Andrea Spanu

An organic transistor-based system for reference-less electrophysiological monitoring of excitable cells

In the last four decades, substantial advances have been done in the understanding of the electrical behavior of excitable cells. From the introduction in the early 70s of the Ion Sensitive Field Effect Transistor (ISFET), a lot of effort has been put in the development of more and more performing transistor-based devices to reliably interface electrogenic cells such as, for example, cardiac myocytes and neurons. However, depending on the type of application, the electronic devices used to this aim face several problems like the intrinsic rigidity of the materials (associated with foreign body rejection reactions), lack of transparency and the presence of a reference electrode. Here, an innovative system based on a novel kind of organic thin film transistor (OTFT), called organic charge modulated FET (OCMFET), is proposed as a flexible, transparent, reference-less transducer of the electrical activity of electrogenic cells. The exploitation of organic electronics in interfacing the living matters will open up new perspectives in the electrophysiological field allowing us to head toward a modern era of flexible, reference-less, and low cost probes with high-spatial and high-temporal resolution for a new generation of in-vitro and in-vivo monitoring platforms.

Ultrathin, flexible and multimodal tactile sensors based on organic field-effect transistors

In this study, a novel approach to the fabrication of a multimodal temperature and force sensor on ultrathin, conformable and flexible substrates is presented. This process involves coupling a charge-modulated organic field-effect transistor (OCMFET) with a pyro/piezoelectric element, namely a commercial film of poly-vinylene difluoride (PVDF). The proposed device is able to respond to both pressure stimuli and temperature variations, demonstrating the feasibility of the approach for the development of low-cost, highly sensitive and conformable multimodal sensors. The overall thickness of the device is 1.2 μm, being thus able to conform to any surface (including the human body), while keeping its electrical performance. Furthermore, it is possible to discriminate between simultaneously applied temperature and pressure stimuli by coupling sensing surfaces made of poled and unpoled spin-coated PVDF-trifluoroethylene (PVDF-TrFE, a PVDF copolymer) with OCMFETs. This demonstrates the possibility of creating multimodal sensors that can be employed for applications in several fields, ranging from robotics to wearable electronics.

Organic FET device as a novel sensor for cell bioelectrical and metabolic activity recordings

Organic based transistors for biochemical sensing and cellular applications are becoming an alternative approach to standard technology because of their attractive features (e.g., low-cost, mechanical flexibility, enhanced biocompatibility). A particular configuration of organic FET, namely Organic Charge Modulated FET (OCMFET) is here proposed as a sensor for both electrical and metabolic activity of electroactive cells. Its peculiar structure allows sensing any local charge variation occurring in the sensing area without any chemical modification of the surface, making it a very interesting tool in electrophysiology and biosensing applications.

Low voltage organic charge modulated FETs: A flexible approach for the fabrication of high sensitive biosensors (Conference Presentation)

Charge Modulated OTFTs represent a versatile tool for the realization of a wide range of sensing applications. The architecture is based on a floating gate organic transistor whose sensitivity to a specific target is obtained by properly functionalizing a part of the floating gate with a sensing layer that can be chosen according to the specific external stimulus to be sensed. In this work we will show that such devices can be routinely fabricated on highly flexible, ultra-conformable thin films and that they can be employed, with no need of any chemical modification of the sensing area, for monitoring pH variations featuring a super-nernstian sensitivity. Interestingly, we will also show that the proposed approach has been applied for monitoring cell metabolic activity, demonstrated with a preliminary validation. In addition this device can be used for monitoring electrical activity of excitable cells, thus giving rise to a new family of highly sensitive, reference-less, and low-cost devices for a wide range of bio-sensing applications. Finally, we will also demonstrate that using a different sensing layer it is possible to employ the same device architecture for the realization of matrices of multimodal tactile transducers capable to detect at the same time temperature and pressure stimuli, and that being fabricated on sub-micrometer thin film can be conformably transferred on whatever kind of surface allowing the reproduction of the sense of touch.

Flexible temperature sensors based on charge modulated organic thin film transistors

In this work, we introduce a novel approach for the fabrication of temperature sensors. The devices are based on the integration of an Organic Charge Modulated Field Effect Transistor (OCMFET) with a pyroelectric polymeric element. Thanks to the optimization of the gate dielectric structure the fabricated sensors can be operated at very low voltages, and moreover, are fabricated on highly flexible plastic substrates. The results demonstrate that the sensors are able to detect in a very reproducible way, temperature variations from 20 °C up to 50 °C. This architecture represents a simple and innovative solution for the realization of conformable sensing systems for applications in tactile sensing as well as in wearable electronics.

Bioelectrical and metabolic activity recordings by means of organic field effect transistors

The introduction, in the early 70s, of the Ion Sensitive Field Effect Transistor (ISFET), completely revolutionized the biosensing field thanks to its versatility and the reliability of its transduction principle. Since then, a lot of different ISFET-based biosensors have been studied and realized for a great number of applications. Among them, a fast growing field of application is the electrophysiological field, in which ISFET-based sensors are employed for the detection of several parameters of electroactive cells, such as their electrical and metabolic activity. Here an innovative system based on a particular kind of Organic Thin Film Transistor (OTFT), called Organic Charge Modulated FET (OCMFET), is presented as a flexible, transparent, and low cost alternative to common ISFETs for the transduction of the electrical and metabolic activity of electrogenic cells. The exploitation of organic electronics in the electrophysiological field may bring several advantages over the existing techniques, thus introducing a novel paradigm in the way in which we interface living systems.