Maria Rosa Antognazza

A hybrid bioorganic interface for neuronal photoactivation

A key issue in the realization of retinal prosthetic devices is reliable transduction of information carried by light into specific patterns of electrical activity in visual information processing networks. Soft organic materials can be used to couple artificial sensors with neuronal tissues. Here, we interface a network of primary neurons with an organic blend. We show that primary neurons can be successfully grown onto the polymer layer without affecting the optoelectronic properties of the active material or the biological functionality of neuronal network. Moreover, action potentials can be triggered in a temporally reliable and spatially selective manner with short pulses of visible light. Our results may lead to new neuronal communication and photo manipulation techniques, thus paving way to the development of artificial retinas and other neuroprosthetic interfaces based on organic photodetectors.

A polymer optoelectronic interface restores light sensitivity in blind rat retinas

Interfacing organic electronics with biological substrates offers new possibilities for biotechnology due to the beneficial properties exhibited by organic conducting polymers. These polymers have been used for cellular interfaces in several fashions, including cellular scaffolds, neural probes, biosensors and actuators for drug release. Recently, an organic photovoltaic blend has been exploited for neuronal stimulation via a photo-excitation process. Here, we document the use of a single-component organic film of poly(3-hexylthiophene) (P3HT) to trigger neuronal firing upon illumination. Moreover, we demonstrate that this bio-organic interface restored light sensitivity in explants of rat retinas with light-induced photoreceptor degeneration. These findings suggest that all-organic devices may play an important future role in sub-retinal prosthetic implants.

Sub-Micrometer Charge Modulation Microscopy of a High Mobility Polymeric n-Channel Field-Effect Transistor

After two decades of fundamental research and steady development, solution processable organic fi eld-effect transistors (OFETs) have recently reached a mature stage that preludes their adoption in a variety of commercial applications from light-weight, stretchable, large-area sensors to low-cost, fl exible electronic circuits. [ 1–5 ] Despite the fact that fi eld-effect mobilities ( μ fe ) exceeding 1 cm 2 V − 1 s − 1 for both pand n-channel OFETs are now achievable with commercial, off-the-shelf conjugated organic small molecules and polymers, [ 4 ] fundamental studies are still strongly needed because of an incomplete understanding of the main mechanisms governing charge injection and transport in such devices. [ 7–9 ] To this extent, probing techniques capable of providing local information regarding mobility, fi eld, and charge distribution along the channel of a working device would be greatly benefi cial. Of particular interest for organic semiconductors is the relationship between microstructure and charge transport properties. This is even more evident in the case of recently developed high-mobility and stable n-channel OFETs, [ 6 ] in which the unusual face-on orientation of molecules has confounded expectations of what is required for effective charge transport. Scanning Kelvin-probe miscroscopy (SKPM) [ 7 ] is a powerful technique that allowed to map the potential profi le along the channels of OFETs with resolution better than 50 nm. [ 8 , 9 ]

Photothermal cellular stimulation in functional bio-polymer interfaces

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.

Organic photoelectrochemical cells with quantitative photocarrier conversion

Efficient solar-to-fuel conversion could be a cost-effective way to power the planet using sunlight. Herein, we demonstrate that Organic Photoelectrochemical Cells (OPECs) constitute a versatile platform for the efficient production of solar fuels. We show that the photogenerated carriers at the organic active layer can be quantitatively extracted to drive photoelectrochemical reactions at the interface with a liquid solution. Indeed, an unprecedented photocurrent of 4 mA cm−2 is extracted for an OPEC device, comparable to that of a solid-state device with similar optical properties. Through the careful choice of the selective contact and the redox couple in the liquid medium, we can tune the energetics of the system and activate either oxidative or reductive chemistry. The design rules to drive the desired electrochemical reaction are provided based on a comprehensive study of the energetic aspects of OPEC configuration. Finally, we demonstrate that OPEC devices effectively produce hydrogen in acetonitrile when a cobaloxime based homogeneous catalyst is present in the solution, and HCl is used a source of protons.

