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

2019/11/9 1

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 研究概要 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 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 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 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 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 れらを固定化し、励起光照射下でのI-V特性を調査した。 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 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 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 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 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 - Key proteins in photosynthesis

Chloroplast CO2 H2O Glucose O2

Photosystems are promising materials for new light sensing devices. Photo-electric conversion Φ ≈ 100 %

Q PC

Photosystem II (PSII)

Cyt. b6/f

H2O ½ O2 + 2H+ Fd FNR

Thylakoid membrane ATP Synthaze

Photosystem I (PSI) e- Photosystem I Gold nanoparticle Gate of FET Photon

Input (light signal) Output (electric signals)

“Bio-photosensor” invented by our research group e-

Terasaki, N. Hiraga, T. Inoue, Y. Nishihara, H. Minakata,

• M. Fujii, M. et al. Biochimica et Biophysica Acta,

Bioenergetics 2007, 1767, 653-659.

Previous research on PSI

PSI = New material for light sensors

Development of the previous research

Use a small electrode to fabricate the light sensor

 The electrode is small.  One single photon ➝ One signal

Previous system Ideal system

 The electrode was large.  A large number of photons ➝ One signal One signal Light

PSI particles Potentiostat

➝ Convert every single photon into an electric signal

Signals Photons

PSI

2019/11/9 2 Graphene field effect transistors for sensors

Highly sensitive detection

• f biological and chemical

molecules.

Structure of graphene FETs Change in the drain current induced by biomolecules

Zaifuddin, N. M. et al. J. Appl. Phys. 2013, 52, 06GK04-1/06GK04-4. Ohno, Y. et al. Biosens. Bioelectron. 2010, 26, 1727-1730.

My research objective

Drain Small-sized graphene PSI Gold nanoparticles (AuNPs)

Linker molecule

Top gate

Silicon Substrate

Source hν ΔIsd

A light sensor based on PSI, AuNPs and graphene FET for the single photon detection Electron transfer ➝ Change in the source-drain current (Isd) e-

Synthesis of gold nanoparticles

HAuCl4aq

hexanethiol

Au

tetraoctylamm-

• nium bromide

toluene

[TBA]+ AuCl4-

NaBH4

5 10 15 20 25 30 35 40 45

Counts Diameter (nm)

Size distribution Average diameter 2.3±0.6 nm Transmission electron microscopy (TEM) analysis

20 nm

PSI and graphene FET

PSI : Tokyo University of Science (Prof. Tomo’s lab)

• T. elongatus (BP-1)

Isolation and purification

Graphene FET: Tokyo University of Agriculture and Technology (Prof. Maehashi’s lab)

Source Drain Graphene 12 µm 5 µm PSI in buffer solution 52 graphene samples

2 µm

2019/11/9 3 Functionalization of the electrode

DMF 1 h AuNPs CH2Cl2 24 h Au Graphene

• 2. Coupling

reagent (EDC / NHS) PSI Phosphate buffer2 h 1. PSI Au

AuNP deposition on graphene PSI immobilization

Au Au

Immobilized AuNPs or PSI on graphene

5 10 0.5 1 1.5 2

Height (nm) Position (µm)

5 10 0.5 1 1.5 2

Position (µm)

AuNPs (1 µM, 24 h) PSI (100 nM, 2 h) AuNPs : 4-6 nm

(including protecting ligands)

PSI : 8-10 nm

Graphene on a Si substrate Deposition of AuNP or PSI

Atomic force microscopy (AFM) analysis

400 nm 400 nm 5 10 15 20 0.2 0.4 0.6 0.8 1

Position (µm)

Immobilized AuNPs and PSI on a graphene FET

PSI + AuNP ≈ 14 nm AFM image of PSI and AuNP on graphene

Deposition of AuNP and PSI AuNPs in CH2Cl2 PSI in buffer

Scanning electron microscopy (SEM) analysis

1 µm Gold electrode Graphene Height AuNPs 4-6 nm PSI 8-10 nm

200 nm

FET measurements - Experimental setup

Excitation light

Rubber pool Drain Source Reference electrode Electrolyte Electrode Electrolyte: 100 mM NaClO4, 250 mM NaAsc, 2.5 mM DCIP, 20 mM MES (pH 6.4)

Tran, T.-T.; Mulchandani, A. Trends in Analytical Chemistry 2016, 79, 222-232.

Illumination of excitation light ➝ Charge transfer (PSI/AuNPs) ➝ Shifts in CNPs

Charge neutrality point (CNP) VG ≈ ≈

Source-drain current (Isd) against Gate voltage (VG)

2019/11/9 4

6.4 6.8 7.2 7.6 8 140 160 180 200

Isd (µA) VG (mV) 1 2 3 4 5

6 8 10 12 50 100 150 200

Isd (µA) VG (mV) 1 2 3 4 5

FET measurements - Results

CNP1 CNP2 1 + 1７2 mV + 146 mV 2 + 172 mV + 146 mV 3 + 174 mV + 150 mV 4 + 175 mV + 150 mV 5 + 174 mV + 152 mV

CNP2 CNP1 1: dark 2: 680 nm Intensity = 20% 3: 440 nm Intensity = 20% 4: 440 nm Intensity = 40% 5: dark

Blue light irradiation ➝ h+ doping of graphene

Source-drain current under illumination

+2 mV +4 mV

Mechanisms of the hole doping effect

－ － PSI

e-

Light

+ + +

Isd h+

Reference electrode

Asc Asc+

－ － Light

+ + +

Isd h+

Reference electrode

O2 ions Source Drain Drain Source

Mechanism 1 : Gating effect Mechanism 2 : Electron transfer

e.g. Charged proteins adsorbed

• n the graphene FET

Kim, J. E.; No, Y. H.; Kim, J. N.; Shin, Y. S.; Kang, W. T.; Kim. Y. R.; Kim, K. N.; Kim, Y. H., Yu, Q. J. Appl.

• Phys. Lett. 2017, 110, 203702.

e-

e.g. Redox reactions on the surface of graphene FET

Improvement : Increase the Debye length

𝝁𝑬 = 𝟏. 𝟒𝟔 𝑱𝟐/𝟑

lD

𝑱 : inonic strength

Maehashi, K.; Ohno, Y.; Matsumoto, K. Nanobiosensors in Disease Diagnosis 2016, 5, 1-13.

Weak ionic strength Detection of large molecules Debye length [lD] = Thickness of the electric double layer Biomolecules larger than lD cannot be detected.

Introduce hexylamine to increase the Debye length

• r

Hexylamine

80 82 84 86 160 200 240 280

Isd (µA) VG (mV)

No shift in the CNPs Positive CNP (+227 mV)

Results – Light irradiation and CNP shifts

85 86 87 88 89

• 300
• 250
• 200
• 150

Isd (µA) VG (mV)

Without hexylamine With hexylamine

Dark 680 nm Dark 680 nm

Unstable I-V curves Negative CNP (-203 mV)

2019/11/9 5 Effect of hexylamine

Adsorbed anions ➝ Positive CNPs Without hexylamine With hexylamine ○

Hydrophobic environment was introduced by hexylamine. The I-V curves were unstable under the negative VG.

Hexylamine

+ + + +

Adsorbed Asc-

• graphene

Si

• Adsorbed hexylamine

➝ Negative CNPs

Two possible solutions

• 1. Use cationic and anionic

detergents

Cationic detergent

+ +

• Anionic

detergent Asc-

• 2. Decrease the concentration
• f the electrolyte

Increase in the Debye length & Neutral surface charge ➝ Improvement in the sensitivity toward the light

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

• ptimizing the electrolyte composition.