Intraparticle and Interparticle Transferable DNA Walker Supported by DNA Micelles for Rapid Detection of MicroRNA

Lighting up Lipidic Nanoflares with Self-Powered and Multivalent 3D DNA Rolling Motors for High-Efficiency MicroRNA Sensing in Serum and Living Cells

Intelligent DNA nanomachines are powerful and versatile molecular tools for bioimaging and biodiagnostic applications; however, they are generally constrained by complicated synthetic processes and poor reaction efficiencies. In this study, we developed a simple and efficient molecular machine by coupling a self-powered rolling motor with a lipidic nanoflare (termed RMNF), enabling high-contrast, robust, and rapid probing of cancer-associated microRNA (miRNA) in serum and living cells. The lipidic nanoflare is a cholesterol-based lipidic micelle decorated with hairpin-shaped tracks that can be facilely synthesized by stirring in buffered solution, whereas the 3D rolling motor (3D RM) is a rigidified tetrahedral DNA scaffold equipped with four single-stranded "legs" each silenced by a locking strand. Once exposed to the target miRNA, the 3D RM can be activated, followed by self-powered precession based on catalyzed hairpin assembly (CHA) and lighting up of the lipidic nanoflare. Notably, the multivalent 3D RM that moves using four DNA legs, which allows the motor to continuously and acceleratedly interreact with DNA tracks rather than dissociate from the surface of the nanoflare, yielded a limit of detection (LOD) of 500 fM at 37 °C within 1.5 h. Through the nick-hidden and rigidified structure design, RMNF exhibits high biostability and a low false-positive signal under complex physiological settings. The final application of RMNF for miRNA detection in clinical samples and living cells demonstrates its considerable potential for biomedical imaging and clinical diagnosis.

Fluid Multivalent Recognition Accelerating and Boosting Upconversion Luminescence-Activated DNA Nanomachines for Rapid and Sensitive In Vivo Imaging

By integrating near-infrared (NIR) light-dependent optical control and DNA walkers-based signal amplification, upconversion luminescence-activated DNA nanomachines hold great potential in conducting an in vivo analysis. For the typical DNA nanomachines, the immobile multivalent recognition interface greatly compromised the reaction kinetics and amplification efficiency due to the cleavage-dependent response mode. In this work, novel upconversion luminescence-activated DNA nanomachines with a fluid multivalent recognition interface were reported for rapid and sensitive in vivo imaging. As a proof-of-concept study, the photolocked DNAzyme-based walker system was anchored on the surface of phospholipid membrane-coated upconversion nanoparticles through the cholesterol-phospholipid interaction to acquire a fluid multivalent recognition interface. Upon sequential inputs of NIR light and metal ions, the formed DNA nanomachines were autonomously initiated and generated a cascade of amplified signal. Relative to the typical DNA nanomachines, the proposed ones possess an accelerated reaction rate and an improved amplification capability owing to a higher local concentration by the lateral mobility. The present work provides a versatile alternative for performing precise and highly efficient in vivo analysis.

The rate-limiting procedure of 3D DNA walkers and their applications in tandem technology

DNA walkers, artificial dynamic DNA nanomachines, can mimic actin to move rapidly along a predefined nucleic acid track. They can generally be classified as one- (1D), two- (2D), and three-dimensional (3D) DNA walkers. In particular, 3D DNA walkers demonstrate amazing sustainable walking ability, strong enrichment ability, and fantastic signal amplification ability. In light of these, 3D DNA walkers have been widely used in fields such as biosensors, bioanalysis and cell imaging. Most notably, the strong compatibility of 3D DNA walkers allows their integration with a range of amplification strategies, effectively enhancing signal transduction and amplifying biosensor sensing signals. Herein, we first systematically expound the walking principle of the 3D walkers in this review. Then, by presenting representative examples, the research direction of 3D walkers in recent years is discussed. Furthermore, we also categorize and evaluate diverse tandem signal amplification strategies in 3D walkers. Finally, the challenges and development trends of 3D DNA walkers in the emerging field of analysis are carefully discussed. It is believed that this work can provide new ideas for researchers to quickly understand 3D DNA walkers and their applications in diverse biosensors.

Well-Aligned Track-Accelerated Tripedal DNA Walker for Photoelectrochemical Recognition of Dual-miRNAs Based on Molecular Logic Gates

Post-transcriptional regulators, microRNAs (miRNAs), are involved in the occurrence and progression of various diseases. However, due to the complexity of disease-related miRNA regulatory networks, the typing and identification of miRNAs have remained challenging. Herein, a linear ladder-like DNA nanoarchitecture (LDN) was constructed to promote the movement efficiency of the tripedal DNA walker (T-walker), which was combined with the DNA-based logic gates and the PTCDA@PDA/CdS/WO₃ photoelectrode to develop a novel biosensor for the detection of dual-miRNAs. Two miRNAs, miR-122 and miR-21, were used as targets to operate the logic module, while its output, trigger strands (TSs), initiated a catalytic hairpin assembly (CHA) reaction to form a T-walker. By using LDN as the track, the T-walker efficiently unfolded hairpin 4, which further hybridized with the alkaline phosphatase-modified hairpin 5 (AP-H5). The remaining AP can catalyze the ascorbic acid 2-phosphate (AAP) into ascorbic acid (AA), an ideal electron donor, thus resulting in a photocurrent change. The photocurrent signals of both AND and OR gates displayed a linear relationship with the logarithm of dual-miRNA concentrations with detection limits of 10.1 and 13.6 fM, respectively. Moreover, the intelligent and rational design of DNA tracks gives impetus to create a well-organized sensing interface with wide application in clinical diagnosis and cancer monitoring.

