Bionanoelectronics: getting close to the action

Bio-nano hybrid materials based on bacteriorhodopsin: Potential applications and future strategies

This review presents an overview of recent progress in the development of bio-nano hybrid materials based on the photoactive protein bacteriorhodopsin (bR). The interfacing of bR with various nanostructures including colloidal nanoparticles (such as quantum dots and Ag NPs) and nanoparticulate thin films (such as TiO2 NPs and ZnO NPs,) has developed novel functional materials. Applications of these materials are comprehensively reviewed in two parts: bioelectronics and solar energy conversion. Finally, some perspectives on possible future strategies in bR-based nanostructured devices are presented.

Multiplexed free-standing nanowire transistor bioprobe for intracellular recording: a general fabrication strategy

Recent advance in free-standing nanowire transistor bioprobes opens up new opportunities of accurately interfacing spatially unobstructed nanoscale sensors with live cells. However, the existing fabrication procedures face efficiency and yield limitations when working with more complex nanoscale building blocks to integrate, for example, multiplexed recordings or additional functionalities. To date, only single-kinked silicon nanowires have been successfully used in such probes. Here we establish a general fabrication strategy to mitigate such limitations with which synthetically designed complex nanoscale building blocks can be readily used without causing significant penalty in yield or fabrication time, and the geometry of the probe can be freely optimized based on the orientation and structure of the building blocks. Using this new fabrication framework, we demonstrate the first multiplexed free-standing bioprobe based on w-shaped silicon kinked nanowires that are synthetically integrated with two nanoscale field-effect transistor devices. Simultaneous recording of intracellular action potentials from both devices have been obtained of a single spontaneously beating cardiomyocyte.

L-Asparagine crystals with wide gap semiconductor features: optical absorption measurements and density functional theory computations

Results of optical absorption measurements are presented together with calculated structural, electronic, and optical properties for the anhydrous monoclinic L-asparagine crystal. Density functional theory (DFT) within the generalized gradient approximation (GGA) including dispersion effects (TS, Grimme) was employed to perform the calculations. The optical absorption measurements revealed that the anhydrous monoclinic L-asparagine crystal is a wide band gap material with 4.95 eV main gap energy. DFT-GGA+TS simulations, on the other hand, produced structural parameters in very good agreement with X-ray data. The lattice parameter differences Δa, Δb, Δc between theory and experiment were as small as 0.020, 0.051, and 0.022 Å, respectively. The calculated band gap energy is smaller than the experimental data by about 15%, with a 4.23 eV indirect band gap corresponding to Z → Γ and Z → β transitions. Three other indirect band gaps of 4.30 eV, 4.32 eV, and 4.36 eV are assigned to α3 → Γ, α1 → Γ, and α2 → Γ transitions, respectively. Δ-sol computations, on the other hand, predict a main band gap of 5.00 eV, just 50 meV above the experimental value. Electronic wavefunctions mainly originating from O 2p-carboxyl, C 2p-side chain, and C 2p-carboxyl orbitals contribute most significantly to the highest valence and lowest conduction energy bands, respectively. By varying the lattice parameters from their converged equilibrium values, we show that the unit cell is less stiff along the b direction than for the a and c directions. Effective mass calculations suggest that hole transport behavior is more anisotropic than electron transport, but the mass values allow for some charge mobility except along a direction perpendicular to the molecular layers of L-asparagine which form the crystal, so anhydrous monoclinic L-asparagine crystals could behave as wide gap semiconductors. Finally, the calculations point to a high degree of optical anisotropy for the absorption and complex dielectric function, with more structured curves for incident light polarized along the 100 and 101 directions.

Free-standing kinked nanowire transistor probes for targeted intracellular recording in three dimensions

Recording intracellular (IC) bioelectrical signals is central to understanding the fundamental behaviour of cells and cell networks in, for example, neural and cardiac systems. The standard tool for IC recording, the patch-clamp micropipette is applied widely, yet remains limited in terms of reducing the tip size, the ability to reuse the pipette and ion exchange with the cytoplasm. Recent efforts have been directed towards developing new chip-based tools, including micro-to-nanoscale metal pillars, transistor-based kinked nanowires and nanotube devices. These nanoscale tools are interesting with respect to chip-based multiplexing, but, so far, preclude targeted recording from specific cell regions and/or subcellular structures. Here we overcome this limitation in a general manner by fabricating free-standing probes in which a kinked silicon nanowire with an encoded field-effect transistor detector serves as the tip end. These probes can be manipulated in three dimensions within a standard microscope to target specific cells or cell regions, and record stable full-amplitude IC action potentials from different targeted cells without the need to clean or change the tip. Simultaneous measurements from the same cell made with free-standing nanowire and patch-clamp probes show that the same action potential amplitude and temporal properties are recorded without corrections to the raw nanowire signal. In addition, we demonstrate real-time monitoring of changes in the action potential as different ion-channel blockers are applied to cells, and multiplexed recording from cells by independent manipulation of two free-standing nanowire probes.