Fluorescence is a suitable tool to detect and quantify accurately biomolecules in situ thanks to bioimaging techniques. As a matter of fact, cysteine (Cys), homocysteine (Hcys) and Glutathione (GSH) are essential biological thiols relevant to the growth of cells and tissues in living systems. Alterations in the levels of these specific biological thiols have been linked to a number of diseases, such as liver damage, neutral tube defects, Alzheimer’s, and various types of cardiovascular and renal illnesses. Thus, the detection of these amino acids (AA) is highly important to detect, understand and treat these kind of diseases.

To this aim, we have designed a fluorescent sensor based on the BODIPY dye, featuring unsaturated esters at the a-pirrolic position. Both aromatic arms act as reactive sites for these AA and allow the shift of the emission towards the red-edge, thereby, ensuring deeper penetration into tissues. The photophysical signatures of this compound are very sensitive to the presence of these AA (even at the micromolar scale) in the surrounding environments. Thus, up to three channels are available to monitor and quantify AA; the loss of red emission and, mainly, the remarkable increase of the green and yellow fluorescence. Moreover, this ratiometric sensor behaves also as colorimetric sensor, hence, the sensing of the AA in the biological media can be visualized quickly and easily by ‘‘naked eye’’.