Stephen G. Parker

FURTHER DEFINING SPECTRAL TYPE "Y" AND EXPLORING THE LOW-MASS END OF THE FIELD BROWN DWARF MASS FUNCTION

We present the discovery of another seven Y dwarfs from the Wide-field Infrared Survey Explorer (WISE). Using these objects, as well as the first six WISE Y dwarf discoveries from Cushing et al., we further explore the transition between spectral types T and Y. We find that the T/Y boundary roughly coincides with the spot where the J-H colors of brown dwarfs, as predicted by models, turn back to the red. Moreover, we use preliminary trigonometric parallax measurements to show that the T/Y boundary may also correspond to the point at which the absolute H (1.6 µm) and W2 (4.6 µm) magnitudes plummet. We use these discoveries and their preliminary distances to place them in the larger context of the Solar Neighborhood. We present a table that updates the entire stellar and substellar constituency within 8 parsecs of the Sun, and we show that the current census has hydrogen-burning stars outnumbering brown dwarfs by roughly a factor of six. This factor will decrease with time as more brown dwarfs are identified within this volume, but unless there is a vast reservoir of cold brown dwarfs invisible to WISE, the final space density of brown dwarfs is still expected to fall well below that of stars. We also use these new Y dwarf discoveries, along with newly discovered T dwarfs from WISE, to investigate the field substellar mass function. We find that the overall space density of late-T and early-Y dwarfs matches that from simulations describing the mass function as a power law with slope -0.5 < α < 0.0; however, a power-law may provide a poor fit to the observed object counts as a function of spectral type because there are tantalizing hints that the number of brown dwarfs continues to rise from late-T to early-Y. More detailed monitoring and characterization of these Y dwarfs, along with dedicated searches aimed at identifying more examples, are certainly required.

Light-Induced Hydrogel Based on Tumor-Targeting Mesoporous Silica Nanoparticles as a Theranostic Platform for Sustained Cancer Treatment

Herein, we report a facile fabrication of a polymer (azobenzene and α-cyclodextrin-functionalized hyaluronic acid) and gold nanobipyramids (AuNBs) conjugated mesoporous silica nanoparticles (MSNs) to be used as an injectable drug delivery system for sustained cancer treatment. Because of the specific affinity between the hyaluronic acid (HA) on MSNs and the CD44 antigen overexpressed on tumor cells, the MSNs can selectively attach to tumor cells. The nanocomposite material then exploits thermoresponsive interactions between α-cyclodextrin and azobenzene, and the photothermal properties of gold nanobipyramids, to in situ self-assemble into a hydrogel under near-infrared (NIR) radiation. Upon gelation, the drug (doxorubicin)-loaded MSNs carriers were enclosed in the HA network of the hydrogel, whereas further degradation of the HA in the hydrogel due to the upregulation of hyaluronidase (HAase) around the tumor tissue will result in the release of MSNs from the hydrogel, which can then be taken by tumor cells and deliver their drug to the cell nuclei. This design is able to provide a microenvironment with rich anticancer drugs in, and around, the tumor tissue for time periods long enough to prevent the recrudescence of the disease. The extra efficacy that this strategy affords builds upon the capabilities of conventional therapies.

Molecularly engineered surfaces for cell biology: from static to dynamic surfaces.

Surfaces with a well-defined presentation of ligands for receptors on the cell membrane can serve as models of the extracellular matrix for studying cell adhesion or as model cell surfaces for exploring cell-cell contacts. Because such surfaces can provide exquisite control over, for example, the density of these ligands or when the ligands are presented to the cell, they provide a very precise strategy for understanding the mechanisms by which cells respond to external adhesive cues. In the present feature article, we present an overview of the basic biology of cell adhesion before discussing surfaces that have a static presentation of immobile ligands. We outline the biological information that such surfaces have given us, before progressing to recently developed switchable surfaces and surfaces that mimic the lipid bilayer, having adhesive ligands that can move around the membrane and be remodeled by the cell. Finally, the feature article closes with some of the biological information that these new types of surfaces could provide.

Biointerfaces on indium-tin oxide prepared from organophosphonic acid self-assembled monolayers.