Electrostatic Interaction-Induced Aggregation-Induced Emission-Type AgAu Bimetallic Nanoclusters as a Highly Efficient Electrochemiluminescence Emitter for Ultrasensitive Detection of Glial Fibrillary Acidic Protein

Herein, the aggregation-induced emission (AIE)-type carboxymethyl chitosan (CMCS)@6-aza-2-thiothymine (ATT) templated AgAu bimetallic nanoclusters (CMCS@ATT-AgAu BMNCs) with superior electrochemiluminescence (ECL) emission were first synthesized to construct a biosensor for the ultrasensitive detection of glial fibrillary acidic protein (GFAP). Impressively, unlike the traditional AIE-type bimetallic nanoclusters (BMNCs) obtained by complicated multi-step synthesis, the AIE-type CMCS@ATT-AgAu BMNCs were prepared by the electrostatic interaction between the negatively charged ATT and positively charged CMCS, in which the molecule ATT was served as a capping and reducing agent of bimetal ions. In addition, a rapidly moving cholesterol labeled DNA walker was constructed to move freely on the lipid bilayer to increase its moving efficiency, and the well-regulated DNA was intelligently designed to further improve its walking efficiency for rapid and ultrasensitive detection of GFAP with a limit of detection (LOD) as low as 73 ag/mL. This strategy proposed an avenue to synthesize highly efficient BMNCs-based ECL emitters, which have great potential in ultrasensitive biosensing for early diagnosis of diseases.

A General Signal Amplifier of Self-Assembled DNA Micelles for Sensitive Quantification of Biomarkers

Owing to the excellent structural rigidity and programmable reaction sites, DNA nanostructures are more and more widely used, but they are limited by high cost, strict sequence requirements, and time-consuming preparation. Herein, a general signal amplifier based on a micelle-supported entropy-driven circuit (MEDC) was designed and prepared for sensitive quantification of biomarkers. By modifying a hydrophobic cholesterol molecule onto a hydrophilic DNA strand, the amphiphilic DNA strand was first prepared and then self-assembled into DNA micelles (DMs) driven by hydrophobic effects. The as-developed DM showed unique advantages of sequence-independence, easy preparation, and low cost. Subsequently, amplifier units DMF and DMTD were successfully fabricated by connecting fuel strands and three-strand duplexes (TDs) to DMs, respectively. Finally, the MEDC was triggered by microRNA-155 (miR-155), which herein acted as a model analyte, resulting in dynamic self-assembly of poly-DNA micelles (PDMs) and causing the recovery of cyanine 3 (Cy3) fluorescence as the DMTD dissociated. Benefiting from the "diffusion effect", the MEDC herein had a nearly 2.9-fold increase in sensitivity and a nearly 97-fold reduction in detection limit compared to conventional EDC. This amplifier exhibited excellent sensitivity of microRNAs, such as miR-155 detection in a dynamic range from 0.05 to 4 nM with a detection limit of 3.1 pM, and demonstrated outstanding selectivity with the distinguishing ability of a single-base mismatched sequence of microRNAs. Overall, the proposed strategy demonstrated that this sequence-independent DNA nanostructure improved the performance of traditional DNA probes and provided a versatile method for the development of DNA nanotechnology in biosensing.

Telomerase-initiated three-dimensional DNAzyme motor for monitoring of telomerase activity in living cells

Telomerase (TE) is recognized as a potential biomarker for early diagnosis, monitoring and treatment of cancer. At present, most of the methods for TE detection are only applicable to in vitro assays, and unsuitable for in vivo applications. Though a few intracellular probes have been reported to have good specificity for TE, they do not involve signal amplification, which hinders their applicability in scenarios requiring high sensitivity. It is rather challenging to develop highly sensitive biosensors for intracellular TE detection due to the difficulty in design TE probes with both high specificity and compatibility with signal amplification in living cells. Herein, a highly sensitive and selective three-dimensional DNAzyme motor for monitoring of TE activity in living cells was developed by innovatively integrating TE-mediated chain replacement reaction with a three-dimensional DNA walker. Specifically, the DNAzyme motor was constructed by assembling both DNAzyme substrates and swing arms made up of a hairpin-structured DNAzyme and a telomeric primer onto gold nanoparticles. TE in cells can activate the DNAzyme motor to carry out continuous chain replacement and substrate cutting reactions, and hence realize signal amplification in living cells. The DNAzyme motor was successfully utilized to monitor the dynamic changes of TE activity in four types of cells. Due to the advantages of simple synthesis, good biocompatibility and high sensitivity and specificity for TE, the proposed DNAzyme motor is expected to have great application potential in the early diagnosis of cancer.

