Achiral double-decker phthalocyanine assemble into helical nanofibers for electrochemically chiral recognition of tryptophan

Due to the unique role of homochirality in our life, efficiently sensing chiral biomolecules is essential for the health and well-being of people. However, electrochemically chiral recognition based on the assemblies of achiral building blocks was still rarely developed. Herein, depending on the co-assembly of achiral double-decker phthalocyanines (EuPc2-8) with poly-L-lysine at the air/water interface, discrimination enantiomers of tryptophan (Trp) even quantitatively can be achieved. The air/water interfacial assembly of achiral double-decker phthalocyanines (EuPc2-8) with poly-L-lysine forms long helical nanofibers with single-molecule-sized diameters, as well as optical activity. The nanostructures and different properties of EuPc2-8/poly-L-lysine helical nanofibers have been thoroughly characterized. The electrochemically chiral recognition of tryptophan is attributed to the unequal interactions between tryptophan enantiomers and EuPc2-8/poly-L-lysine co-assemblies, as verified by the calculated combination energy of EuPc2-8/poly-L-lysine with L- or D-Trp molecules. Therefore, the enrichment of L-Trp molecules rather than D-Trp molecules within EuPc2-8/poly-L-lysine assemblies can be achieved due to subtle features of double-decker phthalocyanines co-assemblies with supramolecular chirality, which results in electrochemically chiral discrimination. These results open new approach for developing efficient and low-cost electrochemically chiral sensor based on the assembly of achiral building blocks.