Determination of DNA by Rayleigh light scattering enhancement of molecular “light switches”

A novel fluorescent silver ion biosensor based on nucleic acid molecular "light switch"

As one of nucleic acid molecular "light switch", Ru(bipy)(2)(dppx)(2+) is a good probe for the determination of double-helical DNA, which displays intense fluorescence when double-helical DNA is present. However, the fluorescence of Ru(bipy)(2)(dppx)(2+) is quenched when Ag(+) is added to the Ru(bipy)(2)(dppx)(2+)-DNA system. Based on the quenching of the fluorescence of Ru(bipy)(2)(dppx)(2+)-DNA system by Ag(+), a simple, rapid and specific method for Ag(+) determination was proposed. In the optimum conditions, Ag(+) concentration versus Ru(bipy)(2)(dppx)(2+) fluorescence intensity gave a linear response in the range from 0.2 to 6.0 microM with a detection limit (3sigma) of 3.2 x 10(-8) M. The proposed method has been applied to determine the Ag(+) in water samples and sulfadiazine silver cream successfully. Because of the intense fluorescence of Ru(bipy)(2)dppx(2+) when DNA is present, the interaction between Ag(+) and DNA was confirmed by fluorescence microscopy and the phenomenon of the fluorescence images agreed well with the results. The possible mechanism of the reaction was also discussed by circular dichroism spectra and isothermal titration calorimetry.

Stopped-flow kinetic fluorimetric studies of the interaction of Ru(II) complex with DNA and its analytical application

A simple, rapid, and sensitive stopped-flow kinetic fluorometric approach was established for the assay of DNA in synthetic samples and real samples by using the measures of initial reaction rate. The increased initial reaction rate is in proportion to the concentration of DNA in the range of 2.0x10(-8)M to 2.1x10(-6)M. The optimum conditions for various parameters on which the binding of Ru(phen)(2)(dppz)(2+) to DNA depends, were investigated. The influence of various surfactants on the interaction was discussed. Furthermore, stopped-flow techniques were employed to determine kinetic parameters of Ru(phen)(2)(dppz)(2+) binding to DNA under pseudo-first-order conditions. It was found that the interaction of Ru(phen)(2)(dppz)(2+) with DNA was very fast. A two-step reaction mechanism, a fast phase followed by a slow phase, was proposed.