TiC MXene quantum dots as an efficient fluorescent probe for bioflavonoid quercetin quantification in food samples.

Background: Quercetin (QC) is known as a typical antioxidant as a bioflavonoid, and its quick, sensitive, and specific detection is crucial for assessing food products. In this study, for the purpose of luminescence-based sensing of QC, bright bluish-green emissive quantum dots of N-doped MXene-based titanium carbide (TiC) were fabricated. Recently, MXene quantum dots (MX-QDs), the rapidly emerging zero-dimensional nanomaterials made from two-dimensional transition metal carbides, have attracted much interest due to their unique physical and chemical features. These include the extremely large surface-to-volume ratio, biocompatibility, luminescence tunability, and hybridization capability while retaining properties of their two-dimensional counterpart including good conductivity and charge transferability.

Results: The fabricated TiC MX-QDs had a quantum yield of 8.13 % at the emission wavelength of λ = 465 nm and displayed excellent photostability with great colloidal stability. It was found that introducing QC to near TiC MX-QDs reduced their fluorescence signals due to quenching effects. These quenching effects that occurred in a very broad linear range of QC (25-600 nM) enabled QC to be sensed quantitatively with the limit of detection of QC (1.35 nM), being the lowest ever reported to date. The quenching phenomena that caused such excellent sensitivity could be accounted for by combined effects of static quenching/radiation-free complex formation and inner filter effects (IFE) of TiC MX-QDs with QC.

Significance: In addition, the quenching-based detection demonstrated excellent specificity against structurally relevant interferants. Therefore, the presented sensing strategies with TiC MX-QDs-based fluorescence quenching can be one of the strongest candidates as a reliable and cost-effective solution to highly sensitive quantification of QC in food samples.