Supporting Information Controlled Charge Trapping and Retention in Large- Area Monodisperse Protein Metal-Nanoparticle Conjugates Chang-Hyun Kim,, Ghibom Bhak, Junghee Lee, Sujin Sung, Sungjun Park, Seung R. Paik,*, and Myung-Han Yoon*, School of Materials Science and Engineering and Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea School of Chemical and Biological Engineering, Institute of Chemical Processes, College of Engineering, Seoul National University, Seoul 08826, Republic of Korea *E-mail: srpaik@snu.ac.kr (S.R.P.); mhyoon@gist.ac.kr (M.-H.Y.). S-1
EXPERIMENTAL DETAILS Purification of -synuclein ( S) Human S protein was purified according to procedures reported previously. S1 In brief, S cloned in the prk172 vector was over-expressed in Escherichia coli BL21 (DE3). The cell lysate was heat-treated and then subjected to DEAE-Sephacel anion-exchange, Sephacryl S-200 size-exclusion, and S-Sepharose cation-exchange chromatography. The completely purified S was stored in aliquots at -80 ºC. Preparation of S-coated gold nanoparticles ( S-Au NPs) The S-Au NP conjugates were prepared by incubating a mixture of 400- l Au NP colloidal solution (BBI international, ND) and 50- l S (1 mg/ml in 20 mm MES at ph 6.5) at 4 ºC for 12 h. The conjugates made of 5-, 10-, and 30-nm Au NPs were washed three times via centrifugation at 16,100 x g for 90, 60, and 5 min, respectively. After each centrifugation, the S-Au NP pellets were re-suspended with 400 l of fresh 20 mm MES at ph 6.5 Fabrication and characterization of organic field-effect transistors (OFETs) The bottom-gate top-contact OFETs were fabricated according to the following protocols. Heavily doped p-type silicon (p + -Si) wafers with thermally grown 200-nm SiO 2 served as a common gate electrode/gate insulator platform. These substrates were ultrasonically cleaned by sequentially placing them in baths of deionized water, acetone, and isopropanol (5-min sonication for each). For the S-Au NP monolayer formation, the pellets of S-Au NPs were resuspended with 400 l of 50 mm citrate at ph 4.5, and then a 200- l droplet of the conjugate solution was placed onto the substrates (1.5 cm x 1.5 cm) pre-treated with oxygen plasma S-2
(CUTE-MPR, FEMTO SCIENCE, Korea) at 60 W (45 sccm) for 10 min. The particle adsorption was carried out through incubation in a humid chamber at 40 C for 3 h. In the case of preparing a low-density monolayer with 30-nm Au NPs, the adsorbing conjugate solution was diluted 8- fold with 50 mm citrate at ph 4.5. The resulting S-Au NP monolayer on SiO 2 /p + -Si wafers was washed two times with 20 % MeOH at 4 C and then purged with nitrogen gas. A 50-nm thick pentacene film (triple-sublimed grade, 99.995 %, used as-purchased from Sigma-Aldrich) was then deposited by thermal evaporation in a vacuum chamber using a shadow mask to define patterned semiconducting channels (base pressure: 1.5 10-6 Torr, deposition rate: 0.25 A /s). After changing the shadow mask, 50 nm of Au was vacuum-evaporated in another chamber, forming source/drain contacts with a channel width and length of 500 m and 50 m, respectively (base pressure: 5 10-6 Torr, deposition rate: 0.3 A /s). The current-voltage characteristics of the OFETs were measured using a Keithley 4200-SCS Parameter Analyzer in the dark under an ambient atmosphere. X-ray photoelectron spectroscopy (XPS) characterization XPS analysis was carried out using AXIS Ultra DLD (Kratos, UK) with a monochromatic Mg Ka (1253 ev) X-ray source of 40 ev pass energy under ultra-high vacuum (~ 10-9 torr). N 1s peak (~ 399.5 ev) and Au 4f 7/2,5/2 (~ 84.1/84.9 ev) were measured with high-resolution scans from 390 to 410 ev and 80 to 90 ev, respectively. Contact angle measurements Optical images and contact angles of water droplets on either bare SiO 2 substrate or S-Au NP monolayer adsorbed on SiO 2 were obtained by monitoring with a drop shape analyzer S-3
