Wenpeng Liu

Tuning the Resonant Frequency of Resonators Using Molecular Surface Self-assembly Approach

In this work, a new method to tune the resonant frequency of microfabricated resonator using molecular layer-by-layer (LbL) self-assembly approach is demonstrated. By simply controlling the polymer concentration and the number of layers deposited, precisely tuning the frequency of microfabricated resonators is realized. Due to its selective deposition through specific molecular recognitions, such technique avoids the high-cost and complex steps of conventional semiconductor fabrications and is able to tune individual diced device. Briefly, film bulk acoustic resonator (FBAR) is used to demonstrate the tuning process and two types of LbL deposition methods are compared. The film thickness and morphology have been characterized by UV-vis reflection spectra, ellipsometer and AFM. As a result, the maximum resonant frequency shift of FBAR reaches more than 20 MHz, meaning 1.4% tunability at least. The minimum frequency shift is nearly 10 kHZ per bilayer, indicating 7 ppm tuning resolution. Pressure cooker test (PCT) is performed to evaluate the reliability of LbL coated FBAR. Furthermore, applications for wireless broadband communication and chemical sensors of LbL coated FBAR have been demonstrated.

On-chip surface modified nanostructured ZnO as functional pH sensors

Zinc oxide (ZnO) nanostructures are promising candidates as electronic components for biological and chemical applications. In this study, ZnO ultra-fine nanowire (NW) and nanoflake (NF) hybrid structures have been prepared by Au-assisted chemical vapor deposition (CVD) under ambient pressure. Their surface morphology, lattice structures, and crystal orientation were investigated by scanning electron microscopy (SEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM). Two types of ZnO nanostructures were successfully integrated as gate electrodes in extended-gate field-effect transistors (EGFETs). Due to the amphoteric properties of ZnO, such devices function as pH sensors. We found that the ultra-fine NWs, which were more than 50 μm in length and less than 100 nm in diameter, performed better in the pH sensing process than NW-NF hybrid structures because of their higher surface-to-volume ratio, considering the Nernst equation and the Gouy-Chapman-Stern model. Furthermore, the surface coating of (3-Aminopropyl)triethoxysilane (APTES) protects ZnO nanostructures in both acidic and alkaline environments, thus enhancing the device stability and extending its pH sensing dynamic range.

Acoustically Triggered Disassembly of Multilayered Polyelectrolyte Thin Films through Gigahertz Resonators for Controlled Drug Release Applications

Controlled drug release has a high priority for the development of modern medicine and biochemistry. To develop a versatile method for controlled release, a miniaturized acoustic gigahertz (GHz) resonator is designed and fabricated which can transfer electric supply to mechanical vibrations. By contacting with liquid, the GHz resonator directly excites streaming flows and induces physical shear stress to tear the multilayered polyelectrolyte (PET) thin films. Due to the ultra-high working frequency, the shear stress is greatly intensified, which results in a controlled disassembling of the PET thin films. This technique is demonstrated as an effective method to trigger and control the drug release. Both theory analysis and controlled release experiments prove the thin film destruction and the drug release.

Biofouling Removal and Protein Detection Using a Hypersonic Resonator

Nonspecific binding (NSB) is a general issue for surface based biosensors. Various approaches have been developed to prevent or remove the NSBs. However, these approaches either increased the background signals of the sensors or limited to specific transducers interface. In this work, we developed a hydrodynamic approach to selectively remove the NSBs using a microfabricated hypersonic resonator with 2.5 gigahertz (GHz) resonant frequency. The high frequency device facilitates generation of multiple controlled microvortexes which then create cleaning forces at the solid-liquid interfaces. The competitive adhesive and cleaning forces have been investigated using the finite element method (FEM) simulation, identifying the feasibility of the vortex-induced NSB removal. NSB proteins have been selectively removed experimentally both on the surface of the resonator and on other substrates which contact the vortexes. Thus, the developed hydrodynamic approach is believed to be a simple and versatile tool for NSB removal and compatible to many sensor systems. The unique feature of the hypersonic resonator is that it can be used as a gravimetric sensor as well; thus a combined NSB removal and protein detection dual functional biosensor system is developed.

A Universal Biomolecular Concentrator To Enhance Biomolecular Surface Binding Based on Acoustic NEMS Resonator

In designing bioassay systems for low-abundance biomolecule detection, most research focuses on improving transduction mechanisms while ignoring the intrinsically fundamental limitations in solution: mass transfer and binding affinity. We demonstrate enhanced biomolecular surface binding using an acoustic nano-electromechanical system (NEMS) resonator, as an on-chip biomolecular concentrator which breaks both mass transfer and binding affinity limitations. As a result, a concentration factor of 105 has been obtained for various biomolecules. The resultantly enhanced surface binding between probes on the absorption surface and analytes in solution enables us to lower the limit of detection for representative proteins. We also integrated the biomolecular concentrator into an optoelectronic bioassay platform to demonstrate delivery of proteins from buffer/serum to the absorption surface. Since the manufacture of the resonator is CMOS-compatible, we expect it to be readily applied to further analysis of biomolecular interactions in molecular diagnostics.

Directly trapping of nanoscale biomolecules using bulk acoustic wave resonators

Techniques that can manipulate micro or macro biomaterials like cells and organisms have been of interest for a wide range of applications from biochemistry to clinical diagnostics and many clever techniques have been developed. However, methods with the ability to directly manipulate nanoscale biomaterials (e.g. proteins or DNAs) are still challenging due to physical limitations like Brownian motions. Here, according to theoretical design of the stagnation point in the medium which is formed by bulk-acoustic-wave-resonator-induced acoustic streaming, we experimentally realize trapping of biomolecules characterized by length scales at nanometer. We expect bulk acoustic wave resonator (BAWR) to become a powerful tool (e.g. biosensor and bioactuator) to revolutionize the fundamental and applied research for nanoscale biomaterials manipulation.

Trapping of biomolecules using bulk acoustic wave resonators

This work highlights a new on-chip biomolecule trapping method. We systematically studied the device performance in liquid, and provide a hydrodynamic combined acoustic method to trap micro-and nano-scaled bioparticles.

Larger depth of field for optical imaging methods

The depth of field for optical imaging system is restricted according to its structure parameters. It is obviously when optical microscopy is used, which depth of field is very small and it is lesser with larger amplification ratio. In the paper, three main methods to extend the depth of field will be shown, and their merits and shortcomings will be analyzed. The first method is to use optical mask. It is easy to achieve satisfied results with calculation simulation, but it is difficult to produce this mask if it is complicated. The second method is to use image processing. Many images can be obtained with scanning of imaging system in the direction of depth. Using image processing method, the information of each image will be extracted, then to compose a new image with them. It is a hard work to capture these scanning images. And it is difficult to achieve real time image. The last method is to combine the method of optical mask and image processing. The larger depth of field for optical imaging methods can extend the image range that can be used in the field of optical microscopy and scanning image system.

New color image processing with color filter array for single chip camera

A color image of digital camera is obtained by interpolated CFA (Color Filter Array) data from single sensor digital camera. Using JPEG compression method to interpolated data, the maximal compression ratio is less than 90:1. In this paper, an improved compression method is discussed which applied JPEG compression to raw data after two luminance components had been processed further. Results show that CPSNR of improved method is the highest among conventional method and existing methods while the compression ratio is over 90:1. And another attractive result is the image quality is better when the compression ratio up to 120:1, and the conventional JPEG compression method is helpless at such compression ratio. The further work will be concentrate on its application with hardware support.