Yu-Yen Huang

Microscale Magnetic Field Modulation for Enhanced Capture and Distribution of Rare Circulating Tumor Cells

Immunomagnetic assay combines the powers of the magnetic separation and biomarker recognition and has been an effective tool to perform rare Circulating Tumor Cells detection. Key factors associated with immunomagnetic assay include the capture rate, which indicates the sensitivity of the system, and distributions of target cells after capture, which impact the cell integrity and other biological properties that are critical to downstream analyses. Here we present a theoretical framework and technical approach to implement a microscale magnetic immunoassay through modulating local magnetic field towards enhanced capture and distribution of rare cancer cells. Through the design of a two-dimensional micromagnet array, we characterize the magnetic field generation and quantify the impact of the micromagnets on rare cell separation. Good agreement is achieved between the theory and experiments using a human colon cancer cell line (COLO205) as the capture targets.

Flux or speed? Examining speckle contrast imaging of vascular flows.

Speckle contrast imaging enables rapid mapping of relative blood flow distributions using camera detection of back-scattered laser light. However, speckle derived flow measures deviate from direct measurements of erythrocyte speeds by 47 ± 15% (n = 13 mice) in vessels of various calibers. Alternatively, deviations with estimates of volumetric flux are on average 91 ± 43%. We highlight and attempt to alleviate this discrepancy by accounting for the effects of multiple dynamic scattering with speckle imaging of microfluidic channels of varying sizes and then with red blood cell (RBC) tracking correlated speckle imaging of vascular flows in the cerebral cortex. By revisiting the governing dynamic light scattering models, we test the ability to predict the degree of multiple dynamic scattering across vessels in order to correct for the observed discrepancies between relative RBC speeds and multi-exposure speckle imaging estimates of inverse correlation times. The analysis reveals that traditional speckle contrast imagery of vascular flows is neither a measure of volumetric flux nor particle speed, but rather the product of speed and vessel diameter. The corrected speckle estimates of the relative RBC speeds have an average 10 ± 3% deviation in vivo with those obtained from RBC tracking.

Computational Analysis of Microfluidic Immunomagnetic Rare Cell Separation from a Particulate Blood Flow

We describe a computational analysis method to evaluate the efficacy of immunomagnetic rare cell separation from non-Newtonian particulate blood flow. The core procedure proposed here is calculation of local viscosity distributions induced by red blood cell (RBC) sedimentation. Numerical calculation methods have previously been introduced to simulate particulate behavior of individual RBCs. However, due to the limitation of the computational power, those studies are typically capable of calculating only a very small number (less than 100) of RBCs and are not suitable to analyze many practical separation methods for rare cells such as circulating tumor cells (CTCs). We introduce a sedimentation and viscosity model based on our experimental measurements. The computational field is divided into small unit control volumes, where the local viscosity distribution is dynamically calculated based on the experimentally found sedimentation model. For analysis of rare cell separation, the local viscosity distribution is calculated as a function of the volume RBC rate. The direction of gravity has an important role in such a sedimentation-involved cell separation system. We evaluated the separation efficacy with multiple design parameters including the channel design, channel operational orientations (inverted and upright), and flow rates. The results showed excellent agreement with real experiments to demonstrate the effectiveness of our computational analytical method. We demonstrated higher capture efficiency with the inverted microchannel configuration.We conclude that proper direction of blood sedimentation significantly enhances separation efficiency in microfluidic devices.

Plasmonic nanograting tip design for high power throughput near-field scanning aperture probe

We design nanogratings consisting of concentric plasmonic resonance grooves on the metallic sidewalls of near-field scanning probe aperture to increase the power throughput without losing the imaging resolution. Nanograting tip design involves choosing the proper pitch length and the cut location of grooves. Four different nanograting designs are evaluated, as compared with standard single aperture pyramidal near-field scanning probe without grating patterns. We show that, by adding nano-grooves at the location of electromagnetic field intensity-maximum along interface and with the pitch period matching the surface plasmon wavelength, the power throughput can be greatly increased by at least a factor of 530 at 405nm UV wavelength with 100nm diameter aperture probe.

Magnetic-Actuated Stainless Steel Scanner for Two-Photon Hyperspectral Fluorescence Microscope

We present a fluorescence two-photon laser scanning microscope that uses a soft-magnetic stainless steel microscanner to generate a 2-D Lissajous scanning pattern. The wide-scanning low-voltage driven gimbaled torsional stainless steel microelectromechanical systems (MEMSs) scanner is designed and then fabricated using electrical discharge machining. This technology offers unique advantages by allowing larger mirror surface areas (4 mm \(\times5\) mm) to enhance the fluorescence collection efficiency at low incoming signal level, and providing a rapid prototyping and low-cost alternative to silicon-based MEMS devices, particularly when large displacements and large field of view are required. A maximum total optical scan angle (TOSA) of 20.6° at 112 Hz for a drive power of 200 mW is required for the slow-scan movement, whereas the fast-scan movement occurs at the resonance frequency of 1268 Hz and has a TOSA of 26.6° using a drive power of 400 mW. The soft-magnetic microscanner incorporated in the two-photon hyperspectral fluorescence microscope demonstrates its applicability in two-photon hyperspectral imaging of circulating cancer cells, stem cells, and biological tissue with extrinsic fluorophores.

Plasmonic nanoprobe integrated with near-field scanning microscope

Plasmonic enhanced scanning nanoprobes are designed, fabricated, and integrated with near-field scanning microscopic (NSOM) system for multi-functional nanoscale perturbation, detection and imaging. Both transmission scanning measurements and simulations are demonstrated and analyzed.

Near-field plasmonic enhancement via nanogratings on hollow pyramidal aperture probe tip

We present the design of hollow near-field scanning microscope (NSOM) probe with nanogratings-on-tip to transport and concentrate localized surface plasmonic polariton (SPP) wave. By adding nano-grooves started from the intensity-maximum locations of lowest transmission mode and with pitch period supporting the metal-air interface SPP mode, the power throughput is increased at over 530 times comparing with single aperture probe with 405nm source and 100nm diameter aperture size. Two types of nanograting probe designs are chosen for fabrication and the power enhancement comparison is examined by probing the near-field fluorescent intensity of excited uniform quantum dots (QDs) layer via micro-contact printing method.

Design, fabrication, and control of scanning plasmonic probe for near-field photolithographic applications

We report the design, fabrication and operation of a scanning plasmonic probe compatible with a fully customized Near-field Scanning Microscope system. The probe is a silicon cantilever with a hollow pyramidal probe tip. A silicon dioxide layer was thermally grown to form the probe. A 100 nm thick aluminum layer was then e-beam evaporated onto the released probe tip to form the metal-dielectric interface for surface plasmonic wave propagation. A 500 nm diameter aperture was subsequently milled with the Focus Ion Beam. The probe was controlled with a built-in scanning controller for the probe-sample distance using a force sensing tuning fork. A tapered optical fiber, connected to 405 nm wavelength laser source, was aligned to the backside of the probe tip to serve as the light source. The transmitted light through the aperture was used to expose the photoresist (AZ 5209E), on a piece of cover glass attached on the tuning fork. The probe was controlled for near-field photolithography, where a series of 15 exposures, varied from 0 to 8 minutes, were carried out on the photoresist stepwise at 6.5 μm separation with subsequent 60 seconds development time. The transmitted light beam spot was simulated with a Full Width Half Maximum of 227 nm. Atomic Force Microscope measurement showed a 200 nm lateral resolution for the photolithography. The depths and widths of the developed patterns were linearly correlated with increasing exposure time, showing slopes of 0.76 nm/second and 1.4 nm/second respectively.