The synthesis, characterization, and stability of porphyrin nanoparticles of 20-200 nm diameter presented herein is general for meso arylporphyrins. The elegance of the method lies in its simplicity. This work shows that the agent used to prevent agglomeration can be covalently attached to the dye forming the particle or be part of the solvent system. It also demonstrates that these and other types of dyes with a range of photonic properties do not need to be prepared by inclusion in external matrices or by designed self-assembly a priori. The matrix may severely limit the functionality of the particles in the former case, and at present this size of particle is difficult to achieve via the latter.

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A simple yet versatile method was developed to prepare a low-density polymerization initiator gradient, which was combined with surface-initiated atom transfer radical polymerization (ATRP) to produce a well-defined poly(2-hydroxyethyl methacrylate) (HEMA) gradient substrate. A smooth variation in film thickness was measured across the gradient, ranging from 20 A to over 80 A, but we observed a nonmonotonic variation in water contact angle. Fits of X-ray reflectivity profiles suggested that at the low graft density end, the polymer chain structure was in a "mushroom" regime, while the polymer chains at high graft density were in a "brush" regime. It was found that the "mushroom" region of the gradient could be made adhesive to cells by adsorbing adhesion proteins, and cell adhesion could be tuned by controlling the density of the polymer grafts. Fibroblasts were seeded on gradients precoated with fibronectin to test cellular responses to this novel substrate, but it was found that cell adhesion did not follow the expected trend; instead, saturated cell adhesion and spreading was found at the low grafting density region.