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RF sheath heating as well as secondary electron acceleration play important role in the radio-frequency (RF) hollow cathode discharge (HCD). HCDs form in cylindrical cavities in the cathode, and one can use an array of such cavities to create large area HCDs. The plasma in the hollow cavities can become more intense due to the hollow cathode effect (HCE) under certain conditions. In this study, a single hollow cathode hole is modeled using Particle-in-Cell/Monte Carlo simulation. In this model, using charge density of particles, Poisson equation is solved for electric potential, which yields the electric field. Using this electric field, all charged particles’ velocities are updated and the particles are moved. This PIC code considers particle collisions with each other and with neutral fluid using a Monte Carlo model. Statistics of these collisions are used to determine how electron energy is dissipated in the plasma. RF hollow cathode behavior is characterized for different hole size, pressure and RF voltage. The plasma penetrates inside the hollow cathode hole with increase in pressure, leading to HCE enhancement. With increase in hole size, plasma penetrates further into the hole at a given pressure. At high RF voltage, plasma density enhancement is limited as plasma spreads over larger volume. To evaluate the effect of RF sheath heating, the hollow cathode discharge is modeled at different frequencies ranging from high to low frequency. To understand the importance of secondary electron acceleration on the discharge, we modeled the discharge for different secondary electron emission coefficients. In order to determine the collective behavior of an array of hollow cathode holes, a reduced order model based on a neural network is developed utilizing the detailed PIC modeling results. Preliminary results using the reduced order model are also presented.

Nicotine dependence is thought to arise in part because nicotine permeates into the endoplasmic reticulum (ER), where it binds to nicotinic receptors (nAChRs) and begins an “inside-out” pathway that leads to up-regulation of nAChRs on the plasma membrane. However, the dynamics of nicotine entry into the ER are unquantified. Here, we develop a family of genetically encoded fluorescent biosensors for nicotine, termed iNicSnFRs. The iNicSnFRs are fusions between two proteins: a circularly permutated GFP and a periplasmic choline-/betaine-binding protein engineered to bind nicotine. The biosensors iNicSnFR3a and iNicSnFR3b respond to nicotine by increasing fluorescence at [nicotine] 75%. Reducing nicotine intake by 10-fold decreases activation to ∼20%. iNicSnFR3a and iNicSnFR3b also sense the smoking cessation drug varenicline, revealing that varenicline also permeates into the ER within seconds. Our iNicSnFRs enable optical subcellular pharmacokinetics for nicotine and varenicline during an early event in the inside-out pathway.

Herein we report the one-pot synthesis of a fluorescent polymer-like material (pCD) by exploiting ruthenium-doped carbon dots (CDs) as building blocks. The unusual spectral profiles of pCDs with double-humped periodic excitation dependent photoluminescence (EDPL), and the regular changes in their corresponding average lifetime indicate the formation of high energy donor states and low energy aggregated states due to the overlap of molecular orbitals throughout the chemically switchable π-network of CDs on polymerization. To probe the electronic distribution of pCDs, we have investigated the occurrence of photoinduced electron transfer with a model electron acceptor, menadione using transient absorption technique, corroborated with low magnetic field, followed by identification of the transient radical ions generated through electron transfer. The experimentally obtained B1/2 value, a measure of the hyperfine interactions present in the system, indicates the presence of highly conjugated π-electron cloud i...

Herein we have engineered a smart nuclear targeting thiol-modified riboflavin-gold nano assembly, RfS@AuNPs, which accumulates selectively in the nucleus without any nuclear-targeting peptides (NLS/RGD) and shows photophysically in vitro DNA intercalation. A theoretical model using Molecular Dynamics has been developed to probe the mechanism of formation and stability as well as dynamics of the RfS@AuNPs in aqueous solution and within the DNA microenvironment. The RfS@AuNPs facilitate the binucleated cell formation that is reflected in the significant increase of DNA damage marker, γ-H2AX as well as the arrest of most of the HeLa cells at the pre-G1 phase indicating cell death. Moreover, a significant upregulation of apoptotic markers confirms that the cell death occurs through the apoptotic pathway. Analyses of the microarray gene expression of RfS@AuNPs treated HeLa cells show significant alterations in vital biological processes necessary for cell survival. Taken together, our study reports a unique nuclear targeting mechanism through targeting the riboflavin receptors, which are upregulated in cancer cells and induce apoptosis in the targeted cells.

