Overcome Debye Length Limitations for Biomolecule Sensing Based on Field Effective Transistors

Biosensors based on field effective transistor(FET)have aroused tremendous attention in the past few years owning to their huge application in drug discovery,disease diagnosis and environmental monitoring.The FET biosensors possess small volume,high sensitivity at ultra-low concentration,considerable mechanical strength,as well as excellent stability in solution,which plays a vital role in the point of care testing(POCT)systems.Recent advances have summarized some progress involved in the improvement of morphology and structure of channel materials,the functionalization of organic molecule,the influence of device operation and sensing environment on the detecting performance.However,for FET biosensors,the charge screening phenomena were inevitable in the solution,which seriously degrade the device performance.In this article,we summarize recent advances to overcome debye length limitations for biomolecule sensing based on FET.We will firstly describe the charge screening mechanism,then focous on the strategy to overcome charge screening,including synthesizing special channel materials with crumpled morphology,designing aptamer binding mode,and modulating device measurement.Finally,we discuss the major challenges and perspectives about overcoming debye length limitations of FET biosensors.These summaries provide further insights to realize real-time,lable-free,high-sensitivity FET sensors for medical healthcare.

Nano-channel-based physical and chemical synergic regulation for dendrite-free lithium plating

Uncontrollable dendrite growth resulting from the non-uniform lithium ion(Li^(+))flux and volume expansion in lithium metal(Li)negative electrode leads to rapid performance degradation and serious safety problems of lithium metal batteries.Although N-containing functional groups in carbon materials are reported to be effective to homogenize the Li^(+)flux,the effective interaction distance between lithium ions and N-containing groups should be relatively small(down to nanometer scale)according to the Debye length law.Thus,it is necessary to carefully design the microstructure of N-containing carbon materials to make the most of their roles in regulating the Li^(+)flux.In this work,porous carbon nitride microspheres(PCNMs)with abundant nanopores have been synthesized and utilized to fabricate a uniform lithiophilic coating layer having hybrid pores of both the nano-and micrometer scales on the Cu/Li foil.Physically,the three-dimensional(3D)porous framework is favorable for absorbing volume changes and guiding Li growth.Chemically,this coating layer can render a suitable interaction distance to effectively homogenize the Li^(+)flux and contribute to establishing a robust and stable solid electrolyte interphase(SEI)layer with Li-F,Li-N,and Li-O-rich contents based on the Debye length law.Such a physical-chemical synergic regulation strategy using PCNMs can lead to dendrite-free Li plating,resulting in a low nucleation overpotential and stable Li plating/stripping cycling performance in both the Li||Cu and the Li||Li symmetric cells.Meanwhile,a full cell using the PCNM coated Li foil negative electrode and a LiFePO4 positive electrode has delivered a high capacity retention of~80%after more than 200 cycles at 1 C and achieved a remarkable rate capability.The pouch cell fabricated by pairing the PCNM coated Li foil negative electrode with a NCM 811 positive electrode has retained~73%of the initial capacity after 150 cycles at 0.2 C.

Electro-osmotic flow of a second-grade fluid in a porous microchannel subject to an AC electric field

Studies on electro-osmotic flows of various types of fluids in microchannel are of great importance owing to their multifold applications in the transport of liquids, particularly when the ionized liquid flows with respect to a charged surface in the presence of an external electric field. In the case of viscoelastic fluids, the volumetric flow rate differs significantly from that of Newtonian fluids, even when the flow takes place under the same pressure gradient and the same electric field. With this end in view, this paper is devoted to a study concerning the flow pattern of an electro-osmotic flow in a porous microchannel, which is under the action of an alternating electric field. The influence of various rheological and electro-osmotic parameters, e.g., the Reynolds number, Debye-Huckel parameter, shape factor and fluid viscoelasticity on the kinematics of the fluid, has been investigated for a secondgrade viscoelastic fluid. The problem is first treated by using analytical methods, but the quantitative estimates are obtained numerically with the help of the software MATHEMATICA. The results presented here are applicable to the cases where the channel height is much greater than the thickness of the electrical double layer comprising the Stern and diffuse layers. The study reveals that a larger value of the Debye-Huckel parameter creates sharper profile near the wall and also that the velocity of electro-osmotic flow increases as the permeability of the porous microchannel is enhanced. The study further shows that the electro-osmotic flow dominates at lower values of Reynolds number. The results presented here will be quite useful to validate the observations of experimental investigations on the characteristics of electro-osmotic flows and also the results of complex numerical models that are necessary to deal with more realistic situations, where electro-osmotic flows come into the picture, as in blood flow in the micro-circulatory system subject to an electric field.

