A single-stranded DNA (ssDNA) aptamer specific for 6'-sialyllactose (6'-SL) was screened through magnetic separation-based SELEX and post-SELEX truncation and used to construct unique aptamer bio-dots for sensitive detection of 6'-SL. Eighteen rounds of screening were conducted during the SELEX process. The ssDNA aptamer Apt9 (Kd = 152.3 nM) with a length of 79 nucleotides (nt) was demonstrated as the optimal aptamer candidate after affinity and specificity evaluation. Then, Apt9 was truncated and optimized according to secondary structure and molecular docking. A 35 nt truncated aptamer Apt9-1 (Kd = 91.75 nM) with higher affinity than Apt9 was finally obtained. Furthermore, Apt9-1 was used to synthesize bio-dots as a new recognition element of 6'-SL, and the aminobenzene boric acid functionalized carbon dots were employed as the other recognition element. With the respective fluorescent characteristics, the two quantum dots (QDs) were made a pair to construct a 6'-SL fluorescent biosensor. The linear detection range of the biosensor is 10 μM to 5 mM, and the detection limit is 0.9 μM. With the advantages of time-saving, high efficiency, and simplicity in the actual sample detection, the screened aptamer and dual-QD-based biosensor have broad application prospects in 6'-SL detection.
Keywords: 6′-sialyllactose; SELEX; aptamer; bio-dots; fluorescent biosensor.