As photonic devices become more complex, the need for efficient nonlinear materials and streamlined fabrication methods has increased. Typically, fabrication of compact, integrated, nonlinear photonic devices involve expensive procedures and environments within a cleanroom. Largely due to the need for phase matching constraints, many of these materials and methods have limited nonlinear efficiency. Recently, low-loss 3D printed waveguides have been demonstrated and hence are an attractive alternative that does not require a cleanroom. In this work, second harmonic generation near telecom wavelengths with a very low-cost 3D printed waveguide and nonlinear ENZ material platform is demonstrated with an efficiency exceeding 1.2%.
A scalable method of fabricating microscale devices in a low resource environment is shown using 3D printing. Microdevices are typically fabricated using silicon microfabrication techniques that require high resources, such as a cleanroom, that inhibits device fabrication in low resource environments. In this work, the use of 3D printing to make microfluidic devices for particle sorting, PCR detection and low-loss integrated waveguides is reviewed. The demonstrations are all performed in a low resource environment, without the use of a cleanroom, with an inexpensive custom 3D printer and off-the-shelf resin. The microdevices are made within a few minutes with training at the sophomore undergraduate level. This demonstrated a scalable fabrication method that is inexpensive, quick and facile.
A 3D printed microfluidic device for particle sorting was demonstrated using syringe-based fluid flow. Flow speeds of 192 μm/s were shown. This demonstrated an inexpensive, quick and facile fabrication approach to microfluidic particle sorting.
3D printed rib waveguides were demonstrated with dimensions from 11 to 30 μm wide, 5 to 31 μm tall and had ribs between <500 nm and 11 μm tall. The structures were made using a custom stereolithography 3D printer and a formulated hydrogel resin with UV light exposures of one second. The waveguides were characterized using the cutback method and showed losses of 1.0 to 1.6 cm-1 and coupling coefficients of <0.9. This demonstrates a very quick and inexpensive method to fabricate planar rib waveguides without the need for a cleanroom and promising for more complex integrated devices.
A 3D printed (3DP) microfluidic polymerase chain reaction (PCR) device was demonstrated by detecting synthetic SARS-CoV-2 at 106 copies/μL. The microfluidic device was fabricated using stereolithography 3DP and had a reaction volume of ~22 nL. The microdevice showed PCR amplification with 85 base synthetic ssDNA targets and primers designed for a SARS-CoV-2-specific region. The device was 2.5 times faster compared to a qPCR instrument with >60,000 times smaller reagent volume. The 3DP microdevice is a promising technology to significantly reduce the manufacturing costs of microfluidic devices that could be used towards point-of-care applications.
Ridge waveguides were three-dimensional printed using a stereolithography printer and hydrogel resin formulation. The ridge waveguides were 13, 20, and 30 μm wide, 3 to 6 μm high, and 4.4 mm long. The loss of the waveguides was measured using the cutback method and ranged between 0.28 and 1.2 cm − 1 (or 1.2 and 5.2 dB / cm) with transmittances up to 0.94 (0.27 dB coupling loss) using 635 nm light. Our work demonstrates a quick and inexpensive method to fabricate integrated photonic chips with the promise to fabricate more complex photonic devices and systems.
Ridge waveguides were 3D printed using a stereolithography 3D printer and hydrogel resin formulation. The ridge waveguides were 13, 20 and 30 μm wide, 3-6 μm high and 4.4 mm long. The loss of the waveguides was measured using the cutback method and ranged between 0.28 and 1.2/cm (or 1.2 and 5.2 dB/cm) with transmittances up to 0.94 using 635 nm light. This work demonstrates a quick and inexpensive method to fabricate integrated photonic chips with the promise to fabricate more complex photonic devices.
A 3D printed microfluidic device for Caenorhabditis elegans analysis. The biocompatibility of the 3D printed poly(ethylene glycol) diacrylate hydrogel resin was conducted and had no observable effect on worm lifespans. Worm organ morphology was directly observable through the microfluidic device and low autofluorescence was demonstrated using genetically-modified pharynx fluorescent worms.
KEYWORDS: Viruses, Signal to noise ratio, Point-of-care devices, Microfluidics, 3D printing, Ultraviolet radiation, Glasses, Lab on a chip, Digital micromirror devices, Digital Light Processing
A 3D printed microarray device towards COVID 19 (SARS-COV-2) detection with a limit-of-detection of <167 nM was demonstrated. An array of 1,166 microwells, 116 x 116 μm in size, were 3D printed and synthetic targets and probes specific to COVID-19 spike-proteins were detected to demonstrate a device towards point-of-care COVID-19 detection.
We demonstrate the fabrication of micropore and nanopore features in hollow antiresonant reflecting optical waveguides to create an electrical and optical analysis platform that can size select and detect a single nanoparticle. Micropores (4 µm diameter) are reactive-ion etched through the top SiO2 and SiN layers of the waveguides, leaving a thin SiN membrane above the hollow core. Nanopores are formed in the SiN membranes using a focused ion-beam etch process that provides control over the pore size. Openings as small as 20 nm in diameter are created. Optical loss measurements indicate that micropores did not significantly alter the loss along the waveguide.
