Surface plasmon resonance was used to measure binding of proteins from solution to poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes end-grafted from gold surfaces by atom transfer radical polymerization (ATRP). PDMAEMA brushes were prepared with a variety of grafting densities and degrees of polymerization. These brushes displayed charge selective protein uptake. The extent of uptake for net negatively charged bovine serum albumin (BSA) scaled linearly with the surface mass concentration of grafted PDMAEMA, regardless of grafting density. BSA was bound at a constant ratio of 120 DMAEMA monomer units per protein molecule for all brushes examined. The equivalent three-dimensional concentration of BSA bound in the brush (i.e., the bound BSA surface excess concentration divided by the brush thickness) decreased monotonically with decreasing grafting density. The concentration of BSA bound within brushes prepared at higher grafting densities was comparable with the aqueous protein solubility limit. BSA desorption from the brush required changes in solution pH and/or ionic strength to eliminate its net electrostatic attraction to PDMAEMA. Net positively charged lysozyme was completely rejected by the PDMAEMA brushes.

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We report the synthesis of CdS quantum dot (QD)-poly(acrylate) nanocomposites using a recently developed catalytic system where activators are generated by electron transfer for atom-transfer radical polymerization (ATRP) in a miniemulsion. The QD surface was functionalized with a tris(alkyl)phosphine, previously modified with an ATRP chlorine initiator, and subsequent controlled polymerization was carried out from the functionalized surface of nanoparticles. The final material showed a high homogeneity and the QDs were evenly dispersed. The optical-absorption edge in the visible spectra of the nanocomposites attests the presence of the CdS QDs. Quantum confinement effects were assigned, though a blue shift in relation to the optical spectrum of the initial QDs has been observed.

The particular properties of nanometer-sized inorganic materials are of central importance to the design of modern composite materials such as polymer composites, coatings, or cosmetic products where particle additives are used to improve mechanical, thermal, transport, or optical properties. [1][2][3][4][5][6][7] However, in many instances the improvement of some performance characteristic is compromised by a loss in transparency that results from the scattering of visible light by the embedded particle inclusions -a consequence of the significantly different refractive index n of most inorganic materials and the organic embedding medium. For applications that capitalize on optical transparency, the scattering of particle inclusions presents severe limitations to the maximum concentration of filler particles as well as the design possibilities of the organic-matrix composites. For optically isotropic particles with linear dimensions significantly less than the wavelength of light, the particle scattering cross-section is given by C sca ∼ V p 2 (Da) 2 (with V p denoting the particle volume and Da the polarizability of the particle within the embedding medium). [8,9] Since Da ∼ (e p -e m )/(e p + 2e m ) >> 0 (with e i = n i 2 denoting the dielectric constant of medium 'i'; 'p', and 'm' represent the particle and embedding medium, respectively) for most inorganic/organic material combinations, significant scattering can arise even for small particle sizes.In this Communication we demonstrate that the scattering of inorganic particles can efficiently be suppressed by grafting of polymers of appropriate composition, molecular weight, and grafting density from the particles' surface such as to match the effective dielectric constant of the resulting coreshell particle to the dielectric constant of the embedding medium. Key to the presented approach is the observation that for core-shell particles with a size less than the wavelength of light the optical properties are approximately equal to those of a homogeneous particle with an effective dielectric constant that depends on the optical properties and volume fractions of the respective constituents.[10] In particular, for a core-shell particle at wavelengths larger than the particle dimension the particles' effective dielectric constant is given by Maxwell-Garnett theory as e eff e shell 1 3 fx 1 À fx 1Here, x = 1/3 (e core -e shell )/(e core -1/3 (e core -e shell )), e core and e shell represent the dielectric constant of the particle-core and shell, respectively, and f = V core /(V core + V shell ) is the relative particle-core volume. [11][12][13][14][15][16] Scattering will be suppressed if the effective dielectric constant of the core-shell particle equals the dielectric constant of the embedding medium. [10,17] Equation 1 thus provides a design criterion for the synthesis of quasi-transparent particle additives, i.e., by grafting a shell with a dielectric constant greater than (less than) the one of the embedding media to a particle core that has a dielectri...