Youmin Wang

MEMS scanner enabled real-time depth sensitive hyperspectral imaging of biological tissue

We demonstrate a hyperspectral and depth sensitive optical scattering diffusion imaging microsystem, where fast scanning is provided by a CMOS compatible 2-axis MEMS mirror. By using lissajous scanning patterns, large field-of-view (FOV) of 1.2cm × 1.2cm images with lateral resolution of 100µm can be taken at 1.3 frame-per-second (fps). Hyperspectral and depth-sensitive images were acquired on phantom samples consisting of quantum dots (QDs) patterned at various depths in PDMS, showing 6 nm spectral resolution and 0.43 wavelength per second acquisition speed. Images were also acquired on biological sample of porcine epitheliu m with QDs placed underneath the surface.

Portable oral cancer detection using a miniature confocal imaging probe with a large field of view

We demonstrate a MEMS micromirror enabled handheld confocal imaging probe for portable oral cancer detection, where a comparatively large field of view (FOV) was generated through the programmable Lissajous scanning pattern of the MEMS micromirror. Miniaturized handheld MEMS confocal imaging probe was developed, and further compared with the desktop confocal prototype under clinical setting. For the handheld confocal imaging system, optical design simulations using CODE VR® shows the lateral and axial resolution to be 0.98 µm and 4.2 µm, where experimental values were determined to be 3 µm and 5.8 µm, respectively, with a FOV of 280 µm×300 µm. Fast Lissajous imaging speed up to 2 fps was realized with improved Labview and Java based real-time imaging software. Properties such as 3D imaging through autofocusing and mosaic imaging for extended lateral view (6 mm × 8 mm) were examined for carcinoma real-time pathology. Neoplastic lesion tissues of giant cell fibroma and peripheral ossifying fibroma, the fibroma inside the paraffin box and ex vivo gross tissues were imaged by the bench-top and handheld imaging modalities, and further compared with commercial microscope imaging results. The MEMS scanner-based handheld confocal imaging probe shows great promise as a potential clinical tool for oral cancer diagnosis and treatment.

Monolithic integration of binary-phase Fresnel zone plate objectives on 2-axis scanning micromirrors for compact microscopes.

We demonstrated a unique monolithic integration of Fresnel elliptical zone plate (EZP) objective on a 2-axis staggered vertical comb-drive micromirror with 500 μm by 800 μm surface area via direct patterning of reflective binary phase modulation elements on a silicon chip. The need for focusing optics is thus obviated, simplifying the micro-endoscope assembly and improving its form factor. The design of binary phase EZP was guided by simulations based on FFT based Rayleigh-Sommerfeld diffraction model. For dual-axis scanning angles up to 9º by 9º at the image plane, the simulated diffracted Airy disks on a spatial map have been demonstrated to vary from 10.5 μm to 28.6 μm. Micromirrors scanning ±9º (optical) about both axes are patterned with elliptical zones designed for 7 mm focal length and 20þ off-axis 635-nm illumination using 635 nm laser. Videos of samples acquired with ~15 μm lateral resolution over 1mm × 0.35 mm field of view (FOV) at 5.0 frames/second using the device in both transmission and reflectance modes bench-top single-fiber laser scanning confocal microscope confirmed the applicability of the device to micro-endoscopy.

Embedded metallic focus grating for silicon nitride waveguide with enhanced coupling and directive radiation.

We design a compact embedded metallic elliptical focus grating coupler based on gold or silver that efficiently interconnects free space with silicon nitride waveguide at 632.8 nm wavelength. The 3D far-field radiation pattern for the proposed grating coupler shows much higher gain and directivity towards free space coupling than that of the etched grating coupler. Specifically the free space transmission efficiency achieves 65% for silver grating coupler. It can also further enhance the fluorescence signal detection for Cy-5 fluorophore by isolating peak diffraction angle for 10°. The dense system integration capability shows the application potential for on-chip interfacing sub-wavelength light processing circuits and near-field fluorescent biosensors with far-field detection of superb radiation directivity and coupling efficiency.

Handheld Diffuse Reflectance Spectral Imaging (DRSi) for in-vivo characterization of skin.

Diffuse reflectance spectroscopy provides a noninvasive means to measure optical and physiological properties of tissues. To expand on these measurements, we have developed a handheld diffuse reflectance spectral imaging (DRSi) system capable of acquiring wide field hyperspectral images of tissue. The image acquisition time was approximately 50 seconds for a 50x50 pixel image. A transport model was used to fit each spectra for reduced scattering coefficient, hemoglobin concentration and melanin concentration resulting in optical property maps. The system was validated across biologically relevant levels of reduced scattering (5.14% error) and absorption (8.34% error) using tissue simulating phantoms. DRSi optical property maps of a pigmented skin lesion were acquired in vivo. These trends in optical properties were consistent with previous observations using point probe devices.

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.

Attenuation corrected fluorescence extraction using spatial frequency domain imaging system

In this paper, we present a novel approach to retrieve attenuation corrected fluorescence (ACF) in the image field. This approach can be applied to improve tumor identification for both diagnosis and treatment purpose. Furthermore, this approach will facilitate the development of fluorescence image-guided surgery.

Integrated Grating-Nanoslot Probe Tip for Near-Field Subwavelength Light Confinement and Fluorescent Sensing

We demonstrate a near-field sub-wavelength light confinement probe tip comprised of compact embedded metallic focus grating (CEMFG) coupler and photonic crystal (PhC) based λ/4 nano-slot tip, in terms of its far-field radiation directivity and near-field sub-wavelength light enhancement. The embedded metallic grating coupler increases the free space coupling at tilted coupling angle of 25° with over 280 times light intensity enhancement for 10 μm coupler size. Further, 20 nm air slot embedded in single line defect PhC waveguide are designed, using the impedance matching concept of the λ/4 “air rod”, to form the TE mode light wave resonance right at the probe tip aperture opening. This leads to the light beam spot size reduction down to λ/20. The near-field center peak intensity is enhanced by 4.2 times from that of the rectangular waveguide input, with the total enhancement factor of 1185 from free space laser source intensity. The near-field fluorescence excitation and detection also demonstrate its single molecular enhanced fluorescence measurement capability.

MEMS scanner enabled real-time depth sensitive hyperspectral imaging

We demonstrate a hyperspectral and depth sensitive optical scattering diffusion imaging microsystem, where fast scanning is provided by a CMOS compatible 2-axis MEMS mirror. By using lissajous scanning patterns, large field-of-view (FOV) of 1.2cm × 1.2cm images with lateral resolution of 100µm can be taken at 1.3 frame-per-second (fps). Hyperspectral and depth-sensitive images were acquired on phantom samples consisting of quantum dots (QDs) patterned at various depths in PDMS, showing 6 nm spectral resolution and 0.43 wavelength per second acquisition speed. Images were also acquired on biological sample of porcine epitheliu m with QDs placed underneath the surface.

Magnetic-actuated stainless steel micro-scanner for confocal hyperspectral fluorescence microscope

This paper presents the fabrication, characterization and imaging results of a wide-scanning, low voltage driven and electrical discharge machining (EDM) process fabricated stainless steel micro-scanner based real-time confocal hyperspectral fluorescence microscope for skin cancer detection.