Tetrakis(4-sulfonatophenyl)porphyrin (TSPP) was immobilized on patterned paper and used as a sensor for heavy metal ions in an advanced organic chemistry course. The resulting sensor could detect Hg[superscript 2+] and Cd[superscript 2+] ions colorimetrically, while Cu[superscript 2+] ion resulted in fluorescence quenching, thus demonstrating a multiplex capability of this paper-based sensor. From the synthesis of the porphyrin to the fabrication of the sensor, advanced undergraduate chemistry students gained first-hand experience with a classical organic synthesis, and also witnessed its application within 2-3 full-day laboratory sessions. This experiment is a good demonstration of how an easily synthesized compound can be exploited to tackle an important problem in real-world situations.