Fibers are a versatile platform because standard methods are available for the hierarchical assembly of individual fibers into controllable patterns (e.g., fabrics). Here, we report a method to biofunctionalize individual fibers by the reversible binding of proteins, and we suggest the potential of fiber assemblies by generating simple multifiber structures. Specifically, we use chitosan fibers and show that nickel can mediate assembly of histidine-tagged proteins to these fibers. Initial studies with the model His-GFP demonstrate the concept of nickel-mediated protein assembly. Subsequent studies with a His-tagged streptococcal antibody-binding protein (protein G) demonstrate the assembly of antibodies to generate antibody-presenting fibers. Antibody assembly onto the fiber was shown to be controllable, and antigen-binding to these antibody-presenting fibers was measured. Importantly, antibody and antigen were observed to penetrate substantially into the individual fibers (tens of microns) to allow the assembly of pmole levels of protein per cm of fiber length. Finally, antibody-presenting fibers with different specificities were assembled into simple one- and two-dimensional structures, and individual fibers in these fiber assemblies were observed to capture their respective antigens from antigen mixtures. The potential of fiber assemblies for multiplexed analysis is discussed.