A Solid‐State Protein Junction Serves as a Bias‐Induced Current Switch

Abstract

As ample-type protein monolayer,t hat can be as tepping stone to practical devices,c an behave as an electrically driven switch. This feat is achieved using ar edox protein, cytochrome C( CytC), with its heme shielded from direct contact with the solid-state electrodes.A binitio DFT calculations,c arried out on the CytC-Aus tructure,s howt hat the coupling of the heme,t he origin of the protein frontier orbitals,tothe electrodes is sufficiently weak to prevent Fermi level pinning.T hus,e xternal bias can bring these orbitals in and out of resonance with the electrode.Using acytochrome C mutant for direct SÀAu bonding,a pproximately 80 %o ft he Au-CytC-Au junctions showatgreater than 0.5 Vbias aclear conductance peak, consistent with resonant tunneling.The onoff change persists up to room temperature,d emonstrating reversible,b ias-controlled switching of ap rotein ensemble, which,with its built-in redundancy,provides arealistic path to protein-based bioelectronics.

Mechanical Deformation and Electronic Structure of a Blue Copper Azurin in a Solid-State Junction

“…We used the OpenMX open source package, which is an efficient DFT code based on highly optimized numerical pseudoatomic orbitals (PAOs) [45,46]. We followed a similar approach to that we used in our previous work on gas-phase azurins [11] and cytochrome C [47]. The initial geometries for the DFT calculations were obtained from selected frames of the previous MD simulations, including the whole protein (1929 atoms) and the parts of the substrate and the tip closest to the protein.…”

The Role of Metal Ions in the Electron Transport through Azurin-Based Junctions

“…In the case of the metal-substituted proteins studied in [15], the low-temperature results showed evidence for coherent transport; it was suggested that both tunneling and hopping are possible, however, depending on the temperature and the type of junction [35]. For the present study, we are particularly interested in the possibility of fully-coherent transport, which was suggested by the temperature-independence of the conductance measured in several experiments based on azurins [8,11,23,26,32,[36][37][38][39]. In [34], various types of configurations were studied, in which an STM tip was contacted to a blue-copper azurin in three different ways: in blinking mode (in which the tip is kept at a fixed distance from the surface and the protein is allowed to attach to the tip spontaneously), via top indentation (in which the tip is brought closer to the protein) and by lateral indentation (in which the tip approaches the protein sideways).…”

“…Research in this field has been carried out on various fronts. On the one hand, remarkable effort has been made to understand the exact nature of the charge transfer mechanism in protein-based junctions as well as to identify the components which play the dominant role in the transport process [8][9][10][11]. On the other hand, the possibility of modifying the conductance properties by the insertion of mutations [3,10,11] has also attracted a lot of interest.…”

“…Azurins are one of the proteins which have been studied the most in the field of protein-based electronics; additionally, they have long been the object of many computational studies because of their key role in biological functions [21]. Over the years, various experimental techniques have been adopted to measure the conductance of proteins [6,8,10,[22][23][24][25][26][27][28][29][30][31][32][33]. In this work, we focus on structures which are likely to be formed during the experiments based on STM (Scanning Tunneling Microscopy), which are generally designed to measure the conductance of a single protein.…”

Nanofabrication Techniques in Large-Area Molecular Electronic Devices

“…Additionally, it has been experimentally and theoretically proved that it is possible to tune molecular electron transfer rates in electron transfer proteins (ETpr's) through (i) chemical modifications and changes in the redox center, as well as the locations of the donor, the acceptor, and the bridge moieties within the ETpr's structure [220,[224][225][226][227][228] (ii) modifying the solvent environment [229], and importantly, (iii) orientation relative to the electrode and changing the strength of the protein-electrode coupling [230][231][232]. The study of large-area protein-based molecular electronic devices has been carried out mainly by the self-assembly method [148,149] via an appropriate linker. DNA has also focused the interest of researchers in the molecular electronics community due to several reasons, including (i) superior self-assembly properties [233,234]; (ii) its unique electrical properties [235], and (iii) its potential use in bioelectronics devices.…”