Ethan G. Keeler

Photonic Crystal Optical Tweezers with High Efficiency for Live Biological Samples and Viability Characterization

We propose and demonstrate a new optical trapping method for single cells that utilizes modulated light fields to trap a wide array of cell types, including mammalian, yeast, and Escherichia coli cells, on the surface of a two-dimensional photonic crystal. This method is capable of reducing the required light intensity, and thus minimizing the photothermal damage to living cells, thereby extending cell viability in optical trapping and cell manipulation applications. To this end, a thorough characterization of cell viability in optical trapping environments was performed. This study also demonstrates the technique using spatial light modulation in patterned manipulation of live cell arrays over a broad area.

Progress of MEMS Scanning Micromirrors for Optical Bio-Imaging

Microelectromechanical systems (MEMS) have an unmatched ability to incorporate numerous functionalities into ultra-compact devices, and due to their versatility and miniaturization, MEMS have become an important cornerstone in biomedical and endoscopic imaging research. To incorporate MEMS into such applications, it is critical to understand underlying architectures involving choices in actuation mechanism, including the more common electrothermal, electrostatic, electromagnetic, and piezoelectric approaches, reviewed in this paper. Each has benefits and tradeoffs and is better suited for particular applications or imaging schemes due to achievable scan ranges, power requirements, speed, and size. Many of these characteristics are fabrication-process dependent, and this paper discusses various fabrication flows developed to integrate additional optical functionality beyond simple lateral scanning, enabling dynamic control of the focus or mirror surface. Out of this provided MEMS flexibility arises some challenges when obtaining high resolution images: due to scanning non-linearities, calibration of MEMS scanners may become critical, and inherent image artifacts or distortions during scanning can degrade image quality. Several reviewed methods and algorithms have been proposed to address these complications from MEMS scanning. Given their impact and promise, great effort and progress have been made toward integrating MEMS and biomedical imaging.

MEMS scanning micromirror for optical coherence tomography

This paper describes an endoscopic-inspired imaging system employing a micro-electromechanical system (MEMS) micromirror scanner to achieve beam scanning for optical coherence tomography (OCT) imaging. Miniaturization of a scanning mirror using MEMS technology can allow a fully functional imaging probe to be contained in a package sufficiently small for utilization in a working channel of a standard gastroesophageal endoscope. This work employs advanced image processing techniques to enhance the images acquired using the MEMS scanner to correct non-idealities in mirror performance. The experimental results demonstrate the effectiveness of the proposed technique.

A Scanning Micro-Mirror with an Adjustable Focal Length for Endoscope Applications

In this work, we report design, fabrication and characterization of a 3-D scanning micro-mirror device that combines 2-D beam scanning with focus control in the same device using micro-electro-mechanical-systems (MEMS) technology. The micro-mirror consists of a biaxial gimbal structure for 2-D beam scanning, and a deformable mirror membrane surface to achieve focus control. The micro-mirror with 800 micrometer diameter is designed to be sufficiently compact and efficient so that it can be incorporated into an endoscopic imaging probe. Using the focus-tracking MEMS scanning mirror, we achieved an optical scanning range of >16 degrees with <;40 V actuation voltage at resonance and a tunable focal length between infinity and 25 mm with <;100 V applied bias. We have also obtained imaging results using a micro-mirror with beam scanning-only function in both time-domain and spectral-domain optical coherence tomography systems.

MEMS resonant mass sensor with enabled optical trapping

Microresonators have an unmatched ability to detect the minute masses of single particles or biological cells. Precise measurement of cell mass, and its physical properties, is necessary to answer fundamental biological questions, with implications in cell biology, pharmacology, and medicine. This paper investigates the use of photonic-crystal-mediated optical trapping toward increasing the precision and applicability of this highly sensitive technique, discussing device design, fabrication, implementation, and preliminary results.

Optical modulation and manipulation of neurons and cells with high efficiency through quantum dots and photonic crystals

Nanomaterials such as semiconductor quantum dots and nanostructures such as photonic crystals can interact with light in unique ways due to their nms to sub-μm feature size. This enables versatile applications with high efficiencies. In this paper, we focus on biological applications, specifically, photostimulation and optical manipulation of cells. We report photostimulation and activation of neurons with very low optical intensity (0.0036 mW/mm2) through colloidal quantum dots. We also demonstrate efficient optical manipulation of cells and nanoparticles on a 2-D photonic crystal platform. Particles as small as 100 nm can be trapped with ∼16 μW/μm2 optical intensity.

MEMS Resonator and Photonic Crystal Integration for Enhanced Cellular Mass Sensing

This work describes the design and fabrication steps of a MEMS resonant-beam structure that utilizes optical trapping technology and microfluidics in an attempt to enhance the precision and accuracy of cellular-mass sensing devices.