Conductive Thiophene-Based Fibers Assembled by Living Cells as Novel Bioelectronic Materials

In recent years, it has been observed that living cells can be employed as active synthesis platforms for the assembly of intrinsically biocompatible bioelectronic materials. This process, which lies at the interface between living and non-living matter, is of fundamental interest since self-assembly in-vivo could allow circumvention of the blood-brain barrier, enabling the delivery of large aggregates or even devices to the brain. Within this context, thiophene-based compounds are pivotal materials for organic bioelectronics, owing to their biocompatibility and their capability for both electronic and ionic conduction.<br/>Here, we report on the cell-mediated assembly of semiconductive nanofibers composed entirely of dithienothiophene-S,S-dioxide (DTTO) aggregates. This molecule spontaneously penetrates the cell membrane, and fibers originate inside cells with the aggregation of the DTTO. These fibers grow “through” cells, reaching and piercing the plasma membrane in one cell to penetrate the adjacent cell, without causing cell death. We extensively characterized the photophysics of DTTO molecules during the various stages of fiber production through steady-state and time-resolved spectroscopy. We observed that the fibers are formed entirely from DTTO aggregates, which dictate the conductivity of the nanostructured material, and described the interaction between DTTO molecules and the protein scaffold. By complementing the spectroscopic data with theoretical calculations, single crystal X-ray diffraction and electrical conductivity measurements, we discovered an extended polymorphism of DTTO in the solid state. Our results suggest that the aggregation occurring in living cells is somewhat unique to the biotic phase, involving at least part of the cell machinery. As the fibers exhibit electrical conductivity, they present a method to directly stimulate cells or to induce artificial gap junctions between cells, potentially affecting signal propagation as occurs in cardiomyocytes, or in general, influencing cell population behavior.<br/>Further studies on the fiber production process are in progress, aiming to pave the way for a wide range of new cell-mediated syntheses of materials or devices.