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The interaction between the conjugated polyelectrolyte poly{[9,9-bis(6'-N,N,N-trimethylammonium)hexyl]fluorene-phenylene} bromide (HTMA-PFP) and human serum albumin (HSA) has been investigated from changes observed in both the spectroscopic properties of HTMA-PFP and the intrinsic fluorescence of HSA. Absorption and fluorescence spectra of HTMA-PFP suggest that HTMA-PFP and HSA form polymer-protein complexes due to electrostatic interactions between the cationic side chains of HTMA-PFP and the negatively charged surface of the protein. Interaction between both macromolecules induces an increase in the fluorescence signal of HTMA-PFP, which suggests that hydrophobic forces also contribute to the polymer-protein complex stabilization. In addition, this interaction causes a decrease in the HSA fluorescence, partially due to static quenching and energy transfer between both macromolecules. Effects of HTMA-PFP on the thermal stability and protein conformation were explored from CD experiments. Results indicate that as polymer is added it binds to HSA and initiates unfolding. This unfolding process induces HTMA-PFP chains to become more extended, disrupting backbone interactions and increasing polymer fluorescence intensity.

Cryo-etch scanning electron microscopy (cryo-etch SEM) of aqueous gels composed of colloidal silica nanoparticles in the 1-40 nm range and liposomes of ∼200 nm gave unique morphologies. The aqueous gels are frozen at subcooled liquid nitrogen and fractured to obtain a fresh surface. High-vacuum sublimation of ice from the freshly exposed surface (etching) results in the formation of a hierarchy assembly, characterized by granular fences composed of colloidal silica and liposomes surrounded by empty areas in which amorphous ice originally resided. The biocompatible character of this ice segregation induced self-assembly (ISISA) process that allows for the preservation of the structural integrity of liposomes within the assembly is demonstrated by fluorescence anisotropy performed at the binary colloidal aqueous gels and differential scanning calorimetry and electron microscopy at the hierarchy assembly. The resulting assembly shows an interesting dual character, with one colloidal entity supporting the structure (e.g., silica) and the other providing functionality (e.g., liposomes).

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