All-Solution-Processing of Nanoporous and Wrinkled Electrodes on Polymer Substrates for Use in Electrochemical Biosensing

Multi-lengthscale electrodes that combine features from the nanometer to millimeter scale are of tremendous interest for use in electrochemical biosensors due to their increased analytical sensitivity and their enhanced interaction with biomolecular analytes. In this paper, we present a benchtop rapid prototyping approach based on all-solution-processing for creating multi-lengthscale electrodes on polymer substrates. Multi-lengthscale electrodes are created by combining xurography, nanoparticle self-assembly, electroless deposition, and polymer-induced thin film wrinkling. Xurography is used to develop a mask for implementing the electrode configuration on polymeric substrates with micrometer resolution. A nanoparticle seed layer is deposited with the aid of molecular linkers to direct the electroless deposition processes to desired locations on the substrate. Electroless deposition is used to create a uniform and conductive thin film on a shrinkable polymer substrate. Thin film wrinkling induced using a shape memory polymer is then used to develop tunable wrinkles with minimum feature sizes in the micro/nanoscale. It is observed that the structural parameters of the wrinkled film such as pore density, wrinkle wavelength, and wrinkle peak-to-valley values are controllable by varying the electroless deposition duration. This structural variability is then used to tune the functional parameters of the electrodes such as sheet resistance and electroactive surface area. The combination of electroless deposition with polymer-induced thin film wrinkling results in thin films having a sheet resistance of 0.39±0.04 Ω/□, which is comparable to films of the same thickness deposited by sputtering. We used the electrodes developed here for enzyme-free glucose detection due to their high surface area induced by the combination of porosity and wrinkling. The results demonstrate that the sensitivity of these electrodes can be tuned by varying the electroless deposition duration. The optimal porous and wrinkled electrodes demonstrate a sensitivity of 23 µA/mM.cm2 for enzyme free glucose detection, which is 18 times larger than the sensitivity measured with planar electrodes. In sum, an all-solution-processing method is developed, which allows electrodes of various configurations, with tunable features from the nanometer to millimeter scale to be created in a matter of hours. The structural tunability offered by this fabrication method, allows the functional parameters of the electrodes such as sheet resistance, electro-active surface area, and analytical sensitivity to be tuned. The application of the porous and wrinkled electrodes created in this work to enzyme-free glucose detection is demonstrated.