A label-free colorimetric progesterone aptasensor based on the aggregation of gold nanoparticles

The authors describe an aptasensor for the detection of the gonadal hormone progesterone (P4) in aqueous solution. Gold nanoparticles (AuNPs) were coated with a P4-specific aptamer, and such particles do not aggregate in presence of NaCl due to the presence of the aptamer coating. If, however, progesterone is added, it will bind to the aptamer and release it from the surface. The uncoated AuNPs, on addition of NaCl, will aggregate and a color change from red (520 nm) to blue (650 nm) can be visually detected or photometrically quantified. The ratio of the absorbances at 650 and 520 nm is linearly related to the P4 concentration in the range from 2.6 to 800 nM. The complete detection range extends from 2.6 to 1400 nM, and the detection limit is 2.6 nM. Water containing various potential interferents, as well as tap water and urine, were spiked with P4 and the recoveries of P4 are in the range of 89.7-117.5%, 84.4-115.0% and 94.7-118.8%, respectively. This assay has a large potential with respect to the visual and instrumental determination of P4 in aquatic environment and urine.