A Green and Low-Cost Laboratory Experiment to Illustrate Fluorescence and FRET for Undergraduate Students Using Everyday Highlighters

We describe a green, low-cost, 3 h qualitative laboratory experiment for undergraduate students that uses commercially available Stabilo Boss Original highlighters dissolved in water and ethanol to illustrate core concepts in molecular photophysics, including electronic transitions, absorption and emission spectroscopy, the Stokes shift, solvatochromism, and Förster resonance energy transfer (FRET). While FRET is increasingly covered in undergraduate physical chemistry courses, hands-on experiments remain rare─leaving theoretical knowledge disconnected from practical experience. The fluorescent inks of commercially available highlighters provide a remarkably accessible means to address this need, allowing students to uncover multistep FRET in an everyday object directly inspired by a recent research study. By relying solely on widely available household products and two low-hazard solvents, the experiment requires no specialized reagents, generates minimal waste, and is broadly deployable in institutions equipped with a spectrofluorimeter. Implemented with 47 second-year undergraduate students across four sessions over two academic years, the experiment enabled students to engage with learning outcomes spanning both disciplinary learning and experimental competences. High assessment scores and positive student survey responses provide encouraging evidence of good student performance and engagement within the 3 h format. Beyond the undergraduate laboratory, the experiment can be extended to excitation spectra or fluorescence lifetime measurements at the Master’s level, adapted for science outreach activities, or used as a standalone classroom demonstration based on the striking fluorescence observations under colored light illumination.