Antibody-powered lighting-up fluorescence immunosensor based on hemin/G-quadruplex-quenched DNA-hosted dual silver nanoclusters as emitters

Abstract

Immunosensors with many merits such as simplicity, high sensitivity and selectivity are intriguing for the detection of antibodies, especially bivalent antibody (e.g. anti-digoxin antibody, DigA). In this work, we report a sensitive immunosensor for DigA based on the switchable fluorescence of DNA-templated silver nanoclusters (AgNCs) modulated by hemin/G-quadruplex (hGq). To explore the fluorescing performance of one hGq-quenching dual-AgNCs (d-AgNCs), here we design a functional hosting DNA strand (HGH) encoding with one centered G-rich segment for forming hGq complex in the presence of hemin and K+, two terminated C-rich template sequences for the identical clustering of d-AgNCs, and two flanked symmetric domains for specific recognizing and linking. Because of the photoexcited electron transfer process to the stacked hGq, the originally presynthesized d-AgNCs colocalized in two ends are non-emissive, which are retainable after complementarily hybridizing with two recognizable single strands that are both tagged with a digoxigenin hapten, a Fab fragment. Upon introducing DigA, the steric strain associated with the affinity binding of two haptens results in the opening and stretch of hGq in a coil spacer, thereby lighting-up the d-AgNCs fluorescence. Based on one-step signal switch stimulated by targeting antibody, this label-free immunosensor strategy is of high specificity and sensitivity with low picomolar detection limit, as well as simplification, rapidness and cost-effectiveness.