Paul Muellner

Integrated polymer-based Mach-Zehnder interferometer label-free streptavidin biosensor compatible with injection molding

We report the development of a Mach-Zehnder interferometer biosensor based on a high index contrast polymer material system and the demonstration of label-free online measurement of biotin-streptavidin binding on the sensor surface. The surface of the polyimide waveguide core layer was functionalized with 3-mercaptopropyl trimethoxy silane and malemide tagged biotin. Several concentrations of Chromeon 642-streptavidin dissolved in phosphate buffered saline solution were rinsed over the functionalized sensor surface by means of a fluidic system and the biotin-streptavidin binding process was observed in the output signal of the interferometer at a wavelength of 1310 nm. Despite the large wavelength and the comparatively low surface sensitivity of the sensor system due to the low index contrast in polymer material systems compared to inorganic material systems, we were able to resolve streptavidin concentrations of down to 0.1 μg/ml. The polymer-based optical sensor design is fully compatible with cost-efficient mass production technologies such as injection molding and spin coating, which makes it an attractive alternative to inorganic optical sensors.

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).

Flexible thin-film polymer waveguides fabricated in an industrial roll-to-roll process

The fabrication of flexible low-loss, thin-film, foil-based polymer waveguides with grating couplers employing a high-volume industrial roll-to-roll process is demonstrated. The embossed waveguides feature propagation losses of less than 1 dB/cm (633 nm, TE polarization), bending losses of 0.4-0.8 dB/360° for bending radii as small as 2 mm, and grating coupling efficiencies of up to 25%. In addition, the waveguides possess a thermo-optic coefficient of -1.58×10(-4) 1/°C. The fabricated waveguides are promising candidates for short-distance data communication as well as for sensing applications.

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.

Lateral leakage in symmetric SOI rib-type slot waveguides

We theoretically investigate the lateral leakage of rib-type slot waveguides caused by coupling between the TM-like slot mode and a TE slab mode using a finite element method eigenmode analysis and the variational mode-matching method.

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.

Monitoring light scattering characteristics of adherent cell cultures using a lab-on-a-chip

We have developed a μ-fluidic biochip capable of monitoring in real-time cellular phenotype dynamics by non-invasively assessing cell viability and reproduction over long periods of time. The μ-fluidic biochip contains integrated organic photodiodes that continuously perform light scattering measurements of adherent cell populations. In the presented work, we experimentally show that light scattering measurements are an effective label-free method for accurately assessing cell number variations. Furthermore, results obtained from 3D FDTD simulations indicate that side scatter characteristics of cells allow in principle predictions on cellular health status.

Optical biosensor technologies for molecular diagnostics at the point-of-care

Label-free optical schemes for molecular biosensing hold a strong promise for point-of-care applications in medical research and diagnostics. Apart from diagnostic requirements in terms of sensitivity, specificity, and multiplexing capability, also other aspects such as ease of use and manufacturability have to be considered in order to pave the way to a practical implementation. We present integrated optical waveguide as well as magnetic nanoparticle based molecular biosensor concepts that address these aspects. The integrated optical waveguide devices are based on low-loss photonic wires made of silicon nitride deposited by a CMOS compatible plasma-enhanced chemical vapor deposition (PECVD) process that allows for backend integration of waveguides on optoelectronic CMOS chips. The molecular detection principle relies on evanescent wave sensing in the 0.85 μm wavelength regime by means of Mach-Zehnder interferometers, which enables on-chip integration of silicon photodiodes and, thus, the realization of system-on-chip solutions. Our nanoparticle-based approach is based on optical observation of the dynamic response of functionalized magneticcore/ noble-metal-shell nanorods (‘nanoprobes’) to an externally applied time-varying magnetic field. As target molecules specifically bind to the surface of the nanoprobes, the observed dynamics of the nanoprobes changes, and the concentration of target molecules in the sample solution can be quantified. This approach is suitable for dynamic real-time measurements and only requires minimal sample preparation, thus presenting a highly promising point-of-care diagnostic system. In this paper, we present a prototype of a diagnostic device suitable for highly automated sample analysis by our nanoparticle-based approach.

Integrated optical waveguide and nanoparticle based label-free molecular biosensing concepts

We present our developments on integrated optical waveguide based as well as on magnetic nanoparticle based label-free biosensor concepts. With respect to integrated optical waveguide devices, evanescent wave sensing by means of Mach- Zehnder interferometers are used as biosensing components. We describe three different approaches: a) silicon photonic wire waveguides enabling on-chip wavelength division multiplexing, b) utilization of slow light in silicon photonic crystal defect waveguides operated in the 1.3 μm wavelength regime, and c) silicon nitride photonics wire waveguide devices compatible with on-chip photodiode integration operated in the 0.85 μm wavelength regime. The nanoparticle based approach relies on a plasmon-optical detection of the hydrodynamic properties of magnetic-core/gold-shell nanorods immersed in the sample solution. The hybrid nanorods are rotated within an externally applied magnetic field and their rotation optically monitored. When target molecules bind to the surfaces of the nanorods their hydrodynamic volumes increase, which directly translates into a change of the optical signal. This approach possesses the potential to enable real-time measurements with only minimal sample preparation requirements, thus presenting a promising point-of- care diagnostic system.

Silicon photonic wire Bragg grating for on-chip wavelength (de)multiplexing employing ring resonators

We present the design and experimental demonstration of a highly reflective silicon photonic wire Bragg grating operated for TM-polarized light at a wavelength of 1550 nm.