Quantitative measurements of dielectrophoresis in a nanoscale electrode array with an atomic force microscopy

Abstract

Nanoelectronic devices integrated with dielectrophoresis (DEP) have been promoted as promising platforms for trapping, separating, and concentrating target biomarkers and cancer cells from a complex medium. Here, we visualized DEP and DEP gradients in conventional nanoelectronic devices by using multi-pass atomic force microcopy techniques. Our measurements directly demonstrated a short range DEP only at sharp step edges of electrodes, frequency dependent DEP polarity, and separation distance dependent DEP strength. Additionally, non-uniform DEP along the edges of the electrodes due to a large variation in electric field strength was observed. The strength and apparent working distance of DEP were measured to be an order of a few nN and 80 nm within the limited scale of particles and other parameters such as an ionic strength of the medium. This method provides a powerful tool to quantify the strength and polarity of DEP and allows optimizing and calibrating the device's operating parameters including the driving field strength for the effective control and manipulation of target biomolecules.

Selective Manipulation of Biomolecules with Insulator-Based Dielectrophoretic Tweezers

“…Figures 1d and 1e depict the spatial distributions of ∇E 2 over and across the electrodes when an external AC voltage V ac (7 V pp , f = 50 kHz) is applied between two electrodes. Without the tip, the strong ∇E 2 were formed only at the sharp electrode edges due to the inhomogeneity of the electric field created by the external AC voltage, which agrees with our previous experimental observations 31,35 . In the presence of the tip between the two electrodes, an additional strong ∇E 2 around the tip end was created (Figure 1d and Figure S1).…”

“…Depending on the dielectric responses of the objects and the surrounding medium, the external fields induce an instantaneous force F DEP = 1/4α∇| E | 2 acting on the objects with the effective polarizability α of the object, which is associated with the frequency-dependent CM factor. , For the spherical particles, spatially asymmetric force due to the inhomogeneous field gradient in the medium drives the movement of the polarized particles either by attracting or repelling them from the medium to regions of strong electric fields, such as the electrode edge or the tip end. Such frequency-dependent CM factors, polarizability, and DEP are in excellent agreement with many experimental observations and computational simulations, ours included. , …”

“…For the spherical particles, spatially asymmetric force due to the inhomogeneous field gradient in the medium drives the movement of the polarized particles either by attracting or repelling them from the medium to regions of strong electric fields, such as the electrode edge or the tip end. Such frequency-dependent CM factors, polarizability, and DEP are in excellent agreement with many experimental observations and computational simulations, ours included 1,31 .…”

“…Our iDEP tweezers exploit the interdigitated electrode array, which has proven to be quite useful for dielectrophoretic separation in previous studies. − The device consists of planar gold electrode arrays defined by the standard optical lithography technique on a SiO 2 substrate, similar to our previous work , (Figure c, see Experimental Section for details) and an insulator tip controlled by an xyz manipulator between a pair of interdigitated electrodes.…”

“…The interdigitated electrode arrays are prepared by the standard optical lithography technique on a SiO 2 substrate as described previously 31 . The width of electrodes, gaps between the electrodes, and the height of the electrodes were 16 μm, 25 ~ 40 μm, and 140 nm, respectively.…”