Electronic nanodevices based on self-assembled metalloproteins

A key challenge of the current research in nanoelectronics is the realization of biomolecular devices. The use of electron-transfer proteins, such as the blue copper protein azurin (Az), is particularly attractive because of their natural redox properties and self assembly capability. We present in this work our results about the fabrication, characterization and modeling of devices based on such redox protein. The prototypes of biomolecular devices operate in the solid state and in air . The charge transfer process in protein devices can be engineered by using proteins with different redox centers (metal atoms) and by controlling their orientation in the solid state through different immobilization methods. A biomolecular electron rectifier has been demonstrated by interconnecting two gold nanoelectrodes with an azurin monolayer immobilized on SiO2. The device exhibits a clear rectifying behavior with discrete current steps in the positive wing of the current–voltage curve, which are ascribed to resonant tunnelling through the redox active center. On the basis of these results we have designed an azurin-based transistor. The three terminal device exhibits an ambipolar behavior as a function of the gate bias, thus opening the way to the implementation of a new generation of logic architecture, such as fully integrated biomolecular logic gate

Projecting the nanoworld: Concepts, results and perspectives of molecular electronics

A bottom-up approach is a promising alternative to build nanodevices and/or nanomachines starting from molecular building blocks. The idea of molecular electronics comes from a farsighted paper by Aviram and Ratner, predicting that single molecules with a donor–spacer–acceptor structure would have rectifying properties when placed between two electrodes. Today, molecular electronics is emerging as an alternative to Si-nanoelectronics for building integrated devices. This review aims to give an overview of this emerging field, analysing the concepts, the key results and the perspectives

Nanofabrication for Molecular Scale Devices

The predicted 22-nm barrier which is seemingly going to put a final stop to Moore’s law is essentially related to the resolution limit of lithography. Consequently, finding suitable methods for fabricating and patterning nanodevices is the true challenge of tomorrow’s electronics. However, the pure matter of moulding devices and interconnections is interwoven with research on new materials, as well as architectural and computational paradigms. In fact, while the performance of any fabrication process is obviously related to the characteristic of the materials used, a particular fabrication technique can put constraints on the definable geometries and interconnection patterns, thus somehow biasing the upper levels of the computing machine. Further, novel technologies will have to account for heat dissipation, a particularly tricky problem at the nanoscale, which could in fact prevent the most performing nanodevice from being practically employed in complex networks. Finally, production costs – exponentially growing in the present Moore rush – will be a key factor in evaluating the feasibility of tomorrow technologies. The possible approaches to nanofabrication are commonly classified into top-down and bottom-up. The former involves carving small features into a suitable bulk material; in the latter, small objects assemble to form more complex and articulated structures. While the present technology of silicon has a chiefly top-down approach, bottom-up approaches are typical of the nanoscale world, being directly inspired by nature where molecules are assembled into supramolecular structures, up to tissues and organs. As top-down approaches are resolution-limited, boosting bottom-up approaches seems to be a good strategy to future nanoelectronics; however, it is highly unlikely that no patterning will be required at all, since even with molecular-scale technologies there is the need of electrically contacting the single elements and this most often happens through patterned metal contacts, although all-molecular devices were also proposed. Here, we will give some insight into both top-down and bottom-up without the intention to be exhaustive, because of space limitations

Micro/nanoscale patterning of nanostructured metal substrates for plasmonic applications.

The ability to precisely control the pattern of different metals at the micro- and nanoscale, along with their topology, has been demonstrated to be essential for many applications, ranging from material science to biomedical devices, electronics, and photonics. In this work, we show a novel approach, based on a combination of lithographic techniques and galvanic displacement reactions, to fabricate micro- and nanoscale patterns of different metals, with highly controlled surface roughness, onto a number of suitable substrates. We demonstrate the possibility to exploit such metal films to achieve significant fluorescence enhancement of nearby fluorophores, while maintaining accurate spatial control of the process, from submicron resolution to centimeter-sized features. These patterns may be also exploited for a wide range of applications, including SERS, solar cells, DNA microarray technology, hydrophobic/hydrophilic substrates, and magnetic devices

A protein-based three terminal electronic device.

