No abstract

The non‐covalent affinity of photoresponsive molecules to biotargets represents an attractive tool for achieving effective cell photo‐stimulation. Here, an amphiphilic azobenzene that preferentially dwells within the plasma membrane is studied. In particular, its isomerization dynamics in different media is investigated. It is found that in molecular aggregates formed in water, the isomerization reaction is hindered, while radiative deactivation is favored. However, once protected by a lipid shell, the photochromic molecule reacquires its ultrafast photoisomerization capacity. This behavior is explained considering collective excited states that may form in aggregates, locking the conformational dynamics and redistributing the oscillator strength. By applying the pump probe technique in different media, an isomerization time in the order of 10 ps is identified and the deactivation in the aggregate in water is also characterized. Finally, it is demonstrated that the reversible modulation of membrane potential of HEK293 cells via illumination with visible light can be indeed related to the recovered trans→cis photoreaction in lipid membrane. These data fully account for the recently reported experiments in neurons, showing that the amphiphilic azobenzenes, once partitioned in the cell membrane, are effective light actuators for the modification of the electrical state of the membrane.

Current technologies to monitor formation and disruption in in vitro cell cultures are based either on optical techniques or on electrical impedance/resistance measurement, which often rely on cumbersome and time‐consuming measurements and data analyses. In this paper, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)‐based organic electrochemical transistors (OECTs) are proposed with channel areas specifically designed and dimensioned as fast and real‐time monitoring devices for a large variety of cell lines, with a broad range of tissue resistance. In particular, it is investigated how and why two device configurations provide a different response to leaky‐barrier (NIH‐3T3) and strong‐barrier (CaCo‐2) cell lines growth and detachment, achieving a continuous monitoring also for leaky‐barrier cell layer growth and detachment. Data are collected using the transistor dynamic behavior to a DC potential pulse on the gate, providing an excellent time resolution and thus enhancing the amount of information that can be collected for fast biological processes (<5 s).

We present a series of cationic membrane-targeted azobenzene molecules, with the aim to understand how variations in molecular architecture influence the relative optical and biological properties. 1,4-Amino-substituted azobenzene was chosen as the switching unit while the number of linked alkyl chains and their cationic end-group were systematically varied. Their photophysics, membrane partitioning, and electrophysiological efficacy were studied. We found that the polar end group is a key-factor determining the interaction with the phospholipid heads in the plasma membrane bilayer and consequently the ability to dimerize. The monosubstituted photoswitch with a pyridinium-terminated alkyl chain was found to be the best candidate for photostimulation. This study provides a structure-property investigation that can guide the chemical engineering of a new generation of molecular photo-actuators.

The use of light for triggering skeletal and cardiac muscles allows lower invasiveness higher selectivity and unprecedented possibility to target individual cells or even subcellular compartments in a temporally and spatially precise manner. Because cells are in general transparent, this requires the development of suitable interfaces that bestow light sensitivity to living matter. In the present work, successfully demonstrated is the use of conjugated polymer films as transducer to optically enhance the contraction rate of a human and patient‐specific cardiac in vitro cell model. By different experimental approaches, the coupling mechanism to the photothermal effect is assigned. This work extends the range of application of the polymer‐mediated cell photostimulation phenomenon to cardiac muscle cells, opening up possible applications in cardiac therapy and for implementation of in vitro studies.

Substrate engineering for steering cell growth is a wide and well‐established area of research in the field of modern biotechnology. Here we introduce a micromachining technique to pattern an inert and transparent polymer matrix blended with a photoactive polymer. We demonstrate that the obtained scaffold combines the capability to align with that to photostimulate living cells. This technology can open up new and promising applications, especially where cell alignment is required to trigger specific biological functions, e.g., generate powerful and efficient muscle contractions following an external stimulus.

has boosted the field of large-area flexible and printed electronics. These advances have enabled a plethora of applications such as organic light-emitting diodes, [1,2] organic photovoltaics, [3,4] organic thermoelectrics, [5,6] organic field-effect transistors (OFETs), [7][8][9][10] organic (bio)sensors, [11][12][13] and neuromorphic devices. [14,15] In this context, organic field-effect transistors (OFETs) are not only relevant for their direct technological application, but they also represent an ideal test-bed to investigate thin-film electrical properties. Organic semiconductors are typically classified in two main families, namely conjugated polymers and small molecules. The former, polymers, are particularly appealing as a result of their solution processability, and OFETs with charge mobility above the standard for hydrogenated amorphous silicon (0.5-1 cm 2 V −1 s −1 ) have been extensively reported. [16] The latter, small molecules, are prone to arrange in ordered molecular crystals, and through several years of chemical tailoring and fine tuning of the films processing, small-molecule OFETs with field-effect mobility >10 cm 2 V −1 s −1 have been achieved. [17][18][19] The chemical root of the π-conjugation of these materials is associated with the sp 2 -hybridization of carbon atoms in their backbone. This peculiar trait is also common to Solution-processed, large-area, and flexible electronics largely relies on the excellent electronic properties of sp 2 -hybridized carbon molecules, either in the form of π-conjugated small molecules and polymers or graphene and carbon nanotubes. Carbon with sp-hybridization, the foundation of the elusive allotrope carbyne, offers vast opportunities for functionalized molecules in the form of linear carbon atomic wires (CAWs), with intriguing and even superior predicted electronic properties. While CAWs represent a vibrant field of research, to date, they have only been applied sparingly to molecular devices. The recent observation of the field-effect in microcrystalline cumulenes suggests their potential applications in solution-processed thin-film transistors but concerns surrounding the stability and electronic performance have precluded developments in this direction. In the present study, ideal field-effect characteristics are demonstrated for solution-processed thin films of tetraphenyl[3]cumulene, the shortest semiconducting CAW. Films are deposited through a scalable, large-area, meniscus-coating technique, providing transistors with hole mobilities in excess of 0.1 cm 2 V −1 s −1 , as well as promising operational stability under dark conditions. These results offer a solid foundation for the exploitation of a vast class of molecular semiconductors for organic electronics based on sp-hybridized carbon systems and create a previously unexplored paradigm.

Photothermal perturbation of the cell membrane is typically achieved using transducers that convert light into thermal energy, eventually heating the cell membrane. In turn, this leads to the modulation of the membrane electrical capacitance that is assigned to a geometrical modification of the membrane structure. However, the nature of such a change is not understood. In this work, we employ an all-optical spectroscopic approach, based on the use of fluorescent probes, to monitor the membrane polarity, viscosity, and order directly in living cells under thermal excitation transduced by a photoexcited polymer film. We report two major results. First, we show that rising temperature does not just change the geometry of the membrane but indeed it affects the membrane dielectric characteristics by water penetration. Second, we find an additional effect, which is peculiar for the photoexcited semiconducting polymer film, that contributes to the system perturbation and that we tentatively assigned to the photoinduced polarization of the polymer interface.