Wireless Electromechanical Readout of Chemical Information

Collecting electrochemical information concerning the presence of molecules in a solution is usually achieved by measuring current, potential, resistance, or impedance via connection to a power supply. Here, we suggest wireless electromechanical actuation as a straightforward readout of chemical information. This can be achieved based on the concept of bipolar electrochemistry, which allows measuring the presence of different model species in a quantitative way. We validate the concept by using a free-standing polypyrrole film. Its positively polarized extremity participates in an oxidation of the analyte and delivers electrons to the opposite extremity for the reduction of the polymer. This reduction is accompanied by the insertion of counterions and thus leads to partial swelling of the film, inducing its bending. The resulting actuation is found to be a linear function of the analyte concentration, and also a Michaelis–Menten type correlation is obtained for biochemical analytes. This electromechanical transduction allows an easy optical readout and opens up very interesting perspectives not only in the field of sensing but also far beyond, such as for the elaboration of self-regulating biomimetic systems

Synthesis, characterization of platinum(II) complexes of Schiff base ligands and evaluation of cytotoxic activity of platinum nanoparticles

New cytotoxic mononuclear Pt(II) coordination complexes of ligands {hydrazinecarboxamide (L1H) and hydrazinecarbothioamide (L2H) of 2-hydroxy-1-naphthaldehyde} have been synthesized. Free ligands, their metal complexes, and metal nanoparticles have been characterized based on elemental analysis, melting point, and molecular weight determinations, magnetic measurements, SEM, IR, 1H NMR, and UV–Visible spectra. Square planar geometry has been proposed to the complexes. The ligands and their complexes exhibit antimicrobial effects against various strains of bacteria and fungi. Platinum(II) nanoparticles were prepared by using green technique. The gel electrophoresis clearly exhibits that the metal complexes along with the ligands show cleavage activity on DNA of Escherichia coli (ATCC 25922). The newly synthesized complexes manifested significant in vitro cytotoxicity against human MCF-7 breast adenocarcinoma cancer cell line with cell death mainly caused by apoptosis. Further, nanoparticles of Pt complex exhibited MCF-7 cell multiplication through induction of apoptotic cell death.</p

Effective Noncovalent Functionalization of Poly(ethylene glycol) to Reduced Graphene Oxide Nanosheets through γ‑Radiolysis for Enhanced Lubrication

High-quality reduced graphene oxide (rGO) nanosheets (NSs) were synthesized by the oxidation of graphite followed by hydrazine treatment for the reduction of the oxygen functionalities. γ-Radiolysis was then used for the functionalization of the rGO-NSs with poly­(ethylene glycol) 200 (PEG200). The functionalization resulted in the intercalation of PEG200 molecules in rGO through hydrogen bonding between the hydroxyl groups of rGO and the oxygen atoms of PEG200 molecules. This resulted in an increase in the <i>d</i> spacing of the graphene sheets and a decrease in the defect density of the carbon network in the rGO. The friction coefficient and wear of sliding steel surfaces were reduced by 38% and 55%, respectively, when 0.03 mg mL^–1 PEG200-functionalized rGO dispersed in PEG200 was used. The lubrication properties can be described by bipolar interactions between PEG200 and rGO, leading to effective dispersion. Chemical analysis of wear particles showed decomposition of rGO into nanosized graphite domains, as exhibited by mechanical energy produced in tribo-contact. Moreover, these domains formed effective and stable tribofilms on the steel wear tracks that easily sheared under the action of contact stress. This significantly enhanced the antifriction and antiwear properties, resulting in improved oxidation resistance of PEG200 under the tribo-contact. It was found that, at high rGO concentrations, the lubrication efficiency decreased as a result of graphene–graphene intersheet collisions, producing mechanical energy and chemical defects at contact interfaces

Effect of Orientation on Bulk and Surface Properties of Sn-doped Hematite (α-Fe₂O₃) Heteroepitaxial Thin Film Photoanodes

The orientation dependence on the photoelectrochemical properties of Sn-doped hematite photoanodes was studied by means of heteroepitaxial film growth. Nb-doped SnO₂ (NTO) was first grown heteroepitaxially on <i>c</i>, <i>a</i>, <i>r</i>, and <i>m</i> plane single crystal sapphire substrates in three different orientations. Hematite was then grown in the (001), (110), and (100) orientations on the NTO films. The structural, morphological, optical, and photoelectrochemical properties of the photoelectrodes were studied. The hematite photoanodes possessed high crystallinity and smooth surfaces. Hole scavenger measurements made in H₂O₂-containing electrolyte revealed that the flux of photogenerated holes arriving at the surface was not significantly affected by orientation. Cathodic shifts in the onset potential for water photo-oxidation of up to 170 mV were observed for (110) and (100) oriented hematite photoanodes as compared to (001) oriented films. These results suggest that varying the orientation of heteroepitaxial thin film Sn-doped hematite photoelectrodes primarily affects charge transfer into the electrolyte arising from the surface properties of the different crystal faces rather than affecting hole transport through the bulk under illumination. Electrochemical techniques were then used to probe the existence of surface states which were found to vary with both exposed crystal face as well as foreign dopant inclusion. Kelvin probe force microscopy (KPFM) measurements revealed correlation between the work function of the hematite films (measured in air) and the flat-band and onset potentials for water photo-oxidation (in alkaline aqueous solution)

Defect Segregation and Its Effect on the Photoelectrochemical Properties of Ti-Doped Hematite Photoanodes for Solar Water Splitting

Optimizing the photoelectrochemical performance of hematite photoanodes for solar water splitting requires better understanding of the relationships between dopant distribution, structural defects, and photoelectrochemical properties. Here, we use complementary characterization techniques including electron microscopy, conductive atomic force microscopy (CAFM), Rutherford backscattering spectroscopy (RBS), atom probe tomography (APT), and intensity-modulated photocurrent spectroscopy (IMPS) to study this correlation in Ti-doped (1 cat. %) hematite films deposited by pulsed laser deposition (PLD) on F:SnO2 (FTO)-coated glass substrates. The deposition was carried out at 300 °C followed by annealing at 500 °C for 2 h. Upon annealing, Ti was observed by APT to segregate to the hematite/FTO interface and into some hematite grains. Since no other pronounced changes in microstructure and chemical composition were observed by electron microscopy and RBS after annealing, a nonuniform Ti redistribution seems to be the reason for reduced interfacial recombination in the annealed films, as observed by IMPS. This results in a lower onset potential, higher photocurrent, and larger fill factor with respect to the as-deposited state. This work provides atomic-scale insights into the microscopic inhomogeneity in Ti-doped hematite thin films and the role of defect segregation in their electrical and photoelectrochemical properties