(G-249) Design and Fabrication of a Flexible Opto-Electric Biointerface for Multimodal Optical Fluorescence and Electrical Recording

Introduction:: Optical fluorescence and electrical monitoring of cell activity are two powerful approaches to study organ functions. Simultaneous recording of optical and electrical data types will provide complementary information from and take advantage of each approach. However, devices that can concurrently record optical signals from the same cell population underneath the microelectrodes have not been widely explored and remain a grand technical challenge. This work presents an innovative flexible opto-electric device that monolithically integrates transparent gold nanogrid microelectrodes directly above microscale light-emitting diodes, photodetectors, and optical filters to achieve co-localized crosstalk-free optical fluorescence and electrical recording.

Materials and Methods::



The fabrication process began by spin coating polydimethylsiloxane on a glass carrier substrate as the adhesive layer for a 25 μm thick polyethylene terephthalate film. A 7 μm thick SU-8 2007 was spin coated on the PET film followed by metal interconnect patterning using AZ nLOF 2070, e-beam deposition of Cr/Cu, and liftoff. The μ-LED emits blue light with the peak at 462 nm. The blue μ-LED and μ-PD were micro-transfer printed onto the Cr/Cu cathodes and anodes using soft lithography defined PDMS elastomeric stamps followed by a reflow soldering process Absorber dye ABS 473 (Exciton) was mixed into a transparent SU-8 2007 photoresist, spin coated, and patterned on the μ-PD as the optical filter for blue light. Another 150 μm thick SU-8 layer was used as the passivation layer for the optoelectronic components. The device was then prepared for EBL with PMMA A4 followed by deposition and lift off of Cr/Au (20/40 nm). A top SU-8 2007 layer defined the 50 μm diameter microelectrode window and encapsulated the rest of the device.

Material properties were assessed by examining optical and electrical components with spectrophotometry, electrochemical impedance spectroscopy, cyclic voltammetry, spectrometry, and current-voltage characterization. Biocompatibility and mechanical compliance were examined using benchtop tests such as PBS soaking, bending, and thermal tests. A specialized benchtop recording assay was used to test the multimodal electrical and optical recording by measuring a sine wave in Oregon Green BAPTA-1/PBS solution, with and without electrical recording.










Results, Conclusions, and Discussions:: The optimized gold nanogrid microelectrodes show an excellent optical transparency ( >81%) and a low normalized 1 kHz electrochemical impedance (6.3 Ω cm²). The optical recording subsystem offers high wavelength selectivity ( >1,300) and linearity (R² > 0.99) for exciting and capturing green fluorescence from various fluorescent reporters in measurement ranges relevant for in vivo applications with minimal thermal effects. The opto-electric device exhibits remarkable durability under soaking for 40 days and repetitive mechanical bending for 5000 cycles. The work may provide a versatile approach for constructing mechanically compliant biointerfaces containing crosstalk-free optical and electrical modalities with widespread application potentials in basic and clinical research.

Acknowledgements (Optional): : S.N.O. and N.Q. contributed equally to this work. This work was financially supported by the National Science Foundation, grants number 2011093 and 2131682, and The George Washington University Cross-Disciplinary Research Fund. The authors thank The George Washington University Nanofabrication and Imaging Center for its facilities and support for device fabrication.

References (Optional): :



Obaid, Sofian N., Nathaniel Quirion, Jade Dominique Torres Balansag, Nicolas Daza, Xinyu Shi, Zhiyuan Chen, and Luyao Lu. “Design and Fabrication of a Flexible Opto-Electric Biointerface for Multimodal Optical Fluorescence and Electrical Recording.” ACS Applied Electronic Materials 5, no. 3 (March 28, 2023): 1688–96.https://doi.org/10.1021/acsaelm.2c01732.