Nucleation and growth mechanism of electropolymerization of methylene blue (MB) in a basic medium and the effect of preparation potential on poly(MB) film structure were investigated by using cyclic voltammetry, potentiostatic current-time transient, scanning tunneling microscopy (STM), atomic force microscopy (AFM), and UV-vis. absorption spectroscopy techniques. Electropolymerization of MB has been achieved by potentiodynamic (cyclic voltammetry) and potentiostatic (constant potential) techniques. The potentiostatic current-time transients fitted with a theoretical model and morphological studies indicate that nucleation and growth mechanism of poly(MB) starts with a progressive layer-by-layer nucleation and growth besides random adsorption. Nucleation and growth of poly(MB) follows a process between progressive layer-by-layer and 3-D instantaneous mechanism resulting in highly-oriented poly(MB) nanofibers with increasing poly(MB) film thickness. Cyclic voltammetry and morphological studies exhibit that poly(MB) film structure changes depending on the preparation potential. Poly(MB) films prepared at the potential values of 900 and 950 mV show a well-ordered, smooth surface but at the potential values higher than 1000 mV, rough polymer surface arises as overoxidation takes place. UV-vis. absorption spectra of poly(MB) film and MB monomer show three peaks. The peak at 410 nm for poly(MB) shows 100 nm blue shift when compared to the MB monomer and is attributed to poly(MB) formation on the electrode.

A flexible and free-standing graphene-based hybrid paper was successfully fabricated by successive applications of vacuum filtration and electropolymerization. First, a suspension including graphene oxide (GO) and silver nanoparticles (AgNPs) was prepared, and GO/AgNPs paper was obtained by vacuum-filtration of this suspension through a membrane. This GO/AgNPs paper was transformed to rGO/AgNPs paper by using both chemical reduction with HI and thermal annealing procedures. rGO/AgNPs/poly(PyY) hybrid paper electrode was formed by electropolymerization of Pyronin Y (PyY) on rGO/AgNPs paper electrode from a PyY monomer-containing (pH 1.0) solution. Structural, chemical, and morphological characterization of this hybrid paper was carried out by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy, infrared spectroscopy, UV-vis absorption spectroscopy, four-point probe conductivity measurement, and cyclic voltammetry techniques. Electrooxidation of nitrite on rGO/AgNPs/poly(PyY) hybrid paper electrode has been achieved at 860 mV with a linear range of 0.1-1000 μM, sensitivity of 13.5 μAμM(-1)cm(-2), and a detection limit of 0.012 μM. Amperometry studies have shown that the hybrid paper electrode is suitable for amperometric determination of nitrite in both standard laboratory samples and real samples. Moreover, this paper electrode selectively detects nitrite even in the presence of 100-fold common ions and exhibits an excellent operational stability and good flexibility.

Highly flexible graphene/poly(methylene blue)/AgNPs composite paper was successfully prepared for amperometric biosensing of NADH. For this purpose, a dispersion including graphene oxide (GO), methylene blue (MB) and silver nanoparticles (AgNPs) was prepared and GO/MB/AgNPs paper was acquired by vacuum‐filtration of this dispersion through a suitable membrane. After peeling it off from membrane, it was transformed to rGO/MB/AgNPs paper by performing reduction with hydriodic acid. In a three‐electrode cell, which is containing 0.1 M phosphate buffer solution (pH: 9.0), rGO/MB/AgNPs paper was used as working electrode and rGO/poly(MB)/AgNPs composite paper was generated by surface‐confined electropolymerization of MB using successive cyclic voltammetry approach in a suitable potential window. Characterization of this composite paper was carried out by using scanning electron microscopy, scanning tunneling microscopy, X‐ray photoelectron spectroscopy, powder X‐ray diffraction spectroscopy, Raman spectroscopy, four‐point probe conductivity measurement and cyclic voltammetry techniques. Flexible rGO/poly(MB)/AgNPs composite paper has demonstrated high sensitivity, wide linear range and low detection limit for amperometric quantification of NADH.

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