2019/11/9 Photosystems - Key proteins in photosynthesis - PowerPoint PPT Presentation

2019/11/9 Photosystems - Key proteins in photosynthesis 東京大学 大学院理学系研究科 山野井 慶徳 シアノバクテリアの光化学系Iを活用した電極の作製と物性評価 FNR CO 2 Glucose 研究概要 Fd 本研究では、光合成タンパク質複合体の高い光電変換能を最大限に利用するた H 2 O O 2 め、これらのタンパク質と微小電極を組み合わせた光センサを構築した。具体的 Photosystem II Photosystem I には、グラフェンFET上に金ナノ粒子と光化学系Iを固定化し、グラフェンの I - V (PSII) (PSI) 特性変化から光を検出する手法について研究を行った。まずグラフェン上にナノ Cyt. 粒子と光化学系Iを固定化する最適条件を見出した。続いてグラフェンFET上にこ b 6 /f れらを固定化し、励起光照射下での I - V 特性を調査した。 ATP Thylakoid Chloroplast Q Synthaze membrane 今後の展望 研究結果をもとに、最終的には微小電極上に1つの光化学系Iを固定化し、電圧 H 2 O e - PC 測定によって単電子移動を観測することを目指している。電気化学測定によって ½ O 2 + 2H + 単電子移動を捉えられれば、生体分子を用いた単光子検出システムとして、学術 Photo-electric conversion 上、応用上ともに重要な成果となる。 現在は、グラフェンFET上の金ナノ粒子と光化学系Iを用いて微弱光の検出を目 Φ ≈ 100 % 指している。本研究を通して、グラフェンを用いた光検知という新たな研究領域 を開拓できる。 Photosystems are promising materials for new light sensing devices. Previous research on PSI Development of the previous research “Bio-photosensor” invented by our research group Previous system Ideal system Input (light signal) Photons Photon Light PSI particles PSI Potentiostat Photosystem I e - Gold Output (electric signals) nanoparticle One signal Signals  The electrode was large.  The electrode is small. Gate of FET  A large number of photons  One single photon ➝ One signal ➝ One signal Terasaki, N. Hiraga, T. Inoue, Y. Nishihara, H. Minakata, M. Fujii, M. et al. Biochimica et Biophysica Acta, Bioenergetics 2007, 1767 , 653-659. Use a small electrode to fabricate the light sensor PSI = New material for light sensors ➝ Convert every single photon into an electric signal 1

2019/11/9 Graphene field effect transistors for sensors My research objective A light sensor based on PSI, AuNPs and graphene FET Structure of graphene FETs Change in the drain current for the single photon detection induced by biomolecules Gold hν Top gate PSI nanoparticles (AuNPs) Drain Linker e - molecule ΔI sd Source Small-sized Ohno, Y. et al. Biosens. Bioelectron. 2010, 26, 1727-1730. graphene Highly sensitive detection Silicon Substrate of biological and chemical Electron transfer ➝ Change in the source-drain current (I sd ) Zaifuddin, N. M. et al. J. Appl. Phys . 2013 , 5 2, molecules. 06GK04-1/06GK04-4. Synthesis of gold nanoparticles PSI and graphene FET PSI : Tokyo University of Science (Prof. Tomo’s lab) tetraoctylamm- hexanethiol T. elongatus (BP-1) PSI in buffer solution onium bromide [TBA] + AuCl 4- HAuCl 4 aq Isolation and Au purification toluene NaBH 4 2 µm Transmission electron Size distribution microscopy (TEM) analysis 45 40 Graphene FET: Tokyo University of Agriculture and Technology 35 (Prof. Maehashi’s lab) 30 Average diameter Counts Graphene 25 2.3 ± 0.6 nm 20 15 10 5 52 graphene Source Drain 12 µm 0 samples 20 nm 5 µm Diameter (nm) 2

