Ratiometric fluorescent detection of vitamin B6 cofactor pyridoxal using lysine coated gold nanoclusters and doxorubicin†

Conventional methods for vitamin B₆ detection in food samples often suffer from low selectivity and complex sample preparation, limiting their practical application. In this study, a fluorescence-based approach was developed for the ratiometric detection of vitamin B₆ pyridoxal (PY) using blue-emitting lysine-gold nanoclusters (Lys-AuNCs, λ_em = 420 nm) and doxorubicin (DOX, λ_em = 590 nm) as a fluorescent indicator. With the addition of DOX to the Lys-AuNCs, nano-assembly DOX-Lys-AuNCs formed via electrostatic attraction, and the Förster resonance energy transfer (FRET) from the Lys-AuNCs (donor) to DOX (acceptor) caused fluorescence quenching at 420 nm. With the addition of PY to the nano-assembly DOX-Lys-AuNCs, PY is post-functionalized over the surface of Lys-AuNCs by forming Schiff base with the functionalized lysine, which displaced DOX and inhibited the FRET process. The blue emission of Lys-AuNCs was restored and red-shifted from 420 nm to 445 nm, whereas the DOX emission was quenched at 590 nm. With an estimated detection limit of 3.25 μM, the nano-assembly DOX-Lys-AuNCs was successfully employed to quantify PY in food samples. These results supported the practical applicability of DOX-Lys-AuNCs for the selective and sensitive detection of vitamin B₆ in food samples.