An RNase H-powered DNA walking machine for sensitive detection of RNase H and the screening of related inhibitors

Temporally controlled multistep division of DNA droplets for dynamic artificial cells

Synthetic droplets mimicking bio-soft matter droplets formed via liquid-liquid phase separation (LLPS) in living cells have recently been employed in nanobiotechnology for artificial cells, molecular robotics, molecular computing, etc. Temporally controlling the dynamics of synthetic droplets is essential for developing such bio-inspired systems because living systems maintain their functions based on the temporally controlled dynamics of biomolecular reactions and assemblies. This paper reports the temporal control of DNA-based LLPS droplets (DNA droplets). We demonstrate the timing-controlled division of DNA droplets via time-delayed division triggers regulated by chemical reactions. Controlling the release order of multiple division triggers results in order control of the multistep droplet division, i.e., pathway-controlled division in a reaction landscape. Finally, we apply the timing-controlled division into a molecular computing element to compare microRNA concentrations. We believe that temporal control of DNA droplets will promote the design of dynamic artificial cells/molecular robots and sophisticated biomedical applications.

Programmably engineered stochastic RNA nanowalker for ultrasensitive miRNA detection

A programmably engineered stochastic RNA nanowalker powered by duplex-specific nuclease (DSN) is developed. By utilizing poly-adenine-based spherical nucleic acids (polyA-SNA) to accurately regulate the densities of DNA tracks, the nanowalker showcases its capability to identify miRNA-21, miRNA-486, and miRNA-155 with quick kinetics and attomolar sensitivity, positioning it as a promising option for cancer clinical surveillance.

An amplification-free CRISPR/Cas12a-based fluorescence assay for ultrasensitive detection of nuclease activity

Nuclease, such as RNase H and DNase I, plays key roles in plenty of cellular processes and could be potential therapeutic target for drug development. It is necessary to establish rapid and simple-to-use methods to detect nuclease activity. Herein, we develop a Cas12a-based fluorescence assay without any nucleic acid amplification steps for ultrasensitive detection of RNase H or DNase I activity. By our design, the pre-assembled crRNA/ssDNA duplex triggered the cleavage of fluorescent probes in the presence of Cas12a enzymes. However, the crRNA/ssDNA duplex was selectively digested with the addition of RNase H or DNase I, which leaded to fluorescence intensity changes. Under optimized conditions, the method exhibited good analytical performance, achieving a limit of detection (LOD) as low as 0.0082 U/mL for RNase H and 0.13 U/mL for DNase I, respectively. The method was feasible for analysis of RNase H in human serum and cell lysates, as well as for screening of enzyme inhibitors. Moreover, it can be adopted to image RNase H activity in living cells. Together, this study provides a facile platform for nuclease detection and could be expanded for other biomedical research and clinical diagnostics.

A visual detection strategy for SARS-CoV-2 based on dual targets-triggering DNA walker

SARS-CoV-2, a highly transmissible and mutagenic virus, made huge threats to global public health. The detection strategies, which are free from testing site requirements, and the reagents and instruments are portable, are vital for early screening and play a significant role in curbing the spread. This work proposed a silver-coated glass slide (SCGS)/DNA walker based on a dual targets-triggering mechanism, enzyme-catalyzed amplification, and smartphone data analysis, which build a portable visual detection strategy for the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) gene. By this method, the detection was reflected by the ultraviolet absorbance changes and visible color changes to the naked eye which was analyzed by Red-Green-Blue (RGB) data analysis via smartphone within 30 min, simplifying the detection process and shortening the detection time. Meanwhile, the dual targets-triggering mechanism and dual signal amplification strategy ensured detection specificity and sensitivity. Further, the practicability was verified by the detection of the real sample which provided this method an application potential in SARS-CoV-2 rapid detection.

DNA-functionalized gold nanoparticles: Modification, characterization, and biomedical applications

With the development of technologies based on gold nanoparticles (AuNPs), bare AuNPs cannot meet the increasing requirements of biomedical applications. Modifications with different functional ligands are usually needed. DNA is not only the main genetic material, but also a good biological material, which has excellent biocompatibility, facile design, and accurate identification. DNA is a perfect ligand candidate for AuNPs, which can make up for the shortcoming of bare AuNPs. DNA-modified AuNPs (DNA-AuNPs) have exciting features and bright prospects in many fields, which have been intensively investigated in the past decade. In this review, we summarize the various approaches for the immobilization of DNA strands on the surface of AuNPs. Representative studies for biomedical applications based on DNA-AuNPs are also discussed. Finally, we present the challenges and future directions.

Nucleic acid isothermal amplification-based soft nanoarchitectonics as an emerging electrochemical biosensing platform

The emergence of nucleic acid isothermal amplification strategies based on soft nanoarchitectonics offers a new dimension to the traditional electrochemical technique, particularly because of its flexibility, high efficiency, and increased sensitivity for analytical applications. Various DNA/RNA isothermal amplification strategies have been developed for the design and fabrication of new electrochemical biosensors for efficient and important biomolecular detection. Herein, we provide an overview of recent efforts in this research field and the strategies for signal-amplified sensing systems, with their biological applications, current challenges and prospects in this promising new area.

