Smart surface for elution of protein-protein bound particles: nanonewton dielectrophoretic forces using atomic layer deposited oxides

Abstract

By increasing the strength of the negative dielectrophoresis force, we demonstrated a significantly improved electrokinetic actuation and switching microsystem that can be used to elute specifically bound beads from the surface. In this work using atomic layer deposition we deposited a pinhole free nanometer-scale thin film oxide as a protective layer to prevent electrodes from corrosion, when applying high voltages (>20 V(pp)) at the electrodes. Then, by exciting the electrodes at high frequency, we capacitively coupled the electrodes to the buffer in order to avoid electric field degradation and, hence, reduction in dielectrophoresis force due to the presence of the insulating oxide layer. To illustrate the functionality of our system, we demonstrated 100% detachment of anti-IgG and IgG bound beads (which is on the same order of magnitude in strength as typical antibody-antigen interactions) from the surface, upon applying the improved negative dielectrophoresis force. The significantly enhanced switching performance presented in this work shows orders of magnitude of improvement in on-to-off ratio and switching response time, without any need for chemical eluting agents, as compared to the previous work. The promising results from this work vindicates that the functionality of this singleplexed platform can be extended to perform a multiplexed bead-based assay where in a single channel an array of proteins are patterned each targeting a different antigen or protein.

Figure 1

Bead-based multiplexed assay. Each element of an array in the capture region is immobilized with a different protein each targeting a specific protein that is coated on the micrometer-sized beads. Unbound beads are washed out of the channel. Specifically bound beads on each element of the array are eluted one-by-one from the array and are quantified downstream as they pass through. Here, applying voltage V₁ turns nDEP on, resulting in elution of specifically bound beads from the surface of the 1st set of interdigitated electrodes.

Figure 2

(a) Simplified equivalent circuit model of the two neighboring electrodes in the interdigitated electrode pair. R refers to the resistance of the channel. C_ox is the capacitance of the deposited oxide layer for each electrode-oxide-electrolyte interface, and C_par is the parasitic capacitance. (b,c) Simulated voltage drop spectrum (b) and electric field spectrum (c) across the oxide capacitance at each electrode-buffer interface for various oxide thicknesses.

Figure 3

(a) Impedance spectrum (measured vs curve-fitted model) between the two neighboring electrodes in the interdigitated electrode pair. (b,c) Characterized vs simulated voltage drop spectrum (b) and electric field spectrum (c) across the deposited 10-nm SiO₂ layer on the electrodes.

Figure 4

Upper bound on the voltage tolerance of the improved DEP device is limited by the bubble formation inside the channel due to the generated heat. The device integrity was preserved throughout the above procedure.

Figure 5

(a) Percentage of the beads remaining on the surface. (b) Bead detachment time profile at a flow rate of 0.15 µL min⁻¹ using the improved vs original DEP device. (c,d) The corresponding raw video snapshots of the beads distribution (c) before (d) after turning nDEP on. The remaining beads on the electrode region are actually detached and are passing through. Similarly, the small difference between the two nonelectrode regions in parts c and d are mainly due to the moving beads passing by (but appearing as stationary in a single frame) as verified by the image-processing software.