Nicotine permeates into the endoplasmic reticulum (ER) where it begins an “inside-out” pathway that leads to addiction. Shivange et al. develop genetically encoded nicotine biosensors and show that nicotine and varenicline equilibrate in the ER within seconds of extracellular application.

A two-dimensional plasma model that includes the full set of Maxwell equations is used to understand the physics of very high frequency capacitively coupled plasmas. The effect of radio frequency (RF) source power, inter-electrode gap and gas mixture (Ar, Ar/SF 6 , Ar/CF 4 ) on the plasma characteristics is investigated. The computational results show that the plasma spatial profile is influenced by both electrostatic and electromagnetic effects. The electrostatic power deposition is stronger at the electrode edges due to electric field enhancement at corners. Therefore, when the electrostatic effects are dominant, the plasma density peaks off-axis. Due to a standing electromagnetic wave in the chamber, the electron density peak moves to the chamber center under conditions where electromagnetic effects become strong. Inductive heating due to the radial electromagnetic electric field can also influence the plasma spatial profile. The relative importance of electromagnetic and electrostatic effects is found to be a function of the RF source power, the inter-electrode gap and the plasma electronegativity. While the electron density peaks on-axis at a low source power, inductive power deposition at higher source powers shifts the electron density peak towards the electrode edge. Electrostatic power deposition makes the plasma more uniform at smaller inter-electrode gaps. Due to a lower electron density and a larger applied RF potential, electrostatic effects become more dominant in electronegative discharges.

We introduce a new rhodamine-rhodanine-based "turn-on" fluorescent sensor (RR1) and describe its application for detection of mercury, including in solution, in live cells, and in a living vertebrate organism. The sensor RR1, which is a one-pot synthesis from rhodamine B, undergoes a rapid and irreversible 1:1 stoichiometric reaction with Hg(2+) in aqueous medium. Using fluorescence correlation spectroscopy (FCS), RR1 was shown to detect the presence of as low as a 0.5 pM concentration of Hg(2+). It may also lend itself to tagging with biomolecules and nanoparticles, leading to the possibility of organelle-specific Hg detection. Results of experiments with mammalian cells and zebrafish show that RR1 is cell and organism permeable and that it responds selectively to mercury ions over other metal ions. In addition, real-time monitoring of inorganic mercury ion uptake by cells and live zebrafish using this chemosensor shows that saturation of mercury ion uptake occurs within 20-30 min in cells and organisms. We also demonstrate the acquisition of high-resolution real-time distribution maps of inorganic mercury (Hg(2+)) in the zebrafish brain by using a simple fluorescence confocal imaging technique.

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 engineered Ru:CNDEDAs is quenched efficiently by photoinduced electron transfer (PET) phenomenon. By exploiting the PET process, we also develop an important sensing platform for quantifying toxic and carcinogenic quinone derivatives in live HeLa cells that can be used for drug screening. Moreover, the distribution pattern of these photoluminiscent nanodots in HeLa cells is studied to demonstrate their utilities as endosomal markers.

A one-dimensional coupled particle-in-cell and fluid model is used to understand power dynamics at low gas pressures in a capacitively coupled Ar discharge. For the range of gas pressure (5-500 mTorr) and excitation frequency (30-120 MHz) examined, the electrons absorb power at the sheath edge during sheath expansion. Energetic electron beams are generated at the edge of the expanding sheath, which are responsible for plasma production and sustenance. These energetic electrons are able to reach the opposite sheath at low gas pressures and return some of their energy during deceleration in the sheath. As a result, peak electron density decreases significantly below 10 mTorr. Above 50 mTorr, peak electron density is relatively insensitive to pressure as beam electrons deposit most of their energy in the plasma bulk. Secondary electron emission is found critical for plasma sustenance at 30 MHz, while sheath electron heating is the dominant electron heating mechanism at higher frequencies.