Highly Efficient Quadruped DNA Walker Guided by Ordered DNA Tracks for Rapid and Ultrasensitive Electrochemical Detection of miRNA-21

Herein, a long period liner DNA tandem (Lr-DNT) was intelligently designed as DNA track for quadruped DNA walker (q-walker) to run in an orderly and efficient manner, which could be applied to construct an electrochemical biosensor for rapid and ultrasensitive detection of microRNA-21 (miRNA-21). Impressively, benefiting from the orderliness and equidistance of Lr-DNT, the q-walker could be endowed with a high controllability, directionality as well as a quite short reaction time down to 20 min compared with those of traditional DNA walkers walked on the stochastic tracks. Once the target miRNA-21 interacted with the locked q-walker, the q-walker could be activated to expeditiously cleave Lr-DNT for releasing amounts of signal probes ferrocene (Fc) with the assistance of the Nt.BbvCI enzyme. This way, the developed q-walker could not only readily overcome the problem of low reaction efficiency but also address the drawback of time consumption in a previous strategy. As a proof of concept, the prepared biosensor could accomplish sensitive detection of target miRNA-21 with a detection limit down to 31 aM. As a result, this tactic gave impetus to design high-performance sensing platform with ultimate application in clinical sample analysis and nucleic acid based cancer diagnostics.

Highly Efficient Electrochemiluminescence Based on Luminol/MoS2 Quantum Dots@Zeolitic Imidazolate Framework-8 as an Emitter for Ultrasensitive Detection of MicroRNA

Herein, a highly efficient electrochemiluminescence (ECL) emitter, luminol/MoS₂ quantum dots@zeolitic imidazolate framework-8 (Lu/MoS₂ QDs@ZIF-8), with a positive charge was prepared to construct a novel luminol-H₂O₂-MoS₂ QD ternary ECL system for ultrasensitive detection of microRNA-21 (miRNA-21). The porous Lu/MoS₂ QDs@ZIF-8 was beneficial for reducing the accessible distance between various participants in the ternary system wherein co-reaction accelerator MoS₂ QDs promoted H₂O₂ to generate superoxide anion radicals (O₂^•-), which instantaneously reacted with luminol to produce robust ECL signals. Simultaneously, the positively charged Lu/MoS₂ QDs@ZIF-8 facilitated the enrichment of O₂^•- to further improve the ECL efficiency of luminol. Impressively, compared with the traditional binary luminol-H₂O₂ system, the ECL efficiency of this ternary system was increased by 12.7 times. In the aid of a target-cycled and endogenous adenosine triphosphate-driven signal amplification strategy, the biosensor with Lu/MoS₂ QDs@ZIF-8 as an ECL emitter achieved ultrasensitive detection for miRNA-21 with a detection limit of 14.6 aM. This work provides a promising perspective to construct a highly efficient ECL ternary system for biomolecule detection and potential disease diagnosis.

Dynamic 3D DNA Rolling Walkers via Directional Movement on a Lipid Bilayer Supported by Au@Fe3O4 Nanoparticles for Sensitive Detection of MiRNA-16

Currently reported polyfluorene-based fluorescence detection usually shows high background signal and low detection sensitivity. This work developed a novel three-dimensional (3D) DNA rolling walker via directional movement on a lipid bilayer (LB) supported by Au@Fe₃O₄ nanoparticles (NPs) in a polyfluorene-based fluorescence system so that it could achieve significantly improved detection sensitivity and almost zero-background signal detection for miRNA-16. First, the carboxyl-functionalized poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadazole)] polymer nanoparticles (c-PFBT PNPs) covalently bonded with amino-labeled single-strand CP and further hybridized with single-strand AP to prepare AP-CP-coupled c-PFBT PNP probes. Meanwhile, Au@Fe₃O₄ NPs were developed as efficient fluorescence quenchers and served as the matrix for assembling the LB. The resulting Au@Fe₃O₄@LB assembled cholesterol-labeled orbital DNA L1 and L2 and further assembled hairpins H1 and AP-CP-coupled c-PFBT PNP probes to construct DNA nanomachines. Then, the target miRNA-16 was introduced to initiate the rolling circle amplification (RCA) reaction and form dynamic DNA rolling walkers, thus releasing single-strand CP-coupled c-PFBT PNP probes. The magnetic separation effect of Au@Fe₃O₄ NPs made it possible to detect the fluorescence signal from the released probes, thus achieving almost zero-background signal detection for miRNA-16 with a low detection limit of 95 aM. The flexible interfaces provided by the LB endowed the DNA rolling walkers with high binding efficiency and low derailment probability, thus achieving significantly improved detection sensitivity. The developed strategy provided an attractive polyfluorene-based fluorescence platform with high-sensitivity and low-background signals.