A fluorescent sensor was fabricated for the detection of radon based on the daughter lead inducing G-rich aptamer T30695 to form G-quadruplex.According to the characteristics of radon radioactive decay

it only takes about 3.82 days for radon to decay and form a stable daughter lead

and 210Pb derived from radon decay is very stable.The half-life period of the stable daughter（210Pb）resulted from radon is 21 years

and the lead daughter product could be used as the target for detection.When there was no lead in the system

T30695 combined with its complementary chain to form a double-stranded DNA structure

and the fluorescent signal of N-methyl mesoporphyrin IX（NMM）was weak.When the system contained daughter lead

aptamer T30695 was induced to form a G-quadruplex structure

and NMM combined with G-quadruplex structure to produce strong fluorescence.Within a certain range

the fluorescence intensity is positively correlated with the concentration of Pb2+ and radon.There existed a linear relationship btween the fluorescence value（ΔIF）of reaction system and Pb2+ concentration in the range of 5.13×10-9-1.25×10-7 mol/L

with a linear regression equation of ΔIF=77.30+5.05c

a detection limit of 1.54×10-9 mol/L and a correlation coefficient（r）of 0.995 0.The detection limit for radon was 1.07×104 Bq?h/m3.