Optical pH Measurements with Water Dispersion of Polyaniline Nanoparticles and Their Redox Sensitivity

A new method for optical pH and redox measurements with a commercially available water dispersion of polyaniline (PANI) nanoparticles (mean particle size, 46 nm) is presented. The pH measurements are based on the acid−base equilibrium of PANI and were carried out either by combining both the automated sequential injection analysis (SIA) and UV−visible spectrophotometric techniques or with a fiber-optic light guide. In the former case, the detection was done in continuous mode at λ = 800 nm by using the SIA technique for transporting the sample to a flow-through cell, which was placed in the light path of the photometer. With the fiber-optic light guide, the detection was done in batch mode at λ = 400 and 580 nm. In both methods, fresh pH reagent (PANI) solution was used in each measurement, thus overcoming the problem with hysteresis (memory effect), which is usually observed with PANI films. The PANI nanoparticles were characterized with UV−visible spectroscopy in pH buffer solutions between pH 2−12 and a protonation constant of log = 4.4 was calculated from these data. Fast pH measurements can be done between pH 6 and 10.5 depending on the measuring technique. It is possible to determine pH with an accuracy of 0.1 pH unit between pH 8 and 10.5 (RSD, 0.5−2%). Redox transitions typical for PANI films were also observed for water solutions of PANI nanoparticles in the presence of the hexacyanoferrate(II/III) and the iron(II/III) oxalate redox couples. The absorbance at λ = 875 nm is linearly dependent on the logarithm of the concentration ratio (0.1−10) of the iron oxalate redox couple

Direct Electrochemistry of Glucose Oxidase and Biosensing for Glucose Based on Graphene

We first reported that polyvinylpyrrolidone-protected graphene was dispersed well in water and had good electrochemical reduction toward O2 and H2O2. With glucose oxidase (GOD) as an enzyme model, we constructed a novel polyvinylpyrrolidone-protected graphene/polyethylenimine-functionalized ionic liquid/GOD electrochemical biosensor, which achieved the direct electron transfer of GOD, maintained its bioactivity and showed potential application for the fabrication of novel glucose biosensors with linear glucose response up to 14 mM

The Role of the Exciplex State in Photoinduced Electron Transfer of Phytochlorin−[60]Fullerene Dyads

The photoinduced electron transfer (ET) in five structurally different phytochlorin-fullerene dyads was studied in polar and nonpolar solvents using femtosecond fluorescence up-conversion and pump−probe transient-absorption techniques. Small changes in the structures of the dyads result in considerable changes in the ET properties and allow the determination of reorganization energies of the photoinduced reactions and electronic couplings between the initial and final states. After the excitation of the phytochlorin moiety to the second excited singlet state, the dyads relax rapidly to the first excited singlet state of phytochlorin. The first excited singlet state of phytochlorin is in equilibrium with an intramolecular exciplex state. In polar benzonitrile, the exciplex undergoes an electron transfer, and a complete-charge-separated (CCS) state is formed with a quantum yield close to unity. In contrast to the previously studied phytochlorin−fullerene dyads, the dyads in the present study form the CCS state also in nonpolar toluene with a yield influenced by minor changes in the molecular structure. The new dyads have a weaker phytochlorin−fullerene interaction due to longer separation distances between the two moieties. Therefore, the energies of the exciplex states are increased, and thus, their formation rates are reduced. In addition, the rates and yields of the complete charge separations are increased both in polar and nonpolar solvents. In benzonitrile, the reorganization energies for the transitions from the exciplex to the CCS and from the CCS to the ground state are 0.38 and 1.05 eV, respectively. The electronic couplings between the corresponding initial and final states of the two transitions mentioned above are 22 and 15 cm-1

Water-Soluble Graphene Covalently Functionalized by Biocompatible Poly-l-lysine

Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups of poly-l-lysine, which provided a very biocompatible environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H2O2 based on linking peroxidase onto PLL-functionalized graphene was investigated

Solid-Contact Ion-Selective Electrodes with Highly Selective Thioamide Derivatives of <i>p</i>-<i>tert</i>-Butylcalix[4]arene for the Determination of Lead(II) in Environmental Samples

Thioamide derivatives of <i>p</i>-<i>tert</i>-butylcalix­[4]­arene were used as ionophores in the development of solid-contact ion-selective electrodes based on conducting polymer poly­(3,4-ethylenedioxythiophene)/polystyrene sulfonate (PEDOT/PSS) which was synthesized by electrodeposition on the glassy carbon electrodes. The typical ion-selective membranes with optionally two different plasticizers [bis­(2-ethylhexyl)­sebacate (DOS) and 2-nitrophenyl octyl ether (NPOE)] were investigated. The potentiometric selectivity coefficients were determined by separate solution method (SSM) for Pb²⁺ over Cu²⁺, Cd²⁺, Ca²⁺, Na⁺, and K⁺. High selectivity toward Pb²⁺ was obtained. By applying two conditioning protocols, a low detection limit log­(<i>a</i>_DL) ≈ −9 was achieved. The fabricated ion-selective electrodes were used to determine Pb²⁺ concentration in environmental samples. The obtained results were compared to analysis done by inductively coupled plasma mass spectrometry (ICPMS)