Visual and Fluorescent Detection of Tyrosinase Activity by Using a Dual-Emission Ratiometric Fluorescence Probe

In this work, we designed a dual-emission ratiometric fluorescence probe by hybridizing two differently colored quantum dots (QDs), which possess a built-in correction that eliminates the environmental effects and increases sensor accuracy. Red emissive QDs were embedded in the silica nanoparticle as reference while the green emissive QDs were covalently linked to the silica nanoparticle surface to form ratiometric fluorescence probes (RF-QDs). Dopamine (DA) was then conjugated to the surface of RF-QDs via covalent bonding. The ratiometric fluorescence probe functionalized with dopamine (DA) was highly reactive toward tyrosinase (TYR), which can catalyze the oxidization of DA to dopamine quinine and therefore quenched the fluorescence of the green QDs on the surface of ratiometric fluorescence probe. With the addition of different amounts of TYR, the ratiometric fluorescence intensity of the probe continually varied, leading to color changes from yellow-green to red. So the ratiometric fluorescence probe could be utilized for sensitive and selective detection of TYR activity. There was a good linear relationship between the ratiometric fluorescence intensity and TYR concentration in the range of 0.05–5.0 μg mL^–1, with the detection limit of 0.02 μg mL^–1. Significantly, the ratiometric fluorescence probe has been used to fabricate paper-based test strips for visual detection of TYR activity, which validates the potential on-site application

Thermal assisted ultrasonic embossing (a) schematic process; (b) the force and amplitude in an ultrasonic embossing process.

<p>Thermal assisted ultrasonic embossing (a) schematic process; (b) the force and amplitude in an ultrasonic embossing process.</p

SEM images of embossed microstructure (a) longitudinal-stripe style; (b) checked style.

<p>SEM images of embossed microstructure (a) longitudinal-stripe style; (b) checked style.</p

How Does Domain Replacement Affect Fibril Formation of the Rabbit/Human Prion Proteins

<div><p>Background</p><p>It is known that <i>in vivo</i> human prion protein (PrP) have the tendency to form fibril deposits and are associated with infectious fatal prion diseases, while the rabbit PrP does not readily form fibrils and is unlikely to cause prion diseases. Although we have previously demonstrated that amyloid fibrils formed by the rabbit PrP and the human PrP have different secondary structures and macromolecular crowding has different effects on fibril formation of the rabbit/human PrPs, we do not know which domains of PrPs cause such differences. In this study, we have constructed two PrP chimeras, rabbit chimera and human chimera, and investigated how domain replacement affects fibril formation of the rabbit/human PrPs.</p><p>Methodology/Principal Findings</p><p>As revealed by thioflavin T binding assays and Sarkosyl-soluble SDS-PAGE, the presence of a strong crowding agent dramatically promotes fibril formation of both chimeras. As evidenced by circular dichroism, Fourier transform infrared spectroscopy, and proteinase K digestion assays, amyloid fibrils formed by human chimera have secondary structures and proteinase K-resistant features similar to those formed by the human PrP. However, amyloid fibrils formed by rabbit chimera have proteinase K-resistant features and secondary structures in crowded physiological environments different from those formed by the rabbit PrP, and secondary structures in dilute solutions similar to the rabbit PrP. The results from transmission electron microscopy show that macromolecular crowding caused human chimera but not rabbit chimera to form short fibrils and non-fibrillar particles.</p><p>Conclusions/Significance</p><p>We demonstrate for the first time that the domains beyond PrP-H2H3 (β-strand 1, α-helix 1, and β-strand 2) have a remarkable effect on fibrillization of the rabbit PrP but almost no effect on the human PrP. Our findings can help to explain why amyloid fibrils formed by the rabbit PrP and the human PrP have different secondary structures and why macromolecular crowding has different effects on fibrillization of PrPs from different species.</p></div

Synthesis and Characterization of Novel BiVO₄/Ag₃VO₄ Heterojunction with Enhanced Visible-Light-Driven Photocatalytic Degradation of Dyes

Development of efficient photocatalysts for environmental remediation under visible light conditions has obtained much attention in recent years. In this study, the novel BiVO₄/Ag₃VO₄ heterojunction has been successfully fabricated via a hydrothermal process and a facile precipitation reaction. The organic dye Rhodamine B (RhB) was chosen to explore the photocatalytic performance, and it was found that the synthetic sample at 10:1 mol ratio of BiVO₄:Ag₃VO₄ had the highest photocatalytic activity among all the photocatalysts. The RhB was completely degraded (95.9%) under visible light irradiation in 20 min, which was 10 times and 3.4 times higher than those of pristine BiVO₄ and Ag₃VO_4, respectively. Furthermore, the A/10B sample also showed superior degradation activity on the other organic dyes such as methyl blue (MB), methyl red (MR), and methyl violet (MV). It is assumed that the enhanced photocatalytic property could be ascribed to the heterojunction, leading to an effective separation of the photogenerated charges carriers. The responsible photocatalytic mechanism is discussed based on the active species trapping experiments and ESR, and it was found that h⁺ and •OH are for the photocatalytic process

The dimensions of the micro patterns for different molds.

<p>The dimensions of the micro patterns for different molds.</p

The relationship between embossing parameters (a) replication rate; (b) replication uniformity.

<p>The relationship between embossing parameters (a) replication rate; (b) replication uniformity.</p

The analysis of variance results of embossing parameters.

<p>The analysis of variance results of embossing parameters.</p

The temperature testing system (a) schematic of the system; (b) position of the thermocouples.

<p>The temperature testing system (a) schematic of the system; (b) position of the thermocouples.</p

Kinetic parameters of amyloid formation of human chimera or rabbit chimera in the absence and presence of Ficoll 70 or Ficoll 400 by ThT binding assays at 37°C.

<p>Best-fit values of these kinetic parameters were derived from non-linear least squares modeling of a sigmoidal equation as described in the “<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113238#s2" target="_blank">Materials and Methods</a>” to the data plotted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0113238#pone-0113238-g001" target="_blank">Fig. 1</a>. Errors shown are ± S.E.</p><p>Kinetic parameters of amyloid formation of human chimera or rabbit chimera in the absence and presence of Ficoll 70 or Ficoll 400 by ThT binding assays at 37°C.</p