| dc.description.abstract | The gold nanoparticles (GNPs) have become strong candidates for applications in biosensors, as they have high electrical conductivity and catalytic activity, corrosion resistance, biocompatibility, low cytotoxicity, high stability in biological fluids and easy functionalization. One of the most consolidated methodologies in the literature for the synthesis of GNPs is the chemical reduction of Au3+ ions in metallic gold through chemical reducing agents, and any change in the synthesis parameters, as well as the insertion of stabilizing reagents influence the shape and size of the nanoparticles. Considering the above, the objective of this work is to study the synthesis of gold nanoparticles, aiming its application in biosensors. The methodological process was divided into three stages: the first stage consists of the study of the most suitable reducing agent for the synthesis of GNPs, in which the agents Sodium Citrate and Sodium Borohydride were evaluated; in the second stage, other synthesis parameters were evaluated, such as stirring speed, reduction agent addition speed and molar ratio between the reducing agent and precursor; in the third step, the GNPs solution chosen as the promising synthesis was functionalized with Polyethyleneimine to activate its surface and enable the bioreceptor coupling. All syntheses performed showed the characteristic band of metallic gold between 500 and 550 nm in the UV-visible analysis, confirming the formation of gold nanoparticles. The colloidal solutions synthesized with Sodium Citrate showed more intense coloration, the experimental method is simpler and requires less reaction time, compared to GNPs produced with Sodium Borohydride. The characterization analyzes of the samples from the second stage revealed that the higher the stirring speed of the system, the greater the diffusion speed of the chemical species in solution and the smaller the size of the gold nanoparticles. Regarding the molar ratio between precursor and reducing reagents added to the synthesis, it can be concluded that there is an ideal molar ratio and that higher or lower concentrations of the reducing agent in the solution contribute to an increase in the size of GNPs. Finally, regarding the addition speed of the reducing agent in the reaction medium, it can be inferred that a slower addition causes the production of larger nanoparticles, with variability of sizes and agglomerates. The results of the third stage of the work presented the possibility of functionalizing the gold nanoparticles with Polyethyleneimine, which interacts with GNPs by Van der Waals forces. The electrochemical characterization of commercial electrodes modified with functionalized
gold nanoparticles revealed a significant reduction in charge transfer resistance when compared to the unmodified device, due to the conductive capacity of GNPs, contributing to the increased sensitivity of the electrodes in detecting chemical/biological reactions. Thus, it is concluded that it is possible to apply the solution of functionalized gold nanoparticles produced in this work in the construction of biosensors and that the next step of the study should focus on the bioreceptor coupling, which will depend, in turn, on the target biomarker for the diagnosis. | en |
