Ionic effects on the transport characteristics of nanowire-based FETs in a liquid environment

For the development of ultra-sensitive electrical bio/chemical sensors based on nanowire field effect transistors （FETs）, the influence of the ions in the solution on the electron transport has to be understood. For this purpose we establish a simulation platform for nanowire FETs in the liquid environment by implementing the modified Poisson-Boltzmann model into Landauer transport theory. We investigate the changes of the electric potential and the transport characteristics due to the ions. The reduction of sensitivity of the sensors due to the screening effect from the electrolyte could be successfully reproduced. We also fabricated silicon nanowire Schottky-barrier FETs and our model could capture the observed reduction of the current with increasing ionic concentration. This shows that our simulation platform can be used to interpret ongoing experiments, to design nanowire FETs, and it also gives insight into controversial issues such as whether ions in the buffer solution affect the transport characteristics or not.     

Electrical Coupling Between Cells and Graphene Transistors

In this work, both experimental data and a model are presented on the coupling between living cells and graphene solution‐gated field‐effect transistors. Modified HEK 293 cells are successfully cultured on graphene transistor arrays and electrically accessed by the patch clamp method. Transistor recordings are presented, showing the opening and closing of voltage‐gated potassium ion channels in the cell membrane. The experimental data is compared with the broadly used standard point‐contact model. The ion dynamics in the cell–transistor cleft are analyzed to account for the differences between the model and the experimental data revealing a significant increase in the total ionic strength in the cleft. In order to describe the influence of the ion concentration resulting from the cell activity, the ion‐sensitivity of graphene solution‐gated field‐effect transistors is investigated experimentally and modelled by considering the screening effect of the ions on the surface potential at the graphene/electrolyte interface. Finally, the model of the cell–transistor coupling is extended to include the effect of ion accumulation and ion sensitivity. The experimental data shows a very good agreement with this extended model, emphasizing the importance of considering the ion concentration in the cleft to properly understand the cell‐transistor coupling.     

Assemblies of Functional Peptides and Their Applications in Building Blocks for Biosensors

This feature article highlights our recent applications of functional peptide nanotubes, self‐assembled from short peptides with recognition elements, as building blocks to develop sensors. Peptide nanotubes with high aspect ratios are excellent building blocks for a directed assembly into device configurations, and their combined structures with nanometric diameters and micrometric lengths enables to bridge the “nanoworld” and the “microworld”. When the peptide‐nanotube‐based biosensors, which incorporate molecular recognition units, apply alternating current probes to detect impedance signals, the peptide nanotubes behave as excellent building blocks of the transducer for the detection of target analyes such as pathogens, cells, and heavey metal ions with high specificity. In some sensor configurations, the electric signal can be amplified by coupling them with ion‐specific mineralization via molecular recognition of peptides. In general the detection limit of peptide nanotube chips sensors is very low and the dynamic range of detection can be widened by improved device designs.     

High‐Performance Dopamine Sensors Based on Whole‐Graphene Solution‐Gated Transistors

Solution‐gated graphene transistors with graphene as both channel and gate electrodes are fabricated for the first time and used as dopamine sensors with the detection limit down to 1 nM, which is three orders of magnitude better than that of conventional electrochemical measurements. The sensing mechanism is attributed to the change of effective gate voltage applied on the transistors induced by the electro‐oxidation of dopamine at the graphene gate electrodes. The interference from glucose, uric acid, and ascorbic acid on the dopamine sensor is characterized. The selectivity of the dopamine sensor is dramatically improved by modifying the gate electrode with a thin Nafion film by solution process. This work paves the way for developing many other biosensors based on the solution‐gated graphene transistors by specifically functionalizing the gate electrodes. Because the devices are mainly made of graphene, they are potentially low cost and ideal for high‐density integration as multifunctional sensor arrays.     

Porous silicon multilayer stacks for optical biosensing applications

Porous silicon (PS) multilayer stacks were developed for their use as interference filters in the visible range. The optical behavior of these structures was previously simulated by the use of a computational program, from which the optical constants and thickness of the individual PS layers were determined. The possibility of using these structures as biosensors has been explored, based on the significant changes in the reflectance spectra before and after exposing the PS multilayer to proteins (antibodies). In particular, it is shown that there is a notably reduction of reflectance from PS structures when this material is exposed to polyclonal mouse antibodies. Thus, the experimental results open the possibility of developing biosensors based on the variation of the shape and/or position of the optical or photoluminescent spectrum from PS.