Multi-emissive Nile Red-loaded β-cyclodextrin-derived C-nanodots for specific detection of phenylalanine

Multifunctional carbon-based nanostructures are attracting considerable attention because of their low toxicity, excellent optical and chemical properties, and intriguing applications. Currently, the development of carbon-based nanostructures for sensing remains a challenging topic in the biosensing field. Here, we report an unprecedented example of a multi-emissive supramolecular system composed of carbon-nanodots, derived from β-cyclodextrin units by a one-pot thermal process, and Nile Red (NR) hosted in the cyclodextrin cavities (Cdots-βCD/NR). The Cdots-β-CD nanostructures were characterized by spectroscopic techniques, NMR, and atomic force microscopy. The supramolecular Cdots-βCD/NR system exhibited multi-fluorescence emissions at 410 nm and 650 nm, corresponding to the Csp²-core of the carbon nanodots and the encapsulated NR, respectively. The as-prepared Cdots-βCD/NR nanosystem showed high specificity for the detection of phenylalanine (Phe) with a limit of detection (LoD) of 0.49 µM, a limit of quantification (LoQ) of 1.25 µM over a dynamic range of 2-100 µM for the red fluorescence emission (650 nm), and a dynamic range of 20-400 µM for the blue fluorescence emission (410 nm). Good specificity for Phe over tyrosine was demonstrated and supported by molecular modelling simulations. The proposed sensing strategy exhibited good correlation with the results obtained from standard mass spectrometry when applied to human blood samples collected from PKU patients.