An approach to the design of surface stress-based PDMS micro-membrane biosensors - concept, numerical simulations and prototypes

Die BioMEMS(Biological Micro-Electro-Mechanical Systems)-Technologie spielt vor allem für Biosensoren eine entscheidende Rolle im Prozess der Informationsbeschaffung für die technologisch fortschreitende Entwicklung unserer Zivilisation. „Oberflächenspannungsbasierte Biosensoren“ sind eine relativ neue Klasse von Biosensoren, welche die Änderung der freien Energie nutzen (das zugrunde liegende Prinzip jeder Bindungsreaktion), und bieten somit eine universelle Plattform für biologische oder chemische Sensorik. In der Dissertationsschrift wird ein neuer oberflächenspannungsbasierter Polydimethylsiloxan (PDMS)- Mikro-Membran-Biosensor vorgeschlagen, konstruiert, gefertigt und getestet. Der Biosensor besteht aus zwei Haupt-Funktionskomponenten: Mikrofluidik und Sensorik. Jeder Sensor besteht aus zwei Mikro-Membranen, einer aktiven Membran und einer Referenzmembran. Die Biosensoren wurden erfolgreich unter Bewältigung vieler Herausforderungen aufgebaut. Diese lagen insbesondere in den Bereichen Design und Herstellung, wie zum Beispiel der Integration der PDMS-Mikroverarbeitung mit herkömmlichen Verfahren, der Herstellung von „perfekten“ PDMS-Dünnschichten und der Gewinnung der PDMS-Membran. Darüber hinaus wurde eine Klebetechnik, welche unausgehärtes PDMS als Zwischenschicht für die Bindung zwischen Biosensor und Mikrofluidikkomponenten oder -bauteilen nutzt, untersucht und getestet. Für die Prüfung und Anwendung der Biosensoren wurden zwei Biosensor- Testsysteme eingerichtet. Eines mit einem „smart Weißlichtinterferometer“ (smartWLI) und ein anderes mit einem „Fiberoptic Interferometer“ (FOI). Drei Alkanthiol-Moleküle mit verschiedenen funktionellen Endgruppen wurden als Biosensor-Überzugsschichten für die Anwendung getestet. MUA ist das derzeit beste „funktionelle“ Material, um die Membran für den Nachweis von E. coli zu funktionalisieren. Der PDMS-Mikro-Membran-Biosensor auf Basis der Analyse von Oberflächenspannungen besitzt gute Empfindlichkeit, Reproduzierbarkeit und Biokompatibilität. Der Zustand von E. coli-Bakterien kann auf der Grundlage der Analyse der Oberflächenspannungen gemessen werden

Engineering the mechanical properties of graphene nanotube hybrid structures through structural modulation

The excellent multi-functional properties of carbon nanotube (CNT) and graphene have enabled them as appealing building blocks to construct 3D carbon-based nanomaterials or nanostructures. The recently reported graphene nanotube hybrid structure (GNHS) is one of the representatives of such nanostructures. This work investigated the relationships between the mechanical properties of the GNHS and its structure basing on large-scale molecular dynamics simulations. It is found that increasing the length of the constituent CNTs, the GNHS will have a higher Young’s modulus and yield strength. Whereas, no strong correlation is found between the number of graphene layers and Young’s modulus and yield strength, though more graphene layers intends to lead to a higher yield strain. In the meanwhile, the presences of multi-wall CNTs are found to greatly strengthen the hybrid structure. Generally, the hybrid structures exhibit a brittle behavior and the failure initiates from the connecting regions between CNT and graphene. More interestingly, affluent formations of monoatomic chains and rings are found at the fracture region. This study provides an in-depth understanding of the mechanical performance of the GNHSs while varying their structures, which will shed lights on the design and also the applications of the carbon-based nanostructures

Resonance of graphene nanoribbons doped with nitrogen and boron: a molecular dynamics study

Based on its enticing properties, graphene has been envisioned with applications in the area of electronics, photonics, sensors, bioapplications and others. To facilitate various applications, doping has been frequently used to manipulate the properties of graphene. Despite a number of studies conducted on doped graphene regarding its electrical and chemical properties, the impact of doping on the mechanical properties of graphene has been rarely discussed. A systematic study of the vibrational properties of graphene doped with nitrogen and boron is performed by means of a molecular dynamics simulation. The influence from different density or species of dopants has been assessed. It is found that the impacts on the quality factor, Q, resulting from different densities of dopants vary greatly, while the influence on the resonance frequency is insignificant. The reduction of the resonance frequency caused by doping with boron only is larger than the reduction caused by doping with both boron and nitrogen. This study gives a fundamental understanding of the resonance of graphene with different dopants, which may benefit their application as resonators

