Cochlear implants (CIs) provide auditory perception to individuals with severe hearing impairment. However, their ability to encode complex auditory stimuli is limited due, in part, to poor spatial resolution caused by electrical current spread in the inner ear. Directing nerve cell processes towards target electrodes may reduce the problematic current spread and improve stimulatory specificity. In this work, photopolymerization was used to fabricate micro- and nano-patterned methacrylate polymers to probe the extent of spiral ganglion neuron (SGN) neurite and Schwann cell (SGSC) contact guidance based on variations in substrate topographical cues. Micropatterned substrates are formed in a rapid, single-step reaction by selectively blocking light with photomasks which have parallel line-space gratings with periodicities of 10 – 100 μm. Channel amplitudes of 250 nm – 10 μm are generated by modulating UV exposure time, light intensity, and photoinitiator concentration. Gradual transitions are observed between ridges and grooves using scanning electron and atomic force microscopy. The transitions stand in contrast to vertical features generated via etching lithographic techniques. Alignment of neural elements increases significantly with increasing feature amplitude and constant periodicity, as well as with decreasing periodicity and constant amplitude. SGN neurite alignment strongly correlates (r = 0.93) with maximum feature slope. Multiple neuronal and glial types orient to the patterns with varying degrees of alignment. This work presents a method to fabricate gradually-sloping micropatterns for cellular contact guidance studies and demonstrates spatial control of inner ear neural elements in response to micro- and nano-scale surface topography.

Ion gels formed with ABA triblock polymers and ionic liquids (IL) have recently attracted significant attention. Because of their high ionic conductivity, high capacitance, and good mechanical integrity, ion gels prepared from triblock polymers of polystyrene-b-poly(methyl methacrylate)-b-polystyrene (SMS) and polystyrene-b-poly-(ethylene oxide)-b-polystyrene (SOS) and an IL 1-ethyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide ([EMI][TFSI]) have been successfully applied as the dielectric layer in thin film transistors. However, water absorption can negatively affect the stability of the dielectric layer and lead to electrical breakdown. Consequently, the preferred polymer of these two is SMS. However, the high glass transition temperature (T g ) of PMMA limits the usable SMS polymer concentration in order to ensure comparable ionic conductivity to that of SOS ion gel; this constraint limits the modulus of the gel to about 10 3 Pa. In this work, we developed a new ABA triblock ion gel system using poly(ethyl acrylate) (PEA) as a low T g and hydrophobic midblock. The low T g of the midblock ensures the ionic conductivity of the resulting ion gels is comparable to that of SOS ion gels at polymer concentrations up to 50 wt %, which is a significant improvement relative to the currently used SMS ion gels. Additionally, by decreasing the size of the midblock at constant polymer concentration, the modulus and ionic conductivity of the ion gels increase synergistically. This interesting and counterintuitive effect reflects the concurrent increase in the number density and chain stretching of midblocks, accompanied by a net reduction in midblock concentration within the conducting phase. We demonstrate that electrolyte gated transistors (EGTs) made with SEAS ion gels have improved stability under ambient humid conditions in comparison to those made with SOS ion gels.

We report a method to measure DNA hybridization potentiometrically in a manner conducive to portable or hand-held biosensors. An electrolyte-gated transistor (EGT) based on poly(3-hexylthiophene) (P3HT) and an ion-gel serves as a transducer for surface hybridization of DNA. The key aspect of the design is the use of a floating-gate electrode functionalized with ssDNA whose potential is determined by both capacitive coupling with a primary, addressable gate electrode and the presence of adsorbed molecules. When DNA is hybridized at the floating gate, it offsets the primary gate voltage felt by the P3HT semiconductor; the offset is directly measurable and quantitatively related to the number density of dsDNA molecules. The presented sensing strategy can be readily adapted to other biomolecules of interest and integrated into a microfluidic system for field applications of biosensors.

Electrolyte-gated transistors (EGTs) with floating gates (FGs) are an emerging platform for label-free electronic biodetection. Advantages of floating gate EGTs (FG-EGTs) include signal amplification and inherent sensitivity to small voltages, on the order of 10 mV, associated with chemical binding events on the floating gate electrode surface. Here we examine how the performance of these devices depends on their architecture, specifically the relative sizes (areas) of the control gate, the floating gate, and the source–semiconductor–drain channel. The results allow optimization of the geometry for future biodetection studies. Further, using self-assembled monolayer (SAM) chemistry, we also examine the effect of chemisorption on the floating gate on the current voltage (I–V) characteristics. We find the FG-EGTs respond to both interfacial dipoles and capacitance changes and that the I–V behavior can be reasonably predicted with a lumped capacitor model. Overall, this work provides the most detailed picture to date of the operating mechanism of these promising electronic sensing devices.

We report a label-free method to quantify protein levels using a combination of printed electronic and microfluidic technologies. The protein, in this case, ricin, is captured by a floating electrode functionalized with a DNA aptamer. The binding is transduced into an amplified potentiometric signal by a printed, electrolyte-gated transistor (EGT). Microfluidic channels physically separate the active sensor surface from the EGT-transducer, permitting the capture of ricin down to 30 pM (1 ng/mL) in buffer and 300 pM (10 ng/mL) in orange juice and milk in the absence of preconcentration. The assay is flow-based, leading to measurement in minutes since no preprocessing, enzymatic reaction, or rinsing steps are needed. Its easy fabrication, multiplexability, simple operation, and facile analysis, combined with rapid quantitation at clinically relevant levels, make this strategy a promising approach to parallelized monitoring of toxin levels in food and other environmental samples.