Patterned Biolayers of Protein Antigens for Label-Free Biosensing in Cow Milk Allergy

Photonic Crystal Surface Mode Real-Time Imaging of RAD51 DNA Repair Protein Interaction with the ssDNA Substrate

Photonic crystals (PCs) are promising tools for label-free sensing in drug discovery screening, diagnostics, and analysis of ligand-receptor interactions. Imaging of PC surface modes has emerged as a novel approach to the detection of multiple binding events at the sensor surface. PC surface modification and decoration with recognition units yield an interface providing the highly sensitive detection of cancer biomarkers, antibodies, and oligonucleotides. The RAD51 protein plays a central role in DNA repair via the homologous recombination pathway. This recombinase is essential for the genome stability and its overexpression is often correlated with aggressive cancer. RAD51 is therefore a potential target in the therapeutic strategy for cancer. Here, we report the designing of a PC-based array sensor for real-time monitoring of oligonucleotide-RAD51 recruitment by means of surface mode imaging and validation of the concept of this approach. Our data demonstrate that the designed biosensor ensures the highly sensitive multiplexed analysis of association-dissociation events and detection of the biomarker of DNA damage using a microfluidic PC array. The obtained results highlight the potential of the developed technique for testing the functionality of candidate drugs, discovering new molecular targets and drug entities. This paves the way to further adaption and bioanalytical use of the biosensor for high-content screening to identify new DNA repair inhibitor drugs targeting the RAD51 nucleoprotein filament or to discover new molecular targets.

Surface Bragg gratings of proteins patterned on integrated waveguides for (bio)chemical analysis

The incorporation of biomacromolecules onto silicon waveguiding microstructures constitutes a growing trend that pushes towards compact and miniaturized biosensing systems. This paper presents the integration of one-dimensional periodic nanostructures of proteins on the surface of micrometric silicon waveguides for transducing binding events between biomacromolecules. The study demonstrates this new bioanalytical principle by experimental results and theoretical calculations, and proves that rib waveguides (1--1.6-µm width) together with protein gratings (495--515-nm period) display suitable spectral responses for this optical biosensing system. Protein assemblies of bovine serum albumin are fabricated on the surface of silicon nitride waveguides, characterized by electron microscopy, and their response is measured by optical frequency domain reflectometry along the fabrication process and the subsequent stages of the biorecognition assays. Detection and quantification limits of 0.3 and 3.7 µg·mL-1, respectively, of specific antibodies are inferred from experimental dose-response curves. Among other interesting features, the results of this study point towards new miniaturized and integrated sensors for label-free bioanalysis.