁移率。我们对细菌视紫红质（bR）的纳米级介电图像和光谱的研究结果揭示了具有时间常数 τ ∼ 2 ns 和 τ ∼ 100 ns 的德拜弛豫，分别为 bR 视黄醛和α-螺旋的偶极矩的特征。然而，偶极子迁移率，因此，蛋白质的生物物理功能，取决于周围蛋白质的表面水量，并且只有在湿度水平<30%时才能观察到二级结构中的特征迁移率。我们的结果是通过将频率作为第二个基本维度添加到定量介电显微镜中来实现的。这项先进技术成功的关键要素是所采用的外差检测方案、宽带电信号源、高频优化布线、校准程序的开发和精确的有限元建模。我们的研究展示了宽带介电显微镜在单个分子水平上研究细胞生物电学中动态过程的令人兴奋的可能性。此外，该技术可能揭示相关材料科学应用（如半导体研究或纳米电子学）中局部动态过程的奥秘。
