Nanoparticle agglutination: acceleration of aggregation rates and broadening of the analyte concentration range using mixtures of various-sized nanoparticles

SiO(2) particles of various sizes were prepared and surface modified with biotin-chain-end-functionalized poly(ethylene glycol). Dispersions of these particles were prepared, and their aggregation was induced upon the addition of avidin. The aggregate size and growth rate were monitored by DLS analysis, and SEM and TEM images of freeze-dried samples of the aggregate solutions were used to confirm the DLS data and to image the aggregate size and dimension. A linear correspondence between apparent diameter and time was observed, and both the 20 and 300 nm particles aggregated at slower rates than for the 40 nm particles. These observations were attributed to differences in the average functionality of the systems and the different initial concentrations of particles and avidin. The observed aggregation rates of binary combinations of the three particle sizes (i.e., 20 + 40 nm or 40 + 300 nm) were faster than those of the single-sized mixtures. These results were attributed to the faster flux of smaller particles toward larger particles in the mixture solutions as well as to the potentially larger number of productive collisions possible between mixtures of small particles and large particles versus only similarly sized particles. Combinations of the three sizes of particles were studied to find an empirical optimum formulation for generating large aggregates on a short time scale and over a wide range of analyte concentrations.     

Nanotribological properties of alkanephosphonic acid self-assembled monolayers on aluminum oxide: effects of fluorination and substrate crystallinity

Two phosphonic acid (PA) self-assembled monolayers (SAMs) are studied on three aluminum oxide surfaces: the C and R crystallographic planes of single crystal alpha-alumina (sapphire) and an amorphous vapor-deposited alumina thin film. SAMs are either fully hydrogenated CH3(CH2)17PO3H2 or semifluorinated CF3(CF2)7(CH2)11PO3H2. Atomic force microscope (AFM) topographic imaging reveals that the deposited films are homogeneous, atomically smooth, and stable for months in the laboratory environment. Static and advancing contact angle measurements agree with previous work on identical or similar films, but receding measurements suggest reduced coverage here. To enable reproducible nanotribology measurements with the AFM, a scanning protocol is developed that leads to a stable configuration of the silicon tip. Adhesion for the semifluorinated films is either comparable to or lower than that for the hydrogenated films, with a dependence on contact history observed. Friction between each film and the tips depends strongly upon the type of molecule, with the fluorinated species exhibiting substantially higher friction. Subtle but reproducible differences in friction are observed for a given SAM depending on the substrate, revealing differences in packing density for the SAMs on the different substrates. Friction is seen to increase linearly with load, a consequence of the tip's penetration into the monolayer.     

Nanoscale conductivity mapping of hybrid nanoarchitectures: ultrathin poly(o-phenylenediamine) on mesoporous manganese oxide ambigels

We use conductive-probe atomic force microscopy (CP-AFM) to characterize and image hybrid electrode structures comprising mesoporous manganese oxide (MnO2) ambigel nanoarchitectures coated with an ultrathin (<10 nm) electrodeposited layer of poly(o-phenylenediamine), PPD. Native MnO2 ambigel films, supported on indium tin oxide (ITO) substrates, exhibit spatially uniform conductivity that correlates well with the topography of the MnO2 film, confirming that the nanoscopic oxide network is effectively wired to the underlying ITO substrate. Following the self-limiting electrodeposition of the PPD coating onto the high-surface-area (>200 m2 g(-1)) MnO2 ambigel, the resulting hybrid structures display an approximately 20-fold reduction in conductivity, as determined from CP-AFM measurements. The CP-AFM imaging studies confirm that the ultrathin, insulating PPD layer conformally and homogeneously coats the conductive nanoarchitecture. CP-AFM imaging of PPD-MnO2 hybrid electrodes following electrochemical cycling in an aqueous acid electrolyte reveals that the ultrathin PPD coating serves as an effective barrier to the electrolyte, protecting the underlying MnO2 nanoarchitecture from electrochemical dissolution.     

Multiple hydrogen bonding for reversible polymer surface adhesion

Specific and reversible adhesion of a terminal thymine-functionalized polystyrene (PS-thymine) was demonstrated for a silicon surface with complementary adenine recognition sites. A novel adenine-containing triethoxysilane (ADPTES), which was suitable for covalent attachment to silanol containing surfaces, was synthesized in one step from adenine and 3-isocyanatopropyl triethoxysilane (IPTES). 1H and 13C NMR spectroscopy and fast atom bombardment mass spectroscopy confirmed the chemical structure, and 29Si NMR spectroscopy indicated the absence of any premature hydrolysis of the alkoxysilane derivative. X-ray photoelectron spectroscopy (XPS) and water contact angle measurements indicated the attachment of PS-thymine to silicon surfaces that were modified with a mixture of ADPTES and 3-mercaptopropyl triethoxysilane (MPTES). PS-thymine attachment to surfaces that were modified with only MPTES was not observed. The exclusive attachment of PS-thymine to an ADPTES/MPTES-modified surface confirmed hydrogen bonding-mediated adenine-thymine association to silicon surfaces containing a sufficiently low concentration of adenine recognition sites. Although PS-thymine attachment to the ADPTES/MPTES-modified surfaces was insensitive to THF rinsing, the PS-thymine was completely removed from the surface upon DMSO rinsing because of the disruption of adenine-thymine hydrogen bonding with a more polar aprotic solvent. PS-thymine was successfully reattached to the ADPTES/MPTES-modified surface following the DMSO rinse, demonstrating the solvato-reversible nature of the adenine-thymine association.     

