Side Chain Modification of Conjugated Polymers for Bioelectronics and Biological Applications

Organic bioelectronics is the convergence of organic electronics and biology. Motivated by the unique combination of both electronic and ionic conductivity, organic semiconducting materials have been applied in OECTs for sensing applications to translate bio-logical signals into a quantitative electrical reading. Due to their carbon-based structure and flexibility, CPs can achieve improved biocompatibility compared to inorganic devices as they are intrinsically “softer”, avoiding mechanical mismatch and the need for surface compatibilizing layers. These promising materials have broad potential to be used in applications such as biosensors, drug delivery, and neural interfaces. In the second chapter, a series of lysine-functionalized DPP3T semiconducting polymers, outline their synthesis, and demonstrate that these particular polymers allow neuron cells to adhere and grow, in comparison to unfunctionalized polymers, where cells quickly die. Through covalent attachment of small lysine units, the conjugated polymer backbone and cells can directly electrically communicate, favorable for neural signals recording/stimulating. In the third chapter, NDI-based semiconducting polymers are selected for lysinefunctionalization, giving protein-like surfaces for neurons to attach, grow and form a network without the need of an intermediate PDL coating. Most importantly, this careful choice of NDI backbone allows lysinated-NDI polymers to operate in OECTs with an outstanding normalized transconductance value of 0.25 S/cm. In the fourth chapter, a new technique is presented to biofunctionalize thin film surface of polymers. Two methods including CuAAC and thiol-ene click are demonstrated to be applicable to biofunctionalize surface. In particular, both of them can achieve biocompatible surface by attaching biomolecules at high density while maintaining electrically conductive film. In the final chapter, three series of NDI-T2 are presented synthesized via Stille coupling reaction using different Pd catalysts. Following electrochemical and device characterization, the study of the influence of spacers between backbone and EG chain for performance in OFET and OECT operations is carried out. It is clearly evidenced that electron mobility increases by a factor of 10 with gradual increased spacers for all polymers in OFETs devices. For OECTs, within three series, pNDI-Cx-T2 stands out, especially pNDI-C4-T2 giving the highest reported transconductance at 0.479 S/cm and a low threshold voltage of 0.18 V.