Sensitivity enhancement of an open-cavity-based optoacoustic sensor.

We present a new method for sensitive ultrasound detection using an open-cavity optoacoustic sensor. Our results have demonstrated significant enhancement of detection sensitivity when the open-cavity sensor is used in media with large isothermal compressibility. A near-linear relationship between detected optoacoustic signal strength and isothermal compressibility has been found.

Cell-shape assemblage and nanostructure of akaganéite bioformed in FeCl2 solutions.

Akaganéite (ß-FeOOH) with a tunnel structure typically occupied by chloride can undergo anion-exchange reactions in aqueous solutions for pollutant removal. In this work, we studied bioformation of akaganéite in FeCl2 solutions with Acidithiobacillus ferrooxidans cells at pH 2.9, during 36-h incubation. The obtained products were analyzed and characterized by XRD, FTIR, EDS, FETEM, and HRTEM. Results showed that in acidic media with pH 2.9, the cells facilitated ferrous biooxidation and ferric precipitation. The resulting ferric precipitates were identified as polycrystalline akaganéite powders and had a morphology of nanospindles with a length of less 100 nm. The correlatively chemical formula for akaganéite collected at 1 h was reckoned as Fe8O8(OH)6.71(Cl)1.29 with 6.6% Cl. It was observed that ferric precipitates along exterior structures of cells or their extruded organic polymers grew and assembled into cellular shape. The evolved cell-shape akaganéite assemblages were twice of cells (about 2 µm) in size. These results could contribute to understanding of laboratorial bioformation of akaganéite and its biomineralization in acidic environments and promoting its practical applications.

Studying the effect of PDA@CeO2 nanoparticles with antioxidant activity on the mechanical properties of cells.

Studying the influence of nanomaterials on the microstructure and mechanical properties of cells is essential to guide the biological applications of nanomaterials. In this article, the effects of the first synthesized PDA@CeO2 nanoparticles (NPs) with multiple ROS scavenging activities on cell ultra-morphology and mechanical properties were investigated by atomic force microscopy (AFM). After the cells were exposed to PDA@CeO2 NPs, there was no obvious change in cell morphology, but the Young's modulus of the cells was increased. On the contrary, after the cells were damaged by H2O2, the secreted molecules appeared on the cell surface, and the Young's modulus was decreased significantly. However, PDA@CeO2 NPs could effectively inhibit the reduction of the Young's modulus caused by oxidative stress damage. PDA@CeO2 NPs could also protect F-actin from oxidative stress damage and maintain the stability of the cytoskeleton. This work investigates the intracellular antioxidant mechanism of nanomaterials from the changes in the microstructure and biomechanics of living cells, providing a new analytical approach to explore the biological effects of nanomaterials.

Receptor-mediated cellular uptake of folate-conjugated fluorescent nanodiamonds: a combined ensemble and single-particle study.

Fluorescent nanodiamonds (FNDs) are nontoxic and photostable nanomaterials, ideal for long-term in vivo imaging applications. This paper reports that FNDs with a size of approximately 140 nm can be covalently conjugated with folic acid (FA) for receptor-mediated targeting of cancer cells at the single-particle level. The conjugation is made by using biocompatible polymers, such as polyethylene glycol, as crosslinked buffer layers. Ensemble-averaged measurements with flow cytometry indicate that more than 50% of the FA-conjugated FND particles can be internalized by the cells (such as HeLa cells) through receptor-mediated endocytosis, as confirmed by competitive inhibition assays. Confocal fluorescence microscopy reveals that these FND particles accumulate in the perinuclear region. The absolute number of FNDs internalized by HeLa cells after 3 h of incubation at a particle concentration of 10 microg mL(-1) is in the range of 100 particles per cell. The receptor-mediated uptake process is further elucidated by single-particle tracking of 35-nm FNDs in three dimensions and real time during the endocytosis.

Mussel-inspired functionalization of graphene for synthesizing Ag-polydopamine-graphene nanosheets as antibacterial materials.

Mussels have been shown to attach to virtually all types of inorganic and organic surfaces via their adhesive proteins. The adhesive proteins secreted by mussels contain high concentrations of catechol and amine functional groups, which have similar functional groups with polydopamine (PDA). Inspired by mussels, a mild and environmentally friendly method was used to synthesize Ag nanoparticles (Ag NPs) on functionalized PDA-graphene nanosheets (PDA-GNS) with uniform and high dispersion. First, a uniform layer of PDA was coated on graphene oxide (GO) by polymerizing dopamine (DA) at room temperature. During the process GO was reduced by the DA. The PDA layer on the surface of GNS can be used as a nanoscale guide to form uniform Ag NPs on the surface of PDA-GNS. The obtained Ag-PDA-GNS hybrid materials are characterized by atomic force microscopy, transmission electron microscopy, UV-vis spectroscopy, Raman spectroscopy, X-ray photo-electron spectroscopy, X-ray diffraction, and thermal gravimetric analysis. The resultant Ag-PDA-GNS hybrid materials exhibited strong antibacterial properties to both Gram-negative and Gram-positive bacteria due to the synergistic effect of GNS and Ag NPs.

Fractal self-assembly of single-stranded DNA on hydrophobic self-assembled monolayers.

The self-assembled structures possess superior stability, biocompatibility and mechanical strength, and their study can provide insight into the use of creating novel biomaterials. Atomic force microscopy (AFM) images of single-stranded DNA (ssDNA) nanostructures show that well-ordered organization, high homogeneity, and molecular dimensions fractal-shaped fibers formed on a gold substrate covered with self-assembled monolayers (SAMs) of 1-hexadecanethiol (HDT). The nanoscaled architectures of ssDNA on HDT/Au changed remarkably following the process of diffusion-limited cluster aggregation (DLA) over time. The ssDNA fibers prefer to form on hydrophobic SAMs instead of hydrophilic SAMs, and the ssDNA has to have complementary regions in their sequences. This method might not be used only for the construction of fractal patterns, but also for the design and fabrication of functional DNA-based, self-assembled materials that exhibit self-similarity at multiple length scales.

Nano-Ag-loaded hydroxyapatite coatings on titanium surfaces by electrochemical deposition.

Hydroxyapatite (HA) coatings on titanium (Ti) substrates have attracted much attention owing to the combination of good mechanical properties of Ti and superior biocompatibility of HA. Incorporating silver (Ag) into HA coatings is an effective method to impart the coatings with antibacterial properties. However, the uniform distribution of Ag is still a challenge and Ag particles in the coatings are easy to agglomerate, which in turn affects the applications of the coatings. In this study, we employed pulsed electrochemical deposition to co-deposit HA and Ag simultaneously, which realized the uniform distribution of Ag particles in the coatings. This method was based on the use of a well-designed electrolyte containing Ag ions, calcium ions and l-cysteine, in which cysteine acted as the coordination agent to stabilize Ag ions. The antibacterial and cell culture tests were used to evaluate the antibacterial properties and biocompatibility of HA/Ag composite coatings, respectively. The results indicated the as-prepared coatings had good antibacterial properties and biocompatibility. However, an appropriate silver content should be chosen to balance the biocompatibility and antibacterial properties. Heat treatments promoted the adhesive strength and enhanced the biocompatibility without sacrificing the antibacterial properties of the HA/Ag coatings. In summary, this study provided an alternative method to prepare bioactive surfaces with bactericidal ability for biomedical devices.