Gold-Nanoparticle-Based Detection of the Iodine Content in Kelp: A Teaching Practice on Colorimetric Sensing for the University Basic Chemistry Laboratory

Abstract Gold nanoparticles (Au NPs) are widely used in colorimetric analysis due to their surface plasmon resonance effect. Kelp, being rich in iodine, serves as an important dietary source that is necessary for the synthesis of thyroid hormones in the human body. However, in current undergraduate chemistry laboratory teaching, there is virtually no use of Au NP etching-based regeneration detection systems for analyzing the iodine content in kelp. To address this gap and to align with the principles of green chemistry education, this study designed a teaching activity for university chemistry laboratories. In this design, the iodine in kelp was converted into iodide ions (I–) prior to detection. Kiwifruit juice was employed as both a natural reducing agent and a stabilizer to synthesize Au NPs, which were then used to develop a colorimetric method for I– detection. Finally, students captured color data with smartphones, performed grayscale analysis using ImageJ, constructed calibration curves, and successfully calculated the iodine content in kelp. This activity is designed for second-year undergraduate chemistry majors and can be integrated into an analytical chemistry laboratory course. Feedback from questionnaires and reports indicated a high level of engagement and comprehension of nanoscience concepts. The experiment is safe and feasible, with moderate cost, suitable for widespread adoption in basic university chemistry laboratories.