Dual-functional β-CD@CdS nanorod/WS2 nanosheet heterostructures coupled with strand displacement reaction-mediated photocurrent quenching for an ultrasensitive MicroRNA-21 assay

In this work, we first introduced beta-cyclodextrin-functionalized CdS nanorod (beta-CD@CdS NR)/WS2 nanosheet (NS) heterostructures as dual-functional building blocks for designing an ultrasensitive photoelectrochemical bioassay of microRNA-21 based on cyclic strand displacement reaction (SDR)-mediated Cu2+ quenching and host-guest interaction between beta-CD and adamantane (ADA), in which beta-CD@CdS NR)/WS2 NS heterojunction serves as a signaling and linking unit, and avidin-labeled CuO (Avidin-CuO) nanoparticle as a quenching unit. In the presence of microRNA-21, ADA-labeled hairpin DNA1 was unfolded by DNA hybridization and triggered SDR cycling with the aid of biotin-labeled hairpin DNA2, which generated plenty of double-stranded DNA structures with biotin molecules at the outer terminal point of dsDNA. When Avidin-CuO was immobilized onto the electrode surface via biotin-avidin affinity binding and then dissolved by hydrochloric acid, the released Cu2+ could react with the CdS NR to generate CuxS, leading to a decreased photocurrent response. Under the optimized conditions, this biosensor displayed desirable linearity in the range from 0.1 fM to 10 pM, a low detection limit of 25.1 aM and satisfactory selectivity, and was applied to microRNA-21 analysis in serum samples, holding great potential for early diagnosis of some cancers. (C) 2019 Elsevier Ltd. All rights reserved.