We present a microfluidic system suitable for parallel label-free detection of several biomarkers utilizing a compact imaging measurement system. The microfluidic system contains a filter unit to separate the plasma from human blood and a functionalized, photonic crystal slab sensor chip. The nanostructure of the photonic crystal slab sensor chip is fabricated by nanoimprint lithography of a period grating surface into a photoresist and subsequent deposition of a TiO2 layer. Photonic crystal slabs are slab waveguides supporting quasi-guided modes coupling to far-field radiation, which are sensitive to refractive index changes due to biomarker binding on the functionalized surface. In our imaging read-out system the resulting resonance shift of the quasi-guided mode in the transmission spectrum is converted into an intensity change detectable with a simple camera. By continuously taking photographs of the sensor surface local intensity changes are observed revealing the binding kinetics of the biomarker to its specific target. Data from two distinct measurement fields are used for evaluation. For testing the sensor chip, 1 μM biotin as well as 1 μM recombinant human CD40 ligand were immobilized in spotsvia amin coupling to the sensor surface. Each binding experiment was performed with 250 nM streptavidin and 90 nM CD40 ligand antibody dissolved in phosphate buffered saline. In the next test series, a functionalized sensor chip was bonded onto a 15 mm x 15 mm opening of the 75 mm x 25 mm x 2 mm microfluidic system. We demonstrate the functionality of the microfluidic system for filtering human blood such that only blood plasma was transported to the sensor chip. The results of first binding experiments in buffer with this test chip will be presented.
Guided mode resonance biosensors are of emerging interest as they allow integration on chip with fabrication on mass scale. The guided mode resonances (GMRs), observed in the transmission or reflection spectrum, are sensitive to refractive index changes in the vicinity of the photonic crystal (PhC) surface. Standard measurement setups utilize a collecting lens, focusing the extracted light intensity onto a single-point photo detector. In order to achieve highly miniaturized devices, we consider the integration of planar emitting and detector structures, such as organic light emitting diodes (OLEDs) and organic photo detectors (OPDs), together with the PhC based biosensors, on a single chip. This approach, however, consequently leads to a broadband, multi-angular light excitation as well as to a broadband and multi-angular contribution to the OPD photon count. While GMR effects in PhC slabs with directional light sources have been widely studied, this lens-less scenario requires a deep understanding regarding the broadband and the angular influence of both incident and reflected or transmitted light. We performed finite-difference time-domain (FDTD) calculations for GMR effects in two-dimensional (2D) PhC slabs. We study the effects for broadband emission in the visible spectrum, together with an angular incident beam divergence of up to 80°. We verified the simulated results by performing angle-resolved spectral measurements with a light emitting diode (LED) in a macroscopic, lens-less setup. We further utilize this numerical setup to provide a deeper understanding of the modal behaviour of our proposed OLED and OPD-based integrated biosensor concept.