A novel material composed of Au@SiO₂-(3-Aminopropyl Triethoxysilane) (Au@SiO₂-APTES) was successfully synthesised using the sol–gel method, and was used to modify glassy carbon electrodes. Its effectiveness as a molecular recognition element is evaluated in the design of an electrochemical sensor for the precise detection of dopamine. The Au@SiO₂-APTES composite was analysed using Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. Elemental analysis verified the presence of oxygen, silicon, and gold, with atomic percentages of around 77.19%, 21.12%, and 1.65%, respectively. The corresponding elemental mapping for Au@SiO₂-APTES composite showed that the spatial distribution of all the elements was fairly homogeneous throughout the composite, indicating that the Au NPs are embedded in the silica structures. Traces of dopamine were detected by differential pulse voltammetry with a low limit of detection (S/N = 3) and quantification (S/N = 10) of 1.4 × 10⁻⁸ molL⁻¹ and 4.7 × 10⁻⁸ molL⁻¹, respectively. The Au@SiO₂-APTES composite had two linear ranges: from 4.7 × 10⁻⁸ to 1 × 10⁻⁷ molL⁻¹ and 1.25 × 10⁻⁷ to 8.75 × 10⁻⁷ molL⁻¹. Moreover, the sensor showed outstanding selectivity even in the presence of various potential interfering species. It also demonstrated good reusability and signal recovery when tested in human urine and plasma samples spiked with different dopamine concentrations. The electrochemical sensor, constructed using this novel composite material, shows great promise in the selective and sensitive detection of dopamine in the biological matrix. These results underscore the sensor’s capability for practical application in analysing real-world samples.

Pollution by heavy metal ions has a serious impact on human health and the environment, which is why the monitoring of heavy metal ions is of great practical importance. In this work, we describe the development of an electrochemical sensor for the detection of cadmium (Cd²⁺) involving the doping of porous SiO₂ spheres with ZnO nanoparticles. Zinc oxide is chosen as the central dopant in the composite material to increase the conductivity and thus improve the electrochemical detection of Cd²⁺ ions with the SiO₂ spheres. The resulting composite is characterized by electrochemical spectroscopic XRD and microscopic methods. As a result, the developed sensor shows good selectivity towards the targeted Cd²⁺ ions compared to other divalent ions. After optimization of the experimental conditions, the electrochemical sensor shows two different linear ranges between 2.5 × 10⁻¹¹ molL⁻¹ to 1.75 × 10⁻¹⁰ molL⁻¹ and 2 × 10⁻⁹ molL⁻¹ to 1.75 × 10⁻⁹ molL⁻¹, indicating a change from diffusion-controlled to surface-controlled oxidation of Cd²⁺. A detection limit was reached at 4.4 × 10⁻¹¹ molL⁻¹. In addition, it offers good repeatability and recovery, and can detect accurate trace amounts of Cd²⁺ ions in real samples such as tap water or seawater by spiking these samples with known Cd²⁺ concentrations. This setup also provides satisfactory recovery rates in the range of 89–102%.