Eva Melnik

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.

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.

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.

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.

Preparation of Mach-Zehnder interferometric photonic biosensors by inkjet printing technology

Inkjet printing is a versatile method to apply surface modification procedures in a spatially controlled, cost-effective and mass-fabrication compatible manner. Utilizing this technology, we investigate two different approaches for functionalizing label-free optical waveguide based biosensors: a) surface modification with amine-based functional polymers (biotin-modified polyethylenimine (PEI-B)) employing active ester chemistry and b) modification with dextran based hydrogel thin films employing photoactive benzophenone crosslinker moieties. Whereas the modification with PEI-B ensures high receptor density at the surface, the hydrogel films can serve both as a voluminous matrix binding matrix and as a semipermeable separation layer between the sensor surface and the sample. We use the two surface modification strategies both individually and in combination for binding studies towards the detection of the protein inflammation biomarker, C-reactive protein (CRP). For the specific detection of CRP, we compare two kinds of capture molecules, namely biotinylated antibodies and biotinylated CRP-specific DNA based aptamers. Both kinds of capture molecules were immobilized on the PEI-B by means of streptavidin-biotin affinity binding. As transducer, we use an integrated four-channel silicon nitride (Si3N4) waveguide based Mach-Zehnder interferometric (MZI) photonic sensing platform operating at a wavelength of 850nm (TM-mode).

Towards Recycled Paper Based Impedance Biosensor with Wireless Readout

Results are presented regarding the development of recycled paper based impedance biosensors with screen printed interdigitated electrode structures (IDES). The sensors show a response to increasing salt concentrations in the range 30–100 mM NaCl. To prove the feasibility of using recycled paper, biofunctionalization with a glucose sensitive enzyme mixture was performed by inkjet printing. The quantification of the glucose sensitive colour change reaction in paper was investigated and a trend is found in the range of 6–90 mg/dL. Subsequently, measurements with a wireless electronic readout system were performed on an electrochemical assay showing a decrease of the normalized sensor response dependent from the glucose concentration in the range 0–80 mg/dL.

Electromagnetic Characterization and Simulation of a Carbonate Buffer System on a Microwave Biosensor

In order to develop a fast, sensitive and easy-to-produce biosensor, a high-quality microwave split-ring resonator is going to be developed. In the final sensing device, a blood sample will be placed as a droplet on the sensitive area of the sensor. In case of specific target biomolecules binding a shift in resonance frequency will be induced due to the effective permittivity change. This shift in resonance frequency depends on the concentration of biomolecules and is therefore quantitative. The aim of this work is to find a position for the bio-functionalization that providesa measurable frequency shift when the analyte is added. Different areas are tested experimentally and via simulations. Two buffer solutions are used which have to be characterized in terms of its electromagnetic properties in advance. This preliminary study should pave the way for the measurements in real human samples such as serum or plasma.

Silicon nitride waveguide integration platform for medical diagnostic applications

The impressive progress of silicon photonic integrated device technology during the past fifteen years has been primarily driven by the requirements of optical data- and telecommunication. Research and development in silicon photonics has therefore been focused on the telecom wavelengths in the 1.55 μm and 1.31 μm regions and on silicon-on-insulator (SOI) material as waveguide integration platform. The rising cost burden of the traditional healthcare system as well as the increasing health consciousness among people is stimulating the decentralization of healthcare and is creating a strong demand for novel medical diagnostic devices suitable for point-of-care testing. This opens up new possibilities for integrated nanophotonic sensing devices operating in the visible and <; 1.1 μm near infrared region. In this talk, we will present our ongoing research activities on the development of a CMOS-compatible photonic integrated circuit technology platform. This platform relies on silicon nitride waveguides fabricated by low-temperature plasma enhanced chemical vapor deposition (PECVD), which allows their monolithic co-integration with silicon photodiodes and CMOS based electronic read-out circuitry. We have achieved propagation losses of less than 1 dB/cm at a wavelength of 850nm in silicon nitride waveguides processed directly on an optoelectronic CMOS chip employing chemical-mechanical planarization (CMP). We will present the design and experimental validation of various nanophotonic building blocks required for the implementation of medical diagnostic sensing devices. We will show results of optical biosensing experiments based on integrated Mach-Zehnder interferometers and demonstrate how inkjet material printing technology can be effectively used to locally functionalize the optical waveguide transducer components. Moreover, we will discuss the potential of this silicon nitride waveguide based nanophotonic integration platform for the miniaturization of optical coherence tomography systems.

Spin coated thin-film polymer waveguide Mach-Zehnder interferometer for label-free streptavidin detection

We report the development of Mach-Zehnder interferometer biosensors based on spin coated thin-film high index contrast polymer waveguides. Despite the large wavelength of 1310 nm and the comparatively low index contrast in polymers, label-free online detection of streptavidin concentrations as low as 0.1 μg/ml (= 1.66 nMol) was achieved. The polymer-based optical sensor design is fully compatible with cost-efficient mass production technologies such as injection molding and spin coating.