An amide probe as a selective Al3+ and Fe3+ sensor inside the HeLa and a549 cell lines: Pictet–Spengler reaction for the rapid detection of tryptophan amino acid

Abstract

In the present study, an amide-based chemosensor L is reported for the selective determination of tri-positive Al³⁺ and Fe³⁺ metal ions via the fluorescence (FL) “turn-on” state. L can be further used as an Al³⁺ ion sensor in live cells with a significant emission at 430 nm. The receptor showed high binding affinities of 1.045 × 10⁵ and 6.234 × 10⁵ M⁻¹ for Al³⁺ and Fe³⁺, respectively. Furthermore, the chemosensor L also specifically senses tryptophan (Trp) upon the introduction of various amino acids. ESI-MS data and spectroscopic studies indicate a probable intermediate formation through the Pictet–Spengler reaction between amide L and Trp. Trp can be also recognized as a FL quencher in the presence of L + Al³⁺ in an aqueous solution. A PET-based mechanism is proposed for the FL enhancement upon complexation, which is further supported by DFT calculations. Tryptophan, which is the main counterpart of BSA, can be introduced as a real sample to verify the selective PL quenching response. The receptor provides an LOD response of 2.43 × 10⁻⁷ M for the Trp amino acid, suggesting the practical application of tryptophan detection in an aqueous medium for any biological sample.