Organ-on-a-Chip systems are emerging as an important in vitro analysis method for drug screening and medical research. For continuous biomolecular monitoring of the cell culture response, label-free detection within the microfluidic system or in the drainage tube is promising. We study photonic crystal slabs integrated with a microfluidic chip as an optical transducer for label-free biomarker detection with a non-contact readout of binding kinetics. This work analyzes the capability of same-channel reference for protein binding measurements by using a spectrometer and 1D spatially resolved data evaluation with a spatial resolution of 1.2 μm. A cross-correlation-based data-analysis procedure is implemented. First, an ethanol-water dilution series is used to obtain the limit of detection (LOD). The median of all row LODs is (2.3±0.4)×10-4 RIU with 10 s exposure time per image and (1.3±0.24)×10-4 RIU with 30 s exposure time. Next, we used a streptavidin-biotin binding process as a test system for binding kinetics. Time series of optical spectra were recorded while constantly injecting streptavidin in DPBS at concentrations of 1.6 nM, 3.3 nM, 16.6 nM and 33.3 nM into one channel half as well as the whole channel. The results show that localized binding within a microfluidic channel is achieved under laminar flow. Furthermore, binding kinetics are fading out at the microfluidic channel edge due to the velocity profile.
Keywords: diffusion; in-channel referencing; lab-on-a-chip; label-free biosensor; microfluidics; organ-on-a-chip; photonic crystal biosensor; protein binding kinetics; spatially resolved spectral analysis.