Darkfield microscopy is an extremely sensitive imaging and sensing modality due to its very low
background. Metal nanoparticles as small as 20nm can been detected by darkfield imaging setups.
However, traditional darkfield microscopes are bulky and require special illumination condensers,
which limits their application in point-of-care biosensing. In this paper, we present a miniaturized
darkfield microscope based on liquid metallic on-chip condensers and imaging lenses. This microscope
is fully compatible with PDMS microfluidics and can be attached to a smartphone camera to build a
complete handheld biosensing system with very high sensitivity and low cost.
We propose an analytical framework to build a microfluidic microsphere-trap array device that enables simultaneous, efficient, and accurate screening of multiple biological targets in a single microfluidic channel. By optimizing the traps’ geometric parameters, the trap arrays in the channel of the device can immobilize microspheres of different sizes at different regions, obeying hydrodynamically engineered trapping mechanism. Different biomolecules can be captured by the ligands on the surfaces of microspheres of different sizes. They are thus detected according to the microspheres’ positions (position encoding), which simplifies screening and avoids target identification errors. To demonstrate the proposition, we build a device for simultaneous detection of two target types by trapping microspheres of two sizes. We evaluate the device performance using finite element fluidic dynamics simulations and microsphere-trapping experiments. These results validate that the device efficiently achieves position encoding of the two-sized microspheres with few fluidic errors, providing the promise to utilize our framework to build devices for simultaneous detection of more targets. We also envision utilizing the device to separate, sort, or enumerate cells, such as circulating tumor cells and blood cells, based on cell size and deformability. Therefore, the device is promising to become a cost-effective and point-of-care miniaturized disease diagnostic tool.
This paper presents a liquid metal based on-chip optofluidic grating spectrograph integrated with polydimethylsiloxane (PDMS) microfluidics for biomedical applications such as handheld fluorescence-actuated cell sorting, fluorescence immunosensing and Raman spectroscopy. We designed a Czerny-Turner spectrograph with 1.4nm spectral resolution, 300nm FSR and a footprint of 1cm by 2cm. The spectrograph structure was fabricated in PDMS using conventional replica molding soft lithography, and then filled with room temperature liquid metal, Gallium-Indium-Tin Alloy. The material and fabrication method is fully compatible with PDMS microfluidics, which allowed us to integrate a sheath flow based microfluidic cell focusing system with the spectrograph on the same substrate. This integration represents an important step towards a handheld flow cytometer. In addition, as a new class of on-chip optofluidic components, liquid metallic optical elements such as mirrors, gratings and pinholes will likely find other applications for building miniaturized optofluidic systems.
We have demonstrated flexible packaging and integration of CMOS IC chips with PDMS microfluidics. Microfluidic channels are used to deliver both liquid samples and liquid metals to the CMOS die. The liquid metals are used to realize electrical interconnects to the CMOS chip. As a demonstration we integrated a CMOS magnetic sensor die and matched PDMS microfluidic channels in a flexible package. The packaged system is fully functional under 3cm bending radius. The flexible integration of CMOS ICs with microfluidics enables previously unavailable flexible CMOS electronic systems with fluidic manipulation capabilities, which hold great potential for wearable health monitoring, point-of-care diagnostics and environmental sensing.
We build a microfluidic trap-based microsphere array device. In the device, we design a novel geometric structure of the trap array and employ the hydrodynamic trapping mechanism to immobilize the microspheres. We develop a comprehensive and robust framework to optimize the values of the geometric parameters to maximize the microsphere arrays’ packing density. We also simultaneously optimize multiple criteria, such as efficiently immobilizing a single microsphere in each trap, effectively eliminating fluidic errors such as channel clogging and multiple microspheres in a single trap, minimizing errors in subsequent imaging experiments, and easily recovering targets. Microsphere-trapping experiments have been performed using the optimized device and a device with un-optimized geometric parameters. These experiments demonstrate easy control of the transportation and manipulation of the microspheres in the optimized device. They also show that the optimized device greatly outperforms the un-optimized one.
