Abstract
Bioelectronics is an emergent multidisciplinary field that combines biology and electronics for theragnostic applications.In particular, bio-hybrid interfaces to investigate biotic/abiotic and bioelectrical activity of living cells in vitro is at the forefront of bioelectronics. In this field, organic semiconductors, especially conjugated polymers, are surely the most promising electronic materials, due to their mixed electronic and ionic conductivity, combined with their excellent versatility when interacting with biological systems. Among the various conjugated polymers that are emerging, poly(3-hexylthiophene) (P3HT) is a widely used one that absorbs light in the visible light spectrum. It has gained attention, initially, for photovoltaic applications[1] and then for photoactivable interfaces [2] as a potential interactor with living systems. Therefore, its ability to absorb visible light is growing an increasing interest in light-mediated cell modulation and stimulation[3], which provides the great advantage of high selectivity and spatial resolution, and low/no invasiveness. Thus, it represents an alternative to electrical stimulation to elicit physiological responses for studying molecular mechanisms involved in basic and biomedical research. P3HT can also generate photoelectrochemical currents, driving faradaic reactions and altering the electrophysiology of cells. Photoinduced physiological effects mediated by P3HT have been observed in a number of in vitro [3]and in vivo models[4]. Based on these considerations, it is of uttermost importance to characterize P3HT films in general, and specifically for these applications. The aim of this work is to compare the optoelectrical properties of P3HT bio-hybrid interfaces consisting of P3HT deposited on ITO glass substrates via spray coating technique, at three different concentrations (2,5,10 mg/ml). The P3HT sprayed films were characterized by considering: morphology, wettability, and optoelectrical properties. The morphological properties were evaluated using an atomic force microscopy technique, while the wettability was estimated by determining the contact angle of a water drop. The specific surface and optoelectrical properties were measured using a potentiostat together with a LED light source (Red, Green, and Blue colored lights). The evaluation of the optoelectrical properties required the interchange of a phase of dark (10 s) and a phase of light exposition (10 s) for the induction of photocurrent, measured through the chronoamperometry, with the induction of photovoltage, measured through the chronopotentiometry. Obtained results have shown the ability of the polymer to respond to specific wavelengths of light in the visible spectrum and gave the possibility to select the best concentration of the polymer for the interaction with in vitro biological systems, thus for optimal biohybrid interface. Biocompatibility of the spray-coated semiconductive polymer was investigated in vitro by measuring the growth curves of SH-SY5Y cells at three different time points (24, 48, and 72h). This experiment has highlighted that cells are able to survive and grow on the polymer confirming that P3HT is a suitable bio-hybrid interface for biological systems, paving the way to use it in more complex in vitro systems.