Target Deoxyribonucleic Acid-Recycled Lighting-Up Amplifiable Ratiometric Fluorescence Biosensing of Bicolor Silver Nanoclusters Hosted in a Switchable Deoxyribonucleic Acid Construct

Abstract

Ratiometric assays of label-free dual-signaling reporters with enzyme-free amplification are intriguing yet challenging. Herein, yellowand red-silver nanocluster (yH-AgNC and rH-AgNC) acting as bicolor ratiometric emitters are guided to site-specifically cluster in two template signaling hairpins (yH and rH), respectively, and originally, both of them are almost non-fluorescent. The predesigned complement tethered in yH is recognizable to a DNA trigger (T OC ) related to SARS-CoV-2. With the help of an enhancer strand (G 15 E) tethering G-rich bases (G 15 ) and a linker strand (LS), a switchable DNA construct is assembled via their complementary hybridizing with yH and rH, in which the harbored yH-AgNC close to G 15 is lighted-up. Upon introducing T OC , its affinity ligating with yH is further implemented to unfold rH and induce the DNA construct switching into closed conformation, causing T OC -repeatable recycling amplification through competitive strand displacement. Consequently, the harbored rH-AgNC is also placed adjacent to G 15 for turning on its red fluorescence, while the yH-AgNC is retainable. As demonstrated, the intensity ratio dependent on varying T OC is reliable with high sensitivity down to 0.27 pM. By lighting-up dualcluster emitters using one G 15 enhancer, it would be promising to exploit a simpler ratiometric biosensing format for bioassays or clinical theranostics.

Target DNA-Activating Proximity-Localized Catalytic Hairpin Assembly Enables Forming Split-DNA Ag Nanoclusters for Robust and Sensitive Fluorescence Biosensing

“…Short and specific DNA-templated multinuclear Ag nanoclusters (DNA/AgNCs) are formed by the stable coordination between nucleobases and reduced Ag atoms. , Because of the movement of their metal-like valence electrons among discrete electronic states, the resulting DNA/AgNC adducts exhibit intense optical absorption in biosensing and imaging. − As previously reported, the size, geometry, and electronic structure of DNA/AgNC conjugates are strongly influenced by nucleobase sequence and/or structure, thereby regulating the cluster spectra from near-ultraviolet to near-infrared. , Thus, the color and brightness of cluster adducts are drastically altered between hybridized versus single-stranded oligonucleotides. , This is the foundation to activate and “turn on” fluorescent biosensors via the affinity binding of a target DNA with a specific element, achieving greater gain in detection sensitivity. An interesting study focused on the spectra and photophysics of a green-fluorescent Ag 10 6+ cluster anchored in a two-split contiguous single-stranded oligonucleotide as the parent scaffold .…”

Metal Nanoclusters in Point-of-Care Sensing and Biosensing Applications

“…Schematic presentation of dual signaling DNA-AgNCs nanoprobe for determination of SARS-CoV-2 gene sequence. Reproduced from ref . Copyright 2022, American Chemical Society.…”

“…The intensity of the PL ratio varies with the concentration of T OC and is capable of detecting with high sensitivity, with a LOD of 0.27 pM. 338 DNA tweezers are dynamic nanodevices developed with DNA nanotechnology that can be reversibly switched between two open and closed statuses after adding a second DNA strand. 339 These nanomachines have been proved to be ideal tools with the capability of employing biosensing frameworks for their prompt directional movements caused by an external stimulus (e.g., a target DNA sequence, protein, or other environmental conditions like pH).…”

Detection of cancer‐associated miRNA using a fluorescence switch of AgNC@NA and guanine‐rich overhang sequences

“…Other strategies using G overhangs have been demonstrated in recent years due to the excellent AgNC emissive properties used as a readout strategy and the convenience of their incorporation into larger nucleic acid-based assemblies. [29][30][31][32][33] We first look at the optical properties of AgNCs templated by RS30-dC 12 DNA oligonucleotide. Different lengths and compositions of DNA overhangs were then paired with the RS30 template to study their effects on the electronic properties of the AgNCs, such as quantum yield and colour.…”