Sulfur dioxide gas sensing at room temperature based on tin selenium/tin dioxide hybrid prepared via hydrothermal and surface oxidation treatment

In this paper,a novel SnSe/SnO_(2) nanoparticles(NPs) composite has been successfully fabricated through hydrothermal method and surface oxidation treatment.The as-prepared sample was characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM).A series of morphological and structural characteristics confirm that the SnSe/SnO_(2) NPs composite shows a core-shell structure with a SnO_(2) shell with thickness of 6 nm.The prepared SnO_(2) NPs and SnSe/SnO_(2) NPs composite were applied as gas-sensing materials,and their gas-sensing properties were investigated at room temperature systematically.Experimental results show that the response value of the SnSe/SnO_(2) composite sensor toward 100×10^(-6) SO_(2) is 15.15%,which is 1.32 times higher than that of pristine SnSe(11.43%).And the SnSe/SnO_(2) composite sensor also has a detection limit as low as 74×10^(-9) and an ultra-fast response speed.The enhanced gas-sensing performance is attributed to the formation of p-n heterojunction between SnSe and SnO_(2) and the appropriate SnO_(2) shell thickness.

Driving Force of Molecular/Ionic Superfluid Formation

Ordered-and high-flux flow of molecules and ions in biological channels is considered as a quantumconfined superfluid,which is highly important in chemical reactions and bioinformation transmission.However,the driving forces for these ordered arrangements of molecules and ions in confined spaces have not been discussed.Herein,we demonstrate that the driving force of molecular/ionic superfluid formation is the attraction-repulsion balance of particles under the effect of interfacial confinement.

The Bipolar Field-Effect Transistor:Ⅷ.Longitudinal Gradient of Longitudinal Electric Field(Two-MOS-Gates on Pure-Base)

This paper evaluates the electric current terms from the longitudinal gradient of the longitudinal electric field in Bipolar Field-Effect-Transistors（BiFETs） with a pure base and two MOS gates operating in the unipolar（electron） current mode.These nMOS-BiFETs,known as nMOS-FinFETs,usually have electrically short channels compared with their intrinsic Debye length of about 25μm at room temperatures.These longitudinal electric current terms are important short-channel current components,which have been neglected in the computation of the long-channel electrical characteristics.This paper shows that the long-channel electrical characteristics are substantially modified by the longitudinal electrical current terms when the physical channel length is less than 100 nm.

Dopingless impact ionization MOS(DL-IMOS)—a remedy for complex process flow

We propose a unique approach for realizing dopingless impact ionization MOS （DL-IMOS） based on the charge plasma concept as a remedy for complex process flow. It uses work-function engineering of electrodes to form charge plasma as surrogate doping. This charge plasma induces a uniform p-region in the source side and an n-region in the drain side on intrinsic silicon film with a thickness less than the intrinsic Debye length. DL-IMOS offers a simple fabrication process flow as it avoids the need of ion implantation, photo masking and complicated thermal budget via annealing devices. The lower thermal budget is required for DL-IMOS fabrication enables its fabrication on single crystal silicon-on-glass substrate realized by wafer scale epitaxial transfer. It is highly immune to process variations, doping control issues and random dopant fluctuations, while retaining the inherent advantages of conventional IMOS. To epitomize the fabrication process flow for the proposed device a virtual fabrication flow is also proposed here. Extensive device simulation of the major device performance metrics such as subthreshold slope, threshold voltage, drain induced current enhancement, and breakdown voltage have been done for a wide range of electrodes work-function. To evaluate the potential applications of the proposed device at circuit level, its mixed mode simulations are also carried out.