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ABSTRACT Despite their high power density, microsupercapacitors (MSCs) are impractical for many energy storage applications due to their limited energy density. Their energy density can be increased by shaping the electrodes into 3D structures with high specific surface area (SSA). Direct printing of nanoporous 3D electrodes is a promising approach for achieving high SSA. However, conventional nanoscale 3D printing is too slow due to point‐by‐point processing. Here, we have employed the projection two‐photon lithography technique to fabricate nanoporous 3D electrodes via a rapid layer‐by‐layer mechanism. The 3D MSC electrodes are engineered as an array of nanoporous polymeric micropillars that are printed with customizable spacing and count over a 0.25 cm²area. After printing, these micropillars are conformally coated with titanium nitride to form conductive 3D electrodes, which exhibit a specific capacitance of 361 μF/cm². This is two orders of magnitude higher than the capacitance of the flat surface and exceeds the capacitance of both traditional bare electrodes, such as single‐wall carbon nanotubes (< 100 μF/cm²), and electrodes produced by photo‐polymerization 3D printing (˜200 μF/cm²). As our work demonstrates that high energy density 3D electrodes can be rapidly fabricated, it significantly expands the utility of MSCs as miniaturized energy storage devices. 

Biosensors based on Electrochemical Impedance Spectroscopy (EIS) detect the binding of an analyte to a receptor functionalized electrode by measuring the subsequent change in the extracted charge-transfer resistance (R_CT). In this work, the stability of a long chain alkanethiol, 16-mercaptohexadecanoic acid was compared to that of a polymer-based surface linker, ortho-aminobenzoic acid (o-ABA). These two classes of surface linkers were selected due to the marked differences in their structural properties. The drift in R_CTobserved for the native SAM functionalized gold electrodes was observed to correlate to the drift in the subsequent receptor functionalized SAM. This indicates the importance of the gold-molecule interface for reliable biosensing. Additionally, the magnitude of the baseline drift correlated to the percentage of thiol molecules improperly bound to the gold electrode as evaluated using X-ray Photoelectron Spectroscopy (XPS). Alternatively, the o-ABA functionalized gold electrodes demonstrated negligible drift in the R_CT. Furthermore, these polymer functionalized gold electrodes do not require a stabilization period in the buffer solution prior to receptor functionalization. This work emphasizes the importance of understanding and leveraging the structural properties of various classes of surface linkers to ensure the stability of impedimetric measurements.