The quantum dot-FRET-based detection of vitamin B12 at a picomolar level.

Herein we report the picomolar level detection of vitamin B12 (VB12) using orange-red emitting ligand-free Mn 2+ -doped ZnS quantum dots (QDs; λ em = 587 nm) in an aqueous dispersion. Sensing was achieved following the quenching of the luminescence of the Mn 2+ -doped ZnS QDs with an increasing concentration of VB12. The Stern-Volmer constant was determined to be 5.2 × 10 10 M -1 . Importantly, the Mn 2+ -doped ZnS QDs exhibited high sensitivity towards VB12, with a limit of detection as low as 1.15 ± 0.06 pM (in the linear range of 4.9-29.4 pM) and high selectivity in the presence of interfering amino acids, metal ions, and proteins. Notably, a Förster resonance energy transfer (FRET) mechanism was primarily proposed for the observed quenching of luminescence of Mn 2+ -doped ZnS QDs upon the addition of VB12. The Förster distance ( R o ) and energy transfer efficiency ( E ) were calculated to be 2.33 nm and 79.3%, respectively. Moreover, the presented QD-FRET-based detection may bring about new avenues for future biosensing applications.