Yonggang Jiang

Preparation of biosilica structures from frustules of diatoms and their applications: current state and perspectives

Frustules, the silica shells of diatoms, have unique porous architectures with good mechanical strength. In recent years, biologists have learned more about the mechanism of biosilica shells formation; meanwhile, physicists have revealed their optical and microfluidic properties, and chemists have identified ways to modify them into various materials while maintaining their hierarchical structures. These efforts have provided more opportunities to use biosilica structures in microsystems and other commercial products. This review focuses on the preparation of biosilica structures and their applications, especially in the development of microdevices. We discuss existing methods of extracting biosilica from diatomite and diatoms, introduce methods of separating biosilica structures by shape and sizes, and summarize recent studies on diatom-based devices used for biosensing, drug delivery, and energy applications. In addition, we introduce some new findings on diatoms, such as the elastic deformable characteristics of biosilica structures, and offer perspectives on planting diatom biosilica in microsystems.

Fabrication of a vibration-driven electromagnetic energy harvester with integrated NdFeB/Ta multilayered micro-magnets

This paper describes the fabrication of MEMS-based electromagnetic energy harvesters for scavenging energy from the ambient vibration. The novel energy harvester is fabricated by bonding a vibrator with embedded micro-magnets and a stator with integrated microcoils. The micro-magnets are formed by using sputtering deposition of NdFeB/Ta multilayered magnetic films with a thickness of 10 µm and silicon molding techniques. High-aspect-ratio silicon micro-springs are fabricated using deep reactive ion etching to achieve large vibration amplitude. The microcoils fabricated by electroplating processes are serially connected for multiplication of the output voltages from individual magnet-coil units. The energy harvester is successfully fabricated and wire-bonded for characterization. The maximum voltage output of the energy harvester at 115 Hz is approximately 2 mV, which corresponds to a power density of 1.2 nW cm−3. The performance of the energy harvester could be greatly improved by protecting the micro-magnets from oxidation and decreasing the spacing between the vibrator layer and the stator layer.

Electromagnetic energy harvester by using buried NdFeB

This study describes the fabrication and measurement of an electromagnetic-type energy harvester by using buried NdFeB/Ta multilayer films. The energy harvester is fabricated by bonding a vibratory mass with buried micro-magnets and a stator with integrated micro-coils together. The performance of the micro-magnets was enhanced by new methods of a mechanical polishing process of buried NdFeB. The output power of the energy harvester was improved to 760 pW with an applied vibration amplitude of 48 μmp-p at 94.9 Hz.

Biosilica structures obtained from Nitzschia , Ditylum , Skeletonema , and Coscinodiscus diatom by a filtration-aided acid cleaning method

A filtration-aided acid cleaning method was used to collect biosilica structures from a diatom culture medium, natural seawater, or water bloom. Cell extraction, acid cleaning, and acid removal were all performed on a polytetrafluoroethylene (PTFE) filter cloth, significantly improving the treatment capacity and efficiency of the traditional acid wash method. Five typical diatoms were cultivated in the laboratory for acid cleaning. Different growth speeds were introduced, and different process parameters for acid cleaning were utilized. After the acid cleaning, biosilica structures were collected from the frustules of diatoms using different methods. Girdle bands and valves of Coscinodiscus sp. were separated by floating of the valves. Central spines of Ditylum brightwellii and valves of Skeletonema costatum were separately collected by settling or filtration. Rod-like frustules, such as those of Bacillaris paradoxa, are not suitable for large quantities of acid wash. The silica structures were observed and tested using an AFM-calibrated glass needle to determine their elasticity. Elasticity tests showed that ringent girdle bands are more flexible than complete ones (Coscinodiscus sp.) and that both long-chain clusters of Nitzschia palea and central spines of D. brightwellii have certain elasticities. The required pressure for deforming or breaking the biosilica structures of diatoms was also determined.

Hydrofluoric acid-assisted bonding of diatoms with SiO2-based substrates for microsystem application

Diatom, with delicate three-dimensional porous structures and texture, has a promising application in micro-nanotechnology especially biosensing. In order to achieve a diatom-based compound substrate, a fabrication technique is developed for hydrofluoric acid (HF) bonding of diatom with SiO2-based substrate at a temperature as low as 80 °C. The bonding conditions are optimized with various HF concentrations and applied pressure. The optimized HF concentration is found to be in the range of 0.8% to 1.2% and applied pressure is from 0.4.0 MPa to 0.6.0 MPa. The morphological integrity and nano-microscale substructures of the diatoms after bonding are characterized. The bonding strength is approximately 0.435 MPa.

Fabrication of All-SiC Fiber-Optic Pressure Sensors for High-Temperature Applications

Single-crystal silicon carbide (SiC)-based pressure sensors can be used in harsh environments, as they exhibit stable mechanical and electrical properties at elevated temperatures. A fiber-optic pressure sensor with an all-SiC sensor head was fabricated and is herein proposed. SiC sensor diaphragms were fabricated via an ultrasonic vibration mill-grinding (UVMG) method, which resulted in a small grinding force and low surface roughness. The sensor head was formed by hermetically bonding two layers of SiC using a nickel diffusion bonding method. The pressure sensor illustrated a good linearity in the range of 0.1–0.9 MPa, with a resolution of 0.27% F.S. (full scale) at room temperature.

Bonding of diatom frustules and Si substrates assisted by hydrofluoric acid

Diatoms, with hierarchical micro/nanoscale porous silica structures, have promising application in micro-nanotechnology especially biochemical sensing. In order to explore their potential and prepare diatom based substrates for biochemical sensor application, a fabrication technology for bonding diatom frustules and Si substrates was developed. The bonding process was carried out at 75 °C and assisted by hydrofluoric acid (HF). The bonding mechanism was discussed and several bonding conditions were adjusted to keep the morphological integrity of diatom frustules after bonding. The bonding pressure was optimized from 2.0 × 104 Pa to 3.0 × 104 Pa and the HF concentration from 0.4% to 0.6%. And the optimal shear bonding strength achieved was 0.72 MPa. In addition, bonded diatom frustules were further used as masks to obtain nano gold pillar arrays for surface-enhanced Raman scattering (SERS) detection.

Diatom based biosensor for high sensitive fluorescence detection based on a spin-on glass bonding technique

Diatom, with delicate nanoscale porous SiO2 structures, has a promising application in biosensing. We bond diatoms with SiO2 substrate using spin-on glass (SOG) as interlayer to acquire a high performance diatom based fluorescence detecting biosensor. As diatoms can improve proteins density, diatom based biosensors have higher sensitivity compared with traditional protein sensors. This biosensor is fully made of SiO2 which can be modified for biomass attachment. Nanoscale structures of bonded diatoms are better preserved than any related works. The highest bonding strength is 0.6 MPa. Human immunoglobulin G (IgG) is attached on traditional protein sensors and diatom based biosensors as antibody. After hybridized with Cy3-goat anti-human IgG, the diatom based biosensor provides a fluorescence detection signal 2.5 times higher than the traditional one. Given improved fluorescence detecting sensitivity, this new kind of diatom based biosensor can be widely used for various protein detections.