Waveguide Mach-Zehnder biosensor with laser diode pumped integrated single-mode silicon nitride organic hybrid solid-state laser.

Single-mode organic solid-state lasers with direct emission into an optical waveguide are attractive candidates for cost-efficient coherent light sources employed in photonic lab-on-a-chip biosensors. Here, we present a combination of a dye-doped organic solid-state distributed feedback laser with a highly sensitive optical waveguide Mach-Zehnder interferometer on a silicon nitride photonic platform. This organic-hybrid laser allows for optical pumping with a laser diode in an alignment tolerant manner, which facilitates applications in point-of-care diagnostics. The sensitivity to bulk refractive index changes and the concentration dependent binding of streptavidin on a polyethyleneimine-biotin functionalized surface was studied to demonstrate the practicability of this cost-efficient coherent light source for optical waveguide biosensors.

In vivo human retinal swept source optical coherence tomography and angiography at 830 nm with a CMOS compatible photonic integrated circuit.

Photonic integrated circuits (PIC) provide promising functionalities to significantly reduce the size and costs of optical coherence tomography (OCT) systems. This paper presents an imaging platform operating at a center wavelength of 830 nm for ophthalmic application using PIC-based swept source OCT. An on-chip Mach-Zehnder interferometer (MZI) configuration, which comprises an input power splitter, polarization beam splitters in the sample and the reference arm, and a 50/50 coupler for signal interference represents the core element of the system with a footprint of only [Formula: see text]. The system achieves 94 dB imaging sensitivity with 750 [Formula: see text]W on the sample, 50 kHz imaging speed and 5.5 [Formula: see text]m axial resolution (in soft tissue). With this setup, in vivo human retinal imaging of healthy subjects was performed producing B-scans, three-dimensional renderings as well as OCT angiography. These promising results are significant prerequisites for further integration of optical and electronic building blocks on a single swept source-OCT PIC.

Toward optical coherence tomography on a chip: in vivo three-dimensional human retinal imaging using photonic integrated circuit-based arrayed waveguide gratings.

In this work, we present a significant step toward in vivo ophthalmic optical coherence tomography and angiography on a photonic integrated chip. The diffraction gratings used in spectral-domain optical coherence tomography can be replaced by photonic integrated circuits comprising an arrayed waveguide grating. Two arrayed waveguide grating designs with 256 channels were tested, which enabled the first chip-based optical coherence tomography and angiography in vivo three-dimensional human retinal measurements. Design 1 supports a bandwidth of 22 nm, with which a sensitivity of up to 91 dB (830 µW) and an axial resolution of 10.7 µm was measured. Design 2 supports a bandwidth of 48 nm, with which a sensitivity of 90 dB (480 µW) and an axial resolution of 6.5 µm was measured. The silicon nitride-based integrated optical waveguides were fabricated with a fully CMOS-compatible process, which allows their monolithic co-integration on top of an optoelectronic silicon chip. As a benchmark for chip-based optical coherence tomography, tomograms generated by a commercially available clinical spectral-domain optical coherence tomography system were compared to those acquired with on-chip gratings. The similarities in the tomograms demonstrate the significant clinical potential for further integration of optical coherence tomography on a chip system.

Multi-channel swept source optical coherence tomography concept based on photonic integrated circuits.

In this paper, we present a novel concept for a multi-channel swept source optical coherence tomography (OCT) system based on photonic integrated circuits (PICs). At the core of this concept is a low-loss polarization dependent path routing approach allowing for lower excess loss compared to previously shown PIC-based OCT systems, facilitating a parallelization of measurement units. As a proof of concept for the low-loss path routing, a silicon nitride PIC-based single-channel swept source OCT system operating at 840 nm was implemented and used to acquire in-vivo tomograms of a human retina. The fabrication of the PIC was done via CMOS-compatible plasma-enhanced chemical vapor deposition to allow future monolithic co-integration with photodiodes and read-out electronics. A performance analysis using the results of the implemented photonic building blocks shows a potential tenfold increase of the acquisition speed for a multi-channel system compared to an ideal lossless single-channel system with the same signal-to-noise ratio.

Human IgG detection in serum on polymer based Mach-Zehnder interferometric biosensors.

We report a new method for detecting human IgG (hIgG) in serum on integrated-optical Mach-Zehnder interferometer biosensors realized in a high index contrast polymer material system. In the linear range of the sensor (5-200 nM) we observed excellent signal recoveries (95-110%) in buffer and serum samples, which indicate the absence of matrix effects. Signal enhancement was reached by using secondary anti-human IgG antibodies, which bind to immobilized target IgGs and allow detecting concentrations down to 100 pM. This polymer based optical sensor is fully compatible with cost-efficient mass production technologies, which makes it an attractive alternative to inorganic optical sensors. Graphical abstract of the hIgG measured on polymer based photonic sensors using a direct binding assay and a signal enhancement strategy with secondary antibodies.

Streptavidin binding as a model to characterize thiol-ene chemistry-based polyamine surfaces for reversible photonic protein biosensing.

Biotin- and iminobiotin-bonded surfaces obtained by thiol-ene chemistry and subsequent modification with polyamines were characterized with respect to streptavidin-binding capacity and reversibility for photonic biosensing using X-ray photoelectron spectroscopy and Mach-Zehnder-interferometric sensors. The streptavidin-iminobiotin system was exploited for reversible multilayer deposition and determination of affinity constants on each layer.

Monitoring dynamic interactions of tumor cells with tissue and immune cells in a lab-on-a-chip.

A complementary cell analysis method has been developed to assess the dynamic interactions of tumor cells with resident tissue and immune cells using optical light scattering and impedance sensing to shed light on tumor cell behavior. The combination of electroanalytical and optical biosensing technologies integrated in a lab-on-a-chip allows for continuous, label-free, and noninvasive probing of dynamic cell-to-cell interactions between adherent and nonadherent cocultures, thus providing real-time insights into tumor cell responses under physiologically relevant conditions. While the study of adherent cocultures is important for the understanding and suppression of metastatic invasion, the analysis of tumor cell interactions with nonadherent immune cells plays a vital role in cancer immunotherapy research. For the first time, the direct cell-to-cell interactions of tumor cells with bead-activated primary T cells were continuously assessed using an effector cell to target a cell ratio of 10:1.

Nonlinearity of optimized silicon photonic slot waveguides.

In this numerical study, we show that by exploiting the advantages of the horizontal silicon slot wave-guide structure the nonlinear interaction can be significantly increased compared to vertical slot waveguides. The deposition of a 20 nm thin optically nonlinear layer with low refractive index sandwiched between two silicon wires of 220 nm width and 205 nm height could enable a nonlinearity coefficient gamma of more than 2 x 10(7) W(-1)km(-1).

Lateral leakage in symmetric SOI rib-type slot waveguides.

We theoretically investigate the lateral leakage in fully symmetric horizontal rib-type slot waveguides caused by coupling between the TM-like slot mode and a TE slab mode. The leakage mechanism is described and the dependence on the geometry parameters is studied using the variational mode-matching method. In addition, the effective-index method to solve the transcendent eigenmode equation of rib-type slot waveguides is applied and compared with the aforementioned rigorous numerical method. We show that this semi-analytical approach yields results with sufficiently high accuracy. For design purposes the influence of structural deviations caused by the fabrication process is studied. We show that the usable range of the geometry parameters can be widely extended by exploiting leakage suppressing mechanisms.