A Novel DNAzyme Signal Amplification-based Colorimetric Method for RNase H Assays

A simple visual strategy was developed for the RNase H colorimetric measurement using DNAzyme-mediated signal amplification. When RNase H was presented, the RNA strand of the duplex formed by the G-rich DNA sequence (G-Rich) and its complementary RNA sequence (cp-RNA) was digested, releasing G-Rich to form HRP-mimicking DNAzymes of the G-quadruplex/hemin complexes in the presence of hemin. These DNAzymes catalyze the oxidation reaction of the substrate of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) to produce green-color products of ABTS^•-, allowing for the detection of RNase H. A horseradish peroxidase (HRP)-mimicking DNAzyme of the G-quadruplex/hemin complex was used to mediate the signal amplification in the sensing strategy, resulting in high selectivity and sensitivity. This proposed colorimetric method shows a low detection limit of 0.04 U/mL, with a detection range of 0.1 to 3 U/mL. Moreover, this colorimetric method has been successfully used for RNase H assays in complicated biosamples, such as cell lysates. These results indicate that our colorimetric method not only detects RNase H in an ideal system, but also in real samples.

DNA-based ribonuclease detection assays

Ribonucleases are useful as biomarkers and can be the source of contamination in laboratory samples, making ribonuclease detection assays important in life sciences research. With recent developments in DNA-based biosensing, several new techniques are being developed to detect ribonucleases. This review discusses some of these methods, specifically those that utilize G-quadruplex DNA structures, DNA-nanoparticle conjugates and DNA nanostructures, and the advantages and challenges associated with them.

A CHA-based DNA stochastic walker that traverses on cell membranes

DNA walkers, imitating protein motors, are a class of nucleic acid nanodevice that can move along a precisely defined "track". With a promising future in materials and biotechnology, DNA walkers have gained extensive attention among researchers. Here, we introduce a catalytic hairpin assembly (CHA)-based DNA walker on cell membranes. We designed hairpin strand (H1) modified cells as tracks. Driven by DNA strand exchange, catalytic strands move on cell membranes and other hairpin strands (H2) in the solution are loaded on cells. Additionally, we also introduce a CHA-based DNA motor and use the motor for cell membrane target sensing.

An integrated fluorescence biosensor for microRNA detection based on exponential amplification reaction-triggered three-dimensional bipedal DNA walkers

Sensitive and specific miRNA detection is essential for the early cancer diagnosis. In this work, we design a fluorescent microRNA biosensor based on exponential amplification reaction (EXPAR) and nicking endonuclease-powered three-dimensional (3-D) bipedal DNA walkers (BDW). Target microRNA initiates EXPAR with the help of polymerase and nicking endonuclease to generate the large number of BDW in solution. The newly generated BDW can be continuously assembled onto polystyrene microsphere track co-modified with fluorescence-labeled DNA strand. Thus, in the presence of nicking endonuclease, the walking machine is activated to produce enhanced fluorescent signal in the supernatant. Besides, we prove that BDW holds the faster walking speed than single-legged DNA walker (SDW) based on comparative study. Under optimal conditions, the proposed amplification method owns a wide linear range from 10 fM to 5 nM with a detection limit down to 5.2 fM. The reaction time of the assay takes about 70 min. The combination of enzyme-assisted EXPAR in solution and enzyme-powered BDW on particle significantly increases the signal amplification efficiency and improves the detection sensitivity. Therefore, our method has enormous potential for the application of BDW-related biosensors.

DNAzyme-powered DNA walking machine for ultrasensitive fluorescence aptasensing of kanamycin

A DNAzyme-powered DNA walking machine was constructed to develop the fluorescence aptasensing for sensitive detection of kanamycin. The aptamer for kanamycin is partially hybridized with complementary DNA (cDNA) modified on magnetic beads (MBs). The specific interaction of target and aptamer triggered the cDNA to be free tentatively, which captured walker DNA. Then the autonomous motion of DNA walker on MBs surface was propelled via DNAzyme digestion of recognition sites. The signal probe was separated, and the amplified fluorescence signal was achieved by the accumulation of the signal probe. Kanamycin was used as a model analyte, and the developed assay achieves a detection limit of 0.00039 ng·mL^-1 (S/N = 3) within a linear detection range from 0.001 to 2000 ng·mL^-1. This aptasensing strategy can be extended for detection of other antibiotics by adapting corresponding target recognition aptamer sequence. Graphical abstract The fluorescence aptasensing for sensitive detection of kanamycin based on DNAzyme-powered DNA walking machine was constructed.

Ribonuclease-Responsive DNA Nanoswitches

DNA has been used in the construction of dynamic DNA devices that can reconfigure in the presence of external stimuli. These nanodevices have found uses in fields ranging from biomedical to materials science applications. Here, we report a DNA nanoswitch that can be reconfigured using ribonucleases (RNases) and explore two applications: biosensing and molecular computing. For biosensing, we show the detection of RNase H and other RNases in relevant biological fluids and temperatures, as well as inhibition by the known enzyme inhibitor kanamycin. For molecular computing, we show that RNases can be used to enable erasing, write protection, and erase-rewrite functionality for information-encoding DNA nanoswitches. The simplistic mix-and-read nature of the ribonuclease-activated DNA nanoswitches could facilitate their use in assays for identifying RNase contamination in biological samples or for the screening and characterization of RNase inhibitors.