Large-scale, all polycrystalline diamond structures transferred onto flexible Parylene-C films for neurotransmitter sensing

Abstract

Boron-doped diamond (BDD) has superior electrochemical properties for bioelectronic systems. However, due to its high synthesis temperature, traditional microfabrication methods have limits to integrating BDD with emerging classes of flexible, polymer-based bioelectronic systems. This paper introduces a novel fabrication solution to this challenge, which features (i) a wafer-scale substrate transfer process with all diamond structures transferred onto a flexible Parylene-C substrate and (ii) Parylene anchors introduced to strengthen the bonding between BDD and Parylene substrates, as demonstrated by peeling test. The electrochemical properties of the transferred BDD-polymer electrodes are evaluated using (i) an outer sphere redox couple Ru(NH3)62+/3+ to study the electron transfer process and (ii) quantitative and qualitative studies of a neurotransmitter redox dopamine/dopamine-o-quinone. A linear response of the BDD sensor to dopamine concentrations of 0.5 μM to 100 μM is observed (R2 = 0.999) with a sensitivity of 0.21 μA/cm2·μM. Examples of fabricated diamond-polymer devices suggest a broad application in advanced bioelectronics and optoelectronics.

Physicochemical and Mechanical Performance of Freestanding Boron-Doped Diamond Nanosheets Coated with C:H:N:O Plasma Polymer

“…In general, the integration of freestanding diamond nanosheets makes it possible to design flexible chemical multielectrode sensors, which could be stable in the aqueous conditions with wide potential windows and low background currents from the diamond, along with mechanical flexibility thanks to the polymer. The transfer of boron-doped diamond (BDD) onto a thin Parylene-C substrate was reported by Fan et al [44], demonstrating uniformity, significant adhesion, and high yield. The use of polynorbornene-based polymer as a flexible diamond base enables spin castability, photodefinability, and flexibility, and improved adhesion [45] and moisture resistance.…”

Flexible, diamond-based microelectrodes fabricated using the diamond growth side for neural sensing

“…Finally, the BDD-Parylene film was released from the carrier substrate by dissolving the sacrificial photoresist in acetone and rinsed with isopropyl alcohol and deionized water. To make a fair comparison, microelectrode probes where the BDD nucleation side was exposed were fabricated using BDD films from the same MW-PACVD batch based on our previously developed method 42 .…”

“…The average current of the forward and reverse sweeps extrapolated from the CVs at different scan rates was used to derive a linear regression curve ( Fig. S1(b)), where the slope defines the double-layer capacitance 42 . Using this method, the double-layer capacitance of the BDD growth side was approximately 10 µF/cm 2 , significantly lower than the C dl of the nucleation side reported in our previous work 42 , which was~24 µF/cm 2 .…”

“…S1(b)), where the slope defines the double-layer capacitance 42 . Using this method, the double-layer capacitance of the BDD growth side was approximately 10 µF/cm 2 , significantly lower than the C dl of the nucleation side reported in our previous work 42 , which was~24 µF/cm 2 . This low capacitance may result from the existence of a space charge region within the near surface of diamond electrodes 47 .…”

“…Previously, we also reported a method for patterning and transferring large-scale BDD structures from solid substrates onto Parylene C thin films. The transferred flexible BDD electrodes have been proven effective for detecting various concentrations of DA with a limit of detection (LOD) of 0.5 µM 42 .…”