12 research outputs found
Spotting 2-D Atomic Layers on Aluminum Nitride Thin Films
The availability of large-area substrates imposes an important constraint on
the technological and commercial realization of devices made of layered
materials. Aluminum nitride films on silicon are shown to be promising
candidate materials as large-area substrates for such devices. Herein, the
optical contrast of exemplar 2D layers - MoS2and graphene - on AlN films has
been investigated as a necessary first step to realize devices on these
substrates. Significant contrast enhancements are predicted and observed on AlN
films compared to conventional SiO2films. Quantitative estimates of
experimental contrast using reflectance spectroscopy show very good agreement
with predicted values.Comment: 17 pages, 8 figures, supplementary informatio
Bright-field Nanoscopy: Visualizing Nano-structures with Localized Optical Contrast Using a Conventional Microscope
Most methods for optical visualization beyond the diffraction limit rely on fluorescence emission by molecular tags. Here, we report a method for visualization of nanostructures down to a few nanometers using a conventional bright-field microscope without requiring additional molecular tags such as fluorophores. The technique, Bright-field Nanoscopy, is based on the strong thickness dependent color of ultra-thin germanium on an optically thick gold film. We demonstrate the visualization of grain boundaries in chemical vapour deposited single layer graphene and the detection of single 40 nm Ag nanoparticles. We estimate a size detection limit of about 2 nm using this technique. In addition to visualizing nano-structures, this technique can be used to probe fluid phenomena at the nanoscale, such as transport through 2D membranes. We estimated the water transport rate through a 1 nm thick polymer film using this technique, as an illustration. Further, the technique can also be extended to study the transport of specific ions in the solution. It is anticipated that this technique will find use in applications ranging from single-nanoparticles resolved sensing to studying nanoscale fluid-solid interface phenomena
Detection of Hepatitis B DNA Sequences on Polyelectrolyte Based Non-Covalently Functionalized Flexible Plastic Substrates
Development of simple functionalization methods to attach biomolecules such as proteins and DNA on inexpensive substrates is important for widespread use of low cost, disposable biosensors. Here, we describe a method based on polyelectrolyte multilayers to attach single stranded DNA molecules to conventional glass slides as well as a completely non-standard substrate, namely flexible plastic transparency sheets. We then use the functionalized transparency sheets to specifically detect single stranded Hepatitis B DNA sequences from samples. We also demonstrate a blocking method for reducing non-specific binding of target DNA sequences using negatively charged polyelectrolyte molecules. The polyelectrolyte based functionalization method, which relies on surface charge as opposed to covalent surface linkages, could be an attractive platform to develop assays on inexpensive substrates for low cost biosensing
Non-covalent functionalization using lithographically patterned polyelectrolyte multilayers for high-density microarrays
We describe a method to fabricate high-density biological microarrays using lithographic patterning of polyelectrolyte multi layers formed by spin assisted electrostatic layer-by-layer assembly. Proteins or DNA can be immobilized on the polyelectrolyte patterns via electrostatic attachment leading to functional microarrays. As the immobilization is done using electrostatically assembled polyelectrolyte anchor, this process is substrate independent and is fully compatible with a standard semiconductor fabrication process flow. Moreover, the electrostatic assembly of the anchor layer is a fast process with reaction saturation times of the order of a few minutes unlike covalent schemes that typically require hours to reach saturation. The substrate independent nature of this technique is demonstrated by functionalizing glass slides as well as regular transparency sheets using the same procedure. Using a model protein assay, we demonstrate that the non-covalent immobilization scheme described here has competitive performance compared to conventional covalent immobilization schemes described in literature. (C) 2012 Elsevier B.V. All rights reserved
Tunable release of ions from graphene oxide laminates for sustained antibacterial activity in a biomimetic environment
Silver has long been recognised for its potent antimicrobial properties, but achieving a slow and longer-term delivery of silver ions presents significant challenges. While several attempts have been made to achieve controlled dosages of silver ions, sustaining their release for more than a few days in a biomimetic environment, particularly in the presence of complex proteins, has not been successfully demonstrated. This challenge is underscored by the absence of technology for sustaining antimicrobial activity, especially in the context of orthopaedic implants where long‐term efficacy, extending beyond seven days, is essential. In this study, we have successfully demonstrated the tunable, slow, and longer-term release of silver ions from the two-dimensional nanocapillaries (1 nm wide) of GO laminates incorporated with Ag ions (Ag-GO) for antimicrobial applications. To closely mimic a physiologically relevant serum-basedenvironment, we introduce a novel in vitro study model using 100% fetal bovine serum (FBS) as the test medium for microbiology, biocompatibility, and bioactivity studies. To emulate fluid circulation in a physiological environment, we challenge our in vitro studies with serum exchange protocols on different days. Our findings show that the Ag-GO coating can sustainably release silver ions at a minimum dosage of 10 μg/cm2/day, providing an effective and sustained antimicrobial barrier for over ten days