Ultrasensitive evanescent wave optical fiber aptasensor for online, continuous, type-specific detection of sulfonamides in environmental water

Sensors capable for online continuous monitoring of total sulfonamides in environmental waters are highly desired due to their adverse effects on ecosystem, unexpected concentration fluctuation, and diversity. At present, no sensor with this capability has been reported. In this study, we evaluated the cross reactivity (CR) of the previously reported sulfadimethoxine-binding aptamer using DNase I assay and found that the aptamer was type-specific to sulfonamides. We then fabricated the first type-specific sulfonamide sensor, where the aptamer was immobilized on the optical fiber of the evanescent wave sensor, followed by the surface coating with Tween 80. The competitive binding of sulfonamides and Cy5.5 labeled complementary DNA enabled the low femtomolar to picomolar sensitivity and the detection of total 14 sulfonamides spiked in the lake water. The sensor also exhibited high selectivity, regeneration capability (40 cycles), stability (65 days), and short detection time (5 min). In addition, we found that the CRs were greatly dependent on the buffer composition. By performing the parallel detections in two buffers, the sensors detected 18 out of the 24 sulfonamides with the diversity coverage higher than commercial ELISA kits. Our aptasensor fills the technical gap for continuous monitoring of total sulfonamides in environmental waters.