Peitao Dong

Magnetically Assisted Surface-Enhanced Raman Spectroscopy for the Detection of Staphylococcus aureus Based on Aptamer Recognition

A magnetically assisted surface-enhanced Raman scattering (SERS) biosensor for single-cell detection of S. aureus on the basis of aptamer recognition is reported for the first time. The biosensor consists of two basic elements including a SERS substrate (Ag-coated magnetic nanoparticles, AgMNPs) and a novel SERS tag (AuNR-DTNB@Ag-DTNB core-shell plasmonic NPs or DTNB-labeled inside-and-outside plasmonic NPs, DioPNPs). Uniform, monodisperse, and superparamagnetic AgMNPs with favorable SERS activity and magnetic responsiveness are synthesized by using polymer polyethylenimine. AgMNPs use magnetic enrichment instead of repeated centrifugation to prevent sample sedimentation. DioPNPs are designed and synthesized as a novel SERS tag. The Raman signal of DioPNPs is 10 times stronger than that of the commonly used SERS tag AuNR-DTNB because of the double-layer DTNB and the LSPR position adjustment to match the given laser excitation wavelength. Consequently, a strong SERS enhancement is achieved. Under the optimized aptamer density and linker length, capture by aptamer-modified AgMNPs can achieve favorable bacteria arrest (up to 75%). With the conventional Raman spectroscopy, the limit of detection (LOD) is 10 cells/mL for S. aureus detection, and a good linear relationship is also observed between the SERS intensity at Raman peak 1331 cm(-1) and the logarithm of bacteria concentrations ranging from 10(1) to 10(5) cells/mL. With the help of the newly developed SERS mapping technique, single-cell detection of S. aureus is easily achieved.

Facile Synthesis of Au-Coated Magnetic Nanoparticles and Their Application in Bacteria Detection via a SERS Method

This study proposes a facile method for synthesis of Au-coated magnetic nanoparticles (AuMNPs) core/shell nanocomposites with nanoscale rough surfaces. MnFe2O4 nanoparticles (NPs) were first modified with a uniform polyethylenimine layer (2 nm) through self-assembly under sonication. The negatively charged Au seeds were then adsorbed on the surface of the MnFe2O4 NPs through electrostatic interaction for Au shell formation. Our newly developed sonochemically assisted hydroxylamine seeding growth method was used to grow the adsorbed gold seeds into large Au nanoparticles (AuNPs) to form a nanoscale rough Au shell. Au-coated magnetic nanoparticles (AuMNPs) were obtained from the intermediate product (Au seeds decorated magnetic core) under sonication within 5 min. The AuMNPs were highly uniform in size and shape and exhibited satisfactory surface-enhanced Raman scattering (SERS) activity and strong magnetic responsivity. PATP was used as a probe molecule to evaluate the SERS performance of the synthesized AuMNPs with a detection limit of 10(-9) M. The synthesized AuMNPs were conjugated with Staphylococcus aureus (S. aureus) antibody for bacteria capture and separation. The synthesized plasmonic AuNR-DTNB NPs, whose LSPR wavelength was adjusted to the given laser excitation wavelength (785 nm), were conjugated with S. aureus antibody to form a SERS tag for specific recognition and report of the target bacteria. S. aureus was indirectly detected through SERS based on sandwich-structured immunoassay, with a detection limit of 10 cells/mL. Moreover, the SERS intensity at Raman peak of 1331 cm(-1) exhibited a linear relationship to the logarithm of bacteria concentrations ranging from 10(1) cells/mL to 10(5) cells/mL.

A

This paper proposes a novel quartz micromachined gyroscope. The structure is designed by using shear stress detection method which can simplify the sidewall electrodes obviously. Furthermore, a tuning fork is introduced by the structure to obtain better differential vibrations. In order to increase the sensitivity of the sensor, the sense beam is designed to be a symmetric tapered beam. The device was fabricated using quartz anisotropic wet etching process. The drive mode frequency is 14.99 kHz, and the quality factor is 7600 in air. The sense mode frequency is 14.25 kHz, and the quality factor is 600 in air. Therefore, this gyroscope can operate at atmosphere pressure properly. The sensor is tested on a rate table through a specially designed readout circuitry. The sensitivity is 23.9 and the nonlinearity is 1.1% in range of . The noise floor is 0.1 .

{\rm Z}

Here we propose a novel quartz micromachined gyroscope. The sensor has a simple cross-fork structure in the x-y plane of quartz crystal. Shear stress rather than normal stress is utilized to sense Coriolis’ force generated by the input angular rate signal. Compared to traditional quartz gyroscopes, which have two separate sense electrodes on each sidewall, there is only one electrode on each sidewall of the sense beam. As a result, the fabrication of the electrodes is simplified and the structure can be easily miniaturized. In order to increase sensitivity, a pair of proof masses is attached to the ends of the drive beam, and the sense beam has a tapered design. The structure is etched from a z-cut quartz wafer and the electrodes are realized by direct evaporation using the aperture mask method. The drive mode frequency of the prototype is 13.38 kHz, and the quality factor is approximately 1,000 in air. Therefore, the gyroscope can work properly without a vacuum package. The measurement ability of the shear stress detection design scheme is validated by the Coriolis’ force test. The performance of the sensor is characterized on a precision rate table using a specially designed readout circuit. The experimentally obtained scale factor is 1.45 mV/°/s and the nonlinearity is 3.6% in range of ±200 °/s.

