Roman Bruck

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.

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.

Multi-step surface functionalization of polyimide based evanescent wave photonic biosensors and application for DNA hybridization by Mach-Zehnder interferometer.

The process of surface functionalization involving silanization, biotinylation and streptavidin bonding as platform for biospecific ligand immobilization was optimized for thin film polyimide spin-coated silicon wafers, of which the polyimide film serves as a wave guiding layer in evanescent wave photonic biosensors. This type of optical sensors make great demands on the materials involved as well as on the layer properties, such as the optical quality, the layer thickness and the surface roughness. In this work we realized the binding of a 3-mercaptopropyl trimethoxysilane on an oxygen plasma activated polyimide surface followed by subsequent derivatization of the reactive thiol groups with maleimide-PEG(2)-biotin and immobilization of streptavidin. The progress of the functionalization was monitored by using different fluorescence labels for optimization of the chemical derivatization steps. Further, X-ray photoelectron spectroscopy and atomic force microscopy were utilized for the characterization of the modified surface. These established analytical methods allowed to derive information like chemical composition of the surface, surface coverage with immobilized streptavidin, as well as parameters of the surface roughness. The proposed functionalization protocol furnished a surface density of 144 fmol mm(-2) streptavidin with good reproducibility (13.9% RSD, n=10) and without inflicted damage to the surface. This surface modification was applied to polyimide based Mach-Zehnder interferometer sensors to realize a real-time measurement of streptavidin binding validating the functionality of the MZI biosensor. Subsequently, this streptavidin surface was employed to immobilize biotinylated single-stranded DNA and utilized for monitoring of selective DNA hybridization. These proved the usability of polyimide based evanescent photonic devices for biosensing application.

Efficient coupling of narrow beams into polyimide waveguides by means of grating couplers with high-index coating

The effect of a thin high-index coating deposited on polyimide waveguide grating couplers was investigated. A comprehensive numerical study was performed using an efficient simulation tool based on a Floquet-Bloch algorithm, and the results of this study were compared with experimentally obtained values for input coupling efficiencies. The application of a high-index coating permits efficient coupling from narrow beams even in material systems with a low index difference. This not only facilitates a denser integration of grating couplers but also permits low-loss lateral tapering to single-mode waveguides.

Sensitivity and design of grating-assisted bimodal interferometers for integrated optical biosensing

The sensitivity of bimodal waveguides for integrated optical biosensors is compared to single mode waveguides and grating-assisted bimodal interferometers are proposed as improved sensor concept. Grating-assisted bimodal interferometers are an elegant and compact sensor concept, which features easy fabrication and overcomes typical weaknesses of classical Mach-Zehnder interferometers. Long period gratings for mode conversion in the proposed sensor concept have been simulated employing the FDTD method. Such gratings give full control over the power distribution in the waveguides modes, which is not possible with other methods. Designs for three typical material systems are given and fabrication tolerances were investigated.

Polymer waveguide based biosensor

Planar-integrated optical biosensors based on the interferometric evanescent wave sensing principle facilitate highly sensitive label-free detection of biomolecules. In this work, we present a novel polymer waveguide device concept that allows for cost effective fabrication of disposable sensor chips by utilizing injection moulding and spin-coating. Surface grating couplers are used in combination with lateral tapers to couple light in and out of the biosensor. The coupling strength of these polymer gratings is increased by applying a thin inorganic high-index coating, which allows reducing the grating size and thus achieving efficient lateral tapering into single mode waveguides. The sensor concept, design of the waveguide components as well as first experimental results of the injection moulding process, the grating couplers and the Mach-Zehnder interferometers are presented.

Efficient small grating couplers for low-index difference waveguide systems

Due to the small coupling strength of waveguide grating couplers in low index contrast material systems such as polymers, the efficient coupling to single-mode waveguides via surface gratings represents a severe challenge. In this work, we demonstrate that the coupling strength of grating couplers in low-index difference waveguide systems can be strongly enhanced by the application of a thin high-index coating (HIC) on top of surface gratings. This allows reducing the grating coupler aperture size without sacrificing efficiency by up to more than an order of magnitude, which enables low-loss lateral tapering to single-mode waveguides.

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.

Argon ion multibeam nanopatterning of Ni–Cu inserts for injection molding

The authors have successfully employed the charged particle nanopatterning (CHARPAN) technology for nanostructuring of a metal mold insert for a conventional injection molding machine. High-precision diamond-milled Ni–Cu mold inserts have been nanopatterned with 10 keV argon ion multibeam milling with feature sizes as small as 50 nm. A variety of structures such as circles, hexagons, and lines in different dimensions, with positive and negative shapes, have been fabricated in the metal mold. These structures have been successfully replicated in polymethylpentene samples by injection molding. To the authors’ best knowledge, the CHARPAN technology is one of the very few technologies that allow for resistless nanostructuring a field size of 25×25 μm2 into a metal mold in a single shot. This is of high importance for the practical injection molding fabrication of nanostructured polymer devices such as optical biosensors.The authors have successfully employed the charged particle nanopatterning (CHARPAN) technology for nanostructuring of a metal mold insert for a conventional injection molding machine. High-precision diamond-milled Ni–Cu mold inserts have been nanopatterned with 10 keV argon ion multibeam milling with feature sizes as small as 50 nm. A variety of structures such as circles, hexagons, and lines in different dimensions, with positive and negative shapes, have been fabricated in the metal mold. These structures have been successfully replicated in polymethylpentene samples by injection molding. To the authors’ best knowledge, the CHARPAN technology is one of the very few technologies that allow for resistless nanostructuring a field size of 25×25 μm2 into a metal mold in a single shot. This is of high importance for the practical injection molding fabrication of nanostructured polymer devices such as optical biosensors.

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.