(627i) Multiplexed Proteomics Using Ultra Dielectrophoresis (uDEP)

Authors: 
Emaminejad, S., Stanford University
Javanmard, M., Stanford Genome Technology Center
Davis, R., Stanford University


Multiplexed Proteomics using Ultra Dielectrophoresis (uDEP)

 

Our goal is to develop a low cost electronic platform for multiplexed detection of protein biomarkers in a complex sample. Our platform is based on performing a bead based immunoassay, where along a single channel an array of antibodies is patterned.  Below each element of the array is a pair of adressable interdigitated electrodes, which can detach the immunobound beads through negative dielectrophoresis (nDEP) force.  The beads are detached region by region and then transported downstream where they are quantified electrically or optically.  The main challenge with this technique lies in providing a strong enough force to detach the beads.  Typically, nDEP provides on the order of a few picoNewtons of force, where the binding force between antibodies and antigens is on the order of hundreds of picoNewtons. By increasing the strength of the nDEP force, we demonstrated enhanced electrokinetic actuation that can be used to elute specifically-bound beads from the surface. When applying high voltages at the electrodes (> 10 V) that are in direct contact with the buffer, DEP force magnitude is limited by electrode corrosion due to electrochemical reactions at the interface of the electrodes and the solution. Using Atomic Layer Deposition we deposited a pinhole free nanometer-scale thin film oxide as a protective layer to prevent electrodes from corrosion. 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 nDEP force due to the presence of the insulating oxide layer. Deposition of thin film oxide layer on the electrodes imposes a number of challenges. First challenge is degradation of the electric field and hence dielectrophoresis force, as a result of the undesired voltage drop across the oxide. To compensate for the voltage drop across the oxide, one may increase the applied voltage at the electrodes, but that may lead to breakdown of the oxide. By analytical derivation and as confirmed through characterization results, we showed that at sufficiently high frequencies (for our device > 1 MHz), the electric field across the oxide layer becomes independent of the thickness, and hence oxide breakdown does not impose limitation on the thickness of the film. Our fabricated electrodes are able to withstand voltages up to 120 Vpp, beyond which bubble formation inside the channel becomes the limiting factor. This results in two orders of magnitude improvement in DEP force, than what was possible with bare gold electrodes. Using this ultra-DEP (uDEP) device, we demonstrated 100% detachment of anti-IgG and IgG bound beads.  The enhanced switching performance shows orders of magnitude of improvement in on-to-off ratio and switching response time, without need for chemical eluting agents, as compared to previous work. In this talk, we will present the operation of the uDEP-based device to perform a multiplexed assay.