Chip-based optical nanoscopy, relying on single molecule localization microscopy has recently been demonstrated to reach 70 nm lateral resolution over wide fields of view (500 µm x 500 µm). To make this technique more sustainable for live-cell imaging we embedded a photonic chip into a microfluidic support that is able to perfuse and thermalize the samples. In this way specimens are maintained under physiological conditions during the imaging which can be a timeconsuming process. The system consists of a multilayer chip with the size of a glass coverslip (60 mm × 24 mm). The sample is illuminated using waveguides that are fabricated from high refractive index material. The waveguide hosts a chamber (17.3 μl) where cells are seeded and perfused with medium. A thin layer (188 µm) of cyclic olefin polymer (COP) seals the chamber and allows optical image acquisition. A thermalizing solution is perfused from the bottom to accurately warm up/cool down the waveguide in a range of 5°C - 45°C. Thus, samples are kept at the proper temperature. As proof of concept and verification of super-resolution imaging, we imaged fluorescent beads perfused across the coated surface (fibronectin 0.2 mg/ml) of the chip, which is needed to guarantee proper cell-to-substrate adhesion.
In this project it was found that Fourier ptychographic microscopy can be improved far beyond its conventional limits via waveguide-based optical systems. Extensive in silico studies showed that images obtained on high-refractive index material waveguide chips in conjunction with hyperspectral illumination light and finely designed waveguide geometries can be combined via a modified phase-retrieval algorithm to yield a resolution below 150 nm.
Super-resolution optical microscopy, commonly referred to as optical nanoscopy, has enabled imaging of biological
samples with a resolution that was only achievable previously using electron microscopy. Optical nanoscopy is a rapidly
growing field, with several different techniques and implementations that overcome the diffraction limit of light.
However, the common nanoscope continues to be a rather complex, expensive and bulky instrument. Direct stochastic
optical reconstruction microscopy (dSTORM) imaging was recently demonstrated using a waveguide platform for
excitation in combination with a simple microscope for imaging. High refractive index waveguide materials have a high
intensity evanescent field stretching around 100-200 nm outside the guiding material, which is ideally suited for total
internal reflection fluorescence (TIRF) excitation over large areas. We demonstrate dSTORM imaging of the plasma
membrane of liver sinusoidal endothelial cells (LSECs) and trophoblasts (HTR-8 cells) using waveguide excitation, with
resolution down to around 70 nm. Additionally, we present TIRF imaging of LSEC micro-tubules over a 500 μm x 500
μm area, laying the foundation for large field of view (f-o-v) nanoscopy.
Waveguide Mach-Zehnder interferometers (MZI) have been successfully used for a number of sensing applications due to their high sensitivity. As the MZI-sensors have a built-in reference, they are ideally not dependent on temperature variations. However, due to their high sensitivity, a temperature difference or an imbalance between the two arms, can give an unwanted temperature dependence of the output signal. Here, we present an experimental study of the temperature sensitivity of waveguide MZI. Three designs, balanced MZI, unbalanced MZI and tapered MZI are studied. In order to investigate the temperature sensitivity of the interferometer, we measure the phase shift at the output of the interferometer as function of temperature. It is found that the balanced MZI is very stable with temperature. For an unbalanced MZI having a 1 mm length difference between the two arms, a small phase shift is observed. The phase shift was less than one period for a 10°C change. The phase shift can be precisely determined for the tapered MZI. Initial measurements of the temperature sensitivity for a balanced, tapered MZI, gave output variations of some 150° for the phase, for a temperature change of 10°C. This corresponds to a temperature difference of 2.6 mK within the oil covering the two arms and demonstrates how sensitive the device is to temperature differences between the sensing and the reference arms.
An integrated optical sensor is developed for measuring gas concentration for subsea and atmospheric applications. The optical sensor is based on a waveguide Mach-Zehnder interferometer (MZI). In MZI, the light is spilt into a sensing and a reference arm and after a certain distance the branches are recombined. The sensing branch is covered with a sensitive layer that has high affinity towards a specified gas. The presence of the gas gives a change in the refractive index of the sensing arm, which is translated into a change in the output signal. With a prior calibration, the change in the output signal is correlated to the gas concentration. The waveguide should be single-mode and it is desirable to have high intensity in
the evanescent field. By using a high refractive index material and a thin waveguide core, the intensity of the evanescent field can be enhanced. Simulations are performed to obtain waveguide parameters with low losses and high sensitivity. The maximum sensitivity at wavelength 785 nm was obtained for a waveguide of core thickness 150 nm, rib height 5 nm and width 1 m for TM polarization. The first measurements of phase sensitivity of 12456π rad/RIU was obtain by the Hydrogen Chlorine (HCl) measurement. This is comparable to the phase sensitivity of 14268π rad/RIU obtained by the simulation.μ
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