CdTe Quantum Dots As A Probe For Interaction Between Salmon Sperm DNA And Riboflavin

Quantum dots (QDs) is also known semiconductor nanocrystal which size is within 10 nm. It is composed of IIIB ~ VB or IIB ~ VIB race element. QDs shows many unique optical and physical chemical characteristics: strong and stable fluorescence intensity, high quantum yields, strong anti-photobleaching ability, anti-chemical degradation, broad excitation spectrum, narrow and tunable emission spectrum, larger stokes shift. In recent years, as a fluorescence probe, QDs has drawn more and more attentions in the field of biology and biomedical applications.The water-soluble QDs was synthesized using mercaptopropionic acid as stabilizer. The interaction of Riboflavin (RF) with salmon sperm DNA was investigated by employing CdTe QDs as a fluorescence probe. In pH 7.25 Britton-Robinson (B-R) buffer solution, the fluorescence emission intensity of RF decreased significantly as the addition of DNA which demonstrated that RF embedded into the double helix of DNA by hydrogen bonds; in the UV-Vis spectra of DNA in the existence of RF hypochromism was shown which evidenced that RF embedded into the base pairs of DNA; the regularly change of circular dichroism (CD) spectra indicated that almost all of RF combined with DNA base, which caused change of the DNA double helix. The consistent conclusions were obtained from fluorescence spectra, UV-Vis spectra and CD spectra, which proved the intercalation between RF and DNA.Salt effect experiments showed that the fluorescence quenching was weakened which caused by a large number of Na+ formed a cation atmosphere around the phosphate anions of DNA as RF embedded into DNA, it is the evidence of intercalation between RF and DNA; thermal denaturation temperature (Tm) of DNA combined with RF was much higher than with CdTe QDs. It is another evidence of intercalation between RF and DNA. The information about different concentration ratios of DNA and RF, such as binding sites, binding constants, interaction modes, was obtained by Scachard equation. All of experimental results proved that intercalation and electrostatic binding existed simultaneously between RF and DNA.