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1 Selective Functionalization of In 2 O 3 -Nanowire Mat Devices Marco Curreli a, Chao Li b, Yinghua Sun b, Bo Lei b, Martin A. Gundersen b, Mark E. Thompson a, *, Chongwu Zhou a,b, * a Department of Chemistry,, University of Southern California, Los Angeles, California b Department of Electrical Engineering Electrophysics, University of Southern California, Los Angeles, CA Supporting Information Supporting Information Available: Experimental details for the synthesis of HQ-PA, device fabrication, surface functionalization, and fluorescence microscopy. Table of Contents Materials S2 Synthesis of HQ-PA...S2 Device fabrication..s4 Surface functionalization....s5 Fluorescence microscopy...s6 Reference. S6 -S 1 -

2 Materials Dry Dichloromethane (DCM) was purchased from DriSolv (max water content: 50ppm); tetrahydrofuran (THF) was freshly distilled from sodium/ketone; triethyl phosphine (Aldrich) was freshly distilled over sodium; Phosphate buffer saline (PBS) was purchased from VWR and the ph adjusted to Bromotrimethylsilane (SiMe 3 Br) was purchased from Alfa Aesar. All other chemicals were purchased from Aldrich and used without further purification. ITO coated glass was provided by Universal Display Corporation (UDC). Synthesis of HQ-PA 1) Bu-Li MeO 2) Br-C4H8-Br P()3 MeO (1) (2) Br O P HO HO SiMe3Br BBr3 (HQ-PA) (3) O P O P 2-(4-Bromobuthyl)-1,4-dimethoxybenzene (1) was synthesized according to literature procedure[ref. 1a]. A solution of 1,4-dimethoxybenzene (12.061g, 87.29mmol) in 120 ml of -S 2 -

3 THF was stirred for 1 minute at RT and then cooled to -78 o C in a nitrogen purged Schlenk flask. A solution of 1.0 M n-butyllithium in hexane (100 mmol) was added dropwise. The mixture was stirred at -78 o C for 15 minutes, warmed to RT and allowed to stir for 1 hour, and then transferred to a second flask containing a solution of 1,4-dibromebutane (31.0 ml, 262mmol) in 100 ml of THF at 0 o C. The mixture was stirred for 4 hours at RT and the reaction was then quenched with 30 ml of saturated NH 4 Cl. The solution was extracted with 3x40mL of CH 2 Cl 2. The combined organic layers were washed with brine, dried over MgSO 4 and the solvent removed under reduced pressure. Unreacted 1,4-dimethoxybenzene was removed by vacuum distillation. The crude product was purified by column chromatography (hexane/dcm 90:10) yielding a colorless oil (16.33g, 69.8%). 1 H-NMR (CDCl 3 ): δ 1.72 (quintet, 2H), 1.87 (quintet, 2H), 2.61 (t, 2H), 3.43 (s, 3H), 3.76 (s, 3H), 3.77 (s, 3H), (m, 3H). 2-(1,4-dimethoxybenzene)-butyl phosphonic acid diethyl ester (2). A solution of compound (1) (6.35g, 23.26mmol) in 15mL of triethylphosphine (127.7 mmol) was refluxed overnight under nitrogen. Excess triethylphosphine was removed in vacuo and the crude product purified by column chromatography using hexane/dcm (50:50) as eluent, yielding a colorless oil (7.18g, 93.5%). 1 H-NMR (CDCl 3 ): δ 1.31 (t, 6H), (m, 6H), 2.59 (t, 2H), 3.76 (s, 3H), 3.77 (s, 3H), (m, 4H), (m, 3H). 2-(1,4-dihydroxybenzene)-butyl phosphonic acid diethyl ester (3). A solution of (2) (3.5g, 10.6mM) in dry CH 2 Cl 2 (8mL) was cooled to -78 o C and a 1M solution of BBr 3 in CH 2 Cl 2 (31mL, 31mM) was added dropwise. The mixture was stirred at RT for 16 hours, quenched with 3mL of saturated NH 4 Cl, and extracted with diethylether. The combined organic layers were -S 3 -