(DSA100, Kruss, Germany). Dynamic light scattering (DLS) spectrophotometry Hydrodynamic diameter of either bare 10-nm Au NPs or S-encapsulated 10-nm Au NPs in 20 mm MES (ph 6.5) were assessed by using DLS spectrophotometer (Zetasizer Nano ZS90, Malvern Instruments Ltd., UK) with 10-mW He-Ne laser emitting light at a wavelength of 633 nm and a detection angle at 90º Field-emission scanning electron microscopy (FE-SEM) analysis S-Au NP monolayer adsorbed on SiO 2 substrates were examined with FE-SEM (SUPRA 55VP, Carl Zeiss, Germany) at 2.0 kv after coating air-dried samples with a 5-nm-thick layer of platinum (BAL-TEC/SCD 005 sputter coater, Switzerland). Atomic force microscope (AFM) analysis Three-dimensional images and height profiles of the S-Au NP monolayers were obtained by AFM. A Dimension-3100 AFM (Veeco Metrology Group, Santa Barbara, CA) was utilized to examine the 5-nm S-Au NP monolayer, and the XE-100 AFM (Park Systems, Korea) was employed for the 10- and 30-nm S-Au NP monolayers. The S-Au NP monolayer on a silicon wafer was scratched with a sharp polyethylene terephthalate (PET) sheet for measuring the height of the monolayer and then analyzed with AFM in tapping mode. The top morphology of the pentacene films in the OFETs were measured by AFM (XE-Bio, Park Systems, South Korea) in tapping mode. S-4
SUPPLEMENTARY DATA Figure S1. Statistical distribution of particle sizes obtained by the DLS measurements, for estimation of the physical dimension of the S encapsulations. The nominal diameter of the particles used for this experiment is 10 nm. S-5
Figure S2. FE-SEM image showing defects and non-uniform packing of S-Au NP conjugates on a SiO 2 surface washed with distilled water. S-6
Figure S3. SEM image showing S-Au NPs agglomerates on a SiO 2 surface after incubation at 60 o C. S-7
1 m 1 m 1 m 1 m Figure S4. SEM images of an S-Au NP (particle size: 10 nm) monolayer in various magnifications. S-8
Figure S5. XPS spectra on an S-Au NP monolayer. (a) Au 4f and (b) N 1s region. S-9
Figure S6. Dual-sweep output characteristics that show the appearance of hysteresis with varying magnitudes and directions in the Au-NP containing transistor samples. S-10
Figure S7. (a) Overlapping of transfer curves measured from seven different transistors on the same substrate for statistical analysis. (b) Statistically estimated device parameters from the results in (a); symbols (circles) correspond to the mean value of each column, and the error bars demarcate the standard deviations. S-11
Figure S8. Change of the transfer curves in response to the enlarged gate-sweep range. S-12
Figure S9. A dual-sweep transfer characteristic measured on an OFET specifically fabricated to determine the electrical effects of S capping. In this device, an S-Au NP monolayer was formed by the normal procedure, however, the organic encapsulation was stripped away via prolonged oxygen-plasma exposure (40 sccm, 50 W, 10 min), before the pentacene deposition. S-13
Figure S10. Upper panel summarizes the measurement protocol that was used to obtain initial, programmed, and erased states of the given device. Lower panel shows the transfer curves recorded as such. S-14
Figure S11. Evolution of the transfer characteristics and the corresponding threshold voltage shift upon applying polarity-alternating and growing V G programming/erasing pulses. S-15
Figure S12. Transient relaxation measurements data for the 10-nm NP sample and the 30-nm NP low density sample. S-16
REFERENCE S1. Paik, S.R.; Lee, J.-H.; Kim. D.-H; Chang, C.-S; Kim, J. Aluminum-Induced Structural Alterations of the Precursor of the Non-Aβ Component of Alzheimer's Disease Amyloid. Arch. Biochem. Biophys. 1997, 344, 325 334. S-17