Quantum dots modified with the Al(III)-pefloxacin complex as a novel bioprobe for the sensitive turn-on and dual-fluorescence detection of dsDNA

We describe a novel fluorescent bioprobe for the sensitive and selective detection of double-stranded DNA (dsDNA). It consists of quantum dots (Q-dots) whose fluorescence is quenched (through photoinduced electron transfer) on covering them with the Al(III)-pefloxacin complex. It is found, however, that dsDNA has an affinity for this complex that is so strong that it can break up the binding to the quantum dots, this leading to a complete recovery of the fluorescence of both the Q-dots and the Al(III)-pefloxacin complex. Dual fluorescence (peaking at 420 and 547 nm) is observed under a single excitation wavelength of 350 nm. Neither ribonucleic acid, bovine serum albumin, nor biologically relevant metal ions are capable of giving this effect. The detection limit (3σ/k) for herring sperm DNA is 15.3 μg L −1 if determined via the fluorescence of the Q-dots, and 48 μg L −1 via the Al(III)-pefloxacin complex. The method was applied to the determination of hsDNA in synthetic samples and gave excellent results. Al 3+ -pefloxacin mesylate (QDs-Al 3+ -PFLX) complex acts as an excellent quencher of the fluorescence of QDs, which was attributed to the photoinduced electron transfer from QDs to Al 3+ -PFLX complex. Due to the strong and specific binding of double-stranded DNA with Al 3+ -PFLX complex, the fluorescence intensity of QDs-Al 3+ -PFLX dyads system is restored