Photonic Biochip

The next generation of Point-of-Care (PoC) tests based on advanced biochips promises to revolutionize the world of medical diagnostics by enabling PoC diagnosis and treatment monitoring, e.g. for personalized medicine and companion diagnostics. Moreover, these biochips can also be used in other application areas like pharma, agri-food, environmental monitoring and forensics.

Our photonic or integrated optical biochips use light to obtain an analytical signal from a biological sample. They combine a high sensitivity with small size and the potential for cost-effective mass production. This makes them particularly suitable for PoC applications. We offer an ultrasensitive photonic biochip based on silicon nitride waveguide technology.

Surface modification is a key step in the production of biochips, since it enables the sensitive and selective detection of the analyte of interest. Our material-selective nanocoating improves the sensitivity and limit of detection, while reducing unwanted non-specific adsorption.

Moreover, we are not developing 'just' a biochip. The nanocoating and biofunctionalization processes are combined with smart solutions for fluidic and optical interfacing in a streamlined process flow. This allows the scalable production of a plug & play component for easy integration in PoC devices for a broad range of applications.




Sensing with light

In photonic biochips light travels through one material (the waveguide), embedded in another material (the cladding). Photonic biochips detect the presence of biomarkers through changes in the optical properties at their surface. Binding of a biomarker to the waveguide causes a change in the local refractive index, which results in a change in the light output of the chip.

Surfix's photonic biochip is based on TripleX waveguide technology developed by our partner Lionix International. This technology uses silicon nitride and silicon oxide as waveguide and cladding materials, respectively. Different waveguide designs have been realized, such as microring resonators (MRR) and Mach-Zehnder interferometers (MZI). Compared to MRRs, the MZI design has the added benefit that the sensitivity can be increased by adjusting the length of the waveguide and introducing an asymmetry in the waveguide design. These asymmetric MZIs (aMZIs) therefore have a superior sensitivity and are the design of choice for the Surfix biochip.

The silicon nitride-based TripleX platform has several advantages over other photonic technologies. Owing to low light losses and an efficient evanescent field, extremely high sensitivities can be achieved. Also, multiple waveguides can be combined on a single chip and fed by a single light source. Furthermore, the platform works with visible light (850 nm), which further increases sensitivity compared to the infrared light (1550 nm) used in other photonic platforms. Moreover, at 850 nm low cost light sources and detectors can be used.




Biofunctionalization

The key requirement for any biosensor is that it only detects a very specific analyte, which may be present in a very low concentration and surrounded by many other components. To ensure that only the analyte of interest is detected, a specific bioreceptor needs to be immobilized on the surface of the transducer element. Bioreceptors can be proteins (antibodies, enzymes), nucleic acids (DNA, RNA), or other biological or biomimetic structures.

For photonic biochips, binding of analyte molecules to the waveguide causes a change in the light output of the sensor. The cladding, on the other hand, does not contribute to the sensor signal. Therefore, it is beneficial to immobilize the bioreceptor only on the waveguide and not on the cladding. This is achieved by Surfix's material-selective nanocoating process. To prevent non-specific adsorption of analytes, an anti-biofouling layer is applied to the cladding in a second surface modification step.




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Applications