Stimulation of Biological Structures on the Nanoscale Using Interfaces with Large Built-In Spontaneous Polarizations.

The electric potential stimulation of biological structures in aqueous environments is well-known to be a result of the gating of voltage-gated ion channels. Such voltage-gated ion channels are ubiquitous in the membranes of a wide variety of cells and they play central roles in a wide variety of sensing mechanisms and neuronal functions in biological systems. Experimental studies of ion-channel gating are frequently conducted using path-clamp techniques by placing a cumbersome external electrode in the vicinity of the extracellular side of the ion channel.

The Use of Semiconductor Quantum Dots with Large, Built-In Spontaneous Polarizations for the Electric Potential Stimulation of Biological Structures on the Nanoscale.

The feasibility of using quantum dots fabricated from materials with built-in spontaneous polarizations for the electric potential stimulation of biological structures in aqueous environments is evaluated by modeling the electric potential produced in the vicinity of such quantum dots. By modeling the external potential created by the spherical nanoscale region of a material with spontaneous polarization, and by considering Debye screening in the vicinity of the quantum dot, it is found that electric potential around these nanostructures is sufficient to cause physiological effects in selected biological systems. These findings suggest that quantum dots may be used in lieu of quantum dots with polarizations produced using an external laser to cause physiological effects.

Role of Confined Optical Phonons in Exciton Generation in Spherical Quantum Dot.

Optical control of excitonic states in semiconducting quantum dots has enabled it to be deployed as a qubit for quantum information processing. For self-assembled quantum dots, these excitonic states couple with phonons in the barrier material, for which the previous studies have shown that such exciton-phonon coupling can also lead to the generation of exciton, paving the way for their deployment in qubit-state preparation. Previous studies on self-assembled quantum dots comprising polar materials have considered exciton-phonon coupling by treating phonon modes as bulk acoustic modes only, owing to nearly the same acoustic property of the dot and barrier material.

Spontaneous Polarization Calculations in Wurtzite II-Oxides, III-Nitrides, and SiC Polytypes through Net Dipole Moments and the Effects of Nanoscale Layering.

Herein, the spontaneous polarization in crystals with hexagonal symmetry are calculated as a function of the number of monolayers composing a nanostructure by adding the dipole moments for consecutive units of the nanostructure. It is shown that in the limit of a large numbers of monolayers that the spontaneous polarization saturates to the expected bulk value of the spontaneous polarization. These results are relevant to understanding the role of the built-in spontaneous polarizations in a variety of nanostructures since these built-in polarizations are generally quite large, on the order of 1 × 10 to 1 × 10 V/m.

High performance ionic-liquid-gated air doped diamond field-effect transistors.

We report successful fabrication of high performance ion-gated field-effect transistors (FETs) on hydrogenated diamond surface. Investigations on the hydrogen (H)-terminated diamond by Hall effect measurements shows Hall mobility as high as ∼200 cm V s. In addition we demonstrate a rapid fabrication scheme for achieving stable high performance devices useful for determining optimal growth and fabrication conditions.

Anharmonic decay of high-frequency LA modes in quasi-isotropic III-nitrides.

We report for the first time an estimation of the spontaneous decay rates at room temperature in a selection of nitride-based nanostructures that are quasi-isotropic. We numerically calculate the phonon distribution functions and the decay rates and find that the decay channel LA → TA + TA dominates over the decay channel LA → LA + TA, which confirms Klemens' prediction [1] that LA phonon will primarily split into two doubly degenerate TA phonons through a greater variety of decay channels compared to the decay of LA into two modes, one belonging to the longitudinal acoustic and the other to the transverse acoustic branch.

Thornber-Feynman carrier-optical-phonon scattering rates in wurtzite crystals.

It is well known that the carrier-optical-phonon scattering rates dominate the carrier-acoustic-phonon scattering rates in many polar materials of interest in electronic and optoelectronic applications. Furthermore, it is known that the Fröhlich coupling constants for carrier-optical-phonon in many materials is close to or great than unity, calling into question the validity of scattering rates based on the Fermi golden rule. In a celebrated paper by Thornber and Feynman it was shown that that the large Fröhlich coupling constant in polar materials does indeed lead to substantial corrections to the Fermi golden rule scattering rates.