Carbon dots (CDs) are 1–10 nm scaled complex nanostructures with a wide range of applications and show unconventional photophysical behavior upon excitation. In this article, we have unveiled some of the underlying mechanisms and excited state dynamics of CDs by perturbing their interface with oxidizing and reducing agents. With no substantial alteration in size of surface-treated oxidized (^OCDs), reduced (^RCDs), and untreated CDs (^UCDs), we observe marked changes in their charge transport properties and diverse spectral signatures in singlet and triplet excited states. Fine tuning of the spectral behavior of nanomaterials is often treated as an outcome of quantum confinement of the excitons. Herein with different spectroscopic techniques along with conducting atomic force microscopy and triplet–triplet absorption, we elucidate that, not just confinement, the structural modification at the surface also dictates optoelectronic behavior by altering some properties such as energy band gap, quantum tunneling across the metal–CD–metal junction, and yield of triplet excitons.

Strategies for simultaneous detection and detoxification of Hg^(2+) using a single sensor from biological and environmental samples are limited and have not been realized in living organisms so far. We report a highly selective, small molecule “turn-on” fluorescent sensor, PYDMSA, based on the cationic dye Pyronin Y (PY) and chelating agent meso-2,3-dimercaptosuccinic acid (DMSA) for the simultaneous detection and detoxification of inorganic mercury (Hg^(2+)). After Hg^(2+) detection, concomitant detoxification was carried out with sufficient efficacy in living samples, which makes the sensor unique. PYDMSA exhibits high selectivity for Hg^(2+) over other competing metal ions with an experimental detection limit of ∼300 pM in aqueous buffer solution. When PYDMSA reacts with Hg2+, the CS–C^9 bond in the sensor gets cleaved. This results in the “turn-on” response of the fluorescence probe with a concomitant release of one equivalent of water-soluble Hg^(2+)–DMSA complex which leads to a synchronous detoxifying effect. The sensor by itself is nontoxic to cells in culture and has been used to monitor the real-time uptake of Hg^(2+) in live cells and zebrafish larvae. Thus, PYDMSA is a unique sensor which can be used to detect and detoxify mercury at the same time in living samples.

Self-organized structures that are spread perpendicular to the radio frequency (RF) current direction have been observed in low temperature RF capacitively coupled plasmas. A fluid plasma model that includes thermoelectric electron energy transport is used to understand how these structures form. The electron thermoelectric transport coefficient is calculated using Bolsig+ for different chemistries and is found to be large for Ar plasma. Thermoelectric electron energy transport, which is driven by particle diffusion, opposes electron thermal conduction and can localize the plasma, leading to periodic structures. To examine these structures in radio frequency (RF) capacitive plasmas, two-dimensional Ar plasma at 13.5 MHz is first simulated without and then with thermoelectric electron energy transport. The charged species densities are perturbed in the simulations, and the growth or decay of different modes with time is observed. The periodicity of the structure is found to be determined by the relative strength of thermoelectric electron energy transport compared to energy conduction and losses. The effect of operating variables such as chemistry and pressure and design variables such as inter-electrode gap and steps in the electrode have been studied. For Ar plasma as pressure is decreased, the plasma peaks become stronger since thermoelectric electron energy transport is enhanced. Within limits, steps in the electrodes can be used to control the location of the periodic structures. For N2 plasma, the periodic structure does not appear as thermoelectric electron energy transport is weak. The spacing between plasma peaks is found to be dependent on pressure, chemistry, and inter-electrode gap.

The highly complex nanostructured framework of carbon dots (CDs) elevates scientific debates regarding their molecular and electronic structures. Here, we are able to highlight the free electron distribution on surface of newly synthesized Ru(III) and amine (ethylenediamine) doped carbon nano dots, Ru:CNDEDAs by identifying CD+• radical ions produced through photoinduced electron transfer to a model quinone drug, menadione (MQ) using laser flash photolysis corroborated with magnetic field of the order of 0.08 T. Amine passivation renders Ru:CNDEDAs surface to be a potential electron donor, which exhibits distance-dependent rapid electron transfer with MQ by chemical engineering with homocystein thiolactone (HCTL) in physiological condition. This modification is basically executed to mimic the post-translational modification (homocysteinylation) of protein–lysine residues by HCTL. Moreover, the high values of hyperfine splitting constants of CDs calculated from the magnetic field effect indicate the presen...

