<p>SUPPLEMENTARY INFORMATION</p><p>NP characterization</p><p>An Ocean Optics USB2000 spectrometer was used to acquire optical spectra of the NPs. </p><p>1H-NMR spectra were obtained using a Bruker Avance 400 MHz NMR Spectrometer. </p><p>Gold particle cores were decomposed with potassium cyanide (KCN) in dueterated- methanol (CD3OD) overnight and filtered through 0.22 μm membrane filter and NMR was used to analyze the resulting free ligands in solution. The integrated peak of the terminal –CH3 group of the OT or brOT was compared with the peak of the –CH2 adjacent to the sulfonate group in order to confirm the estimated stoichiometric compositions on each type of particle. A Philips/FEI CM20 TEM was used to analyze NP core sizes. Total NP size and shape distributions were obtained by Analytical </p><p>Ultracentrifugation (AUC) using a Beckman Optima XL-A, An-60 Ti rotor, scanning absorbance optics, with 12-mm path length double sector centerpieces with sapphire windows and Epon centerpieces. All measurements were made at 520 nm, 20 °C, at a speed of 12,000 r.p.m. with a scanning radial step size of 0.003 cm. Data ranges from over 50 scans were chosen to be representative of the whole run. Figure S1: UV-VIS absorption spectra of NP solution before and after filtering through a</p><p>0.22 μm membrane filter prior to cell incubation illustrating negligible differences in NP concentration lost.</p><p>Figure S2: Calibration curve for 66-34OT. This curve was constructed by preparing NP solutions of varying concentration and measuring their absorption by UV-VIS. It was used to calculate nominal NP concentrations prior to cell incubation. </p>