Enantioselective Fluorescent Imaging of Free Amino Acids in Living Cells

1,1′-Spirobiindane-7,7′-diol (SPINOL)-based chiral aldehydes (R)- and (S)-3, in combination with Zn²⁺, are highly enantioselective fluorescent sensors for structurally diverse chiral amino acids. Application of this enantiomeric sensor pair in HeLa cells containing a free amino acid shows that the chirality-matched sensor–amino acid interaction leads to strong blue emission and chirality mismatch gives only weak fluorescence. This allows a quick determination of the chiral configuration of the free amino acid in the cells. It represents the first enantioselective fluorescent imaging of free amino acids in living cells.