-Axis Quartz Tuning Fork Micromachined Gyroscope Based on Shear Stress Detection

It is reported in the published literature that the resonant frequency of a silicon micromachined gyroscope decreases linearly with increasing temperature. However, when the axial force is considerable, the resonant frequency might increase as the temperature increases. The axial force is mainly induced by thermal stress due to the mismatch between the thermal expansion coefficients of the structure and substrate. In this paper, two types of micromachined suspended vibratory gyroscopes with slanted beams were proposed to evaluate the effect of the axial force. One type was suspended with a clamped-free (C-F) beam and the other one was suspended with a clamped-clamped (C-C) beam. Their drive modes are the bending of the slanted beam, and their sense modes are the torsion of the slanted beam. The relationships between the resonant frequencies of the two types were developed. The prototypes were packaged by vacuum under 0.1 mbar and an analytical solution for the axial force effect on the resonant frequency was obtained. The temperature dependent performances of the operated mode responses of the micromachined gyroscopes were measured. The experimental values of the temperature coefficients of resonant frequencies (TCF) due to axial force were 101.5 ppm/°C for the drive mode and 21.6 ppm/°C for the sense mode. The axial force has a great influence on the modal frequency of the micromachined gyroscopes suspended with a C-C beam, especially for the flexure mode. The quality factors of the operated modes decreased with increasing temperature, and changed drastically when the micromachined gyroscopes worked at higher temperatures.

A Z-axis Quartz Cross-fork Micromachined Gyroscope Based on Shear Stress Detection

A simple, fast, and cost-effective method was developed in this paper for the high-throughput fabrication of nanohole arrays on silicon (Si), which is utilized for antireflection. Wafer-scale polystyrene (PS) monolayer colloidal crystal was developed as templates by spin-coating method. Metallic shadow mask was prepared by lifting off the oxygen etched PS beads from the deposited chromium film. Nanohole arrays were fabricated by Si dry etching. A series of nanohole arrays were fabricated with the similar diameter but with different depth. It is found that the maximum depth of the Si-hole was determined by the diameter of the Cr-mask. The antireflection ability of these Si-hole arrays was investigated. The results show that the reflection decreases with the depth of the Si-hole. The deepest Si-hole arrays show the best antireflection ability (reflection 600 nm), which was about 28 percent of the nonpatterned silicon wafers reflection. The proposed method has the potential for high-throughput fabrication of patterned Si wafer, and the low reflectivity allows the application of these wafers in crystalline silicon solar cells.

Effect of Axial Force on the Performance of Micromachined Vibratory Rate Gyroscopes

This paper describes a rapid, ultra-sensitive, and high-throughput pathogenic DNA identification strategy for infectious diarrheal diseases diagnosis. This strategy is based on specific DNA hybridization and horseradish-peroxidase-catalyzed chemiluminescence (CL) detection. Probe DNA strands are covalently immobilized on the aldehyde-group-modified slide and hybridized with biotin-modified target DNA strands. Horseradish-peroxidase (HRP) is then combined with the target DNA via a biotin-streptavidin linkage. The subsequently added mixture of luminol and hydrogen peroxide is catalyzed by HRP and radiates photons. The photons are collected and read out by a portable imager. The specific detection of target DNA strands was realized at a detection limitation of about 0.75 nM. This strategy facilitates quantitative detection, as indicated by the fact that the CL signals were consistent well with a linear function. This method was applied to identify a myriad of real diarrheal pathogens samples, including Enterohemorrhagic Escherichia coli (EHEC), Vibrio cholerae (VBC), Shigella (SHLA), and Salmonella (SMLA). Triple-assay of six gene sequences from these pathogens was realized, which facilitates accurate, high-throughput identification of diarrheal pathogens. This CL assay strategy is appropriate for application in disease diagnosis and prevention.

Simple, fast, and cost-effective fabrication of wafer-scale nanohole arrays on silicon for antireflection

Parasitic resistance is one of the most prevalent error sources preventing the performance of MEMS vibratory gyroscopes. This paper reports the effect of parasitic resistance on the performance of a MEMS vibratory gyroscope which is suspended with a slanted cantilever. The parasitic resistance and capacitance of the micromachined gyroscope were analyzed. The electrical model of the overall system was built. The transfer function of the gyroscope was derived as a parallel connection of a mass-spring-damper model and a R-C network made of parasitic resistance and capacitance. The parasitic resistance affects on the performance of the frequency response was simulated. The temperature characteristic of the frequency response was tested, which is in accordance with the simulated results. The gain of the frequency response changed about 20% in dBs over the range of 30°C to 60°C.

Ultra-sensitive, high-throughput detection of infectious diarrheal diseases by portable chemiluminescence imaging

The vibration characteristic analysis method for a quartz microgyroscope based on the admittance circle is reported in this paper. Admittance theory is introduced and the admittance circle principle is analysed to study the vibration characteristics of the quartz microgyroscope. The prototype gyroscope was fabricated by micro-electromechanical systems (MEMS) technology. The admittance and phase diagram of the work mode were obtained by vibration mode test systems. Then the admittance circle of the work mode was drawn, and the parameter identification of the transfer function between the voltage and current was completed to analyse the vibration characteristics. Therefore, the vibration characteristic analysis method based on the admittance circle can be used to build the transfer function of the quartz microgyroscope, which is helpful for the design of a high performance quartz microgyroscope.

Effect of parasitic resistance on a MEMS vibratory gyroscopes due to temperature fluctuations

Structure optimization and simulation analysis of the quartz micromachined gyroscope are reported in this paper. The relationships between the structure parameters and the frequencies of work mode were analysed by finite element analysis. The structure parameters of the quartz micromachined gyroscope were optimized to reduce the difference between the frequencies of the drive mode and the sense mode. The simulation results were proved by testing the prototype gyroscope, which was fabricated by micro-electromechanical systems (MEMS) technology. Therefore, the frequencies of the drive mode and the sense mode can match each other by the structure optimization and simulation analysis of the quartz micromachined gyroscope, which is helpful in the design of the high sensitivity quartz micromachined gyroscope.