Morphologies of multicompartment micelles formed by ABC miktoarm star terpolymers

Several new multicompartment micellar structures have been identified by cryogenic transmission electron microscopy (cryoTEM) from the aqueous self-assembly of mu-[poly(ethylethylene)][poly(ethylene oxide)][poly(perfluoropropylene oxide)] (mu-EOF) miktoarm star terpolymers. This work extends our previous studies, in which it was found that, upon decreasing the length of the hydrophilic block (O), the resulting micelles evolved from "hamburger" micelles to segmented worms and ultimately to nanostructured bilayers and vesicles. In the terpolymers examined here segmented ribbons and bilayers were found at an intermediate composition between segmented worms and nanostructured bilayers, provided that the fluoropolymer (F) was the minority component in the micelle core. On the other hand, when the F block exceeded the chain length of the hydrocarbon block (E), the superhydrophobic F block imposed a "double frustration" on the self-assembly of the mu-EOF(2-9-5) terpolymer; while F prefers to minimize its interfacial contact with the O corona, it must occupy the majority of the micellar core. Therefore, a richer variety of multicompartment micelles, including well-defined segmented worms, raspberry-like micelles, and multicompartmentalized worms, were formed from one terpolymer, as revealed by cryoTEM. Despite the complexity and variety of the observed aggregate morphologies, a small number of common structural elements can be invoked to interpret the observed micelles and to relate a given structure to the terpolymer composition.     

Atmospheric chemistry of perfluoroaldehydes (CxF2x+1CHO) and fluorotelomer aldehydes (CxF2x+1CH2CHO): quantification of the important role of photolysis

The UV absorption spectra of CF(3)CHO, C(2)F(5)CHO, C(3)F(7)CHO, C(4)F(9)CHO, CF(3)CH(2)CHO, and C(6)F(13)CH(2)CHO were recorded over the range 225-400 nm at 249-297 K. C(x)F(2)(x)(+1)CHO and C(x)F(2)(x)(+1)CH(2)CHO have broad absorption features centered at 300-310 and 290-300 nm, respectively. The strength of the absorption increases with the size of the C(x)F(2)(x)(+1) group. There was no discernible (<5%) effect of temperature on the UV spectra. Quantum yields for photolysis at 254 and 308 nm were measured. Quantum yields at 254 nm were 0.79 +/- 0.09 (CF(3)CHO), 0.81 +/- 0.09 (C(2)F(5)CHO), 0.63 +/- 0.09 (C(3)F(7)CHO), 0.60 +/- 0.09 (C(4)F(9)CHO), 0.74 +/- 0.08 (CF(3)CH(2)CHO), and 0.55 +/- 0.09 (C(6)F(13)CH(2)CHO). Quantum yields at 308 nm were 0.17 +/- 0.03 (CF(3)CHO), 0.08 +/- 0.02 (C(4)F(9)CHO), and 0.04 +/- 0.01 (CF(3)CH(2)CHO). The quantum yields decrease with increasing size of the C(x)F(2)(x)(+1) group and with increasing wavelength of the photolysis light. The photolysis quantum yield at 308 nm for CF(3)CHO measured here is a factor of at least 8 greater than that reported previously. Photolysis is probably the dominant atmospheric fate of C(x)F(2)(x)(+1)CHO (x = 1-4) and is an important fate of C(x)F(2)(x)(+1)CH(2)CHO (x = 1 and 6). These results have important ramifications concerning the yield of perfluorocarboxylic acids in the atmospheric oxidation of fluorotelomer alcohols.     

Assessing the reproducibility of an analytical method

The reproducibility of a validated analytical method may require reassessment because of various reasons, such as the transfer between laboratories or companies, changes in the instruments or software platforms (or both), or changes in critical reagents, among others. This paper is a demonstration of an assay bridging study in evaluating reproducibility. The approach is simple but very informative and offers many advantages over existing approaches.     

Real-time in situ monitoring of human prostate photodynamic therapy with diffuse light

Photodynamic therapy (PDT) requires oxygen to cause cellular and vascular tumor damage. Tissue oxygen concentration, in turn, is influenced by blood flow and blood oxygenation. Real-time clinical measurement of these hemodynamic quantities, however, is rare. This paper reports the development and application of a probe, combining diffuse reflectance spectroscopy (DRS) for measurement of tumor blood oxygenation and diffuse correlation spectroscopy (DCS) for measurement of tumor blood flow. The instrument was adapted for clinical use during interstitial prostate PDT. Three patients with locally recurrent prostate cancer received 2 mg/ kg motexafin lutetium (MLu) 3 h before illumination and a total light dose of 100 J/cm(2) at 150 mW/cm. Prostrate blood oxygen saturation (StO2) decreased only slightly (approximately 3%) after treatment. On the other hand, prostate blood flow and total hemoglobin concentration over the course of PDT decreased by 50% and 15%, respectively, suggesting MLu-mediated PDT has an anti-vascular effect. While it is certainly impossible to draw definite conclusions from measurements of only three patients, the observed differences in tumor blood flow and blood oxygenation responses during PDT can, in principle, be used to choose among tissue oxygen consumption models and therefore emphasize the potential clinical value for simultaneous monitoring of both parameters.     

Anionic ring-opening polymerization of a strained phosphirene: a route to polyvinylenephosphines

A strained 1-phenyl-2,3-dimethylphosphirene undergoes anionic ring-opening polymerization upon initiation with n-butyl lithium at ambient temperature to yield polyvinylenephosphine, an unsaturated organophosphorus polymer.     

Tuning electron transfer through p-phenyleneethynylene molecular wires

Weak wire-like behavior-with a damping factor (beta) of 0.2 +/- 0.05 A(-1)--has been found in a series of C60-wire-exTTF systems (i.e., p-phenyleneethynylene): these results contrast with previous observations involving p-phenylenevinylene systems.