Now, a label-free biosensor has been defined as “to detect a whole biologically active molecule in real time”. Also, the specificity and sensitivity common to all assays must apply. To be precise, to be fast, to be small, to be integrated and less cost….. Is it possible? In this talk, several results for improving the sensitivity, the specificity and the dynamic range of a label-free optical fiber biosensor will be discussed.
First, a tapered optical fiber refractometer and biosensor modifying their unclad region with the coating of SiO2 and gold nanospheres will be compared to show that the combination of nanosphere-induced absorption and scattering losses and multimode propagation of tapered fiber gives a way to increase its detection range. Second, the results of ultrasensitive label-free detection of cardiac troponin I with optical microfiber coupler is shown when it works around the turning point. The detection limit with a concentration as low as 2fg/mL can be achieved using the proposed immunosensor. This kind of immunosensor has great application potential for biomarkers detection due to its characteristics as simple scheme, fast response and ease to miniaturation.Finally, the Fano and some other extraordinary effects by tapered optical fiber coupled WGMs will be discussed. The functions of several special modes may help to take the challenges of selectivity for plasma detection.
The coded aperture spectrometer can achieve high throughput and high spectral resolution by replacing the traditional single slit with two-dimensional array slits manufactured by MEMS technology. However, the sampling accuracy of coding spectrum image will be distorted due to the existence of system aberrations, machining error, fixing errors and so on, resulting in the declined spectral resolution. The influence factor of the spectral resolution come from the decode error, the spectral resolution of each column, and the column spectrum offset correction. For the Czerny-Turner spectrometer, the spectral resolution of each column most depend on the astigmatism, in this coded aperture spectroscopy, the uncorrected astigmatism does result in degraded performance. Some methods must be used to reduce or remove the limiting astigmatism. The curvature of field and the spectral curvature can be result in the spectrum revision errors.
An investigation of diffuser/nozzle micropumps is presented. Numerical simulations are done using CFD program
ANSYS/Flotran. The simulations show when the opening angel is small, the flow in the diffuser/nozzle is steady, the
mass flow is increasing with the adding opening angle. But when the opening angel continues increasing, the pressure
grads will be bigger than zero. It means that the static pressure is gradually going up along the diverging direction. The
fluid near the wall stops flowing because the velocity decreases rapidly and the dynamic pressure is not big enough to
overcome the increasing of the static pressure. Finally the fluid flows reversely from the backward position of higher
pressure area, this makes the separation flow of fluid, the diffuser is full of reverse fluid. And this results in the dropping
of mass flow at last. The simulations also show that the performance of diffuser with a round inlet is better than that with
a sharp inlet. The mass flow of micropumps with different opening angles, different inlets are measured. The
experimental results agree well with the simulations.
An evanescent wave sensor made of few modes optical fiber was studied. The influence of the geometry of the sensing region, including absorbing medium refractive index n2 and the core radius of the bare fiber a, on the modal fractional power in the cladding was analyzed. The percentage of the mode power in total guiding power was mainly calculated at different launching conditions, such as the incidence angle θi By analyzing the output power fraction from calculation and the experiment, the suitable parameters of the sensor could be chosen and the sensitivity was improved. The results will help the design in some way of this kind of sensor.
Bulk silicon wet etching can be used to fabricate silicon gratings. Wet etching depends on the anisotropic property of monocrystalline silicon. Blazed gratings for different spectral ranges can be fabricated by this method, and facets of grooves are formed by crystallographic planes of the monocrystalline silicon wafer. We develop a method to fabricate blazed gratings using deflecting crystal orientation (111) silicon wafers. The topographies of the samples are measured by SEM and atomic force microscopy (AFM), and the results indicate that the samples have grooves of good uniformity and facets of excellent optical quality.
In the present paper, the authors report their research on fabricating the three-dimensional microstructures on polymers by using the technology of excimer laser direct etching. A kind of mask structure called adhering mask, which can be used to fulfill the direct etching of polymers by a simpler optical system, is introduced. In addition, its fabrication process and optical system of the direct etching are also given in this paper. Finally the three-dimensional microstructures we fabricate by the technology are shown.
So far, the history of silicon gratings has more than 20 years and the development of fabrication methods and applications have improved a lot. Microfabrication process to made silicon gratings can be divided into bulk silicon and surface silicon technology. All these technologies are compatible with the process of MEMS, and this made it possible to fabricate micro spectrometers. We present the fabrication process of a grating by using (111) silicon wafer. The silicon gratings were manufactured using silicon micromachining techniques, as ultraviolet lithography and anisotropic wet etching, achieving good uniformity surface and grating facets of excellent optical quality. Some testing results on the silicon grating are presented.
A modulated continues wave argon ion laser has been used to get lamb waves in silicon membrane. In this report, the basic principle of conversation from optics to thermal then acoustic waves was deduced. The experimental set-up, the analysis of the results and the possible way to obtain a given mode of lamb wave were described.
An important performance criterion for practicable microactuators is the value of output torque. For the torque to be measured is very small, the influence of frictional force and other factors on testing are difficult avoided. So a new noncontact and direct experimental method was proposed, the basic theory and a simple and low-cost design of the measuring instrument is described in this paper. The testing range of shaft torque is from 10-4Nm to 10-7.