Aptamer-based ratiometric fluorescent platform for selective detection of 17β-estradiol in environmental water

17β-estradiol (E2), a potent endocrine-disrupting chemical, is frequently detected in aquatic environments and food samples, where it poses serious ecological and public health risks even at trace levels. Herein, we report a label-free ratiometric fluorescent aptasensor for the sensitive and selective detection of E2, employing ethyl violet (EV) as a near-infrared (NIR) responsive dye and fluorescein (FL) as an internal reference. EV was identified through systematic screening based on its strong fluorescence response upon aptamer binding. The resulting sensor exhibited a pronounced ratiometric response, a low detection limit of 0.25 μM, and excellent selectivity against structural analogues. Its practical performance was validated using farm wastewater samples, yielding recoveries of 94.92-110.49% and relative standard deviations below 6.15%. With an estimated cost of approximately $0.11, this aptasensor provides a simple, economical, and reliable tool for monitoring estrogenic pollutants in complex environmental water samples.