In this paper, a fast and simple strategy for sensitive detection of streptavidin (SA) was proposed based on terminal protection of small molecule-linked DNA and cationic conjugated polymer-mediated fluorescence resonance energy transfer (FRET). In principle, we designed a biotin-labelled DNA probe (P1) as the recognitive probe of SA, along with a complementary DNA probe (P2) to form double-stranded DNA (dsDNA) with P1. SYBR Green I (SG I) as a fluorescent dye was further used to specifically bind to dsDNA to emit stronger fluorescence. The cationic poly[(9,9-bis(6'-N,N,N-triethy-lammonium)hexyl) fluorenylene phenylene dibromide] (PFP) acted as the donor to participate in the FRET and transfer energy to the recipient SG I. In the absence of SA, P1 could not hybridize with P2 to form dsDNA and was digested by exonuclease I (Exo I); thus, only a weak FRET signal would be observed. In the presence of SA, biotin could specifically bind to SA, which protected P1 from Exo I cleavage. Then, P1 and P2 were hybridized into dsDNA. Therefore, the addition of SG I and PFP led to obvious FRET signal due to strong electrostatic interactions. Then, SA can be quantitatively detected by monitoring FRET changes. As the whole reagent reaction was carried out in 1.5 mL EP and detected in the colorimetric dish, the operation process of the detection system was relatively simple. The response time for each step was also relatively short. In this detection system, the linear equation was obtained for SA from 0.1 to 20 nM with a low detection limit of 0.068 nM (S/N = 3). In addition, this strategy has also achieved satisfactory results in the application of biological samples, which reveals the application prospect of this method in the future.
Keywords: FRET; conjugated polymer; streptavidin; terminal protection.