A Novel Non-Planar, Interdigitated Microelectrode Array with a Porous, Flow-through Working Electrode for Highly Sensitive and Selective Detection of Various Chem/Bio-Molecules
Authors: Li Zhenglong , Cheng Yu Hsuan , Kim Hansin , Moura Pedro , Yang Juliana , Basuray Sagnik 
Published: February 2020

Here we present an electrochemical platform that meets the “ASSURED” criteria for Point-of-Care devices set by the World Health Organization. The proposed research will integrate technologies for 1) a flow-through, nanoporous and capacitive electrode, 2) electrochemical sensor capable of label-free, multiplexed, rapid, portable, sensitive and selective detection, 3) non-planar interdigitated microelectrodes, and 4) integrates multiple electrochemical sensing techniques in one chip. Furthermore, the proposed work assesses the applicability of using this platform technology with both faradaic (cyclic voltammetry) and non-faradaic (electrochemical impedance spectroscopy, EIS) electrochemical measurements from the same sensor. The device architecture consists of three layers, namely, a top and bottom glass layer with gold interdigitated microelectrode array (IDμE) and a middle tape layer with the desired channel pattern. Here, Carbon Nanotubes (CNTs) are loaded in the channel, between the two non-planar interdigitated IDμEs, as shown in the figure below. The microfluidic channel in the device is fabricated using medical grade, acrylic double-sided, pressure-sensitive tapes from ARcare® (Tape No: 90880). The tape is cut into shape using a commercially available cutting machine, Cricut®. The CNTs are oxidized to introduce –COOH group into the nanotubes following established protocols. Post -COOH functionalization, the CNT’s are placed in the channel. The double-sided tape is then ripped off, and the device is closed. This room temperature assembly of the device allows us to do multiple tasks like pre-functionalization of the CNT’s, replacing the CNT’s with other nanomaterials that often do not survive harsh microfluidic chip integration. Post-chip assembly, an in-house EDC-NHS on-chip protocol is used to attach a capture biomolecule (oligo DNA or capture antibody) to the –COOH functionalized CNT. Target biomolecule (target DNA or antigen) attachment to CNTs is sensed by observing the shift in EIS/CV/DPV that occurs because of this binding. As shown in the figure, due to the innovative design of the electrode architecture, the electrodes can be connected in multiple different modes and 2/3 electrode connections. It is worthwhile to note that exchanging the CNT with another material like metal-organic framework (MOF) not only changes the electrochemical signal but also results in entirely new electrochemical measurement methodology. The MOF filled chip has been used for Ultrasensitive Detection of Perfluorooctanesulfonate (PFAS). Further, the chip is also used to cascade multiple electrochemical techniques at the same time for enhanced sensitivity and selectivity. The different electrode connections allow us to obtain a rich plethora of physical and chemical characteristics of the flow-through, nonporous, non-planar interdigitated IDμE system. It has allowed us to optimize the electrode architecture for significant improvement in the sensitivity and selectivity of the electrochemical platform.

Acknowledgement: The authors are supported by the National Science Foundation (NSF) Career grant (#1751759): "ASSURED" electrochemical platform for multiplexed detection of Cancer Biomarker Panel using Shear-Enhanced Nanoporous-Capacitive Electrodes.

Figure Caption: The left figure shows the schematic of the different layers of the electrochemical sensor. The right figure shows the multitude of electrical connections and electrode set-ups that can be accomplished with this sensor. In particular we show here the sensor in a 3 electrode set-up with a nanoporous flow-through working electrode that is made of CNT trapped between two non-planar interdigitated micoelectrodes.

Figure 1