Optimization of acridine orange loading on 1:1 layered clay minerals for fluorescence enhancement

Abstract

As a cationic fluorescence dye acridine orange (AO) is commonly used in biology and biochemistry for DNA analyses. In this study the light absorption and fluorescence of AO after being sorbed on kaolinite (Kao) and halloysite (Hal) were investigated. In dilute systems with initial AO concentrations of 1×10−6 to 1×10−4M (0.3–25μmol/g loadings on Kao), both light absorption and fluorescence emission increased as the initial AO concentrations, thus, the amounts of AO sorbed increased. In contrast, the light absorption and fluorescence emission reached maxima at 1×10−5M (3μmol/g) for Hal. In concentrated systems with initial AO concentrations of 5×10−4–5×10−3M (22–57 and 50–126μmol/g AO sorption on Kao and Hal), significant fluorescence quenching was observed and the fluorescence intensity decreased as the initial AO concentrations, thus, the amounts of AO sorbed increased. The results suggested that to achieve maximal fluorescence emission, monomeric AO configuration on the solid surface is a necessity. The AO sorption was mostly attributed to cation exchange between protonated AO and exchangeable cations on Kao and Hal surfaces. As such, both cation exchange capacity and specific surface area of the minerals control the maximal fluorescence emission.