Real milk sample assisted selection of specific aptamer towards sarafloxacin and its application in establishment of an effective aptasensor

A novel real sample assisted SELEX strategy was proposed to rationally select SAR aptamer. Based on this real SELEX strategy, we obtained an aptamer Apt-F2 with higher specificity and SAR binding affinity than Apt-B4 selected by the standard SELEX strategy. Moreover, Apt-F2-based aptasensor showed higher detection sensitivity and slightly better recovery rate of SAR from spiked milk samples than Apt-B4-based aptasensor. All of these results indicated the advantage of the real SELEX strategy superior to traditional SELEX strategy. • Real sample assisted SELEX strategy can rationally select more fitted aptamer. • Real SELEX strategy can make aptamer pre-adapt to real sample. • Apt-F2 with higher specificity and SAR binding affinity was selected by this strategy. • An ease operated fluorescence aptasensor was fabricated based on Apt-F2. • The aptasensor had high sensitivity, specificity and low cost for detection of SAR. The aptamers screened by the classic SELEX strategy or other approaches do not undergo the real sample analysis during the selection process, and the environmental inconsistency between the selection and final detection systems might influence the aptamer characteristics and detection performance. Herein, a novel real sample assisted SELEX selection strategy has been proposed to rationally select the suitable aptamers with high detection performance, using the selection of a sarafloxacin (SAR) specific aptamer as an example. Based on the developed strategy, the aptamer Apt-F2 with higher specificity and SAR binding affinity was obtained as compared to the aptamer Apt-B4 selected by the standard SELEX strategy. Apt-F2 also exhibited a stronger conformational change after binding as compared to Apt-B4. Apt-B4 and Apt-F2 were used as a platform for developing the fluorescent aptasensor. Under optimized conditions, the limit of detection of Apt-B4- and Apt-F2-based aptasensors for SAR was 0.19 and 0.12 ng/mL respectively. Moreover, Apt-F2-based aptasensor also revealed a slightly superior SAR recovery rate from the spiked milk samples. The findings obtained in the study confirmed the advantage of the real SELEX strategy as compared to the traditional version. Further, the characteristics of the aptasensor proposed here also revealed its application potential for detecting SAR in the real milk or other animal-sourced food samples.