Herein we show the development of biointerfaces on indium-tin oxide (ITO) surfaces prepared from organophosphonate self-assembled monolayers. The interfaces were prepared in a stepwise fabrication procedure containing a base monolayer modified with oligo(ethylene oxide) species to which biological recognition ligands were attached. The density of ligands was controlled by varying the ratio of two oligo(ethylene oxide) species such that only one is compatible with further coupling. The final biointerface on ITO was assessed using cell adhesion studies, which showed that the biointerfaces prepared on ITO performed similarly to equivalent monolayers on gold or silicon.

A robust DNA interface on a silicon electrode

Two different interfaces prepared via UV-hydrosilylation of undecylenic acid and 1,8-nonadiyne on silicon(111) have been explored to develop a robust electrochemical DNA sensor. Electrodes modified with undecylenic acid were found to stably immobilise DNA but could not resist the growth of insulating oxides, whereas 1,8-nonadiyne modified electrodes satisfy both requirements.

Strategies To Achieve Control over the Surface Ratio of Two Different Components on Modified Electrodes Using Aryldiazonium Salts

Controlling the composition of an interface is very important in tuning the chemical and physical properties of a surface in many applications including biosensors, biomaterials, and chemical catalysis. Frequently, this requires one molecular component to a minor component in a mixed layer. Such subtle control of composition has been difficult to achieve using aryldiazonium salts. Herein, aryldiazonium salts of carboxyphenyl (CP) and phenylphosphorylcholine (PPC), generated in situ from their corresponding anilines, are electrografted to form molecular platform that are available for further functionalization. These two components are chosen because CP provides a convenient functionality for further coupling of biorecognition species while PPC offers resistance to nonspecific adsorption of proteins to the surface. Mixed layers of CP and PPC were prepared by grafting them either simultaneously or consecutively. The latter strategy allows an interface to be developed in a controlled way where one component is at levels of less than 1% of the total layer.

A photoelectrochemical platform for the capture and release of rare single cells

For many normal and aberrant cell behaviours, it is important to understand the origin of cellular heterogeneity. Although powerful methods for studying cell heterogeneity have emerged, they are more suitable for common rather than rare cells. Exploring the heterogeneity of rare single cells is challenging because these rare cells must be first pre-concentrated and undergo analysis prior to classification and expansion. Here, a versatile capture & release platform consisting of an antibody-modified and electrochemically cleavable semiconducting silicon surface for release of individual cells of interest is presented. The captured cells can be interrogated microscopically and tested for drug responsiveness prior to release and recovery. The capture & release strategy was applied to identify rare tumour cells from whole blood, monitor the uptake of, and response to, doxorubicin and subsequently select cells for single-cell gene expression based on their response to the doxorubicin.Many cell capture systems exist but the characterisation and controlled release of single cells is a challenge. Here, the authors report on the development of a duel trigger release system using a combination of photo and electro triggers to allow for light based analysis without unwanted release.

DNA-hybridisation detection on Si(100) surfaces using light-activated electrochemistry: a comparative study between bovine serum albumin and hexaethylene glycol as antifouling layers.

Light can be used to spatially resolve electrochemical measurements on a semiconductor electrode. This phenomenon has been explored to detect DNA hybridization with light-addressable potentiometric sensors and, more recently, with light-addressable amperometric sensors based on organic-monolayer-protected Si(100). Here, a contribution to the field is presented by comparing sensing performances when bovine serum albumin (BSA) and hexaethylene glycol (OEG6) are employed as antifouling layers that resist nonspecific adsorption to the DNA-modified interface on Si(100) devices. What is observed is that both sensors based on BSA or OEG6 initially allow electrochemical distinction among complementary, noncomplementary, and mismatched DNA targets. However, only surfaces based on OEG6 can sustain electroactivity over time. Our results suggest that this relates to accelerated SiO x formation occasioned by BSA proteins adsorbing on monolayer-protected Si(100) surfaces. Therefore, DNA biosensors were analytically explored on low-doped Si(100) electrodes modified on the molecular level with OEG6 as an antifouling layer. First, light-activated electrochemical responses were recorded over a range of complementary DNA target concentrations. A linear semilog relation was obtained from 1.0 × 10-11 to 1.0 × 10-6 mol L-1 with a correlation coefficient of 0.942. Then, measurements with three independent surfaces indicated a relative standard deviation of 4.5%. Finally, selectivity tests were successfully performed in complex samples consisting of a cocktail mixture of four different DNA sequences. Together, these results indicate that reliable and stable light-activated amperometric DNA sensors can be achieved on Si(100) by employing OEG6 as an antifouling layer.