Ultrafast vibrational energy relaxation of the water bridge

We report the energy relaxation of the OH stretch vibration of HDO molecules contained in an HDO:D(2)O water bridge using femtosecond mid-infrared pump-probe spectroscopy. We found that the vibrational lifetime is shorter (~630 ± 50 fs) than for HDO molecules in bulk HDO:D(2)O (~740 ± 40 fs). In contrast, the thermalization dynamics following the vibrational relaxation are much slower (~1.5 ± 0.4 ps) than in bulk HDO:D(2)O (~250 ± 90 fs). These differences in energy relaxation dynamics strongly indicate that the water bridge and bulk water differ on a molecular scale.     

Concentration Dependence of Vitamin C in Combinations with Vitamin E and Zeaxanthin on Light‐Induced Toxicity to Retinal Pigment Epithelial Cells

The purpose of this study was to determine the effects of increasing concentration of ascorbate alone and in combinations with α‐tocopherol and zeaxanthin on phototoxicity to the retinal pigment epithelium. ARPE‐19 cells were exposed to rose bengal and visible light in the presence and absence of antioxidants. Toxicity was quantified by an assay of cell‐reductive activity. A 20 min exposure to visible light and photosensitizer decreased cell viability to ca 42%. Lipophilic antioxidants increased viabilities to ca 70%, 61% and 75% for α‐tocopherol, zeaxanthin and their combination, respectively. Cell viabilities were ca 70%, 56% and 5% after exposures in the presence of 0.35, 0.7 and 1.4 mm ascorbate, respectively. A 45 min exposure increased cell death to ca 74% and >95% in the absence and presence of ascorbate, respectively. In the presence of ascorbate, zeaxanthin did not significantly affect phototoxicity. α‐Tocopherol and its combination with zeaxanthin enhanced protective effects of ascorbate, but did not prevent from ascorbate‐mediated deleterious effects. In conclusion, there is a narrow range of concentrations and exposure times where ascorbate exerts photoprotective effects, exceeding which leads to ascorbate‐mediated increase in photocytotoxicity. Vitamin E and its combination with zeaxanthin can enhance protective effects of ascorbate, but do not ameliorate its deleterious effects.     

Potentiometry at trace levels in confined samples: ion-selective electrodes with subfemtomole detection limits

We explore here for the first time the direct potentiometric detectability of calcium, lead, and silver ions in amounts on the order of 300 attomoles at 100 picomolar concentrations without any preconcentration, analyte recycling, or electrocatalytic signal enhancement. The results presented here place zero-current potentiometry among the most sensitive electrochemical methods available.     

Potentiometric biosensing of proteins with ultrasensitive ion-selective microelectrodes and nanoparticle labels

We report here for the first time on the use of potentiometry for ultrasensitive nanoparticle-based detection of protein interactions. A silver ion-selective microelectrode is used to detect silver ions oxidatively released from silver enlarged gold nanoparticle labels in a sandwich immunoassay. Since potentiometry is expected to largely maintain its analytical characteristics upon reducing the sample volume, it is anticipated that this approach may form the basis for bioassays with attractive detection limits.     

Synthesis and characterization of high-integrity solid-contact polymeric ion sensors

High-integrity solid-contact (SC) polymeric ion sensors have been produced by using spin casting and electropolymerization techniques in the preparation of the SC employing the conductive polymer, poly(3-octylthiophene) (POT). The physical and chemical integrity of the POT SCs have been evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS). Furthermore, the electrochemical stability of SC polymeric ion sensors has been investigated using electrochemical impedance spectroscopy (EIS). The results of this study demonstrate that electropolymerization and spin casting methods also comprising annealing of the synthesized SC film are capable of producing SCs that are relatively free of imperfections such as pores and pinholes. This leads to electrochemically stable and robust polymeric ion sensors where the SC/sensor interface is resistant to the formation of a detrimental water layer that normally gives rise to spurious ion fluxes and a degradation in the sensitivity and selectivity of the SC polymeric ion sensor.     

Commercially Available Nitrate Ionophores in Potentiometric Sensors are not Superior to Common Ion-exchangers

Nitrate sensing is an important application for potentiometry in environmental applications. Its recognition is by ion-exchangers whose selectivity is governed by the lipophilicity of the ions in solution. Yet, considerable research efforts have been dedicated to the development of such ionophores and some have already been commercialized. This work examines two commercially available nitrate ionophores, nitrate ionophores V and VI, and compares their performance with widely used ion-exchangers by determining the resulting membrane selectivity and complexation to nitrate. Unfortunately, adding a nitrate ionophore to the membrane did not result in improved selectivity. Sandwich membrane experiments indicated that binding interaction is too weak to be measurable, with a logarithmic formation constant of just 1.36±0.14 for ionophore V with nitrate. Ways to improve the reporting of relevant data are suggested.     

Solvatochromic coextraction-based optical carbonate nanosensors

Ionophore-based carbonate-selective sensors have become reliable analytical tools due to their high selectivity and versatility of applications. Nonetheless, successful examples of their implementation in nanoscale devices are yet to be found in the literature. Herein we describe the first attempt to develop carbonate sensors with ionophores using ion-selective nanoemulsions. Classical chromoionophore-based sensors were shown to perform poorly upon transfer to the nanoscale. We hypothesize that this is caused by the heightened surface activity of the ion-ionophore complex. This challenge is overcome by the addition of a positively charged solvatochromic dye X3⁺ to the aqueous phase instead of the sensing particles. The presence of this dye facilitates transfer of carbonate from the particle surface into the sensor bulk, which is followed by an unexpected change of fluorescence with the emergence of a new peak at longer wavelengths, allowing for a ratiometric signal transduction. We have found that this spectral change originates from dye hyper-polarization by the charged moiety of carbonate complex with the ionophore, in analogy to earlier work with protamine nanosensors. The dye-coextraction-based sensing protocol is shown to be reversible and selective with regard to both anionic and cationic interferences present in the sample and forms the foundation for further mechanistic advances for anion sensing with ionophores.