Voltammetric bienzymatic sensor for sucrose determination in honey

An electrochemical sensor based on nanostructured planar carbon electrodes (nanoSPCE) modified with a SiO2 biocomposite film containing MnO2 particles and enzymes glucose oxidase and invertase was developed. MnO2 particles obtained by electrochemical deposition possessed electrocatalytic activity toward hydrogen peroxide. Glucose oxidase (GOx) and invertase (Inv) were encapsulated into SiO2 film by method of electroassisted deposition. The electrode modified with biocomposite film nanoSPCE/MnO2/GoX/Inv/SiO2 was electroactive toward sucrose. The indicator reaction was oxidation of H2O2 – the product of bienzymatic reaction which was catalyzed by MnO2 on the electrode surface. The linearity range of the calibration graph for the voltametric determination of sucrose using developed modified electrode is 0.017-0.342 mg/ml, the detection limit is 0.006 mg/ml. The obtained nanoSPCE/MnO2/GoX/Inv/SiO2 electrode demonstrated satisfactory stability of the analytical signal during one month of operation. The developed method was used for sucrose determination in the honey samples. The 50-fold molar excess of glucose and fructose does not interfere the determination of sucrose.

Reactive Insertion of PEDOT-PSS in SWCNT@Silica Composites and its Electrochemical Performance

Hybrid silica-modified materials were synthesized on glassy carbon (GC) electrodes by electroassisted deposition of sol-gel precursors. Single-wall carbon nanotubes (SWCNTs) were dispersed in a silica matrix (SWCNT@SiO2) to enhance the electrochemical performance of an inorganic matrix. The electrochemical behavior of the composite electrodes was tested against the ferrocene redox probe. The SWCNT@SiO2 presents an improvement in the electrochemical performance towards ferrocene. The heterogeneous rate constant of the SWCNT@SiO2 can be enhanced by the insertion of poly(3,4-Ethylendioxythiophene)-poly(sodium 4-styrenesulfonate) PEDOT-PSS within the silica matrix, and this composite was synthesized successfully by reactive electrochemical polymerization of the precursor EDOT in aqueous solution. The SWCNT@SiO2-PEDOT-PSS composite electrodes showed a heterogeneous rate constant more than three times higher than the electrode without conducting polymer. Similarly, the electroactive area was also enhanced to more than twice the area of SWCNT@SiO2-modified electrodes. The morphology of the sample films was analyzed by scanning electron microscopy (SEM).

Affinity of Electrochemically Deposited Sol–Gel Silica Films towards Catecholamine Neurotransmitters

Dopamine, norepinephrine, and epinephrine neurotransmitters can be detected by electrochemical oxidation in conventional electrodes. However, their similar chemical structure and electrochemical behavior makes a difficult selective analysis. In the present work, glassy carbon electrodes have been modified with silica layers, which were prepared by electroassisted deposition of sol–gel precursors. These layers were morphologically and compositionally characterized using different techniques, such as field emission scanning electron microscopy (FESEM), TEM, FTIR, or thermogravimetric analysis–mass spectrometry (TG-MS). The affinity of silica for neurotransmitters was evaluated, exclusively, by means of electrochemical methods. It was demonstrated that silica adsorbs dopamine, norepinephrine, and epinephrine, showing different interaction with silica pores. The adsorption process is dominated by a hydrogen bond between silanol groups located at the silica surface and the amine groups of neurotransmitters. Because of the different interaction with neurotransmitters, electrodes modified with silica films could be used in electrochemical sensors for the selective detection of such molecules.