Electrochemical techniques typically offer numerous potential advantages in terms of simplicity, high sensitivity, fast analysis time, cost-effectiveness, and capability of miniaturization. Electroactive species can be detected directly at the electrode surface through these techniques. Therefore, we are currently focusing on deliberately modifying electrode surfaces to introduce electrochemical surface functionalities, increase the active surface area, and thereby enhance electrochemical sensitivity. These modified electrodes can then be further developed as electrochemical sensors for various medical/healthcare and environmental applications, as well as for food safety control. For example, an electrochemical sensor based on screen-printed electrodes was developed for detecting chloramphenicol (CAP), a widely used antibiotic in human and veterinary medicine. The sensor utilized a composite of amine-functionalized magnetite magnetic nanoparticles combined with reduced graphene oxide, which was then applied to a magnetic screen-printed graphene electrode. The sensor possessed a significantly enhanced surface area, high electrical conductivity, and good electrocatalytic activity, enabling selective, sensitive, and accurate determination of CAP. Moreover, the ferromagnetic property of magnetite, attracted by an external magnet, enhanced the electrochemical process of CAP. Consequently, sensitive electrochemical detection of CAP could be achieved through the electro-reductive pretreatment of CAP, followed by the oxidation of its reduced CAP formed, thereby enhancing the sensor’s performance. This developed electrochemical sensor was successfully applied to determine CAP in food products (e.g. milk and honey) with satisfactory recoveries.