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Ilaria Abdel Aziz1 2 Francesco Roggiani3 Marco Malferrari3 Gabriele Tullii4 Stefania Rapino3 Maria Rosa Antognazza1

1, Center for NanoScience and Technology, Istituto Italiano di Tecnologia, Milano, , Italy
2, Physics, Politecnico di Milano, Milano, , Italy
3, Università di Bologna, Bologna, , Italy
4, National Research Council, Milano, , Italy

Light modulation of cell activity is an active field of research: the possibility of coupling low invasiveness and high resolution assisted the transition from a passive, diagnostic element to an active modulator of cellular physiology. The lack of natural absorbers led to the development of tools able to transduce the optical signal into a biologically readable one, typically through a combination of photo-thermal, photo-electrochemical and photo-capacitive effects. In this framework, organic materials, and in particular poly-thiophene based materials, demonstrated to be reliable for both in vitro and in vivo use [Feyen et al, 2016, Lodola et al, 2017, Zucchetti et al, 2016, Bossio et al, 2018].
In this work, we prove the behaviour of Poly-3-hexyl thiophene (P3HT) as active modulator of redox metabolic signalling. We first demonstrate that the photocatalytic activity of P3HT in aqueous environment is spatially and temporally confined to the illuminated area by means of Scanning ElectroChemical Microscopy (SECM). To study the possible interactions with the photoexcited polymer, in view of in vitro application, we focus our attention on two possible acceptor moieties present in the cell cytosol, namely cytochrome C and oxygen, being their energetic levels well aligned with those of P3HT. The former is a transmembrane protein located across the mitochondrial membrane, being one of the components of the cellular respiration cycle. Its biological relevance is thus associated with the metabolic functions of the cell. By coupling electrochemical and spectro-electrochemical methods, we demonstrate for the first time that a direct, photoinduced electron transfer does occur between P3HT and cytochrome C in extracellular, aqueous environment.
Our results shed light on a technique for active redox modulation of cell metabolism, through on demand, light-activated smart organic interfaces.

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