Visual Recognition of Tryptophan Enantiomers Using Chiral Self Assemblies of Quantum Dots

Discrimination of chiral targets is generally achieved with chiral nanomaterials. However, the limited number of intrinsic chiral nanostructures as well as their complex synthesis procedure has led to the production of chirality-induced nanomaterials as alternatives. Chirality can be induced in nanomaterials by either chirality transfer or the formation of chiral assemblies. Using the latter approach, in this work, we have provided chiral supramolecular assemblies of CdTe quantum dots (QDs) from achiral starting materials. CTAB-QD assemblies showed chiroptical activities, and their orange emission in combination with the blue emission of carbon dots was utilized as a ratiometric chiral recognition platform for enantioselective detection of tryptophan (Trp). Entirely distinct fluorescence response patterns were obtained in the presence of L- and D-Trp. While D-Trp suppressed the fluorescence emission of CTAB-QDs, which was also accompanied by a substantial alteration in the emission color from peach to purple, only slight spectral changes were observed in the presence of L-Trp. The distinct response patterns of the ratiometric assay were further manipulated for the construction of a logic gate system mimicking NOT and OR functions. The applicability of the supramolecular chiral assembly toward enantiomeric excess determination of L-Trp in food supplements was also investigated. The acquired wide range color tonalities enable simple visual tracking of D- and L-Trp with a handheld device such as a smartphone.