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We report on the mutual interaction between poly(3-hexylthiophene) nanoparticles (P3HT-NPs) and human embryonic kidney (HEK-293) cells. P3HT-NPs, prepared in sterile conditions and efficiently uptaken within the live cells cytosol, show well-ordered morphology, high colloidal stability and excellent biocompatibility. Electrophysiology and calcium imaging experiments demonstrate that physiological functions of live cells are fully preserved in the presence of P3HT-NPs. From a complementary point of view, the photophysical properties of P3HT-NPs are also mainly maintained within the cellular environment, as proven by in situ time-resolved photoluminescence. Interestingly, we detect slight modifications in emission spectra and dynamics, which we ascribe to the contribution from the P3HT-NPs surface, possibly due to conformational changes as the result of the interaction with intracellular proteins or the formation of NPs aggregates. This work demonstrates that P3HT-NPs are excellent candidates for use as light sensitive actuators, due to their remarkable physical properties, optimal biocompatibility and capability of interaction with living cells.

The possibility to optically excite the electrical activity of living cells by using exogenous absorbers is gaining more and more interest in the neuroscience and biotechnology community. Conjugated polymers, inherently sensitive to visible light, were recently proposed as candidates to this goal. To date, however, only one polymer type, namely regio-regular poly-3-hexylthiophene, has been tested as the active material. In this work four different conjugated polymers, regarded as prototypes of their category, are investigated as photoactive bio-interfaces. The selected materials have different absorption spectra, morphology, light emission efficiency and charge transport properties. We analyze their key-enabling properties, such as electrochemical stability, surface morphology, wettability, sterilization compatibility, interaction with protein adhesion layers and toxicity, throughout all the necessary steps for the realization of an efficient bio-optical interface. We demonstrate that all considered polymers are characterized by good biocompatibility and cell seeding properties, and can optimally sustain thermal sterilization. Conversely, electrochemical stability and cell photostimulation efficacy can vary a lot among different materials, and should be carefully evaluated case by case. Reported results represent the starting point for the implementation of bio-polymer interfaces sensitive to different colors and, in perspective, for the realization of a three-chromatic artificial visual prosthesis.

Artificially enhancing light sensitivity in living cells allows control of neuronal paths or vital functions avoiding the wiring associated with the use of stimulation electrodes. Many possible strategies can be adopted for reaching this goal, including the direct photoexcitation of biological matter, the genetic modification of cells or the use of opto-bio interfaces. In this review we describe different light actuators based on both inorganic and organic semiconductors, from planar abiotic/biotic interfaces to nanoparticles, that allow transduction of a light signal into a signal which in turn affects the biological activity of the hosting system. In particular, we will focus on the application of thiophene-based materials which, thanks to their unique chemical-physical properties, geometrical adaptability, great biocompatibility and stability, have allowed the development of a new generation of fully organic light actuators for in vivo applications. Artificially enhancing light sensitivity in living cells allows control of neuronal paths or vital functions avoiding the wiring associated with the use of stimulation electrodes. Many possible strategies can be adopted for reaching this goal, including the direct photoexcitation of biological matter, the genetic modification of cells or the use of opto-bio interfaces. In this review we describe different light actuators based on both inorganic and organic semiconductors, from planar abiotic/biotic interfaces to nanoparticles, that allow transduction of a light signal into a signal which in turn affects the biological activity of the hosting system. In particular, we will focus on the application of thiophene-based materials which, thanks to their unique chemical-physical properties, geometrical adaptability, great biocompatibility and stability, have allowed the development of a new generation of fully organic light actuators for in vivo applications.

Hybrid interfaces between organic semiconductors and living tissues represent a new tool for in-vitro and in-vivo applications, bearing a huge potential, from basic researches to clinical applications. In particular, light sensitive conjugated polymers can be exploited as a new approach for optical modulation of cellular activity. In this work we focus on light-induced changes in the membrane potential of Human Embryonic Kidney (HEK-293) cells grown on top of a poly(3-hexylthiophene) (P3HT) thin film. On top of a capacitive charging of the polymer interface, we identify and fully characterize two concomitant mechanisms, leading to membrane depolarization and hyperpolarisation, both mediated by a thermal effect. Our results can be usefully exploited in the creation of a new platform for light-controlled cell manipulation, with possible applications in neuroscience and medicine.