Silicon-Nitride based Photonic Integrated Circuits (PICs) broaden the application scope of PICs outside of telecommunications where it originated from, since the wavelength range over which a waveguide can be designed matches for instance biophotonic applications usually working in the VIS (400-700nm) and NIR (700-1000nm) range. In this paper we show the latest results our silicon-nitride based sensor platform, that consist of an array of several types of interferometric sensors (Microring resonators, Mach-Zehnder interferometers), that are either used as refractive index, absorption or fluorescence sensors. We show the trade-offs between the different sensor types and show why an asymmetric MZI improves the sensitivity of the sensor platform over the MRR with over a factor of 10 down to the 10-8 RIU level. Furthermore we show that using flip-chipped VCSELs as integrated light source a low cost, disposable device is made. For desktop purposes we show how light sources are fiber coupled to the sensing platform creating a high end measurement system. The complete readout system allows for measuring multiple sensors on the chip, enabling multi-analyte measurements as well as improve the total stability of the measurement platform by using on-chip references. Finally we show an overview of measurement results where the sensor platform is functionalized using different interaction layers both local as well as wafer- scale. The results that the sensor platform can be used in for example liquid (blood and saliva) analysis as well as bacteria detection. The platform can be extended with a microfluidic interface for interaction of the optical layer and fluidics. An added integrated on-chip spectrometer allow additional functionality to the presented sensing platform.
Integrated-optical biosensors such as, for example, the microring resonator (MRR) and Mach-Zehnder interferometer, are more and more commercialized, mainly because of their high intrinsic sensitivity in combination with the possibilities they offer for integration in optofluidic devices. Previously, we have described the development and basic characteristics of MRR sensor chips that were fabricated in the TriPleX based silicon-nitride platform1 . In the present work, results are shown for the quantitative and sensitive detection of thrombin with aptamer-modified sensor chips. First, the modified MRR biosensor chips were tested for the binding and detection of thrombin using a repetitive number of binding/regeneration cycles on buffer sample containing 100 nM of thrombin. Then the binding curve was determined using different concentrations of thrombin, which revealed a limit of detection of 1 nM and a dynamic range up to roughly 0.5 μM of thrombin. Results from the thrombin binding experiment showed a stable performance during the course of multiple binding and regeneration cycles.
Integrated optical biosensors based on Mach-Zehnder Interferometers and Microring Resonators are widely used for food/drug monitoring and protein studies thank to their high intrinsic sensitivity, easy integration and miniaturization, and low cost.1, 2 In this study, we present a system to perform antibody interaction analysis using a photonic chip made of an array of six microring resonators (MRRs) based on the TriPleX platform. A compact system is presented where the input light is provided by a Vertical Cavity Surface Emitting Laser (VCSEL) pigtailed to a single mode fiber and operating at a ≈ 850nm wavelength. The output signal is detected by PIN photodetectors placed in the optical signal read-out module (the so-called OSROM) and processed by an easy-to-use Fourier Transform algorithm. Bulk sensitivity (Sb=98±2.1 nm/RIU) and Limit of Detection (LOD=(7.5± 0.5) x10-6 RIU) are measured and appeared to be very similar for the six MRRs on the same chip,3 which is an important property for multianalyte detection. An analysis of the anti-biotin interaction with immobilized biotin is performed by using different concentrations of anti-biotin antibody. The dependence of the resonance wavelength shift from the antibody concentration, as well as the association and the dissociation rate constants are calculated. For the average dissociation constant (KD) of anti-biotin antibody toward immobilized biotin, a value of (1.9±0.5) x10-7M is estimated, which is of the same order of magnitude of other published data.4 Furthermore, the specificity of the interaction is confirmed by using negative control antibodies and by performing competition with free, i.e., dissolved, biotin. In addition, the functional surface of the sensors could be regenerated for repeated measurements up to eight times by using 10 mM glycine/HCl pH 1.5.