Hydrothermally prepared mono-6-SH-β-cyclodextrin capped Mn-doped ZnS quantum dots (β-CD-Mn-ZnS QDs) exhibited dual photoluminescence (PL) at 430 nm and 598 nm, respectively, upon excitation at 315 nm. The PL intensity of β-CD-Mn-ZnS QDs responded to tryptophan enantiomers differently: the D-isomer showed little effect while L-tryptophan displayed a large time-dependent enhancement in the PL intensity of QDs. This chiral selectivity originated from the β-cyclodextrin coating on the surface of Mn-ZnS QDs, which shows different inclusion constants for tryptophan enantiomers. β-CD-Mn-ZnS QDs further selectively hydrolyse L-tryptophan, forming a product that greatly enhances the QD photoluminescence. Based on these findings, a photoluminescence chiral-assay for tryptophan enantiomers was developed. L-Tryptophan can be detected in the presence of its stereoisomer with a detection limit of 5.4 nM in a linear range of 0–6.0 μM.

•Biosensing ATP with a new berberine/exonuclease I probe system is demonstrated.•Exonuclease I is used to recognize and digest ATP-bound aptamers.•The aptasensor gives low background unparalleled by non-enzyme-based assays.•Sensitive and selective detection of ATP is achieved.•A response for ATP in a wide range from 0.5 μM to 17.5 mM is obtained.A novel aptamer-based label-free assay for sensitive and selective detection of ATP was developed. This assay employs a new aptamer/fluorescent probe system that shows resistance to exonuclease I (Exo I) digestion upon binding to ATP molecules. In the absence of ATP, the complex between the ATP-binding aptamer (ATP–aptamer) and a DNA binding dye, berberine, is digested upon the addition of exonuclease I, leading to the release of berberine into solution and consequently, quenched berberine fluorescence. In the presence of ATP, the ATP-binding aptamer folds into a G-quadruplex structure that is resistant to Exo I digestion. Accordingly, berberine is protected in the G-quadruplex structure and high fluorescence intensity is observed. As such, based on the fluorescence signal change, a label-free fluorescence assay for ATP was developed. Factors affecting the analysis of ATP including the concentration of ATP-binding aptamer, reaction time, temperature and the concentration of Exo I were comprehensively investigated. Under optimal conditions, the fluorescence intensity of the sensing system displayed a response for ATP in a wide range up to 17.5 mM with a detection limit of 140 nM.