We describe herein the significance of a sodium citrate and tannic acid mixture in the synthesis of spherical silver nanoparticles (AgNPs). Monodisperse AgNPs were synthesized via reduction of silver nitrate using a mixture of two chemical agents: sodium citrate and tannic acid. The shape, size and size distribution of silver particles were determined by UV–Vis spectroscopy, dynamic light scattering (DLS) and scanning transmission electron microscopy (STEM). Special attention is given to understanding and experimentally confirming the exact role of the reagents (sodium citrate and tannic acid present in the reaction mixture) in AgNP synthesis. The oxidation and reduction potentials of silver, tannic acid and sodium citrate in their mixtures were determined using cyclic voltammetry. Possible structures of tannic acid and its adducts with citric acid were investigated in aqueous solution by performing computer simulations in conjunction with the semi-empirical PM7 method. The lowest energy structures found from the preliminary conformational search are shown, and the strength of the interaction between the two molecules was calculated. The compounds present on the surface of the AgNPs were identified using FT-IR spectroscopy, and the results are compared with the IR spectrum of tannic acid theoretically calculated using PM6 and PM7 methods. The obtained results clearly indicate that the combined use of sodium citrate and tannic acid produces monodisperse spherical AgNPs, as it allows control of the nucleation, growth and stabilization of the synthesis process. Graphical abstractᅟ Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-017-3973-9) contains supplementary material, which is available to authorized users.

Ultrafast time-resolved electronic spectra of the primary events induced in the copper tetrasulfonated phthalocyanine Cu(tsPc)4-) in aqueous solution has been measured by femtosecond pump-probe transient absorption spectroscopy. The primary events initiated by the absorption of a photon occurring within the femtosecond time scale are discussed on the basis of the electron transfer mechanism between the adjacent phthalocyanine rings proposed recently in our laboratory. The femtosecond transient absorption results are compared with the low temperature emission spectra obtained with Raman spectroscopy and the voltammetric curves.

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We developed two glucose biosensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) and polyacrylic acid (PAA) doped with poly(4-lithium styrenesulfonic acid) (PSSLi) or PEDOT and anthranilic acid (AA) doped with poly(4-styrenesulfonic acid) (PSSH). The first one was already mentioned in literature in similar configurations; however, the second one has not been described before. The glucose oxidase was immobilized by means of covalent bonding, which has been proved by spectrophotometric assay with o-dianisidine. Amperometric measurements were carried out for the determination of glucose in phosphate buffer. The prepared electrodes functioned as first-generation glucose biosensors at applied potential E = + 0.6 V during t = 30 s. The elaborated procedure was validated, and all of the statistical parameters met the requirements for biosensors. The presented method was successfully applied for determination of glucose concentration in food samples, such as grape juice and honey. The activity of the presented biosensors was also studied in the presence of ascorbic acid and uric acid, acting as interfering agents.