Dataset

Figure 1: (A) design of electrode pair and gap. (B) dark-field image of electrode pair showing the 8 µm gap, (C) array of electrode pairs with rectangular pads, (D) PDMS microfluidic chamber layout. (E) experiment setup, showing the sample with the golden electrode pairs, the microfluidic chamber and the glass substrate, as well as the light path and the equivalent circuit representing the connected electronic devices. (F) AuNPs trapped at 3 MHz, shown as a bright spot in the middle of the electrode gap, (G) fabricated sample with upper PDMS microfluidic chambers. Figure 2: (A) Dark field image before applied voltage, (B) upon trapping at electrode edges with voltage on (after 90 s), (C) initially when voltage turned off (100 ms), and (D) after a further 3 s showing diffusion of AuNPs away from electrodes (scale bar is 10 µm). (E) shows the normalized scattered intensity taken from the electrode gap, presented as a percentage of the initial value of each curve, vs rf applied voltage. Arrows show intensity at which scattering from cloud trapping rises by >10% (dashed line) at 1 and 2 MHz. Figure 3: (A) Images of electrode gap at increasing rf frequency and V_p=20 V showing trapping of AuNPs in electrode gap centre, scale bar 10 µm, (B) Applied voltage vs time, (C) frequency vs time, (D) dark-field normalized scattered intensity at λ=600 nm at electrode gap centre (within red circle in A) and (E) average integrated dark-field image intensity (in terms of RGB values) in region around electrode gap. Figure 4: (A) Composite model for AuNP with ionic shell suspended in liquid medium. (B) Real part of Clausius-Mossotti factor Re(K^' ) for shell model with σ_m = 228 μS/c, ε_s=0.1*ε_m=7.9 and various σ_s. (C) Total potential at I=3.8 mM, K' = 0.05 and for varying A_H. (D) Total potential at I=3.8 mM, varying K', A_H = 1eV. (e) Barrier height (defined as the difference between local maximum and local minimum of the potential), (F) position of local minimum vs ionic strength. For all cases ζ = -54 mV (measured with Zetasizer Nano, Malvern Panalytical), ε_m = 79, V_p = 20 V.

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