The preparation of cobalt oxide nanowires with gold nanoparticle (AuNP) inclusions (Au-Co(3)O(4) nanowires) via colloidal polymerization of dipolar core-shell NPs is reported. Polystyrene-coated ferromagnetic NPs composed of a dipolar metallic cobalt shell and a gold NP core (PS-AuCoNPs) were synthesized by thermolysis of octacarbonyldicobalt [Co(2)(CO)(8)] in the presence of AuNP seeds and polymeric ligands. The colloidal polymerization process of these dipolar PS-AuCoNPs comprises dipolar nanoparticle assembly and solution oxidation of preorganized NPs to form interconnected cobalt oxide nanowires via the nanoscale Kirkendall effect, with AuNP inclusions in every repeating unit of the one-dimensional mesostructure. Calcination of the polymer-coated nanowires afforded polycrystalline Au-Co(3)O(4) nanowires that were determined to be electroactive. Nanocomposite materials were characterized by transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction, vibrating sample magnetometry, and cyclic voltammetry. We demonstrate that the optical and electrochemical properties of Au-Co(3)O(4) nanowires are significantly enhanced in comparison with hollow Co(3)O(4) nanowires prepared via colloidal polymerization.

Reversible electron injection into pyridine-capped CdSe nanocrystals (pyr-CdSe NCs), tethered to indium-tin oxide (ITO) substrates using mercaptoalkylcarboxylic acids, is characterized using attenuated total reflectance (ATR) spectroelectrochemistry on a planar waveguide. The sensitivity of this technique provides for characterization of redox processes in submonolayer films of pyr-CdSe NCs. Optically determined onset potentials for electron injection, measured as bleaching/recovery of the exciton absorption band, provide estimates for the conduction band edge (E CB ). Potential-modulated attenuated total reflectance (PM-ATR), in which the in-phase and out-of-phase reflectance response is measured as a function of modulation frequency, provides estimates for rates of electron injection. These apparent rate constants are found to be nearly independent of tether chain length, suggesting that communication between tethered NCs and electrochemically less active (i.e., less conductive) regions on the ITO surface is rate-limiting.

We present a method of fabricating microneedles from polyvinylpyrrolidone (PVP) that enables delivery of intact proteins (or peptides) to the dermal layers of the skin. PVP is known to self-assemble into branched hollow fibers in aqueous and alcoholic solutions; we utilized this property to develop dissolvable patches of microneedles. Proteins were dissolved in concentrated PVP solution in both alcohol and water, poured into polydimethylsiloxane templates shaped as microneedles and, upon evaporation of solvent, formed into concentric, fibrous, layered structures. This approach of making PVP microneedles overcomes problems in dosage, uniform delivery and stability of protein formulation as compared to protein-coated metallic microneedles or photopolymerized PVP microneedles. Here we characterize the PVP microneedles and measure the delivery of proteins into skin. We show that our method of fabrication preserves the protein conformation. These microneedles can serve as a broadly useful platform for delivering protein antigens and therapeutic proteins to the skin, for example for allergen skin testing or immunotherapy.

Charge transfer kinetics in immobilized, redox-active films have been studied using both cyclic voltammetry (CV) and electroreflectance (ER) techniques by other groups. 1,2 In these studies, rate constants obtained using ER techniques were higher than those determined from CV data, as observed here. This systematic difference can be explained by considering the following: Adsorption of a monolayer of molecules on a chemically and structurally heterogeneous electrode (e.g., indium-tin oxide) will generate a film that is chemically, structurally and energetically heterogeneous. This heterogeneity will be reflected in a distribution of thermodynamic formal potentials (E 0 ') and apparent rate constants for electron transfer. 3,4 In CV, the potential is scanned over a relatively large range (here it was -250 mV to 250 mV vs Ag/AgCl). At potentials well away from E 0 ' (i.e., at the extremes of the scan range), the large overpotential (E app -E 0 ') provides a sufficient driving force to oxidize and reduce all of the electroactive molecules in the film. In PM-ATR, a modulated potential (E ac ) is applied about the mid-point potential (E dc ) between the anodic and cathodic peaks (E dc ≈ E 0 '). The modulation range, E dc ± E ac , is typically less than 50% of the scan range used in CV (here E dc ± E ac was 44 mV). Thus in PM-ATR, only the subpopulation of electroactive molecules that are oxidized and reduced within E dc ± E ac are probed. This subpopulation should equilibrate more rapidly with the modulated electrode potential (i.e., have a higher k 0 ) relative to the remainder of the film, and thus the k 0 measured for this subpopulation by PM-ATR is expected to be greater than that measured for the entire film by CV.

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Potential modulated attenuated total reflectance (PM‐ATR) spectroscopy has been employed to study charge transfer processes in Prussian blue (PB) films deposited on indium tin oxide (ITO) electrodes. PM‐ATR is a planar waveguide‐based spectroelectrochemical technique in which the optical response of an electroactive film is measured as a function of applied potential and modulation frequency. The multiple internal reflection geometry of PM‐ATR provides a significant sensitivity advantage over the single external reflectance geometry that has been employed in most prior electroreflectance studies. The apparent electron transfer rate of PB on ITO obtained using PM‐ATR was compared to that obtained with conventional cyclic voltammetry; the respective rates, 0.33 ± 0.15 s−1 (n = 3) and 0.71 ± 0.37 s−1 (n = 10), are in good agreement.