Imaging label-free biosensor with microfluidic system

Abstract

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 TiO 2 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 wereimmobilized 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.

Human blood microfluidic test chip for imaging, label-free biosensor

“…The microscopy image in figure 2c reveals that nevertheless a plenitude of blood components pass the filter and reach the cavity. This explains the schlieren observed previously in imaging detection with the photonic crystal sensor [12]. As larger particles deteriorate the label-free detection scheme, we next consider in detail, which particle sizes pass the filter.…”

“…As the quasi-guided mode samples the analyte refractive index, a change in the GMRs occurs. The test chip is placed in the imaging read-out system between two crossed linear polarizing filters and a parallelizing and focussing optic [12]. Because of this set-up only light interacting with the quasi-guided modes is transmitted through the crossed polarizers to the CMOS sensor of a simple camera [13].…”

“…For such an approach the dwell time of the biomarkers on top of the sensor fields need to be optimized. Nevertheless, we performed first binding experiments by immobilizing initially two drops of 1.00 µM of biotinylated bovine serum albumin (BSA-biotin) and then 1.00 µM of streptavidin via covalent coupling on the surface of the photonic crystal [12]. Afterwards, 500 nM BSA-biotin dissolved in phosphate buffer saline were injected into the test chip to simulate measurement conditions as they exist for binding experiments with whole blood.…”

“…In previous works we demonstrated the functionality of a labelfree photonic crystal biosensor and our imaging read-out system by successfully performing detections of 90 nM CD40 ligand antibody as well as of 250 nM streptavidin. Additionally, we suggested the concept of a microfluidic test chip for blood filtration and presented first binding experiments [12]. This system concept is depicted in figure 1.…”

Handheld imaging photonic crystal biosensor for multiplexed, label-free protein detection

“…We here introduce a spectrometer-free handheld biosensor system based on imaging of the integrated intensity change ΔI for binding of biomolecules to a photonic crystal sensor surface. Integrating the photonic crystal sensor surface into a disposable microfluidic chip with filter unit [26] potentially allows for multiparametric biomarker detection in human blood for pointof-care applications. By spotting of specific binding sites for different types of molecules and imaging read out, a geometry-multiplexed detection scheme is realized as schematically shown in Fig.…”