A zero-flow microfluidics for long-term cell culture and detection

A zero-flow microfluidic design is proposed in this paper, which can be used for long-term cell culture and detection, especially for a lab-on-chip integrated with a biosensor. It consists of two parts: a main microchannel; and a circle microchamber. The Finite Element Method (FEM) was employed to predict the fluid transport properties for a minimum fluid flow disturbance. Some commonly used microfluidic structures were also analysed systematically to prove the designed structure. Then the designed microfluidics was fabricated. Based on the simulations and experiments, this design provides a continuous flow environment, with a relatively stable and low shear stress atmosphere, similar to a zero-flow environment. Furthermore, the nutrients maintaining cells’ normal growth can be taken into the chamber through the diffusion effect. It also proves that the microfluidics can realize long-term cell culture and detection. The application of the structure in the field of biological microelectromechenical systems (BioMEMS) will provide a research foundation for microfluidic technology

A Novel Magnetoelastic Immunosensor for Ultrasensitively Detecting Carcinoembryonic Antigen

Abstract A novel wireless immunosensor is developed for the ultra-sensitive detection of carcinoembryonic antigen. The optimum dimension of the microchips, as magnetoelastic sensitive units, was evaluated by simulation and experiments. The unique effects signal amplification and biocompatibility of gold particles contribute to the stability and sensitivity of the sensor. Furthermore, to enhance sensitivity, the working concentrations of antibody and BSA are selected to be 50 mg/mL and 0.1%, respectively. Atom force microscope imaging sheds light on the biological analysis. The Nano-magnetoelastic immunosensor exhibits a linear response to the logarithm of carcinoembryonic antigen (CEA) concentrations ranging from 0.1 to 100 ng/mL, with a detection limit of 2.5 pg/mL. The designed biosensor has merits of excellent stability and sensitivity towards CEA

Control and navigation system for a fixed-wing unmanned aerial vehicle

This paper presents a flight control and navigation system for a fixed-wing unmanned aerial vehicle (UAV) with low-cost micro-electro-mechanical system (MEMS) sensors. The system is designed under the inner loop and outer loop strategy. The trajectory tracking navigation loop is the outer loop of the attitude loop, while the attitude control loop is the outer loop of the stabilization loop. The proportional-integral-derivative (PID) control was adopted for stabilization and attitude control. The three-dimensional (3D) trajectory tracking control of a UAV could be approximately divided into lateral control and longitudinal control. The longitudinal control employs traditional linear PID feedback to achieve the desired altitude of the UAV, while the lateral control uses a non-linear control method to complete the desired trajectory. The non-linear controller can automatically adapt to ground velocity change, which is usually caused by gust disturbance, thus the UAV has good wind resistance characteristics. Flight tests and survey missions were carried out with our self-developed delta fixed-wing UAV and MEMS-based autopilot to confirm the effectiveness and practicality of the proposed navigation method

Engineering the mechanical properties of graphene nanotube hybrid structures through structural modulation

The excellent multi-functional properties of carbon nanotube (CNT) and graphene have enabled them as appealing building blocks to construct 3D carbon-based nanomaterials or nanostructures. The recently reported graphene nanotube hybrid structure (GNHS) is one of the representatives of such nanostructures. This work investigated the relationships between the mechanical properties of the GNHS and its structure basing on large-scale molecular dynamics simulations. It is found that increasing the length of the constituent CNTs, the GNHS will have a higher Young’s modulus and yield strength. Whereas, no strong correlation is found between the number of graphene layers and Young’s modulus and yield strength, though more graphene layers intends to lead to a higher yield strain. In the meanwhile, the presences of multi-wall CNTs are found to greatly strengthen the hybrid structure. Generally, the hybrid structures exhibit a brittle behavior and the failure initiates from the connecting regions between CNT and graphene. More interestingly, affluent formations of monoatomic chains and rings are found at the fracture region. This study provides an in-depth understanding of the mechanical performance of the GNHSs while varying their structures, which will shed lights on the design and also the applications of the carbon-based nanostructures