Total Capture, Convection-Limited Nanofluidic Immunoassays Exhibiting Nanoconfinement Effects.

Understanding nanoconfinement phenomena is necessary to develop nanofluidic technology platforms. One example of nanoconfinement phenomena is shifts in reaction equilibria toward reaction products in nanoconfined systems, which have been predicted theoretically and observed experimentally in DNA hybridization. Here we demonstrate a convection-limited nanofluidic immunoassay that achieves total capture of a target analyte and an apparent shift in the antibody-antigen reaction equilibrium due to nanoconfinement. The system exhibits wavefronts of the target analyte that propagate along the length of the nanochannel at a velocity much slower than that of the carrier fluid. We apply an analytical model describing the propagation of these wavefronts to determine the density of capture antibody binding sites in the enclosed nanochannel for a known concentration of the target analyte. We then use this binding site density to estimate the concentration of solutions with 5× and 10× less analyte. Our analysis suggests that nanoconfinement results in a preference toward binding of the target analyte with the surface-grafted capture antibody, as evidenced by an apparent reduction in the equilibrium dissociation constant. Our findings motivate the advancement of new biomedical and chemical synthesis technologies by leveraging nanoconfinement effects, and demonstrate a useful platform for studying the effect of nanoconfinement on chemical systems.