Kaelyn D. Leake

Hollow waveguides with low intrinsic photoluminescence fabricated with Ta2O5 and SiO2 films

A type of integrated hollow core waveguide with low intrinsic photoluminescence fabricated with Ta(2)O(5) and SiO(2) films is demonstrated. Hollow core waveguides made with a combination of plasma-enhanced chemical vapor deposition SiO(2) and sputtered Ta(2)O(5) provide a nearly optimal structure for optofluidic biofluorescence measurements with low optical loss, high fabrication yield, and low background photoluminescence. Compared to earlier structures made using Si(3)N(4), the photoluminescence background of Ta(2)O(5) based hollow core waveguides is decreased by a factor of 10 and the signal-to-noise ratio for fluorescent nanobead detection is improved by a factor of 12.

Dual-color fluorescence cross-correlation spectroscopy on a planar optofluidic chip.

Fluorescence cross-correlation spectroscopy (FCCS) is a highly sensitive fluorescence technique with distinct advantages in many bioanalytical applications involving interaction and binding of multiple components. Due to the use of multiple beams, bulk optical FCCS setups require delicate and complex alignment procedures. We demonstrate the first implementation of dual-color FCCS on a planar, integrated optofluidic chip based on liquid-core waveguides that can guide liquid and light simultaneously. In this configuration, the excitation beams are delivered in predefined locations and automatically aligned within the excitation waveguides. We implement two canonical applications of FCCS in the optofluidic lab-on-chip environment: particle colocalization and binding/dissociation dynamics. Colocalization is demonstrated in the detection and discrimination of single-color and double-color fluorescently labeled nanobeads. FCCS in combination with fluorescence resonance energy transfer (FRET) is used to detect the denaturation process of double-stranded DNA at nanomolar concentration.

Optical particle sorting on an optofluidic chip

We report size-based sorting of micro- and sub-micron particles using optical forces on a planar optofluidic chip. Two different combinations of fluid flow and optical beam directions in liquid-core waveguides are demonstrated. These methods allow for tunability of size selection and sorting with efficiencies as high as 100%. Very good agreement between experimental results and calculated particle trajectories in the presence of flow and optical forces is found.

Optimization of Interface Transmission Between Integrated Solid Core and Optofluidic Waveguides

Optofluidic waveguides have been integrated with solid core waveguides on silicon using an antiresonant reflecting optical waveguide (ARROW) design. Interface transmission between solid and liquid core waveguides is one of the most important factors for overall optical throughput. The optimization of interface transmission by adjusting the thickness of top waveguide cladding layers was demonstrated experimentally and theoretically. The measured coupling efficiency increases from 18% to 67% and the overall throughput was improved 17× due to improved mode matching while liquid core waveguides maintain a low average loss coefficient.

All-optical particle trap using orthogonally intersecting beams [Invited]

We analyze the properties of a dual-beam trap of orthogonally intersecting beams in the geometrical optics regime. We derive analytical expressions for the trapping location and stability criteria for trapping a microparticle with uncollimated Gaussian beams. An upper limit for the beam waist is found. Optical forces and particle trajectories are calculated numerically for the realistic case of a microparticle in intersecting liquid-core waveguides.

Spectrally reconfigurable integrated multi-spot particle trap

Optical manipulation of small particles in the form of trapping, pushing, or sorting has developed into a vast field with applications in the life sciences, biophysics, and atomic physics. Recently, there has been increasing effort toward integration of particle manipulation techniques with integrated photonic structures on self-contained optofluidic chips. Here, we use the wavelength dependence of multi-spot pattern formation in multimode interference (MMI) waveguides to create a new type of reconfigurable, integrated optical particle trap. Interfering lateral MMI modes create multiple trapping spots in an intersecting fluidic channel. The number of trapping spots can be dynamically controlled by altering the trapping wavelength. This novel, spectral reconfigurability is utilized to deterministically move single and multiple particles between different trapping locations along the channel. This fully integrated multi-particle trap can form the basis of high throughput biophotonic assays on a chip.

Hollow Waveguides With Low Intrinsic Photoluminescence Fabricated With PECVD Silicon Nitride and Silicon Dioxide Films

A new type of integrated hollow core anti-resonant reflecting optical waveguide (ARROW) with low intrinsic photoluminescence (PL) fabricated with plasma-enhanced chemical vapor deposition (PECVD) silicon nitride (SiN) and silicon dioxide (SiO2) films is demonstrated. The waveguide is fabricated by surrounding the hollow core with alternating layers of SiN and SiO2. The thicknesses and indices of the layers are designed to meet an anti-resonance condition. Compared to earlier ARROW structures made by depositing high-temperature (HT) SiN (250 °C), the PL background decreases by a factor of ~ 10 when low-temperature (LT) SiN (100 °C ) films are used. Therefore, LT SiN ARROWs are attractive platforms for sensitive fluorescence and Raman spectroscopy measurements of biomolecules.

Optofluidic bioanalysis: fundamentals and applications

Abstract: Over the past decade, optofluidics has established itself as a new and dynamic research field for exciting developments at the interface of photonics, microfluidics, and the life sciences. The strong desire for developing miniaturized bioanalytic devices and instruments, in particular, has led to novel and powerful approaches to integrating optical elements and biological fluids on the same chip-scale system. Here, we review the state-of-the-art in optofluidic research with emphasis on applications in bioanalysis and a focus on waveguide-based approaches that represent the most advanced level of integration between optics and fluidics. We discuss recent work in photonically reconfigurable devices and various application areas. We show how optofluidic approaches have been pushing the performance limits in bioanalysis, e.g. in terms of sensitivity and portability, satisfying many of the key requirements for point-of-care devices. This illustrates how the requirements for bianalysis instruments are increasingly being met by the symbiotic integration of novel photonic capabilities in a miniaturized system.

Sized-based optical particle sorting using an orthogonal beam in optofluidic waveguides

We demonstrate on-chip, sized-based, optical sorting in optofluidic ARROW waveguides. Large particles are separated out of a mixture of particles of varying size as they pass through an intersecting beam.

Optofluidic waveguides with Ta 2 O 5 cladding layers and low photoluminescence

A new type of hollow core waveguide fabricated with Ta<inf>2</inf>O<inf>5</inf> and SiO<inf>2</inf> films is demonstrated. The photoluminescence background of ARROW waveguides is decreased significantly by replacing Si<inf>3</inf>N<inf>4</inf> with Ta<inf>2</inf>O<inf>5</inf> films, while maintaining low optical losses.