4 washed with brine, dried over MgSO 4, and the solvent removed under reduced pressure. Purification by column chromatography (hexane/acetone, 85:15) afforded a thick, yellowish oil (2.85g, 89.0%). 1 H-NMR (CDCl 3 ): δ 1.31 (t, 6H), (m, 6H), 2.58 (t, 2H), 2.98 (broad s, 2H), (m, 4H), (m, 3H). 2-(1,4-dihydroxybenzene)-butyl phosphonic acid (HQ-PA). SiMe 3 Br (4.0mL, 30.32mmol) was added drop wise under nitrogen to a solution of (3) (2.85g, 9.44mmol) in 10mL of dry CH 2 Cl 2 and stirred for 6 hours. Unreacted SiMe 3 Br and solvent were removed under vacuum, yielding a yellowish oil. This oil was stirred for 2 hours in 10mL of methanol after which the methanol removed under vacuum. The crude product was dissolved in a minimum amount of methanol and recrystalized from diethylether, yielding 2.18g (93.9%). 1 H-NMR (D 2 O): δ (m, 6H), 2.58 (t, 2H), (m, 3H). Device fabrication In 2 O 3 nanowires synthesis and device fabrication. In 2 O 3 nanowires were grown via a laser ablation method on Si/SiO 2 substrate [ref 8 in paper]. Au clusters with a diameter of 10 nm worked as catalyst, and the growth followed vapor-solid-liquid mechanism. Devices were made directly on as-grown nanowires samples by photolithography, followed by Ti (5nm)/Au (50nm) deposition. After lift-off, the device was carefully cleaned before further modification. -S 4 -

5 Surface functionalization ITO and In 2 O 3 NWs device cleaning procedure. ITO sheets were boiled for 5 minutes each in trichloroethylene, acetone, and finally, ethanol. The sheets were then placed in an ozone/uv chamber for 10 minutes. The NWs devices were cleaned by the same procedure of the ITO but placed in the ozone/uv chamber for 3 minutes. Deposition of HQ-PA and monolayer formation. Freshly cleaned ITO sheets or NWs were placed in an aqueous solution of HQ-PA (0.1 mm) at RT, for at least 16 hours. The samples were then washed extensively with water and dried under nitrogen. For the In 2 O 3 NWs a further step was taken to passivate the gold electrodes. The sample was soaked into a 1mM solution of dodecanethiol in hexane at RT overnight. Electrochemical Activation of the Monolayer. Oxidation and reduction of the HQ-PA monolayer were performed in an electrochemical cell using a solution of PBS buffer (ph 7.40) and methanol (95:5) with Pt as counter electrode and Ag/AgCl as a reference electrode. Determination of the monolayer density was done by counting the charge used to oxidize an area of cm 2 and dividing by Faraday s constant and then by 2 (#of electrons consumed per reaction). This showed that the monolayer is closely packed with a surface coverage of 4.9 x10-10 mol/cm 2 or 33.7 Å 2 /molecule. -S 5 -

6 Functionalization of ITO and In 2 O 3 nanowires with DNA oligonucleotides. DNA oligonucleotides used herein were 20 bases in length and were modified with the 5 thiol modifier C6 (Integrated DNA Technologies, Inc). After deprotecting the thiol modifier, the oligonucleotide was purified by chromatography and used immediately. The probe DNA (5 HS-GCT TTG AGG TGC GTG TTT GT, 10 µm in PBS buffer ph7.40) was applied to the sample surface and stored in a humidity chamber in the dark for overnight. The sample was then carefully rinsed with buffer solution to remove excess DNA. For the DNA hybridization, the target DNA (5 -Alex-ACA AAC ACG CAC CTC AAA GC, 5 µm in PBS buffer, PH 7.40, Integrated DNA Technologies, Inc) was applied to the sample surface for 20 minutes, followed by washing with buffer solution. Fluorescence microscopy A Zeiss Axiovert 200M epi-fluorescence microscope (Carl Zeiss, Germany) with 63x waterimmersion objective was used for the fluorescence imaging of Alexa Fluor 546 NHS ester bound to DNA. Alex Fluor 546 from Integrated DNA Technologies had a 555 nm absorbance maximum and 571 nm emission maximum. The observation filter set consisted of 540/25 nm excitation filter, 565 nm dichroic mirror, and 580 nm long-pass emission filter. Images were captured and analyzed with an AxioCam MRm camera and AxioVision3.1 software (Carl Zeiss, Germany). Reference 1a. Hong, H.G.; Park, W. Langmuir 2001, 17, S 6 -