Abstract

Integrated label-free photonic biosensors suit point-of-care (PoC) applications well, as they combine an excellent
limit of detection, a low-cost disposable, limited sample preparation as well as high potential for multiplexing.
The limiting factor for the breakthrough of Si photonic sensors has been the necessity of an expensive infrared
tunable laser, rendering the total cost incompatible with true PoC application. We present a novel sensor,
overcoming this barrier by combining a broadband visible light source with an on-chip spectral filter and SiN
photonics. A Mach-Zehnder interferometer with one arm exposed to the analyte is used as a highly sensitive
transducer. By using flood illumination on the input grating couplers, the alignment conditions are less stringent,
additionally increasing PoC compatibility, in terms of ease of use as well as cost. Bulk characterization of these
devices yields a limit of detection below 10-6 refractive index units, comparable with more expensive refractive
index sensors. Within this research, these sensors are employed to detect Tuberculosis through urine samples.
A number of mycobacterial biomarkers can identify pulmonary TB in the urine samples, but the most promising
markers are the cell wall lipopolysaccharide lipoarabinomannan (LAM) and Ag85B. A proprietary novel antibody
cocktail has been developed, which can specifically detect M. tuberculosis LAM and Ag85B and differentiates
them from non-tuberculous mycobacteria. This will increase the specificity and sensitivity of the developed test
far beyond current immunological tests. In a preliminary experiment, sensor chips were functionalised using
an Azide-ended silane by vapor phase deposition and antibodies were bioconjugated by click-chemistry using a
PEG-based linker. First results indicate the successful detection of 500 pg/ml of Ag85B antigen, illustrating the
potential of this device for the real-time diagnosis of TB.

Related Research Topics

• SiN biosensors operating in the visible

Related Projects

• ICT: POCKET (Development of a low-cost Point-Of-Care test for Tuberculosis detection)