The electrochemical quartz crystal microbalance (EQCM) was used to directly measure the dissolution rate at cathodic potentials, and thus the cathodic corrosion rate, of thin-film analogs of phases in AA2024. Thin films of pure Al, Al-4% Cu, and Al 2 Cu were studied in 0.1 M NaCl containing 0, 10 -4 , or 10 -2 M Cr 2 O 7 . A range of cathodic potentials was studied for each material. The true cathodic current density was calculated from the difference of the net current density and the dissolution rate, which was determined by the EQCM. For pure Al and Al-4Cu, the cathodic corrosion rate was large relative to the net current density, so the true cathodic current density was considerably larger than the measured net current density. The cathodic current density was almost identical to the net current density for Al 2 Cu because the dissolution rate was very small compared to the cathodic reaction rate. Various potentials in the limiting oxygen reduction reaction region were examined, but the effect of the applied potential was small. The presence of dichromate in solution decreased both the cathodic corrosion rate and the cathodic current density on these thin-film analogs. In particular, it decreased more effectively the cathodic reaction rate on Al 2 Cu, which can support faster cathodic reaction rates.

per sphere can be tuned by the concentration of NCs used. Multicolor-coded microspheres have also been realized by incorporating different-sized CdTe NCs into one sphere. As the concentration of NCs in the gel is too small to cause complicated excitonic or electronic interactions between them, the emission color of the resulting multicolor-coded spheres is mainly determined by the ratio of the different-sized NCs. Our preliminary experiments demonstrate that our protocol can be generalized to trap other water-soluble NCs, such as Au and c-Fe 2 O 3 within hydrogel spheres. To load NCs of different size and composition into hydrogel spheres is a topic of ongoing research in our laboratory. Due to the biocompatibility and the flexibility of the modification of surfaces of hydrogel spheres, such NC-loaded microspheres should hold promising prospects in biological applications. In addition, since the loaded CdTe NCs can be released from the PNIPVP spheres, triggered by pH, our protocol also provokes an opportunity for delivery of NCs and even their bioconjugates if considering NCs as a new sort of drug. [12] Experimental N-Isopropylacrylamide (250 mg), 4-vinylpyridine (10 lL), potassium persulfate (20 mg), and N,N¢-methylenebisacrylamide (25 mg) were dissolved in 25 mL of water. The polymerization was conducted at 70 C for 4 h under N 2 . The as-prepared PNIPVP spheres were purified by centrifugation at 2000 g for 10 min and redispersed in water.After incubating PNIPVP spheres with CdTe NCs solution at pH 3 for 5 min, the pH of the mixture was adjusted to pH 4. Upon decanting the supernatant containing excess CdTe NCs after centrifugation at 2000 g for 10 min, CdTe-PNIPVP spheres were redispersed in water of pH 7. To determine the amount of loaded NCs, the absorbance spectra of CdTe-PNIPVP spheres were recorded by using a Cary 50 UV-visible spectrophotometer. In our absorbance measurements, the diffuse reflectance mode was utilized to reduce the strong scattering of the gel spheres. The number of CdTe-PNIPVP spheres was determined by SPLS. Details of the SPLS experimental system and measurement have been described elsewhere [10].Release experiments were conducted by incubating CdTe-PNIPVP spheres in aqueous solutions with pHs ranging from 4 to 13, adjusted by adding 1 M NaOH solution. After removal of CdTe-PNIPVP or PNIPVP spheres by 10 min centrifugation at 2000 g, the supernatants containing released CdTe NCs were analyzed by UV-vis absorption spectroscopy. The release period included the centrifugation time. Using a higher centrifugation speed of 10 000 g, one is able to release most of the loaded CdTe NCs in 1 min. DLS measurements were implemented by a Malvern Zetasizer 3000HS. TEM images were obtained using a Philips CM 120 microscope operating at 80 kV. Luminescence spectra were obtained with a Spex Fluorolog 1680 spectrophotometer (the excitation wavelength is 400 nm). Porous materials possessing ordered pores with well-defined pore size distributions have been studied by many researchers for a long time, ...

We report a microfluidic strategy for creating semipermeable microgels containing metal nanoparticles to directly detect small molecules included in the solution of large adhesive proteins using surface-enhanced Raman scattering. With a capillary microfluidic device, gold nanoparticle-laden microgels are prepared to have uniform size. The microgels allow diffusion of smaller molecules than mesh size of their gel network while excluding larger molecules. This enables the selective infusion of small analytes onto the surface of gold nanoparticles from the solutions of adhesive proteins, thereby providing high Raman intensity by metal-surface enhancement; otherwise, proteins adsorb the surface, which significantly reduces the intensity. Therefore, this microgel platform enables the direct detection of analytes from biological fluids and obviates complicated pre- or post-treatment of samples. In addition, the microgels are able to be injected into target volume such as vessels or living organisms, which are then either recovered for analysis or potentially analyzed in situ. This simple but pragmatic method will provide new opportunity in a wide range of molecular detection applications based on Raman spectrum.

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We investigate the effect of functional groups of pyrene molecules on the electrical sensing performance of single-walled carbon nanotubes (SWNTs) based DNA biosensor, in which pyrenes with three different functional groups of carboxylic acid (Py-COOH), aldehyde (Py-CHO) and amine (Py-NH2) are used as linker molecules to immobilize DNA on the SWNT films. UV/Visible absorption spectra results show that all of the pyrene molecules are successfully immobilized on the SWNT surface via pi-pi stacking interaction. Based on fluorescence analysis, we show that the amide bonding of amine terminated DNA via pyrene containing carboxylic groups is the most efficient to immobilize DNA on the nanotube film. The electrical detection results show that the conductance of Py-COOH modified SWNT film is increased upon DNA immobilization, followed by further increase after hybridization of target DNAs. It indicates that the pyrene molecules with carboxylic acid groups play an important role to achieve highly efficient label-free detection by nondestructive and specific immobilization of DNAs.

The effect of network density of single-walled carbon nanotubes (SWNTs) on the detection of DNA hybridization was investigated. The results show that, in contrast to those having higher densities, SWNTs with low network densities in the conductance range of 0.74 × 10 -7 < G bare < 2.00 × 10 -7 exhibit high sensitivity for detection of immobilized DNAs. The resulting SWNT devices with optimal network densities showed good selectivity in detecting cDNA hybridization. The network density control will provide opportunities to realize practical label free biosensor utilizing commercially available SWNT networks.

A new strategy for fabricating highly ordered chitosan–Au core–shell nano­patterns with tunable surface plasmon resonance (SPR) properties is developed. This strategy combines fabrication of a chitosan nanopattern by using a soft‐nanoimprint technique with selective deposition of Au nanoparticles onto the patterned chitosan surface. The SPR response can be tuned by controlling the features of the resulting Au shell/polymer hybrid pattern, which makes these materials potentially useful in ultrasensitive optical sensors for molecular detection.