New fluorescent metal-ion detection using a paper-based sensor strip containing tethered rhodamine carbon nanodots.

A strip of tethered rhodamine carbon nanodots (C-dots) was designed for selective detection of Al(3+) ion using a Förster resonance energy transfer (FRET)-based ratiometric sensing mechanism. The probe consisted of rhodamine B moieties immobilized on the surface of water-soluble C-dots. Upon exposure to Al(3+), the rhodamine moieties showed a much enhanced emission intensity via energy transfer from the C-dots under excitation at their absorption wavelength. The detection mechanism was related to the Al(3+)-induced ring-opening of rhodamine on C-dots through the chelation of the rhodamine 6G moiety with Al(3+), leading to a spectral overlap of the absorption of C-dots (donor) and the emission of ring-opened rhodamine (acceptor). In addition, a paper-based sensor strip containing the tethered rhodamine C-dots was prepared for practical, versatile applications of Al(3+) sensing. The paper-based sensor could detect Al(3+) over other metal ions efficiently, even from a mixture of metal ions, with increased emission intensity at long-wavelength emission via FRET. Sensing based on FRET of C-dots is color-tunable, can be recognized with a naked eye, and may provide a new platform for specific metal-ion sensing.