Xia Shanhong

A micro amperometric immunosensor for detection of human immunoglobulin

A novel amperometric immunosensor based on the micro electromechanical systems (MEMS) technology, using protein A and self-assembled monolayers (SAMs) for the orientation-controlled immobilization of antibodies, has been developed. Using MEMS technology, an “Au, Pt, Pt” three-microelectrode system enclosed in a SU-8 micro pool was fabricated. Employing SAMs, a monolayer of protein A was immobilized on the cysteamine modified Au electrode to achieve the orientation-controlled immobilization of the human immunoglobulin (HIgG) antibody. The immunosensor aimed at low unit cost, small dimension, high level of integration and the prospect of a biosensor system-on-a-chip. Cyclic voltammetry and chronoamperometry were conducted to characterize the immunosensor. Compared with the traditional immunosensor using bulky gold electrode or screen-printed electrode and the procedure directly binding protein A to electrode for immobilization of antibodies, it had attractive advantages, such as miniaturization, compatibility with CMOS technology, fast response (30 s), broad linear range (50–400 µg/L) and low detection limit (10 μg/L) for HIgG. In addition, this immunosensor was easy to be designed into micro array and to realize the simultaneously multi-parameter detection.

Calculation of Specific Heat for Aluminium Thin Films

We employ Prashers non-dimensional form to analyse the size effects on specific heat of Al thin films. Compared the calculation results of pure aluminium film with the experimental data, it is found that the reduction of phonon states is not the main reason of the size effect on the specific heat Al thin films with thickness from 10 nm to 370 nm. However, the Al thin film in air usually has an oxidation layer and the specific heat of the layer is smaller than Al. By including the contribution of the oxidation layer to the thin-film specific heat, the calculation results are much closer to the experimental data. This may be a possible reason of the size effects on specific heat of Al thin films.

Self-Assembly of Micro-Parts onto Si Substrates at Liquid--Liquid Interface

We report a new approach for the self-assembly of cuboid micro-parts onto Si substrates to construct three-dimensional microstructures. To perform assembly, the Si substrates are prepared with a deep cavity array as binding sites. An aggregate composed of hundreds of uniformly aligned micro-parts is formed at the C10F18–H2O interface. The micro-parts are arranged by passing the substrate through the aggregate of micro-parts, thus the micro-parts are left on the substrate, and then the substrate is vibrated ultrasonically in the solution, making it possible for the micro-parts to fall into the cavities on the substrate. Finally the substrate is pulled out of the solution after assembly. This technique could give a high yield of up to 70%, providing a new method for micro-assembly.

Electric field sensors based on MEMS technology

The design and optimization of two types of novel miniature vibrating Electric Field Sensors (EFSs) based on MicroElectroMechanical Systems (MEMS) technology are presented. They have different structures and vibrating modes. The volume is much smaller than other types of charge-induced EFSs such as field-mills. As miniaturizing, the induced signal is reduced enormously and a high sensitive circuit is needed to detect it. Elaborately designed electrodes can increase the amplitude of the output current, making the detecting circuit simplified and improving the signal-to-noise ratio. Computer simulations for different structural parameters of the EFSs and vibrating methods have been carried out by Finite Element Method (FEM). It is proved that the new structures are realizable and the output signals are detectable.

A micro amperometric immunosensor immobilized with electropolymerized staphylococcal protein a for the detection of salmonella typhimurium

In this paper, a micro amperometric immunosensor based on Micro-Electro-Mechanical Systems technology for the detection of Salmonella typhimurium (S. typhimurium) was constructed by immobilizing a polyclonal antibody (the bio-molecular recognition element) onto the surface of polypyrrole(PPy) /staphylococcal protein A(SPA) modified Pt electrode. Pyrrole doped with SPA was co-electropolymerized onto the working electrode surface by cyclic voltammetry in 10 minutes for orientation-controlled immobilization of salmonella capture antibodies. S. typhimurium with the concentration of 102cfu/ml could be detected by this immunosensor with a controllable and convenient manipulation to effectively modify the sensing surface more rapidly with less consumption of reagent (10µL), which showed the good property of the sensor. It is potential to develop a micro biosensor that can be used for convenient, accurate, cost-effective and real-time sensing of pathogens in food products.

Research on Resonant Low-Velocity Gas Flow Micro-sensor Based on Trichoid Sensillum of Insects

A new resonant micro-sensor modeled on trichoid sensillum of insects which can detect low-velocity gas flow is proposed and fabricated for the first time. The relationship between Reynolds number and drag coefficient which helps determine resistance when gas passes around infinite long beam is obtained numerically and the effect of size choice of infinite long beam on this relationship is put forward. Based on this relationship, theoretical model of this micro-sensor is deduced in which the relationship between the velocity of gas flow and the frequency shift of the resonator is obtained and the linear region of this micro-sensor is found. FEA (finite element analysis) is conducted which asserts that when gas ranges in low Reynolds number, typically when Reynolds number is less than one, there exists excellent linear relationship between input and output of this micro-sensor. What is more, the prototype of this micro-sensor is successfully fabricated.

A new fabrication process for the SOI-based miniature electric field sensor

This paper presents a new fabrication process for the SOI-based novel miniature electric field sensor. This new process uses polyimide film to release the SiO2 layer. Compared with the CO2 critical point release method, it significantly improves the device surface cleanliness and shortens the process flow. The impurity on the base layer is analyzed. The problem of peak and butterfly-type contamination occurring on the base layer of the SOI wafer during the DRIE process is discussed and solved by thickening the photoresist layer and coating with polyimide film twice. This new process could fabricate MEMS sensors and actuators such as SOI-based electric field sensors, gyroscopes, and micro mirrors and can be an alternative fabrication process compared to commercial SOIMUMPS fabrication processes.

A resonant miniature electric field sensor using bulk-micromachining process

Abstract A novel design of a resonant miniature electric field sensor based on microfabrication technology is proposed. The operating principles and specifications, the design structure, and the silicon-based bulk-micromachining fabrication process are presented. The finite element simulation shows that our design can obtain good results in device parameters setting, and its simplicity and low-cost features make it an attractive product for future applications. ∗Supported by the National Natural Science Foundation of China(Grant No. 60172001)

Novel “cathode-on-membrane” VME pressure sensor

This article proposes a novel “cathode-on-membrane” vacuum microelectronic (VME) pressure sensor. Compared with conventional VME pressure sensors, the package process of the new structured sensor is easier to control, and therefore it enable greater potential of mass production and high productivity. The properties of the new sensor have been theoretically investigated by computer simulations; the practical structure has been designed and fabricated; and the package technique has been studied.

Double-gated field emitter arrays for microwave devices

After having a brief discussion on two kinds of structures of double-gated field emitter arrays (DGFEAs), presented in the paper are the design and simulation methods of the DGFEA, and simulation results of its emission characteristics and focusing performance. The results show that by properly introducing a focus gate above a control gate in the FEA, the DGFEA with an aperture focusing structure will produce a parallel electron beam, and its focusing performance can be effectively adjusted through the focus gate voltage; the additional focus gate lowers the arrays emission, but after improvement the maximum emission density of the DGFEA (with a control gate aperture of 1 /spl mu/m and tip spacing of 3 /spl mu/m) may exceed 500 A/cm/sup 2/.