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Experts from the Competence Unit Molecular Diagnostics develop laser diode pumped lab-on-a-chip solution for novel biosensor design.

The sensor group of Rainer Hainberger, Senior Scientist in the Competence Unit Molecular Diagnostics of the AIT Center for Health and Bioresources, has developed a laser diode pumped lab-on-a-chip concept that is able to detect biomolecules in liquid at low cost and without labels. The measurement method can be used to check various liquids for specific molecular biomarkers in medical or environmental tests.

Medical treatment decisions are based on knowledge often gained through laboratory testing of biomedical samples - fluids or tissues. Ideally, an analytical method should be able to detect low analyte concentrations in small sample volumes quickly, cheaply and easily.

Measurement by integrated-optical waveguide interferometry quantifies the change in optical path length and uses it for biochemical detection in biological samples, which are usually optically transparent. In this process, light is sent through an optical waveguide that is in direct contact with the sample fluid and the optical power at the output side is recorded, analysed and interpreted . The precise alignment of the laser beam to the waveguide input for coupling the light is also crucial here. This has always led to problems in previously used measurement configurations, but not in the solution implemented by AIT, in which a narrow-band laser light source is realised directly on the chip. The result is an easy-to-produce and easy-to-use measurement method that could also be used in every general practitioner's office in the future to obtain results directly on site in a short time.


The way interferometric integrated-optical waveguide biosensors work is based on monitoring the output intensity of light, which is directly related to the specific accumulation of target analyte molecules in an interferometer arm as a result of the refractive index change in the immediate vicinity of the waveguide surface.

Based on previous work, the AIT team integrated an organic monomode solid-state laser into an integrated photonic sensor chip with silica/silicon nitride waveguides and used a low-cost, fault-tolerant laser diode as a pump light source. Using a microfluidic device, the laser diode pumped lab-on-a-chip design is capable of measuring analyte concentrations of less than one microgram per milliliter. With the laser output coupled to a Mach-Zehnder interferometer (MZI), the device offers high sensitivity and ease of use, opening the door for future clinical applications. "Our multidisciplinary team was pleased to see that the theoretical work, design efforts and material development resulted in a real biofunctionalised device that works as predicted," says Florian Vogelbacher, a member of the AIT team.

Rainer Hainberger points out that the next steps will include optimising the laser resonator to further lower the laser threshold and reduce dye bleaching. "Now that we have demonstrated a cost-effective solution for generating coherent light on an integrated photonic sensing platform, we believe that integrated photonic sensing concepts will be more attractive for real biosensor applications," he says.

The measurement method is described in detail here:  
The paper: Florian Vogelbacher, Tim Kothe, Paul Muellner, Eva Melnik, Martin Sagmeister, Jochen Kraft, Rainer Hainberger, "Waveguide Mach-Zehnder biosensor with laser diode pumped integrated single-mode silicon nitride organic hybrid solid-state laser,"