Layer-by-layer functionalized nanotube arrays: A versatile microfluidic platform for biodetection

We demonstrate the layer-by-layer (LbL) assembly of polyelectrolyte multilayers (PEM) on three-dimensional nanofiber scaffolds. High porosity (99%) aligned carbon nanotube (CNT) arrays are photolithographically patterned into elements that act as textured scaffolds for the creation of functionally coated (nano)porous materials. Nanometer-scale bilayers of poly(allylamine hydrochloride)/poly(styrene sulfonate) (PAH/SPS) are formed conformally on the individual nanotubes by repeated deposition from aqueous solution in microfluidic channels. Computational and experimental results show that the LbL deposition is dominated by the diffusive transport of the polymeric constituents, and we use this understanding to demonstrate spatial tailoring on the patterned nanoporous elements. A proof-of-principle application, microfluidic bioparticle capture using N-hydroxysuccinimide-biotin binding for the isolation of prostate-specific antigen (PSA), is demonstrated. Nanoscale surface tailoring in 3D for enhanced biomolecule isolation and detection is now possible through layer-by-layer assembly. Next-generation biomedical applications — such as the capture and detection of biological markers at low concentrations — will depend on the systematic functionalization of the surfaces of tiny 3D scaffolds that are confined to intricate shapes. However, the application of existing surface modifications is restricted to planar structures and small particles. Brian Wardle and co-workers from the Massachusetts Institute of Technology, United States, have extended such modifications to complex porous materials. They patterned vertically aligned carbon nanotubes inside microfluidic devices then used successive depositions to produce high-porosity arrays with uniform and conformal coatings of nanoscale thickness and morphology. As proof-of-concept, the team used antibody-linked arrays to capture target antigens, demonstrating the versatility of the platform for future microfluidic applications.