: Because of their natural functional characteristics, involving inter- and intramolecular electron transfer, metalloproteins are good candidates for biomolecular nanoelectronics. In particular, blue copper proteins, such as azurin, can bind gold via a disulfide site present on its surface and they have a natural electron transfer activity that can be exploited for the realization of molecular switches whose conduction state can be controlled by tuning their redox state through an external voltage source. We report on the implementation of a prototype of protein transistor operating in air and in the solid state, based on this class of proteins. The three terminal devices exhibit various functions depending on the relative source-drain and gate-drain voltages bias, opening a way to the implementation of a new generation of logic architectures

Self-assembled extracellular matrix protein networks by microcontact printing.

Physiological patterns of the extracellular matrix protein, laminin-1, were obtained on glass substrates by physisorption-assisted microcontact printing. Besides the well-retained antigenicity confirmed by indirect immunofluorescence assays, we investigated the supramolecular organization of the proteins by atomic force microscopy. We found the characteristic protein self-assembling in polygonal networks with well-defined sub-100 nm quaternary structures of laminin. The formation of these physiological mesh-like protein matrices was obtained by means of one-step soft lithography without any preliminary functionalization of glass, which can be exploited for many possible applications for cell cultures and biomolecular devices

Photodetectors fabricated from a self-assembly of a deoxyguanosine derivative

A metal–semiconductor–metal (MSM) photodetector has been fabricated using as the semiconductor, a self-assembled layer of a DNA basis, namely a deoxyguanosine derivative, deposited between two gold electrodes. These were defined lithographically on a SiO2 substrate, separated by a distance of about 120 nm. The resulting self-assembled guanosine crystal has been deposited in such a way to achieve striking semiconducting properties. We show that with these conditions, the I–V characteristics are independent of the crystal orientation. The device shows a high current response (differential resistance at room temperature ranges in MΩ) which is symmetric with respect to bias sign and dependent on the illumination conditions. This behavior can be explained by taking into account the standard MSM theory and its applications as a photodetector

SFM study of the surface of halogen-bonded hybrid co-crystals containing long-chain perfluorocarbons

Different scanning force microscopy (SFM) techniques were employed to investigate the structure and composition of the fundamental crystal faces of prototype halogen-bonded co-crystals of long-chain perfluorocarbons. These crystals were found to show surfaces with well-defined ledges formed by intersecting crystal planes having different chemical compositions with the perfluorocarbons (PFCs) covering the largest area of the crystal as a reminiscence of the strong segregation observed in the bulk crystal structure

Control of colloidal CaCO3 suspension by using biodegradable polymers during fabrication

Fabrication of homogenous CaCO3 particles is a significant step in assembling polyelectrolyte capsules. It is crucial to control the dimensions, the shape and the charge of the calcium carbonate particles in order to have homogenously separated and charged templates as final result. For this reason, previously. hey have been deeply investigated. Recently, crystallization of CaCO3 was done by adding poly (sodium 4-styrenesulfonate) (PSS) as negatively charged polymer and poly (allylamine hydrochloride) (PAH) as positively charged polymer and the results were surprising. The homogenous particles were separated and they carried the same charge of the used polymer. The aim of this work was to investigate the synthesis process of CaCO3 particles in different experimental conditions: calcium carbonate was produced in presence and in absence of water and with addition of appropriate polymers. In particular, chitosan (CHI) and poly acrylic acid (PAA) were chosen as biodegradable polymers whereas PSS and PAH were chosen as non-biodegradable polymers. Shape and diameter of particles were investigated by using transmission and scanning electron microscopy, elemental composition was inferred by energy dispersive X-ray analyses whereas their charges were explored by using zeta potential

Cytocompatibility and Uptake of Halloysite Clay Nanotubes

Halloysite is aluminosilicate clay with hollow tubular structure of 50 nm external diameter and 15 nm diameter lumen. Halloysite biocompatibility study is important for its potential applications in polymer composites, bone implants, controlled drug delivery, and for protective coating (e.g., anticorrosion or antimolding). Halloysite nanotubes were added to different cell cultures for toxicity tests. Its fluorescence functionalization by aminopropyltriethosilane (APTES) and with fluorescently labeled polyelectrolyte layers allowed following halloysite uptake by the cells with confocal laser scanning microscopy (CLSM). Quantitative Trypan blue and MTT measurements performed with two neoplastic cell lines model systems as a function of the nanotubes concentration and incubation time indicate that halloysite exhibits a high level of biocompatibility and very low cytotoxicity, rendering it a good candidate for household materials and medicine. A combination of transmission electron microscopy (TEM), scanning electron microscopy (SEM), and scanning force microscopy (SFM) imaging techniques have been employed to elucidate the structure of halloysite nanotubes