Microsphere arrays can be used to effectively detect, identify, and quantify biological targets, such as mRNAs, proteins, antibodies, and cells. In this work, we design a microfluidic microsphere-trap array device that enables simultaneous, efficient, and accurate screening of multiple targets on a single platform. Different types of targets are captured on the surfaces of microspheres of different sizes. By optimizing the geometric parameters of the traps, the trap arrays in this device can immobilize microspheres of different sizes at different regions with microfluidic hydrodynamic trapping. The targets are thus detected according to the microspheres’ positions (position-encoding), which simplifies screening and avoids errors in target identification. We validate the design using fluid dynamics finite element simulations by COMSOL Multiphysics software using microsphere of two different sizes. We also performed preliminary microspheretrapping experiments on a fabricated device using microspheres of one size. Our results demonstrate that the proposed device can achieve the position-encoding of the microspheres with few fluidic errors. This device is promising for simultaneous detection of multiple targets and become a cheap and fast disease diagnostic tool.
An amplifier design for broadband Mid-IR buried-hetero (BH) structure epitaxial laser is presented, and
external cavity design based on this amplifier is described. Spectroscopy results characterizing such single
frequency lasers are demonstrated with whispering gallery mode CaF2 disc/ball, saturated absorption in
hollow waveguide and direct chemical analysis in water.
We demonstrated a continuously tunable optofluidic distributed feedback (DFB) dye laser on a monolithic
poly(dimethylsiloxane) (PDMS) elastomer chip. The optical feedback was provided by a phase-shifted higher order
Bragg grating embedded in the liquid core of a single mode buried channel waveguide. We achieved nearly 60nm
continuously tunable output by mechanically varying the grating period with two dye molecules Rhodamine 6G (Rh6G)
and Rhodamine 101 (Rh101). Single-mode operation was obtained with <0.1nm linewidth. Because of the higher order
grating, a single laser, when operated with different dye solutions, can provide tunable output covering from near UV to
near IR spectral region. The low pump threshold (< 1uJ) makes it possible to use a single high energy pulsed laser to
pump hundreds of such lasers on a chip. An integrated array of five DFB dye lasers with different lasing wavelengths
was also demonstrated. Such laser arrays make it possible to build highly parallel optical sensors on a chip. The laser
chip is fully compatible with PDMS based soft microfluidics.
"Optofluidics" is the marriage of optics, optoelectronics and nanophotonics with fluidics. Such integration represents a new approach for dynamic manipulation of optical properties at length scales both greater than and smaller than the wavelength of light with applications ranging from reconfigurable photonic circuits to fluidically adaptable optics to high sensitivity bio-detection currently under development. The capabilities in terms of fluidic control, mixing, miniaturization and optical property tuning afforded by micro-, nano- and electro-fluidics combined with soft lithography based fabrication provides an ideal platform upon which to build such devices. In this paper we provide a general overview of some of the important issues related to the fabrication, integration and operation of optofluidic devices and present three comprehensive application examples: nanofluidically tunable photonic crystals, optofluidic microscopy and DFB dye lasers.
We report on a volume holographic imaging spectrometer (VHIS) system which allows retrieval of a scene's two-dimensional spatial information as well as its spectral information. This is performed using a transmission volume hologram and a simple rotary scanning mechanism. The system has the advantages of high spectral and spatial resolutions and the potential of single-shot, four-dimensional (3D spatial plus 1D spectral) imaging by recording multiple volume holograms in the same material. Also, due to the transmission diffraction geometry, the system automatically eliminates the stray excitation light from the captured signal. We give theoretical analysis of the performance and experimental demonstration using fluorescent CdSe/ZeS quantum dots. The measured quantum dots spectra agree well with the spectra obtained using a conventional spectrometer.
We present two applications of volume holographic filters in the reflection geometry. A passive athermal holographic filter design is realized through the mutual compensation between the temperature coefficients of the bulk hologram and a variable incident angle controlled by a bimetallic cantilever. Seven holograms are multiplexed to constitute a multi-line filter which can be used to emulate specific absorption or emission spectra for spectroscopic applications.