C1q is an important recognition protein in the complement system, which is a major protein cascade in the innate immune system. Upon recognition of a target by C1q, the target is marked for opsonization and destruction. C1q recognizes many pathogenic patterns directly, but an important target is the Fc domain of antibodies binding to their antigen. In this paper, the curvature-dependence of the interaction between IgG and C1q is studied by surface plasmon resonance and quartz crystal microbalance. IgG is organized in similar surface coverage densities on flat polystyrene surfaces and polystyrene nanoparticles of different sizes, and the amount of C1q binding to the IgG is investigated. Nanoparticles in solution were found to aggregate upon incubation with IgG, and therefore a new technique utilizing nanoparticles binding to antifouling polymer brush functionalized surfaces was used to prepare surfaces with nanoparticles for measurements with surface plasmon resonance. Interestingly antigen-bound IgG at the curved surface of nanoparticles showed 5.6 times lower binding of C1q compared to at matched flat surfaces. There was no significant difference between the binding at 100 and 200 nm polystyrene particles. These findings are important for designing drug delivery systems to evade the complement system.

Colloidal suspensions of plasmonic nanoparticles (NPs) are a well-established tool for biomedical applications and enhanced spectroscopy because of their strong optical response. The specific response is greatly dependent on the NP shape. The strong optical activity of chiral NPs has created special interest but fabrication of chiral NPs in solution remains challenging. Here, we present an approach whereby three-dimensional (3D) chiral Au nano-hooks, fabricated with the parallel hole-mask colloidal lithography (HMCL) method, can be lifted off from a glass substrate in a controllable manner by using a combined treatment with oxygen plasma oxidation and a reduction step in solution. This method has the advantage of being based on established techniques and not requiring strong acids or complex substrates as in etching based approaches. We furthermore demonstrate the integration of the hook NPs into reversibly cross-linked hydrogels inspired by mussel catechol chemistry but containing an oxidation resistant catechol analogue grafted onto poly(allylamine) crosslinked by coordination of Al³⁺ and how this facilitates the remote analysis of hydrogel microenvironment, e.g. the water content. The suspended particles are promising candidates for optically active surface-enhanced Raman spectroscopy (SERS), asymmetric photo catalysis or aggregation sensing. The integration into hydrogels to produce functional hydrogels holds benefits for applications of metamaterials in optics, sensing or activation in environmental remediation or drug delivery.