Fluorescence resonance energy transfer (FRET) is one of the powerful tools used to study the dynamics of biomolecules.
By monitoring the energy transferred from a donor fluorophore to an acceptor fluorophore, one can determine the spatial
proximity between the fluorophores on the nanometer scale and thus extract information regarding interactions between
biomolecules. Here we demonstrate a novel way of measuring FRET from oligonucleotides using an integrated
optofluidic chip containing a planar liquid-core waveguide that can guide liquid and light simultaneously. FRET
experiments were carried out using fluorescein and Cy3 labeled oligonucleotides FRET pairs. An excitation laser was
fiber-coupled to a solid-core waveguide perpendicular to the chip's liquid-core channel. A FRET efficiency of 50% was
measured in good agreement with bulk microscopy experiments. By photobleaching the acceptors and manipulating the
fluidic flow, we also demonstrated controllable FRET events: an increase in donor signal, a decrease in acceptor signal
and the recovery of FRET due to the influx of new FRET pairs. The flexibility of our chip design also allows for
improvements such as separate donor and acceptor detection at either chip end using integrated filters.
Antiresonant reflecting optical waveguides (ARROWs) provide a promising approach to realizing high-sensitivity
sensing platforms on planar substrates. We have previously developed ARROW platforms that guide light in
hollow cores filled with liquid and gas media. These platforms include integrated traditional solid waveguides
to direct light into and out of sensing media. To improve the sensitivity of these platforms for optical sensing,
hollow waveguide loss must be reduced. We are working towards this by using anisotropic plasma etching to
create near-ideal hollow ARROW geometries. These structures rely on an etching mask that also serves as the
sacrificial core for the waveguide. This self-aligned process creates a hollow waveguide on a pedestal which is
surrounded by a terminal layer of air in three directions. We previously produced ARROWs by pre-etching the
silicon substrate and aligning the sacrificial core to the pedestal. However, this necessitates using a pedestal
which is wider than the core, leading to higher loss and poor reproducibility. We have also increased the hollow
to solid waveguide transmission efficiency by using a design that coats the sides and top of the hollow core with
a single layer of silicon dioxide. Using this design, we have demonstrated an interface transmission improvement
of more than two times. A much improved optical sensor platform will incorporate both of these features, using
the self-aligned pedestal process for most of the length of the hollow waveguides to decrease loss, and employing
the single layer design only at the interfaces to improve hollow-solid waveguide coupling.
Previously, we created antiresonant reflecting optical waveguides (ARROWs) with hollow cores that guide light through
gas and liquid media. We have demonstrated that these ARROWs can be used in sensing applications with single
particle sensitivity using fluorescence correlation spectroscopy. To increase sensitivity for single molecule sensing, we
have improved our initial designs and fabrication methods to decrease ARROW background fluorescence and improve
transitions between solid and hollow waveguides. Photoluminescence of ARROW layers creates background
fluorescence that masks the desired fluorescence signals. To improve sensitivity, we have optimized the PECVD
ARROW layers to minimize the photoluminescence of each layer. Sensing applications require that hollow waveguides
interface with solid waveguides on the substrate to direct light into and out of test media. Our previous ARROW designs
required light at these interfaces to pass through the anti-resonant layers. Although in theory, high transmission through
ARROW layers can be achieved, in practice, passing through these layers has limited transmission efficiencies. A new
design coats the top and sides of the hollow core with only silicon dioxide, allowing light at interfaces to pass directly
from silicon dioxide into the hollow core. This new design exhibits good mode confinement in the hollow core.
The combination of integrated optics and microfluidics in planar optofluidic devices carries the potential for novel
compact and ultra-sensitive detection in liquid and gaseous media. Single molecule fluorescence detection sensitivity in
planar beam geometry was recently demonstrated in liquid-core antiresonant reflecting optical waveguides (ARROWs)
fabricated on a silicon chip. A key component of a fully integrated single-molecule sensor is the addition of an optical
filtering capability to separate excitation beams from much weaker generated fluorescence or scattering signals. This
capability will eventually allow for integration of the photodetector on the same chip as the optofluidic sensing part. It
has been theoretically shown that the wavelength-dependent transmission of liquid-core ARROWs can be tailored to
efficiently separate excitation and fluorescence. Here, we present the wavelength dependent transmission of air-core
ARROW waveguides, using a highly nonlinear photonic crystal fiber to generate a broadband excitation spectrum, and
the design of liquid-core ARROW waveguides with integrated filter function. The air-core waveguide loss shows
pronounced wavelength dependence in good agreement with the design, demonstrating the potential of tailoring the
optical properties of liquid-core waveguides to accommodate single-molecule sensing on a chip. We also present an
ARROW design to produce wavelength-dependent transmission that is optimized for fluorescence resonance energy
transfer (FRET) studies with high transmission at 573 nm and 668nm, and low transmission at 546 nm.
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