A Novel Cerium Oxide/Gold/Carbon Nanocomposite-Based Electrochemical Sensor for Detecting Hydroxyl Radicals

Abstract

Hydroxyl radicals (•OH), a type of reactive oxygen species (ROS), play a crucial role in maintaining the normal physiological processes of human cells. Nevertheless, an excessive accumulation of these radicals may perturb cellular mechanisms, so triggering the onset of severe diseases, including cancer, neurological disorders, and heart disease. The detection of •OH is thus of utmost importance in the early diagnosis of these disorders. The combination of an electrochemical methodology with a recognition system is considered as a promising approach for the detection of •OH. This is primarily due to its capacity to provide fast and direct readings without the need for any preliminary sample preparation. This study presents the development of a new electrochemical sensor for the detection of •OH. The sensor was developed by modifying a screen-printed carbon electrode (SPCE) with a nanocomposite consisting of cerium oxide nanoclusters (CeOx), gold nanoparticles (AuNPs), and a highly conductive carbon. The synthesis of AuNPs supported by carbon was carried out using a deposition-precipitation process. Subsequently, the meticulous deposition of CeOx nanoclusters onto the AuNPs was achieved by the use of surface organometallic chemistry (SOMC). Energy dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) were applied to assess the distribution of AuNPs on the carbon substrate and their subsequent embellishment with CeOx nanoclusters. The actual loadings of Ce and Au present in the nanocomposite were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were employed to analyze the electrochemical responses resulting from the interaction of the CeOx-Au/Carbon nanocomposite with •OH. The CV results demonstrated that the proposed sensor exhibited the capability to effectively identify the presence of •OH in the Fenton reaction, with a notably low limit of detection of 58 µM. The sensor demonstrated a linear correlation between the current response and the concentration of •OH, within the range of 0.05 to 5 mM. Compared to a sensor modified with CeOx/Carbon, the CeOx-Au/Carbon-modified sensor exhibited enhanced electrochemical performance, as demonstrated by an increased current response and a reduced peak potential difference when detecting •OH radicals. Furthermore, the EIS studies showed that the sensor could distinguish •OH from other comparable ROS, such as hydrogen peroxide (H2O2).