利用細菌視紫紅質以探討類雙閘極有機場效電晶體

Abstract

從嗜鹽古細菌的細胞膜上發現的細菌視紫紅質HmBRI之突變種 HmBRI-D94N是一種由光驅動的氫離子幫浦。HmBRI-D94N內部的全反式retinal在吸收光能之後改變構形，進而使HmBRI-D94N依序放出和吸收一個氫離子。這個光敏感蛋白質可以在光照下瞬間酸化周遭環境，造成一個短時間的pH值變化。本實驗利用HmBRI-D94N氫離子幫浦探討其對於有機場效電晶體 (OFET) 造成的影響。更進一步，HmBRI-D94N是吸收波長為550 nm附近的綠光而受驅動，期望做出對綠光敏感的光感元件。本實驗使用四種高分子，其中三種屬於主要傳遞電洞的p-type高分子材料—P3HT, PDPPT2, PffBT4T，以及一種屬於主要傳遞電子的n-type高分子材料—PNDIT2。這四種共軛高分子都是典型且常應用在OFET的半導體高分子材料，藉由探討氫離子幫浦對於此四種材料的影響，推測出其元件內可能發生的機制。一般元件使用n-doped的silicon wafer作為底部介電質層，而在本實驗所設計的元件中，將光視作為一閘極偏壓，影響置於半導體層上方的細菌視紫紅質，從實驗結果可得知，在綠光的照射下，對於n-type材料並無顯著變化，然而，對於p-type材料卻有光敏性的提升，因此認為retinal在變化構型時存在一偶極矩的改變，進而影響半導體層，形成一類似於雙閘極有機場效電晶體的元件。

HmBRI-D94N is a light-driven proton pump, which is functioned by a series of conformational changes of the retinal inside the protein under light illumination. Conjugated polymers are potential candidates for biological interfacing because they have structural and transport properties that are intermediate to those of the two extremes: soft biological systems and hard inorganic electronics. In this research, fabrication of dual-gate organic field-effect transistors (DG-OFETs) by integrating HmBRI-D94N with conjugated polymers, i.e. P3HT, PDPPT2, PffBT4T, PNDIT2, respectively, is attempted. Conventional n-doped silicon is chosen as the bottom gate, while light serves as the pseudo top gate to modulate the conformation of HmBRI-D94N locating on top of the polymer charge-transporting layer. As a result, HmBRI-D94N shows a marginal effect on the photosensitivity of n-type material devices. However, the photosensitivity of p-type material devices containing HmBRI-D94N is evident, especially under green-light illumination. It is envisaged that HmBRI-D94N functions as a dielectric layer between light and semiconducting layer. Subsequent to the light absorption, the conformational change of HmBRI-D94N would result in the variation in the interfacial dipole between HmBRI-D94N and a p-type polymer, resulting in the threshold-voltage shift and the apparent photosensitivity. DG-OFETs can thus be realized.