Saimon Moraes Silva

Dual Signaling DNA Electrochemistry: An Approach To Understand DNA Interfaces

Electrochemical DNA biosensors composed of a redox marker modified nucleic acid probe tethered to a solid electrode is a common experimental construct for detecting DNA and RNA targets, proteins, inorganic ions, and even small molecules. This class of biosensors generally relies on the binding-induced conformational changes in the distance of the redox marker relative to the electrode surface such that the charge transfer is altered. The conventional design is to attach the redox species to the distal end of a surface-bound nucleic acid strand. Here we show the impact of the position of the redox marker, whether on the distal or proximal end of the DNA monolayer, on the DNA interface electrochemistry. Somewhat unexpectedly, greater currents were obtained when the redox molecules were located on the distal end of the surface-bound DNA monolayer, notionally furthest away from the electrode, compared with currents when the redox species were located on the proximal end, close to the electrode. Our results suggest that a limitation in ion accessibility is the reason why smaller currents were obtained for the redox markers located at the bottom of the DNA monolayer. This understanding shows that to allow the quantification of the amount of redox labeled target DNA strand that hybridizes to probe DNA immobilized on the electrode surface, the redox species must be on the distal end of the surface-bound duplex.

Versatile Fabrication Approach of Conductive Hydrogels via Copolymerization with Vinyl Monomers

Functionalized poly(ethylene dioxythiophene) (f-PEDOT) was copolymerized with two vinyl monomers of different hydrophilicity, acrylic acid and hydroxyethyl methacrylate, to produce electroconductive hydrogels with a range of physical and electronic properties. These hydrogels not only possessed tailored physical properties, such as swelling ratios and mechanical properties, but also displayed electroactivity dependent on the chemical composition of the network. Raman spectroscopy indicated that the functional PEDOT in the hydrogels is in an oxidized form, most likely accounting for the good electrochemical response of the hydrogels observed in physiological buffer. In vitro cell studies showed that cardiac cells respond differently when seeded on hydrogel substrates with different compositions. This study presents a facile approach for the fabrication of electroconductive hydrogels with a range of properties, paving the way for scaffolds that can meet the requirements of different electroresponsive tissues.

Amperometric Electrochemical Platform for Hydrazine Determination Exploiting Reduced Graphene Oxide, Co(Salophen) and DNA: Application in Pharmaceutical Formulations Samples

The present work presents the development of a sensitive and selective amperometric sensor for the determination of hydrazine (HZ) in pharmaceutical formulations using a glassy carbon electrode (GCE) modified with a composite based on Co(Salophen), reduced graphene oxide (rGO) and deoxyribonucleic acid (DNA). The rGO/Co(Salophen)/DNA composite was characterized by using Fourier-transform infrared spectroscopy (FTIR), cyclic voltammetry, and amperometry. The proposed platform presented a well-defined voltammetric profile with a redox couple around 0.32 V vs. Ag/AgCl which showed excellent catalytic activity towards HZ oxidation. The peak current of HZ electrochemical oxidation on the proposed electrochemical platform have changed linearly with the HZ concentration in the range from 2 to 364 μmol L. The proposed platform presented sensitivity, limit of detection, and limit of quantification of 0.056 μA L μmol, 0.54 μmol L, and 1.64 μmol L to HZ, respectively. The relative standard deviation for eight determinations using a solution of 50 μmol L HZ was 0.85%. The proposed sensor was successfully applied for the determination of HZ in pharmaceutical formulations, and the recovery tests showed a good accuracy with recovery percentage between 99 and 101%.

Chapter 8:Dispersible Electrodes: An Approach to Developing Sensing Devices that can Quickly Detect Ultralow Concentrations of Analyte

This chapter presents the ‘dispersible electrodes’ concept, a novel electrochemical detection system to detect ultra-trace levels of analyte in large samples in a reasonable time frame. In this concept instead of the analyte finding the sensor by diffusion or convection, the sensor finds the analyte. Basically, the electrochemical sensor is subdivided into tiny pieces by using conducting gold coated magnetic nanoparticles (Au@MNPs) as active element in the selective capture and direct electroanalytical quantification of the species of interest. The Au@MNPs are dispersed in solution; once the capturing process has completed, a magnetic field is applied and brings the nanoparticles to the sensing interface to carry out the electrochemical measurements. The chapter covers from the synthetic approach of the Au@MNPs to the surface functionalization of the particles, electrochemical characterization, applications, and performance of the dispersible electrodes.