Fluorescence Spectroscopy

Fluorescence Spectroscopy
(i) Fluorescence resonance energy transfer (FRET) is widely used in biology as a molecular ruler (i.e. to estimate distances between two fluorescent molecules). A FRET donor-acceptor pair had a Förster distance of 7.2 nm. If the efficiency of energy transfer between the donor and acceptor was 10%, what is the distance between the donor and acceptor?

(ii) The fluorescence intensity (I0) for an aqueous fluorophore was 100 units in the absence of a quencher, with the lifetime of the excited state (0) being 300 ns (i.e.
3 x 10-7 s). When a quencher was introduced at a concentration of 500 nM (i.e.
500 x 10-9 mol L-1), the fluorescence intensity decreased by 75% (i.e. If = 25 units). Using the information provided, calculate the Stern-Volmer constant (KSV) and the rate constant (kq) for the bimolecular quenching reaction.