Carbon dots (CDs) are known to have a wide range of applications, yet our understanding of their structures and chemistry remains uncertain because of their highly complex nanostructured framework. Here we attempt to elucidate the molecular structure and intrinsic mechanisms governing photoluminescence (PL) of CDs by trapping seven visibly distinct colored intermediates that evolved during pyrolytic metamorphosis of citric acid with dopant Ru(III). The “excitation-dependent” PL of doped CDs, Ru:CDs, can be tuned by ethylenediamine (EDA), yielding “excitation-independent” highly fluorescent nanodots, Ru:CNDEDAs. To mimic the optical and chemical properties of CDs, we devise a unique model cocktail comprising multiple fluorogenic molecules that truly supports the existence of chemically switchable conjugated moieties in CDs. We propose a plausible molecular level framework of CDs on the basis of spectroscopic findings and existing literature regarding thermal decomposition of CA. The PL of chemically engine...

Chiral, multipetal gold nanoflowers (AuNFs) with crystalline tips were synthesized in high yield through the reduction of HAuCl4 in water in the presence of preformed core–satellite Ag nanoparticle (AgNP) seeds. High-resolution transmission electron microscopic (HRTEM) images and tomography reveal the actual crystallographic and 3-dimensional structural profile of the AuNFs. In a first demonstration of this kind, a Hg2+/AuNF combination was shown to catalyze the direct transformation of rhodamine-B to rhodamine-110 in water. The AuNFs were also shown to catalyze reduction of nitroarenes to its corresponding aminoarene with ∼90% conversion efficiency by a single-step, one-pot, eco-friendly protocol. There are numerous opportunities for using these unique AuNFs in catalysis, sensing, imaging, drug delivery, and opto-photonics.

Monoamine neurotransmission is key to neuromodulation, but imaging monoamines in live neurons has remained a challenge. Here we show that externally added ortho-phthalaldehyde (OPA) can permeate live cells and form bright fluorogenic adducts with intracellular monoamines (e.g., serotonin, dopamine, and norepinephrine) and with L-DOPA, which can be imaged sensitively using conventional single-photon excitation in a fluorescence microscope. The peak excitation and emission wavelengths (λ_(ex) = 401 nm and λ_(em) = 490 nm for serotonin; λ_(ex) = 446 nm and λ_(em) = 557 nm for dopamine; and λ_(ex) = 446 nm and λ_(em) = 544 nm for norepinephrine, respectively) are accessible to most modern confocal imaging instruments. The identity of monoamine containing structures (possibly neurotransmitter vesicles) in serotonergic RN46A cells is established by quasi-simultaneous imaging of serotonin using three-photon excitation microscopy. Mass spectrometry of cell extracts and of in vitro solutions helps us identify the chemical nature of the adducts and establishes the reaction mechanisms. Our method has low toxicity, high selectivity, and the ability to directly report the location and concentration of monoamines in live cells.

Amyloid beta (Aβ) aggregation is the likely initiator of Alzheimer's disease (AD), but a molecular level understanding of this process is still lacking. A complicating factor is that aggregation intermediates may be more neurotoxic than the aggregates, but they are difficult to characterize due to their transient nature. Major structural features (dominated by β-sheets) appear to remain conserved from small oligomers to fibrils, providing no specific answers to the puzzle. Single mutations in Aβ linked to early onset AD can potentially provide some clues, but are yet to do so.

Chemically reactive plasmas operating in the 1 mTorr–10 Torr pressure range are widely used for thin film processing in the semiconductor industry. Plasma modeling has come to play an important role in the design of these plasma processing systems. A number of 3-dimensional (3D) fluid and hybrid plasma modeling examples are used to illustrate the role of computational investigations in design of plasma processing hardware for applications such as ion implantation, deposition, and etching. A model for a rectangular inductively coupled plasma (ICP) source is described, which is employed as an ion source for ion implantation. It is shown that gas pressure strongly influences ion flux uniformity, which is determined by the balance between the location of plasma production and diffusion. The effect of chamber dimensions on plasma uniformity in a rectangular capacitively coupled plasma (CCP) is examined using an electromagnetic plasma model. Due to high pressure and small gap in this system, plasma uniformity is found to be primarily determined by the electric field profile in the sheath/pre-sheath region. A 3D model is utilized to investigate the confinement properties of a mesh in a cylindrical CCP. Results highlight the role of hole topology and size on the formation of localized hot-spots. A 3D electromagnetic plasma model for a cylindrical ICP is used to study inductive versus capacitive power coupling and how placement of ground return wires influences it. Finally, a 3D hybrid plasma model for an electron beam generated magnetized plasma is used to understand the role of reactor geometry on plasma uniformity in the presence of E × B drift.