Experimental Design to Enhance Dopamine Electrochemical Detection Using Carbon Paste Electrodes

Efforts have been made on the development of new modified electrodes to be used in the fast determination of neurotransmitters, either in commercial drugs or in biological samples. Determination of dopamine (DA), for example, is of great importance since the lack of this neurotransmitter is related to many neurological disorders, including Parkinson’s and Alzheimer’s diseases. In this paper, we present a detailed electrochemical characterization, as well as DA detection studies of paste electrodes incorporating carbon materials in different allotropic forms, including carbon black modified with intrinsically conducting polymers (Eeonomers®), pristine carbon black, graphite, and carbon nanotubes. Emphasis is put on the smaller particle size and larger specific surface area of CB Eeonomers® materials, which led to an improved electroanalytical performance for the developed devices. The electrodes fabricated with Eeonomers® modified with polyaniline exhibited the higher current response towards DA detection, in addition to the ability of distinguishing DA from its natural interferent, ascorbic acid. Furthermore, a central composite design was used to investigate the influence of pH and electrode composition (proportion of Eeonomers®) on the electrochemical sensing of DA. A greater sensitivity was achieved for 50:50 (w/w) KP20/KPy20 electrode at pH 7.0. The optimized devices showed to be promising tools to perform quick, cheap and sensitive detection of this neurotransmitter in bioanalytical systems.

A sensitive electrochemical DNA biosensor for detecting the genome of a plant growth-promoting bacteria

The challenge of increasing food production while maintaining environmental sustainability can be addressed by using biofertilizers such as Azospirillum, which can enhance plant growth and colonize more than 100 plant species. The success of this biotechnology depends on the amount of plant growth-promoting bacteria associated with the plant during crop development. However, monitoring bacterial population dynamics after inoculation requires time-consuming, laborious, and costly procedures. To address these issues, this study describes an effective electrochemical DNA biosensor to detect Azospirillum brasilense. The biosensor comprises a glassy carbon electrode modified with a nanocomposite based on carbon nanotubes and gold nanoparticles capped with 3-n-propylpyridinium chloride silsesquioxane, followed by the immobilization of a thiolated probe oligonucleotide that binds specifically to the A. brasilense genome (AZOgenome). The nanocomposite was characterized utilizing spectroscopic and morphological methods. Its presence on the biosensor's surface enhanced electrochemical responses due to its excellent electrocatalytic properties, as observed during electrochemical impedance spectroscopy and cyclic voltammetry experiments. The biosensor enabled the detection of AZOgenome after the hybridization event, which alters the electrochemical response of the electrode and was rapidly detected by square wave voltammetry. The detection range of the bacterial genome was 1.17 pmol L-1 to 146.8 pmol L-1, with LOD and LOQ of 0.261 and 0.322 pmol L-1, respectively, and sensitivity of -15.560 μA/log [AZOgenome] (pmol L-1). The biosensor showed good selectivity and reproducibility, with a coefficient of variation of -5.69 %, in addition to satisfactory sensitivity and stability for up to seven weeks. These promising analytical features allowed the quantification of A. brasilense in low concentrations in soil metagenomic DNA samples.