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A filter-based microfluidic device was combined with immunofluorescent labeling as a platform to rapidly detect microbial cells. The coin-sized device consisted of micro-chambers, micro-channels and filter weirs (gap = 1-2 microm), and was demonstrated to effectively trap and concentrate microbial cells (i.e., Cryptosporidium parvum and Giardia lamblia), which were larger in size than the weir gap. After sample injection, a staining solution containing fluorescently-labeled antibodies was continuously provided into the device (flow rate = 20 microl min(-1)) to flush the microbial cells toward the weirs and to accelerate the fluorescent labeling reaction. Using a staining solution that was 10 to 100 times more dilute than the recommended concentration used in a conventional glass method, those target cells with a fluorescent signal-to-noise ratio of 12 could be microscopically observed at single-cell level within 2 to 5 min prior to secondary washing.

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Acoustic radiation force can be used to move micro-sized particles, such as cells, in microfluidic devices. Although the number of particles in a microfluidic device is large, typically 2.5% (weight/volume), the acoustic force acting on a particle is commonly calculated using an analytical formula for a single particle in infinite medium. The interparticle forces are typically ignored as these are not easily accounted for and calculated with simple closed-form solutions. Based on the isothermal theory for an ideal fluid, a numerical scheme is hereby proposed to calculate the total radiation force, including the interparticle forces. The method uses the multipole series expansion and the weighted residual method to solve the governing Helmholtz equation with the necessary boundary conditions on the particle surface. The effect of different parameters on the primary and interparticle forces is studied using the proposed numerical scheme. It is shown that, near the pressure node, the interparticle forces are dominant and configurations of the spheres are determined by the interparticle forces. The proposed numerical scheme can be used for various sizes of spherical particles.

The design, fabrication and characterization of a miniature adjustable-focus endoscope are reported. Such an endoscope consists of a solid tunable lens for optical power tuning, two slender piezoelectric benders for laterally moving the lens elements perpendicular to the optical axis, and an image fiber bundle for image transmission. Both optical and mechanical designs are presented in this paper. Dynamic tuning of optical powers from about 135 diopters to about 205 diopters is experimentally achieved from the solid tunable lens, which contains two freeform surfaces governed by 6-degree polynomials and optimized by ray tracing studies. Results show that there is no obvious distortion or blurring in the images obtained, and the recorded resolution of the lens reaches about 30 line pairs per mm. Three test targets located at various object distances of 20 mm, 50 mm and 150 mm are focused individually by the endoscope by applying different driving DC voltages to demonstrate its adjustable-focus capability.