In recent years, nanotechnology has been one of the major subjects of scientific and technological research. Currently, several applications of nanotechnologies are already available on the market. Particularly relevant are the fields of new materials and sensors, which have excellent potential future applications in the biomedical field. This paper describes a project in which the students were challenged to investigate the properties of gold nanoparticles they synthesized themselves. The activity, suitable for students with good chemical knowledge (last year of high school), is divided into three parts, each taking 2 h. In the first part, gold nanoparticles are synthesized and functionalized. In the second, students purify the sample and analyze its optical properties, focusing on the noncovalent interaction with metallic ions. Last (part three), the students realize a chemosensor for cations using the nanoparticles synthesized. At the end of the project, students use the sensing system they had set up to analyze an unknown sample containing bivalent or monovalent metal cations. The proposed activity turned out to be strongly motivating for the students involved and definitely improved their knowledge in the nanomaterials field. Different analytical techniques, such as UV-vis spectrometry, GPC, and TGA, were used, and consequently, both the understanding and the ability to use them were reinforced.