Many layers make light work: Layer‐by‐layer (LbL) self‐assembly of a dendritic porphyrin (red; see picture) and poly(allylamine hydrochloride) (blue) on polystyrene nanoparticles followed by removal of the polystyrene core produces multifunctional hollow nanocapsules. These species can be both loaded with anticancer drugs and used in photodynamic therapy (PDT) and therefore have potential in combined cancer therapy.

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Poly(ethylene glycol)(PEG)-based interpenetrating polymeric network (IPN) hydrogels were prepared for the application of enzyme immobilization. Poly(acrylamide)(PAAm) was chosen as the other network of IPN hydrogel and different concentration of PAAm networks were incorporated inside the PEG hydrogel to improve the mechanical strength and provide functional groups that covalently bind the enzyme. Formation of IPN hydrogels was confirmed by observing the weight per cent gain of hydrogel after incorporation of PAAm network and by attenuated total reflectance/ Fourier transform infrared (ATR/FTIR) analysis. Synthesis of IPN hydrogels with higher PAAm content produced more crosslinked hydrogels with lower water content (WC), smaller M c and mesh size, which resulted in enhanced mechanical properties compared to the PEG hydrogel. The IPN hydrogels exhibited tensile strength between 0.2 and 1.2 MPa while retaining high levels of hydration (70-81% water). For enzyme immobilization, glucose oxidase (GOX) was immobilized to PEG and IPN hydrogel beads. Enzyme activity studies revealed that although all the hydrogels initially had similar enzymatic activity, enzyme-immobilizing PEG hydrogels lost most of the enzymatic activity within 2 days due to enzyme leaching while IPN hydrogels maintained a maximum 80% of the initial enzymatic activity over a week due to the covalent linkage between the enzyme and amine groups of PAAm.

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Nanofiber-based protein microarrays were fabricated through a combination of electrospinning and hydrogel lithography. Electrospinning generated polystyrene (PS)/poly(styrene-alt-maleic anhydride) (PSMA) fibers with diameters ranging from 0.5 to 1.0 mm and photopatterning of poly(ethylene glycol) (PEG) hydrogel on the electrospun fibers created clearly defined hydrogel microstructures with incorporated nanofibers. The resultant micropatterned nanofibrous substrates were obtained as freestanding and bidirectionally porous sheets, where most of the nanofibers were inserted through the side walls of the hydrogel microstructures. Because of the protein-repellent nature of PEG hydrogels, IgG was selectively immobilized only within the nanofibrous region, creating an IgG microarray. Due to increased surface area, IgG loading in nanofibrous substrates was about six times greater than on planar substrates, which consequently yielded a higher fluorescence signal and faster reaction rate in immunoassays. The capability of encapsulating enzymes made it possible for PEG hydrogels to be used not only for defining protein micropatterns but also for additional biosensor elements. Based on this result, micropatterned nanofibrous substrates consisting of IgG-immobilized nanofibers and enzymeentrapping PEG hydrogels were fabricated, and their potential to simultaneously carry out both immunoassays and enzyme-based assays was successfully demonstrated.

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In this study, we immobilized enzymes by combining covalent surface immobilization and hydrogel entrapment. A model enzyme, glucose oxidase (GOX), was first covalently immobilized on the surface of silica nanoparticles (SNPs) via 3‐aminopropyltriethoxysilane (APTES), and the resultant SNP‐immobilized enzyme was physically entrapped within photopolymerized hydrogels prepared from two different molecular weights (MWs) (575 and 8000 Da) of poly(ethylene glycol)(PEG). The hydrogel entrapment resulted in a decrease in reaction rate and an increase in apparent Km of SNP‐immobilized GOX, but these negative effects could be minimized by using hydrogel with a higher MW PEG, which provides higher water content and larger mesh size. The catalytic rate of the PEG 8000 hydrogel was about ten times faster than that of the PEG 575 hydrogel because of enhanced mass transfer. Long‐term stability test demonstrated that SNP‐immobilized GOX entrapped within hydrogel maintained more than 60% of its initial activity after a week, whereas non‐entrapped SNP‐immobilized GOX and entrapped GOX without SNP immobilization maintained less than 20% of their initial activity. Incorporation of SNPs into hydrogel enhanced the mechanical strength of the hydrogel six‐fold relative to bare hydrogels. Finally, a hydrogel microarray entrapping SNP‐immobilized GOX was fabricated using photolithography and successfully used for quantitative glucose detection. Copyright © 2009 John Wiley & Sons, Ltd.

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