Investigating protein-polymer interactions on a microfluidic platform

Protein-polymer complexation is a phenomenon of critical importance for many biological and chemical processes. To understand such interactions it is critical to have experimental tools that allow one to obtain quantitative information about protein-polymer complexation. We present a simple, flexible, and general platform that enables the study of macromolecular complex formation in solution.; We monitor polymer-protein interactions by means of fluorescence resonance energy transfer (FRET), where the polymer molecules are unlabeled and two populations of protein molecules are fluorescently labeled with a FRET donor and an acceptor pair.; We study a model system of different generations of Poly(amidoamine) PAMAM dendrimers and fluorescently labeled Streptavidin. Under our experimental conditions, the dendrimers are positively charged and streptavidin is negatively charged thus they are driven to form complexes by a strong electrostatic attraction.; We introduce the protein solution into the center of a three lane microfluidic device. The two outer lanes contain polymer or buffer solution. The laminar flow in these channels allows us to directly compare polymer or control solutions interacting with the protein solution by interdiffusion.; We study macromolecular complexation between n proteins and a dendrimer at the reaction front at the interface between protein and polymer lanes. We monitor complex appearance at different positions downstream the main channel by measuring the FRET signal.; The exact solution to the diffusion-reaction problem is not known for the general case in which protein and polymer exhibit different diffusion coefficients. Nevertheless, we demonstrate that it is possible to obtain both qualitative and quantitative information about complex formation.; The microfluidic platform allows one to easily and rapidly screen systems to determine whether or not protein-polymer interactions occur, or compare the complexation behavior of two or more polymers by monitoring complex appearance.; More interestingly, when quantitative information is desired, we can obtain bounds for the reaction stoichiometry (n).; Our microfluidic platform allows us to investigate complexes as they are formed in solution, it is easy and relatively inexpensive to implement, and it only requires the protein molecules to be labeled, something easily accomplished with current techniques and so it could be easily extended to other systems.