Ehsan Eftekhari

Graphene oxide membranes with tunable permeability due to embedded carbon dots

In this communication, we fabricated graphene oxide membranes with tunable permeation by embedding carbon nanodots of controllable sizes.

Anomalous Fluorescence Enhancement from Double Heterostructure 3D Colloidal Photonic Crystals--A Multifunctional Fluorescence-Based Sensor Platform.

Augmenting fluorescence intensity is of vital importance to the development of chemical and biochemical sensing, imaging and miniature light sources. Here we report an unprecedented fluorescence enhancement with a novel architecture of multilayer three-dimensional colloidal photonic crystals self-assembled from polystyrene spheres. The new technique uses a double heterostructure, which comprises a top and a bottom layer with a periodicity overlapping the excitation wavelength (E) of the emitters, and a middle layer with a periodicity matching the fluorescence wavelength (F) and a thickness that supports constructive interference for the excitation wavelength. This E-F-E double heterostructure displays direction-dependent light trapping for both excitation and fluorescence, coupling the modes of photonic crystal with multiple-beam interference. The E-F-E double heterostructure renders an additional 5-fold enhancement to the extraordinary FL amplification of Rhodamine B in monolithic E CPhCs, and 4.3-fold acceleration of emission dynamics. Such a self-assembled double heterostructue CPhCs may find significant applications in illumination, laser, chemical/biochemical sensing, and solar energy harvesting. We further demonstrate the multi-functionality of the E-F-E double heterostructure CPhCs in Hg (II) sensing.

Detection of regional DNA methylation using DNA-graphene affinity interactions

We report a new method for the detection of regional DNA methylation using base-dependent affinity interaction (i.e., adsorption) of DNA with graphene. Due to the strongest adsorption affinity of guanine bases towards graphene, bisulfite-treated guanine-enriched methylated DNA leads to a larger amount of the adsorbed DNA on the graphene-modified electrodes in comparison to the adenine-enriched unmethylated DNA. The level of the methylation is quantified by monitoring the differential pulse voltammetric current as a function of the adsorbed DNA. The assay is sensitive to distinguish methylated and unmethylated DNA sequences at single CpG resolution by differentiating changes in DNA methylation as low as 5%. Furthermore, this method has been used to detect methylation levels in a collection of DNA samples taken from oesophageal cancer tissues.

Sandwich-structured TiO2 inverse opal circulates slow photons for tremendous improvement in solar energy conversion efficiency

Photon management has enabled a true revolution in the development of high-performance semiconductor materials and devices. Harnessing the highest amount of energy from photons relies on the ability to design and fashion structures to trap the light for a longer time inside the device for more electron excitation. The light harvesting efficiency in many thin-film optoelectronic devices is limited due to low photon absorbance. Here we demonstrate for the first time that slow photon circulation in sandwich-structured photonic crystals with two stopbands fine tuned is ideally suited to enhance and spectrally engineer light absorption. The sandwich-structured TiO2 inverse opal possesses two stopbands, whose blue or red edge is respectively tuned to overlap with the electronic excitation energy of TiO2, thereby circulating the slow photons in the middle layer and enhancing light scattering at layer interfaces. This concept, together with the significantly increased control over photon management opens up tremendous opportunities for the realization of a wide range of high-performance, optoelectronic devices, and photochemical reactions.

Biopatterns Created Using Colloidal Templates

Uniformly dispersed colloidal particles can be self-assembled into highly ordered two-dimensional (2D) and three-dimensional (3D) assemblies, which provide an easily accessible template for protein patterning of a length scale typically on hundreds of nanometres. This chapter aims to provide a brief overview on this protein patterning technique and illustrates the applications of both the 2D and 3D colloidal templates.

Selective toxicity of hydroxyl-rich carbon nanodots for cancer research

The toxicity of nanoparticles in a biological system is an integration of effects arising from surface functionality, particle size, ionic dissolution, etc. This complexity suggests that generalization of a material’s toxicity may be inappropriate. Moreover, from a medicinal point of view, toxicity can be used for treatment of malignant cells, such as cancer. In this study, highly biocompatible carbon nanodots (gCDs) were synthesized by reacting citric acid and urea in glycerol, which resulted in abundant hydroxyl functional groups on the particle surface. gCDs show excitation-dependent photoluminescence but with bright green to yellow emission. Importantly, a series of toxicity assessments showed that as-synthesized gCDs possessed exceptional biocompatibilities to various biological entities including 18 bacteria species, Petunia axillaris seedlings, and Artemia franciscana nauplii. Furthermore, the particles were shown to have low to no toxic effects on human embryonic kidney (HEK-293), breast (MCF-7), and oral squamous (CAL-27) carcinoma cell lines. Of particular interest, the gCDs displayed antiproliferative activities against ovarian choriocarcinoma cells (JAr/Jeg-3 cell lines), which may be further explored for cancer drug discovery.

High performance heterojunction photocatalytic membranes formed by embedding Cu2O and TiO2 nanowires in reduced graphene oxide

A heterojunction photocatalytic membrane consisting of Cu2O and TiO2 nanowires between reduced graphene oxide (rGO) sheets was fabricated using a facile process from a colloidal suspension. The resultant membrane exhibits significantly enhanced activity in the UV-vis range, surpassing nanowire dispersions, owing to the heterojunction formation and concurrent electron and hole transfer on rGO sheets. The membrane also possesses increased permeability and photocorrosion resistance. Such a design and fabrication method of an rGO-facilitated heterojunction photocatalytic membrane can be extended to a broad range of energy and environmental applications.