Single Molecule Sensors and Molecular Devices

Activity Abstract

The activities on Single Molecule Sensors carried out by MiNES Group are at different levels, starting from the fabrication of nanoprobes (nanogaps) up to the molecular level modeling on nanodevices, ending with the design of novel nanodevices both based on organic and bio molecules.

On the spot can be considered mostly three activities:

  • Fabrication of NanoGaps by Electromigration and related modeling
  • Realization of Single Biomolecule Sensors
  • Design and Implementation of Molecular Electronics Devices

 

Fabrication of NanoGaps by Electromigration and related modeling

Several activities have been carried out for optimizing the fabrication of NanoGaps by Electromigration. The obtained results have been published in International Journals and the most relevant, for introducing the concept and the approach, is the first one published in Electrochimica Acta, where the concept of fabricating NanoGaps by ElectroMigration is described. In this paper (D. Demarchi, P. Civera, G. Piccinini, M. Cocuzza, and D. Perrone, Electrothermal modelling for EIBJ nanogap fabrication, Electrochimica Acta, vol. 54, pp. 6003–6009, 2009) it is analyzed the technological process at room temperature for applying Electromigration Induced Break Junction technique (EIBJ) to nanogap fabrication. As a consequence a simple and low cost technological process to realize gold nanogaps at room temperature becomes feasible.

nanogap-FESEM-AFM

Than, in the paper “I. Rattalino, P. Motto, G. Piccinini, and D. Demarchi, A new validation method for modeling nanogap fabrication by electromigration, based on the Resistance-Voltage (R-V) curve analysis, Physics Letters A, vol. 376, no. 3, pp. 2134–2140, Jun. 2012” the modeling of nanogap fabrication is explained with more details. This Letter presents the validation of the electromigration model, able to simulate nanogap formation by EIBJ. The estimation of the deepening atomic flux from a statistical set of Resistance–Voltage (R–V) curves, generated during controlled nanogap fabrication, is studied. The validation, related to the first cycle of the R–V curves, is performed by observing a high degree of matching between the numerical and experimental atomic fluxes. This method is useful for providing reliable models of electromigration, which can simulate nanogap formation and become part of the control algorithm in order to improve the fabrication process.

The fabrication custom system, developed by MiNES Group and named NanoCube,  is well described in the paper “P. Motto, M. Crepaldi, G. Piccinini, and D. Demarchi, NanoCube: A Low-Cost, Modular, and High-Performance Embedded System for Adaptive Fabrication and Characterization of Nanogaps, IEEE Trans. Nanotechnology, vol. 13, pp. 322–334, Mar. 2014“, where the embedded modular system, NanoCube, is presented. The modular and flexible system embeds the core circuits for nanogap fabrication, signal conditioning and measurement, and the microprogrammed subsystems. NanoCube runs a real-time Linux operating system, with a fully customizable electromigration algorithm which considers fabrication history to adaptively improve performance.

Other papers related to this topic are:

 

Realization of Single Biomolecule Sensors

BR-RC-Nanogap

The best important reference of the results obtained by MiNES Group in this Activity is the paper “A. Dimonte, S. Frache, V. Erokhin, G. Piccinini, D. Demarchi, F. Milano, G. de Micheli, and S. Carrara, Nanosized Optoelectronic Devices based on Photoactivated Proteins., Biomacromolecules, vol. 13, no. 11, pp. 3503–3509, Oct. 2012” (see reported image, courtesy of ACS Publishing), where nanogaps between gold electrodes have been used to develop optoelectronic devices based on photoactive proteins. Reaction Centers (RC) and Bacteriorhodopsin (BR) have been inserted in nanogaps by drop casting. The work demonstrated that these nanodevices working principle is based on charge separation and photovoltage response.

Metal−molecule−metal junction is the starting point for the realization of a novel series of bio-optoelectronic transistors based on light-sensitive proteins, in which inorganic materials are well-integrated with biologically active elements. In this work it was proved the possibility of fabricating circuits and devices in which proteins can be placed in a nanogap, maintaining light-induced charge-transfer properties. It was possible to elicit resonance in RC in response to a voltage application, whereas, under light, the charge separation induced in the photoactive protein was shown to avoid any current peak. In conclusion, in this work we have demonstrated the RC capability as a switching element, if excited by proper voltage application. It has been shown that the optimal sensitivity of the metal−molecule−metal junction with BR is at 570 nm wavelength.

Other results related to the use of nanogaps in the field of Biomolecular Sensors can be found in:

 

Design and Implementation of Molecular Electronics Devices

This Activity has been carried out exploiting the capability of nanogap fabrication of MiNES Group. Several nanodevices have been realized, comprising the modeling and simulations done at molecular level.

RattalinoOligoThiophenes

One of the most interesting results is reported in “I. Rattalino, V. Cauda, P. Motto, T. Limongi, G. Das, L. Razzari, F. Parenti, E. Di Fabrizio, A. Mucci, L. Schenetti, G. Piccinini, and D. Demarchi, A nanogap–array platform for testing the optically modulated conduction of gold–octithiophene–gold junctions for molecular optoelectronics, RSC Adv., vol. 2, no. 29, pp. 10985–10993, 2012″ (see reported image, courtesy of RSC Publishing) where was studied the light dependent conduction of gold–oligothiophene–gold molecular junctions as a fully–customized platform. The work demonstrated the flexibility and novelty of the platform, and its plug-and-play connection to an external electronic board to perform eight parallel nanogap fabrication and molecular electrical characterization. The octithiophene molecules were synthesized ad-hoc to efficiently self-assembly and selectively bridge the nanogap electrodes upon deposition, which can be carried out directly and in parallel on the 8 nanogap array platforms. The high portability of the platform is well suited for insitu microscopic and spectroscopic analyses. In particular, the electrical functionality of the octithiophene molecular junctions by coupling electrical current–voltage (IV) characterization with fluorescence and Raman spectroscopies were tested. Modulation of the electrical conductance by varying the light excitation wavelength was shown. The proposed ad-hoc platform design makes molecular junctions real working blocks, which can be interfaced with external circuits as electronic components or sensors, overcoming the limitations of usability, cost and portability of traditional molecular contacting methods. In this work we thus demonstrated that the optoelectronic properties of oligothiophenes can be exploited in the form of molecular junctions to fabricate optoelectronic devices for molecular electronics.

Other publications related to this Activity are:

Activity Keywords

  • Nanoprobing (NanoGaps)
  • NanoBioSensors
  • Molecular Electronics Devices
  • Electromigration Induced Break Junction (EIBJ)