A study on the response of FRET based DNA aptasensors in intracellular environment.

This paper presents a study of the response of FRET based DNA aptasensors in the intracellular environment. Herein, we extend previous studies of aptasensors functioning in the extracellular environment to detection of antigens in the intracellular environment. An essential step in this research is the use of a novel means of achieving the endocytosis of aptasensors.

Optimized oxygen deprived low temperature sputtered WO thin films for crystalline structures.

We report a detailed analysis on the effects of processing parameters for sputtered tungsten trioxide (WO) thin nanoscale films on their structural, vibrational and electrical properties. The research aims to understand the fundamental aspects of WO sputtering at relatively low temperatures and in an oxygen deprived environment targeting applications of temperature and oxygen sensitive substrates. Structural analysis indicates that films deposited at room temperature, or substrate temperatures at or below 400 °C with low oxygen partial pressure are amorphous.

Indium Dopant Concentration Effects on Zinc Oxide Nanowires.

We report in detail the effects of varying the concentration of indium as a dopant in ZnO on the structural, vibrational, and optical properties of ZnO nanowires. A highly versatile route to dope zinc oxide nanowires by using vapor-liquid-solid growth is employed. It is observed that the ratio of indium in ZnO reactant has a large impact on properties of indium-doped ZnO nanowires.

Confined and interface optical phonon emission in GaN/InGaN double barrier quantum well heterostructures.

In GaN-based high electron mobility transistors (HEMTs), the fast emission of longitudinal optical (LO) phonons can result in the formation of hot spots near the gate region where high electric fields produce hot electrons. In this work, we investigate the probability of phonon emission as a function of electron energy for confined and interface (IF) phonon modes for wurtzite GaN/InGaN/GaN heterostructures. Hot electrons radiate optical phonons which decay, anharmonically, into acoustic phonons that are essentially heat carriers.

Electron Scattering via Interface Optical Phonons with High Group Velocity in Wurtzite GaN-based Quantum Well Heterostructure.

Here we present a detailed theoretical analysis of the interaction between electrons and optical phonons of interface and confined modes in a wurtzite AlN/GaN/AlN quantum well heterostructure based on the uniaxial dielectric continuum model. The formalism describing the interface and confined mode optical phonon dispersion relation, electron-phonon scattering rates, and average group velocity of emitted optical phonons are developed and numerically calculated. The dispersion relation of the interface phonons shows a convergence to the resonant phonon frequencies 577.

Rapid Detection of Tumor Necrosis Factor-Alpha Using Quantum Dot-Based Optical Aptasensor.

This paper reports an optical "TURN OFF" aptasensor, which is comprised of a deoxyribonucleic acid aptamer attached to a quantum dot on the terminus and gold nanoparticle on the terminus. The photoluminescence intensity is observed to decrease upon progressive addition of the target protein tumor necrosis factor-alpha (TNF- ) to the sensor. For PBS-based TNF- samples, the beacon exhibited 19%-20% quenching at around 22 nM concentration.

Terahertz vibrational signature of bacterial spores arising from nanostructure decorated endospore surface.

This theoretical effort is the first to explore the possible hypothesis that terahertz optical activity of Bacillus spores arises from normal vibrational modes of spore coat subcomponents in the terahertz frequency range. Bacterial strains like Bacillus and Clostridium form spores with a hardened coating made of peptidoglycan to protect its genetic material in harsh conditions. In recent years, electron microscopy and atomic force microscopy has revealed that bacterial spore surfaces are decorated with nanocylinders and honeycomb nanostructures.

Defect induced structural inhomogeneity, ultraviolet light emission and near-band-edge photoluminescence broadening in degenerate InO nanowires.

We demonstrate here defect induced changes on the morphology and surface properties of indium oxide (InO) nanowires and further study their effects on the near-band-edge (NBE) emission, thereby showing the significant influence of surface states on InO nanostructure based device characteristics for potential optoelectronic applications. InO nanowires with cubic crystal structure (c-InO) were synthesized via carbothermal reduction technique using a gold-catalyst-assisted vapor-liquid-solid method. Onset of strong optical absorption could be observed at energies greater than 3.

