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Overcoming the limitations of traditional analytical methods and developing technologies to continuously monitor environments and produce a comprehensive picture of potential endocrine-disrupting chemicals (EDCs) has been an ongoing challenge. Herein, we developed a portable nuclear receptor (NR)-based biosensor within 90 min to perform highly sensitive analyses of a broad range of EDCs in environmental water samples. Based on the specific binding of the fluorescence-labeled NRs with their ligands, the receptors were attached to the EDC-functionalized fiber surface by competing with EDCs in the samples. The biosensor emitted fluorescence due to the evanescent wave excitation, thereby resulting in a turn-off sensing mode. The biosensor showed a detection limit of 5 ng/L E 2 -binding activity equivalent (E 2 -BAE) and 93 ng/L T 3 -BAE. As a case study, the biosensor was used to map the estrogenic binding activities of surface waters obtained from a rural community in the Yellow River basin in China. When the results obtained were compared with those from the traditional yeast two-hybrid bioassay, a high correlation was observed. It is anticipated that the good universality and versatility exhibited by this biosensor for various EDCs, which is achieved by using different NRs, will significantly promote the continuous assessment of global EDCs.

Surface blocking is a well-known process for reducing unwanted nonspecific adsorption in sensor fabrication, especially important in the emerging field where DNA/RNA applied. Bovine serum albumin (BSA) is one of the most popular blocking agents with an isoelectric point at pH 4.6. Although it is widely recognized that the adsorption of a blocking agent is strongly affected by its net charge and the maximum adsorption is often observed under its isoelectric form, BSA has long been perfunctorily used for blocking merely in neutral solution, showing poor blocking performances in the optical-fiber evanescent wave (OFEW) based sensing toward DNA target. To meet this challenge, we first put forward the view that isoelectric BSA (iep-BSA) has the best blocking performance and use an OFEW sensor platform to demonstrate this concept. An optical-fiber was covalently modified with amino-DNA, and further coupled with the optical system to detect fluorophore labeled complementary DNA within the evanescent field. A dramatic improvement in the reusability of this DNA modified sensing surface was achieved with 120 stable detection cycles, which ensured accurate quantitative bioassay. As expected, the iep-BSA blocked OFEW system showed enhanced sensing performance toward target DNA with a detection limit of 125 pM. To the best of our knowledge, this is the highest number of regeneration cycles ever reported for a DNA immobilized optical-fiber surface. This study can also serve as a good reference and provide important implications for developing similar DNA-directed surface biosensors.