Maria Daniela Angione

Carbon based materials for electronic bio-sensing

Bio-sensing represents one of the most attractive applications of carbon material based electronic devices; nevertheless, the complete integration of bioactive transducing elements still represents a major challenge, particularly in terms of preserving biological function and specificity while maintaining the sensors electronic performance. This review highlights recent advances in the realization of field-effect transistor (FET) based sensors that comprise a bio-receptor within the FET channel. A birds-eye view will be provided of the most promising classes of active layers as well as different device architectures and methods of fabrication. Finally, strategies for interfacing bio-components with organic or carbon nano-structured electronic active layers are reported.

Interfacial electronic effects in functional biolayers integrated into organic field-effect transistors

Biosystems integration into an organic field-effect transistor (OFET) structure is achieved by spin coating phospholipid or protein layers between the gate dielectric and the organic semiconductor. An architecture directly interfacing supported biological layers to the OFET channel is proposed and, strikingly, both the electronic properties and the biointerlayer functionality are fully retained. The platform bench tests involved OFETs integrating phospholipids and bacteriorhodopsin exposed to 1–5% anesthetic doses that reveal drug-induced changes in the lipid membrane. This result challenges the current anesthetic action model relying on the so far provided evidence that doses much higher than clinically relevant ones (2.4%) do not alter lipid bilayers’ structure significantly. Furthermore, a streptavidin embedding OFET shows label-free biotin electronic detection at 10 parts-per-trillion concentration level, reaching state-of-the-art fluorescent assay performances. These examples show how the proposed bioelectronic platform, besides resulting in extremely performing biosensors, can open insights into biologically relevant phenomena involving membrane weak interfacial modifications.

Electronic transduction of proton translocations in nanoassembled lamellae of bacteriorhodopsin

An organic field-effect transistor (OFET) integrating bacteriorhodopsin (bR) nanoassembled lamellae is proposed for an in-depth study of the proton translocation processes occurring as the bioelectronic device is exposed either to light or to low concentrations of general anesthetic vapors. The study involves the morphological, structural, electrical, and spectroscopic characterizations necessary to assess the functional properties of the device as well as the bR biological activity once integrated into the functional biointerlayer (FBI)-OFET structure. The electronic transduction of the protons phototranslocation is shown as a current increase in the p-type channel only when the device is irradiated with photons known to trigger the bR photocycle, while Raman spectroscopy reveals an associated C═C isomer switch. Notably, higher energy photons bring the cis isomer back to its trans form, switching the proton pumping process off. The investigation is extended also to the study of a PM FBI-OFET exposed to volatile general anesthetics such as halothane. In this case an electronic current increase is seen upon exposure to low, clinically relevant, concentrations of anesthetics, while no evidence of isomer-switching is observed. The study of the direct electronic detection of the two different externally triggered proton translocation effects allows gathering insights into the underpinning of different bR molecular switching processes.

Volatile general anesthetic sensing with organic field-effect transistors integrating phospholipid membranes

The detailed action mechanism of volatile general anesthetics is still unknown despite their effect has been clinically exploited for more than a century. Long ago it was also assessed that the potency of an anesthetic molecule well correlates with its lipophilicity and phospholipids were eventually identified as mediators. As yet, the direct effect of volatile anesthetics at physiological relevant concentrations on membranes is still under scrutiny. Organic field-effect transistors (OFETs) integrating a phospholipid (PL) functional bio inter-layer (FBI) are here proposed for the electronic detection of archetypal volatile anesthetic molecules such as diethyl ether and halothane. This technology allows to directly interface a PL layer to an electronic transistor channel, and directly probe subtle changes occurring in the bio-layer. Repeatable responses of PL FBI-OFET to anesthetics are produced in a concentration range that reaches few percent, namely the clinically relevant regime. The PL FBI-OFET is also shown to deliver a comparably weaker response to a non-anesthetic volatile molecule such as acetone.

Membrane proteins embedded in supported lipid bilayers employed in field effect electronic devices

A novel bottom-gate top-contact OTFT architecture has been fabricated. In this device, a lipid bilayer structure embedding a photosynthetic membrane protein extracted from Rhodobacter Sphaeroides has been deposited onto the organic semiconductor film (α,ω-dihexylsexythiophene) prior to the evaporation of source and drain gold contacts. The figures of merit of this device were extracted and compared to those obtained for the same OTFT devoid of the biological film. Only slightly lower performances in terms of field-effect mobility (µ) were observed for the lipid bilayer OTFT that exhibits µ=0.007 cm2/Vs. This result constitutes a preliminary important starting point towards the development of novel highly sensitive and selective herbicides sensors.

Field Effect Transistor Sensing Devices Employing Lipid Layers

Field-Effect Transistors comprising layers of lipids have been developed and characterized from the electrical point of view. Lipid layers-OTFT are proposed as novel devices for perspective application in the detection of analytes from aqueous samples.

Innovative electronic biosensors based on organic thin film transistors

To satisfy the demand for fast and smart analytical systems a great interest has been focused on the study and development of novel bio-sensing devices. Electronic transduction can open new perspectives for point-of-care diagnosis actuated by fast, sensitive, selective and reliable biosensors. Recently our group demonstrated the feasibility of the coupling of a biological recognition element to an organic field-effect device [3, 4]. As a further step, investigations on different deposition techniques have been developed, to improve the adhesion and the homogeneity of the biological element onto the organic semiconductor.

Use of lipid bilayers as support for biomolecules integration in OTFT biosensors

Organic thin film transistor (OTFT) technology can be implemented to develop cost-effective and label-free bio-affinity sensor chips, having a field-effect transport directly coupled to a bio-sensing process, useful to high-throughput testing and point-of-care applications. Biological recognition elements such as antibodies or other proteins can be integrated in OTFT devices to confer specificity. In this study the use of lipid bilayers as support for biomolecules immobilization is investigated. Preliminary results in terms of electrical resistance and capacitance of the lipid bilayers are presented.