Enzyme-catalyzed synthesis of a phenolic polymer within layer-by-layer (LbL) constructed polyelectrolyte microcapsules has been introduced. This approach is based on selective permeability of capsule walls for monomer molecules, while biocatalyst and forming polymeric chains cannot leave capsules interior because of high molecular weight. Horseradish peroxidase was encapsulated into four bilayer poly(styrenesulfonate)/poly(allylamine hydrochloride) capsules with an average diameter of 5 µm using pH-driven pore opening. 4-(2-Aminoethyl)phenol hydrochloride (tyramine) was used as a monomer giving easily detectable fluorescent polymeric products after addition of hydrogen peroxide into the system. Filling of the capsules with polymer was confirmed by different methods (AFM, quartz crystal microbalance, and confocal microscopy).

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This study presents the results of polymerization of phenol to yield fluorescent polymer encapsulated within shells fabricated via layer-by-layer (L-b-L) assembly. Hollow polyelectrolyte microcapsules (shells) were prepared using weakly cross-linked melamine formaldehyde (MF) particles. Dissolution of the MF cores was achieved by changing the pH of the solution. Horseradish peroxidase (HRP), the catalyzing enzyme, was loaded in these capsules by taking advantage of the “open/close” mechanism of the capsules by altering the pH. The empty shells were then suspended in a concentrated solution of monomer. Since the monomer is a low molecular weight species, it freely permeates through the polyion wall into the shells. Addition of aliquots of hydrogen peroxide initiated the polymerization reaction and the polymer formed from the ensuing reaction was confined in the shells due to its high molecular weight. The model used for demonstrating this synthesis is polymerization of 4-(2-aminoethyl) phenol hydrochloride commonly known as tyramine hydrochloride to its corresponding polymeric form by reacting it with hydrogen peroxide. Fluorescence spectrometry (FS), confocal laser scanning microscopy (CLSM), and atomic force microscopy (AFM) were the characterization methods employed to confirm polymerization in situ shells.

In order to refine further the material technology for tin-oxide based gas sensing we are exploring the use of precision nanoparticle deposition for the sensing layer. Layers of SnO 2 nanoparticles were grown on Quartz Crystal Microbalance (QCM) resonators using the layer-bylayer self-assembly technique. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Electron Diffraction Pattern (EDP) analyses were performed on the selfassembled layers of Sn0 2 nanoparticles. The results showed that Sn02 nanoparticle films are deposited uniformly across the substrate. The size of the nanoparticles is estimated to be about 3-5 nm. Electrical characterization was done using standard current-voltage measurement technique, which revealed that Sn02 nanoparticle films exhibit ohmic behavior. Calcination experiments have also been carried out by baking the substrate (with self-assembled nanoparticles) in air at 350'C. Results show that 50%-70% of the polymer layers (which are deposited as precursor layers and also alternately in-between Sn02 nanoparticle monolayers) are eliminated during the process.