Hybrid organic–inorganic H2-evolving photocathodes: understanding the route towards high performance organic photoelectrochemical water splitting

A promising, yet challenging, route towards renewable production of hydrogen is the direct conversion of solar energy at a simple and low cost semiconductor/water junction. Despite the theoretical simplicity of such a photoelectrochemical device, different limitations among candidate semiconductor materials have hindered its development. After many decades of research on inorganic semiconductors, a conclusive solution still appears out of reach. Here, we report an efficient hybrid organic–inorganic H2 evolving photocathode, consisting of a donor/acceptor blend sandwiched between charge-selective layers and a thin electrocatalyst layer. The role and stability of the different interfaces are investigated, and the conductive polymer is proven to be an efficient material for a semiconductor/liquid PEC junction. The best performing electrodes show high performances with a photocurrent of 3 mA cm−2 at 0 V vs. RHE, optimal process stability with 100% faradaic efficiency during electrodes lifetime, excellent energetics with +0.67 V vs. RHE onset potential, promising operational activity of several hours and by-design compatibility for implementation in a tandem architecture. This work demonstrates organic semiconductors as a radically new option for efficient direct conversion of solar energy into fuels, and points out the route towards high performance organic photoelectrochemical water splitting.

A hybrid solid-liquid polymer photodiode for the bioenvironment

We demonstrate that a prototypical semiconducting polymer, poly[2-methoxy-5-( 2′ -ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) maintains unaltered its optoelectronic properties throughout the various steps for neural preparation. Films of MEH-PPV, after prolonged immersion in water or buffer solution, are characterized by linear and nonlinear optical spectroscopy. Based on this result, we introduce a hybrid solid-liquid photodiode based on MEH-PPV, in which we use culturing media as liquid, ionic cathodes. The hybrid device is proposed as an active interface between living tissue and conducting polymers for cell diagnostic and neural implants.

Organic-based tristimuli colorimeter

The authors realize three photodiodes based on organic materials, which have photoresponse curves matched to the colorimetric functions of the standard observer. Such a system of detectors is used for realizing a three-stimuli colorimeter. They report the result of measurements in different spectral areas and suggest possible application of the device in color science and artificial vision.

Photostimulation of Whole-Cell Conductance in Primary Rat Neocortical Astrocytes Mediated by Organic Semiconducting Thin Films

Astroglial ion channels are fundamental molecular targets in the study of brain physiology and pathophysiology. Novel tools and devices intended for stimulation and control of astrocytes ion channel activity are therefore highly desirable. The study of the interactions between astrocytes and biomaterials is also essential to control and minimize reactive astrogliosis, in view of the development of implantable functional devices. Here, the growth of rat primary neocortical astrocytes on the top of a light sensitive, organic polymer film is reported; by means of patch-clamp analyses, the effect of the visible light stimulation on membrane conductance is then determined. Photoexcitation of the active material causes a significant depolarization of the astroglial resting membrane potential: the effect is associated to an increase in whole-cell conductance at negative potentials. The magnitude of the evoked inward current density is proportional to the illumination intensity. Biophysical and pharmacological characterization suggests that the ion channel mediating the photo-transduction mechanism is a chloride channel, the ClC-2 channel. These results open interesting perspectives for the selective manipulation of astrocyte bioelectrical activity by non-invasive, label-free, organic-based, photostimulation approaches.

Light-evoked hyperpolarization and silencing of neurons by conjugated polymers.

The ability to control and modulate the action potential firing in neurons represents a powerful tool for neuroscience research and clinical applications. While neuronal excitation has been achieved with many tools, including electrical and optical stimulation, hyperpolarization and neuronal inhibition are typically obtained through patch-clamp or optogenetic manipulations. Here we report the use of conjugated polymer films interfaced with neurons for inducing a light-mediated inhibition of their electrical activity. We show that prolonged illumination of the interface triggers a sustained hyperpolarization of the neuronal membrane that significantly reduces both spontaneous and evoked action potential firing. We demonstrate that the polymeric interface can be activated by either visible or infrared light and is capable of modulating neuronal activity in brain slices and explanted retinas. These findings prove the ability of conjugated polymers to tune neuronal firing and suggest their potential application for the in-vivo modulation of neuronal activity.