Ultrafast carrier dynamics and optical pumping of lasing from Ar-plasma treated ZnO nanoribbons.

It is a well-known fact that ZnO has been one of the most studied wide bandgap II-VI materials by the scientific community specifically due to its potential for being used as exciton-related optical devices. Hence, realizing ways to increase the efficiency of these devices is important. We discuss a plasma treatment technique to enhance the near-band-edge (NBE) excitonic emission from ZnO based nanoribbons.

Aptasensor based optical detection of glycated albumin for diabetes mellitus diagnosis.

Glycated albumin (GA) has been reported as an important biomarker for diabetes mellitus. This study investigates an optical sensor comprised of deoxyribonucleic acid (DNA) aptamer, semiconductor quantum dot and gold (Au) nanoparticle for the detection of GA. The system functions as a 'turn on' sensor because an increase in photoluminescence intensity is observed upon the addition of GA to the sensor.

Graphene oxide and DNA aptamer based sub-nanomolar potassium detecting optical nanosensor.

Quantum-dot (QD) based nanosensors are frequently used by researchers to detect small molecules, ions and different biomolecules. In this article, we present a sensor complex/system comprised of deoxyribonucleic acid (DNA) aptamer, gold nanoparticle and semiconductor QD, attached to a graphene oxide (GO) flake for detection of potassium. As reported herein, it is demonstrated that QD-aptamer-quencher nanosensor functions even when tethered to GO, opening the way to future applications where sensing can be accomplished simultaneously with other previously demonstrated applications of GO such as serving as a nanocarrier for drug delivery.

Molecular beacon anchored onto a graphene oxide substrate.

In this article, we report a graphene oxide-based nanosensor incorporating semiconductor quantum dots linked to DNA-aptamers that functions as a 'turn-off' fluorescent nanosensor for detection of low concentrations of analytes. A specific demonstration of this turn-off aptasensor is presented for the case of the detection of mercury (II) ions. In this system, ensembles of aptamer-based quantum-dot sensors are anchored onto graphene oxide (GO) flakes which provide a platform for analyte detection in the vicinity of GO.

Modulation of voltage-gated conductances of retinal horizontal cells by UV-excited TiO nanoparticles.

This study examines the ability of optically-excited titanium dioxide nanoparticles to influence voltage-gated ion channels in retinal horizontal cells. Voltage clamp recordings were obtained in the presence and absence of TiO and ultraviolet laser excitation. Significant current changes were observed in response to UV light, particularly in the -40 mV to +40 mV region where voltage-gated Na and K channels have the highest conductance.

Polar interface phonons in ionic toroidal systems.

We use the dielectric continuum model to obtain the polar (Fuchs-Kliewer like) interface vibration modes of toroids made of ionic materials either embedded in a different material or in vacuum, with applications to nanotoroids specially in mind. We report the frequencies of these modes and describe the electric potential they produce. We establish the quantum-mechanical Hamiltonian appropriate for their interaction with electric charges.

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).

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.

Biomedical Applications of Quantum Dots, Nucleic Acid-Based Aptamers, and Nanostructures in Biosensors.

This review is a survey of the biomedical applications of semiconductor quantum dots, nucleic acid-based aptamers, and nanosensors as molecular biosensors. It focuses on the detection of analytes in biomedical applications using (1) advances in molecular beacons incorporating semiconductor quantum dots and nanoscale quenching elements; (2) aptamer-based nanosensors on a variety of platforms, including graphene; (3) Raman scattering and surface-enhanced Raman scattering (SERS) using nanostructures for enhanced SERS spectra of biomolecules, including aptamers; and (4) the electrical and optical properties of nanostructures incorporated into molecular beacons and aptamer-based nanosensors. Research done at the University of Illinois at Chicago (UIC) is highlighted throughout since it emphasizes the specific approaches taken by the bioengineering department at UIC.