Safe One-Pot Synthesis of Fluorescent Carbon Quantum Dots from Lemon Juice for a Hands-On Experience of Nanotechnology

A simple synthesis of fluorescent carbon quantum dots from lemon juice is described to introduce advanced high-school students and undergraduate college students to nanoparticle synthesis and quantum dots. The synthesis is based on the carbonization of lemon juice using only a hot plate stirrer. Column chromatography is used to separate different carbon quantum dots according to their size. This laboratory experiment can be carried out within a 2 h laboratory course and introduces the students to (1) nanotechnology and nanoparticle synthesis, using safe and commonly available chemicals. Furthermore, (2) the concept of fluorescence can be visualized in an intriguing manner using a pocket UV lamp. (3) This experiment serves as an introduction into size-exclusion chromatography. (4) An insight into possible sensing applications is given by the specific fluorescence quenching with an iron(III) solution. The experiment has been tested with 80 students in 4 Swiss high schools, and the knowledge of the students was tested before and after the experiment with a questionnaire. The performance increased by 0.42 +/- 0.39 on a grading scale of 1 to 6. The calculated average effect size was 0.76, which is in the range of a medium- to large-effect size, indicating a favorable effect of the experiment on the nanoparticle knowledge of the students.