Sidra Farid

Detection of Interferon gamma using graphene and aptamer based FET-like electrochemical biosensor

One of the primary goals in the scientific community is the specific detection of proteins for the medical diagnostics and biomedical applications. Interferon-gamma (IFN-γ) is associated with the tuberculosis susceptibility, which is one of the major health problems globally. We have therefore developed a DNA aptamer-based electrochemical biosensor that is used for the detection of IFN-γ with high selectivity and sensitivity. A graphene monolayer-based FET-like structure is incorporated on a PDMS substrate with the IFN-γ aptamer attached to graphene. Addition of target molecule induces a change in the charge distribution in the electrolyte, resulting in increase in electron transfer efficiency that was actively sensed by monitoring the change in current from the device. Change in current appears to be highly sensitive to the IFN-γ concentrations ranging from nanomolar (nM) to micromolar (μM) range. The detection limit of our IFN-γ electrochemical biosensor is found to be 83 pM. Immobilization of aptamer on graphene surface is verified using unique structural approach by Atomic Force Microscopy. Such simple and sensitive electrochemical biosensor has potential applications in infectious disease monitoring, immunology and cancer research in the future.

A Graphene and Aptamer Based Liquid Gated FET-Like Electrochemical Biosensor to Detect Adenosine Triphosphate

Here we report successful demonstration of a FET-like electrochemical nano-biosensor to accurately detect ultralow concentrations of adenosine triphosphate. As a 2D material, graphene is a promising candidate due to its large surface area, biocompatibility, and demonstrated surface binding chemistries and has been employed as the conducting channel. A short 20-base DNA aptamer is used as the sensing element to ensure that the interaction between the analyte and the aptamer occurs within the Debye length of the electrolyte (PBS). Significant increase in the drain current with progressive addition of ATP is observed whereas for control experiments, no distinct change in the drain current occurs. The sensor is found to be highly sensitive in the nanomolar (nM) to micromolar ( μM) range with a high sensitivity of 2.55 μA (mM) -1, a detection limit as low as 10 pM, and it has potential application in medical and biological settings to detect low traces of ATP. This simplistic design strategy can be further extended to efficiently detect a broad range of other target analytes.

Analysis on the structural, vibrational and defect states of chlorine treated polycrystalline cadmium telluride structures grown by e-beam evaporation

Temperature dependent photoluminescence (PL) measurements are performed in order to study the defect states in cadmium chloride treated polycrystalline cadmium telluride (CdTe) thin films grown by e-beam evaporation technique. Three luminescence bands are observed including a double peak emission at 1.577 eV and 1.573 eV corresponding to free electron-to- acceptor transition and a donor–acceptor pair (DAP) transition, respectively, along with a broad peak at 1.45 eV. This broad band emission is related to A-center chlorine based complex and also includes longitudinal (LO) phonon emission lines for CdTe spaced by ∼21 meV. Investigation into grain sizes revealed grains of 0.2 μm for as-grown films and ∼2–3 μm for chlorine activated films shown by atomic force microscopy (AFM). Raman analysis indicates that the films have been grown with excess of Te leading to p-type conductivity in the structure, whereas LO phonon mode of polycrystalline CdTe reveals quasi phonon modes nature.

Enhanced optical properties due to indium incorporation in zinc oxide nanowires

Indium-doped zinc oxide nanowires grown by vapor-liquid-solid technique with 1.6 at. % indium content show intense room temperature photoluminescence (PL) that is red shifted to 20 meV from band edge. We report on a combination of nanowires and nanobelts-like structures with enhanced optical properties after indium doping. The near band edge emission shift gives an estimate for the carrier density as high as 5.5 × 1019 cm−3 for doped nanowires according to Motts critical density theory. Quenching of the visible green peak is seen for doped nanostructures indicating lesser oxygen vacancies and improved quality. PL and transmission electron microscopy measurements confirm indium doping into the ZnO lattice, whereas temperature dependent PL data give an estimation of the donor and acceptor binding energies that agrees well with indium doped nanowires. This provides a non-destructive technique to estimate doping for 1D structures as compared to the traditional FET approach. Furthermore, these indium doped na...

Design and Applications of Nanomaterial-Based and Biomolecule-Based Nanodevices and Nanosensors

This review will highlight recent research underlying the design of novel nanodevices and nanosensors that incorporate graphene, nanodots, nanowires, and biomolecules including DNA aptamers and peptides. The emphasis is on models and theory that guide the design of these nanodevices and nanosensors. In selected cases, research designed to test the usefulness of these designs is highlighted in this chapter.

Modeling polycrystalline effects on the device characteristics of cdte based solar cells

There are mainly three different types of losses that accounts for the decrease in the efficiency of polycrystalline CdTe solar cells namely: (1) optical losses resulting from the interface reflections and absorption from the window and buffer layers in superstrate configuration; (2) recombination losses due to the interface between adjacent layers and also at grain boundaries; and (3) electrical losses due to the device series and shunt resistances. Over the years researchers have mostly studied the nature of the optical and electrical losses in single crystalline cells and have put forward various theoretical models to accurately explain their effect on various performance parameters. However the problem gets much complicated for polycrystalline materials as grain size effects can significantly affect these performance parameters such as short circuit current, open circuit voltage and fill factor. In this work we have studied these polycrystalline effects in depth and have presented a comparative analysis using minority carrier lifetime based model to accurately formulate micron scale grain size effects in CdTe based solar cells.

Computational analysis on the emission of ZnO nanowires and coreshell CdSe/ZnS quantum dots deposited on different substrates

Computational analysis on the emission properties of ZnO nano wires (NWs) and coreshell quantum dots (QDs) have been made by considering the effects of scattering mechanism of the incident field and the total electric field from the surface of varied substrates. Simulation results indicate that the substrate (GaAs) having the highest emission intensity showed maximum light scattering from its surface while ITO that has the least emission intensity results in minimum rate of energy that is transferred per unit area. The simulation results proved that emission intensities spectrum is dependent on the type of substrate being used as well as the scattering of light from the surface of substrates and is independent on the type of material being deposited as well as the total electric field from the surface of substrate.

Raman scattering investigations of CdS thin films grown by thermal evaporation

In this study, CdS thin films deposited by thermal evaporation on the ITO coated glass substrate have been annealed at 450°C for constant times of 30 minutes at varied excitation powers in order to study the effects on the optical characteristics of CdS thin films. Raman and Photoluminescence measurements were made at room temperatures for the annealed samples and a comparison was carried out with as grown sample at different laser powers. Results indicate an improved crystalline quality for the annealed films as compared to the as grown samples. Further a shift in the band gap was observed for annealed films with decreased excitation powers.

Submillimolar Detection of Adenosine Monophosphate Using Graphene-Based Electrochemical Aptasensor

In this paper, we present a successful demonstration of a graphene-based field-effect-transistor-like electrochemical nanobiosensor to accurately detect ultralow concentrations of adenosine monophosphate (AMP). Graphene being a two-dimensional material is a suitable option as a sensing element due to its biocompatibility and large surface area. It has also demonstrated surface binding chemistries as well as its ability to serve as a conducting channel. A short 20-base deoxyribonucleic acid (DNA) aptamer is used as the sensing element to ensure that the interaction between the analyte and the aptamer occurs within the Debye length of the electrolyte. The sensor is found to be nonlinear in nature and sensitive in the picomolar (pM) and nanomolar (nM) concentrations of AMP. The linear region of operation is found to be 1 nM–100 μM and percentage change in drain current in this concentration region is calculated as

Spontaneous polarization induced electric field in zinc oxide nanowires and nanostars

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