Embracing (conformational) change

A team at Colarado State University in Fort Collins developed a dual-beam fluorescence fluctuation spectroscopy method to monitor the reaction kinetics of the DNA hairpin. The methods combines single-beam fluorescence autocorrelation spectroscopy, dual beam fluorescence cross-correlation spectroscopy, and photon counting histogram analysis to probe the chemical relaxation properties of molecules in solution. The researchers measured the cross-correlation function of the fluorescence fluctuation while the molecules flowed between two spatially offset probe regions, created by focusing two spatially offset beams from an air-cooled 514.5 nm Ar+ laser. The fluorescence was collected by the objective and monitored using two single-photon-counting avalanche photodiode detectors. The researchers observed the complete folding trajectory of a DNA hairpin molecule containing a 21-nucleotide polythymine loop and a four-base-pair stem.