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 (K
d = 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 (K
d = 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.
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