Sensitive luminescent determination of DNA using the terbium(III)–difloxacin complex

The interaction of the terbium–difloxacin complex (Tb–DFX) with DNA has been examined by using UV–vis absorption and luminescence spectroscopy. The Tb–DFX complex shows an up to 85-fold enhancement of luminescence intensity upon titration with DNA. The long decay times allow additional detection schemes like time-resolved measurements in microplate readers to enhance sensitivity by off-gating short-lived background luminescence. Optimal conditions are found at equimolar concentrations of Tb3+ and DFX (0.1 or 1 μM) at pH 7.4. Under these conditions, the luminescence intensity is linearly dependent on the concentration of ds-DNAs and ss-DNA between 1–1500 ng mL−1 and 4.5–270 ng mL−1, respectively. The detection limit is 0.5 ng mL−1 for ds-DNAs and 2 ng mL−1 for ss-DNA. The mechanism for the luminescence enhancement was also studied.