2019/11/9 Functionalization of the electrode Immobilized AuNPs or PSI on graphene AuNP deposition on graphene Atomic force microscopy (AFM) analysis Deposition of Au AuNP or PSI AuNPs (1 µM, 24 h) PSI (100 nM, 2 h) Graphene AuNPs DMF CH 2 Cl 2 1 h 24 h 400 nm 400 nm Graphene on a Si substrate PSI immobilization AuNPs : 4-6 nm PSI PSI : 8-10 nm (including protecting ligands) Height (nm) 10 10 1. PSI 5 5 Au Au Au 2. Coupling Phosphate 0 0 reagent buffer2 h 0 0.5 1 1.5 2 0 0.5 1 1.5 2 (EDC / NHS) Position (µm) Position (µm) Immobilized AuNPs and PSI on a graphene FET FET measurements - Experimental setup Scanning electron Source-drain current (I sd ) Excitation Deposition of AuNP and PSI microscopy (SEM) analysis against Gate voltage (V G ) light Reference PSI in electrode Graphene Electrolyte Charge neutrality buffer point (CNP) V G Gold electrode ≈ 1 µm Source Drain AuNPs in CH 2 Cl 2 ≈ AFM image of PSI and AuNP on graphene 20 15 Electrode Rubber pool PSI + AuNP Height Tran, T.-T.; Mulchandani, A. Trends in Analytical Chemistry 2016 , 79 , 222-232. 10 ≈ 14 nm AuNPs 4-6 nm Electrolyte: Illumination of excitation light 5 100 mM NaClO 4 , 250 mM PSI 8-10 nm 0 ➝ Charge transfer (PSI/AuNPs) NaAsc, 2.5 mM DCIP, 20 mM 200 nm 0 0.2 0.4 0.6 0.8 1 MES (pH 6.4) ➝ Shifts in CNPs Position (µm) 3

2019/11/9 FET measurements - Results Mechanisms of the hole doping effect Source-drain current under illumination Mechanism 1 : Gating effect Mechanism 2 : Electron transfer 12 1: dark CNP2 CNP1 1 2: 680 nm Intensity = 20% Reference Reference Asc + 10 2 Asc O 2 3: 440 nm Intensity = 20% electrode electrode I sd (µA) Light Light 3 4: 440 nm Intensity = 40% 8 5: dark 4 PSI e - 6 5 CNP1 CNP2 ions e - 0 50 100 150 200 1 + 1 ７ 2 mV + 146 mV V G (mV) － － － － 8 h + h + Source Drain Source Drain 2 + 172 mV + 146 mV + + + + + + +2 mV +4 mV 1 0 0 7.6 3 + 174 mV + 150 mV I sd I sd 2 4 + 175 mV + 150 mV I sd (µA) 7.2 3 e.g. Charged proteins adsorbed e.g. Redox reactions on the 5 + 174 mV + 152 mV 6.8 on the graphene FET surface of graphene FET 4 Blue light irradiation 6.4 5 Kim, J. E.; No, Y. H.; Kim, J. N.; Shin, Y. S.; Kang, W. ➝ h + doping of graphene T.; Kim. Y. R.; Kim, K. N.; Kim, Y. H., Yu, Q. J. Appl. 140 160 180 200 Phys. Lett. 2017 , 110 , 203702. V G (mV) Improvement : Increase the Debye length Results – Light irradiation and CNP shifts Debye length [ l D ] Without hexylamine With hexylamine = Thickness of the electric double layer 89 86 Biomolecules larger than l D cannot be detected. 88 84 l D I sd (µA) 𝝁 𝑬 = 𝟏. 𝟒𝟔 𝑱 �𝟐/𝟑 I sd (µA) 87 𝑱 : inonic strength 82 Dark Dark 86 Weak ionic strength 680 nm 680 nm Maehashi, K.; Ohno, Y.; Matsumoto, K. Nanobiosensors in 80 85 Detection of large molecules Disease Diagnosis 2016 , 5 , 1-13. 160 200 240 280 -300 -250 -200 -150 V G (mV) V G (mV) Hexylamine Introduce hexylamine to No shift in the CNPs Unstable I - V curves or increase the Debye length Negative CNP (-203 mV) Positive CNP (+227 mV) 4

2019/11/9 Effect of hexylamine Two possible solutions With hexylamine Without hexylamine 1. Use cationic and anionic 2. Decrease the concentration detergents of the electrolyte - - Cationic Anionic Hexylamine Adsorbed detergent graphene detergent Asc - + + + + Asc - + + - - - - - - - ○ Si Adsorbed anions Adsorbed hexylamine ➝ Positive CNPs ➝ Negative CNPs Increase in the Debye length & Neutral surface charge Hydrophobic environment was introduced by hexylamine. ➝ Improvement in the sensitivity toward the light The I - V curves were unstable under the negative V G . Conclusions  Gold nanoparticles and photosystem I were immobilized on graphene field effect transistors to fabricate a light sensor.  Light irradiation induced slightly positive shifts in the charge neutrality points of graphene.  Further improvements would be possible by optimizing the electrolyte composition. 5