Open-Box Approach to Measuring Fluorescence Quenching Using an iPad Screen and Digital SLR Camera

Fluorescence quenching is an analytical technique and a common undergraduate laboratory exercise. Unfortunately, a typical quenching experiment requires the use of an expensive fluorometer that measures the relative fluorescence intensity of a single sample in a closed compartment unseen by the experimenter. To overcome these shortcomings, we designed an "open-box" fluorescence quenching method that uses an iPad screen as the excitation source and a digital single-lens reflex (SLR) camera as the detector. This setup enables a complete fluorescence quenching experiment to be performed and an accurate Stern-Volmer plot to be generated by analyzing a single image of six fluorescein samples and applying correction factors. The Stern-Volmer quenching constant (K-SV) calculated using this method was 9.62 +/- 0.27 L mol(-1); fluorometer value, 9.52 +/- 0.40 L mol(-1); literature values, 9.0 +/- 0.2 L mol(-1) and 9.608 L mol(-1). These results demonstrate that, in addition to allowing direct visualization of the chemical processes and simultaneous measurement of multiple samples, this simple method yields quantitative results comparable in accuracy to the more expensive fluorometer.