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Novel reinforced cross-linked lysozyme crystals containing homogeneous dispersions of single-walled carbon nanotubes (SWCNTs) have been produced and characterized. The incorporation of SWCNTs inside lysozyme crystals gives rise to reinforced hybrid materials with tunable mechanical strength and electronic conductivity, while preserving the crystal-quality and morphology. These reinforced crystals show increase catalytic activity at higher temperature, being active even above the denaturation temperature. The electron transport through the crystals have been linked to the content and distribution of SWCNTs inside the crystals. The electron conduction through the crystals is isotropic and very efficient, presenting high conductivity values up to 600 nS at very low (0.05 wt%) SWCNTs concentration. To obtain these crystals a new protocol based on the in situ crystallization of lysozyme in hybrid SWCNTs-peptide hydrogels has been developed. These peptide hydrogels have been able to homogeneously dispersed hydrophobic SWCNTs allowing first, the crystallization of the enzyme lysozyme and secondly, transferring the new properties of the inorganic component to the crystals. Taken together, these hybrid crystals represent a notorious example of the versatility of proteins as biological substrates in the generation of novel functional materials, opening the door to use them in catalysis and bioelectronics at macroscale., Projects BIO2016-74875-P and FIS2017-85954-R (Ministerio de Economía, Industria y Competitividad, MINECO, and Agencia Estatal de Investigación, AEI, Spain, co-funded by Fondo Europeo de Desarrollo Regional, FEDER, European Union) and by Junta de Andalucía (Spain) projects P12-FQM-2721 and P12-FQM-790.

Peptide fibril nanostructures have been advocated as components of future biotechnology and nanotechnology devices. However, the ability to exploit the fibril functionality for applications, such as catalysis or electron transfer, depends on the formation of well-defined architectures. Fibrils made of peptides substituted with aromatic groups are described presenting efficient electron delocalization. Peptide self-assembly under various conditions produced polymorphic fibril products presenting distinctly different conductivities. This process is driven by a collective set of hydrogen bonding, electrostatic, and π-stacking interactions, and as a result it can be directed towards formation of a distinct polymorph by using the medium to enhance specific interactions rather than the others. This method facilitates the detailed characterization of different polymorphs, and allows specific conditions to be established that lead to the polymorph with the highest conductivity.

Protons and electrons are being exploited in different natural charge transfer processes. Both types of charge carriers could be, therefore, responsible for charge transport in biomimetic self-assembled peptide nanostructures. The relative contribution of each type of charge carrier is studied in the present work for fi brils self-assembled from amyloid- β derived peptide molecules, in which two non-natural thiophene-based amino acids are included. It is shown that under low humidity conditions both electrons and protons contribute to the conduction, with current ratio of 1:2 respectively, while at higher relative humidity proton transport dominates the conductance. This hybrid conduction behavior leads to a bimodal exponential dependence of the conductance on the relative humidity. Furthermore, in both cases the conductance is shown to be affected by the peptide folding state under the entire relative humidity range. This unique hybrid conductivity behavior makes self-assembled peptide nanostructures powerful building blocks for the construction of electric devices that could use either or both types of charge carriers for their function.

The incorporation of non-canonical amino acids with aromatic side chains is considered to be a promising way to improve and control the electronic properties of self-assembled peptide nanostructures. In this work, we have studied the influence of aromatic ring heteroatom on the electronic properties of amyloid β-derived peptide fiber networks. We show that the incorporation of furan instead of thiophene side chains results in only small changes in the resistivity of the peptide network, with a threefold increase in the sheet resistance and a small decrease in the contact resistance. These changes can be explained by a twofold decrease in the diameter of the self-assembled fibers. These characteristics open the way to the use of furan- instead of thiophene-based analogues as non-natural side-chain modifications of peptides for electronic applications; this makes the fibrils more biodegradable and biorenewable.

Studies of charge transport through proteins bridged between two electrodes have been the subject of intense research in recent years. However, the complex structure of proteins makes it difficult to elucidate transport mechanisms, and the use of simple peptide oligomers may be an over simplified model of the proteins. To bridge this structural gap, we present here studies of charge transport through artificial parallel coiled-coil proteins conducted in dry environment. Protein monolayers uniaxially oriented at an angle of ∼ 30° with respect to the surface normal were prepared. Current voltage measurements, obtained using conductive-probe atomic force microscopy, revealed the mechano-electronic behavior of the protein films. It was found that the low voltage conductance of the protein monolayer increases linearly with applied force, mainly due to increase in the tip contact area. Negligible compression of the films for loads below 26 nN allowed estimating a tunneling attenuation factor, β(0) , of 0.5-0.6 Å(-1) , which is akin to charge transfer by tunneling mechanism, despite the comparably large charge transport distance. These studies show that mechano-electronic behavior of proteins can shed light on their complex charge transport mechanisms, and on how these mechanisms depend on the detailed structure of the proteins. Such studies may provide insightful information on charge transfer in biological systems.

A method to modulate the signal of field-effect transistor biosensors using an immunosorbent assay is described. A model system is used to show that binding of a secondary antibody, to which highly charged gold colloids are attached, to an analyte on the device floating gate can be used to induce strong electrostatic effects, which affect the device threshold voltage and source-drain current. This process may be used for signal amplification, with the secondary binding specificity allowing for improved signal to noise ratio, which is of great importance for early disease detection.

In this review we discuss our recent efforts directed at understanding the dynamics of catalytic networks, and their utility for performing Boolean logic operations. We start by explaining the “recipe” for the design of experimental, peptide-based, replication networks, and then the approach we take for simulating their kinetics. The studied networks can be manipulated in order to facilitate molecular replication through all 2-input Boolean logic operations, and furthermore the operational catalytic pathways can be wired together to perform more complex computational modules and network motifs. Beyond just simulations and the basic experiments, we show that while in principle all the gates may be constructed, symmetry and order constraints limit the types of logic that may be practically achieved. Finally, we describe the use of adaptive networks that form logic gates by responding to changes in the environment (pH, salt, and light), and the first steps towards realization of the performance of switching and gating molecular electronic devices using the peptides.

We describe a concise, solid support-based synthetic method for the preparation of cyclic d,l-alpha-peptides bearing 1,4,5,8-naphthalenetetracarboxylic acid diimide (NDI) side chains. Studies of the structural and photoluminescence properties of these molecules in solution show that the hydrogen bond-directed self-assembly of the cyclic d,l-alpha-peptide backbone promotes intermolecular NDI excimer formation. The efficiency of NDI charge transfer in the resulting supramolecular assemblies is shown to depend on the length of the linker between the NDI and the peptide backbone, the distal NDI substituent, and the number of NDIs incorporated in a given structure. The design rationale and synthetic strategies described here should provide a basic blueprint for a series of self-assembling cyclic d,l-alpha-peptide nanotubes with interesting optical and electronic properties.

Functional supramolecular chemistry at the single-molecule level. Single strands of DNA can be captured inside α-hemolysin transmembrane pore protein to form single-species α-HL·DNA pseudorotaxanes. This process can be used to identify a single adenine nucleotide at a specific location on a strand of DNA by the characteristic reductions in the α-HL ion conductance. This study suggests that α-HL-mediated single-molecule DNA sequencing might be fundamentally feasible.