Highly Ordered and Field-Free 3D DNA Nanostructure: The Next Generation of DNA Nanomachine for Rapid Single-Step Sensing

Enhanced luminol electrochemiluminescence biosensing system based on highly dispersed bimetallic nanozyme coreaction accelerator and 3D DNA walker signal amplifier

In this work, a platinum-nickel based nanozyme is prepared and used as a coreaction accelerator in the luminol-H2O2 electrochemiluminescence (ECL) system to construct an ECL biosensor for dimethyl phthalate (DMP) detection. The PtNi/NC nanozyme possesses dispersed metal active sites, and the synergistic effect of Pt and Ni endows it with excellent catalytic performance, which effectively converts H2O2 into more superoxide anions, and then significantly enhances the ECL intensity of the luminol system. The ECL mechanism is investigated by combining cyclic voltammetry and ECL with different types of free radical scavengers. Simultaneously, an "off-on" biosensor is constructed by integrating 3D DNA walker with enzyme-free recycling amplification for ultrasensitive detection of DMP. The biosensor based on PtNi/NC nanozyme mediated luminol-H2O2 system and 3D DNA walker exhibits a linear range of 1 × 10-16 to 1 × 10-6 M with a detection limit of 4.3 × 10-17 M (S/N = 3), and displays good stability and specificity. This study demonstrates the advantages of PtNi/NC nanozyme in enhancing the luminol-H2O2 ECL system, providing new strategy for designing efficient ECL emitter and offering a new method for detecting phthalate esters.

A gold nanoparticle conjugated single-legged DNA walker driven by catalytic hairpin assembly biosensor to detect a prokaryotic pathogen

Catalytic hairpin assembly (CHA)-DNA walker allows nanostructures to spontaneously hybridize to the nucleic acids. The localized surface plasmon resonance provides the ability of color-shift for Au nanoparticles (AuNPs) to design a colorimetric biosensor by implementing CHA-DNA walker reaction on AuNPs. A target gene in Klebsiella pneumoniae as the reaction cascade trigger, was selected. H1 and H2 oligonucleotides as the components of the system were designed and verified by NUPACK. The AuNPs were conjugated to H1. The conjugation of the probes to the AuNPs was evaluated using FT-IR. The signal amplification process was conducted at 25℃. TEM imaging, zeta potential, spectroscopy, and gel-electrophoresis were used to examine the conduction of the reaction cascade and specificity. The sensitivity of the method was analyzed using serial dilution of the target. The formation of over-52 bp intermediate secondary structures (which only exist when the reaction happens) was confirmed by gel-electrophoresis. The color distinction between positive (0.08 to 0.058) and negative samples (0.098 to 0.05) was evidenced instantly and in a period of 90 min of the reaction as a drop change of 520 nm intensity absorbance. TEM imaging confirmed the further distance of AuNPs in the positive sample in comparison to that of the negative sample which reveals effective detection of the pathogen. The LOD of the technique was measured as 2.5 nM of the target sequence. The diagnostic approach is a label-free, enzyme-independent approach and can be executed in a single step. It has been designed by employing the CHA-DNA walker system along with the colorimetric properties of AuNPs for the first time, thereby paving the way for more rapid and accurate diagnostic kits.

NIR-photoactivatable DNA nanomachines for spatiotemporally controllable monitoring of microRNA-21 in living cells based on signal amplification strategy

Precise and spatiotemporally controllable analysis of microRNA-21 in living cells is crucial for accurate diagnosis and effective treatment of related diseases. Herein, a near-infrared (NIR)-photoactivatable DNA nanomachine (PUCNPs-NH2/PEG-ZL-DNA) was constructed for the precise analysis and diagnosis of microRNA-21 in tumor cells. Peanut-shaped upconversion nanoparticles (PUCNPs) were employed as the carriers and activators for the intelligent DNA probe, specifically enabling the cleavage of the photocleavable linker (PC-linker) from the hairpin DNA probe (Hp-Dzy) upon exposure to 808 nm irradiation. In the presence of the target microRNA-21, the locker DNA hybridized with microRNA-21 and the DNAzymes was freed to hybridize with the looped portion of the hairpin DNA (Hp-1). Mg2+ was employed as the cofactor, facilitating the precise cleavage of Hp-1, which triggered the restoration of fluorescence signals. Subsequently, DNAzymes exhibited the competency to selectively recognize and engage with additional Hp-1, and the fluorescence signals were effectively amplified by the recycling process. Consequently, the DNA nanomachine exhibited a linear response to microRNA-21 concentrations ranging from 0.5 nM to 1.0 μM, achieving a remarkable detection limit (LOD) of 1.19 nM under the optimal conditions. This strategy is realized through the integration of photocontrollable upconversion nanotechnology with the signal amplification approach, showing feasible prospects for spatiotemporally precise and highly sensitive monitoring of microRNA in tumor cells.

Nanoconfined Silver Nanoclusters Combined with X-Shaped DNA Recognizer-Triggered Cascade Amplification for Electrochemiluminescence Detection of APE1

Apurinic/apyrimidinic endonuclease 1 (APE1), as a vital base excision repair enzyme, is essential for maintaining genomic integrity and stability, and its abnormal expression is closely associated with malignant tumors. Herein, we constructed an electrochemiluminescence (ECL) biosensor for detecting APE1 activity by combining nanoconfined ECL silver nanoclusters (Ag NCs) with X-shaped DNA recognizer-triggered cascade amplification. Specifically, the Ag NCs were prepared and confined in the glutaraldehyde-cross-linked chitosan hydrogel network using the one-pot method, resulting in a strong ECL response and exceptional stability in comparison with discrete Ag NCs. Furthermore, the self-assembled X-shaped DNA recognizers were designed for APE1 detection, which not only improved reaction kinetics due to the ordered arrangement of recognition sites but also achieved high sensitivity by utilizing the recognizer-triggered cascade amplification of strand displacement amplification (SDA) and DNAzyme catalysis. As expected, this biosensor achieved sensitive ECL detection of APE1 in the range of 1.0 × 10-3 U·μL-1 to 1.0 × 10-10 U·μL-1 with the detection limit of 2.21 × 10-11 U·μL-1, rendering it a desirable approach for biomarker detection.

DNA Framework-Based Programmable Atom-Like Nanoparticles for Non-Coding RNA Recognition and Differentiation of Cancer Cells

The cooperative diagnosis of non-coding RNAs (ncRNAs) can accurately reflect the state of cell differentiation and classification, laying the foundation of precision medicine. However, there are still challenges in simultaneous analyses of multiple ncRNAs and the integration of biomarker data for cell typing. In this study, DNA framework-based programmable atom-like nanoparticles (PANs) are designed to develop molecular classifiers for intra-cellular imaging of multiple ncRNAs associated with cell differentiation. The PANs-based molecular classifier facilitates signal amplification through the catalytic hairpin assembly. The interaction between PAN reporters and ncRNAs enables high-fidelity conversion of ncRNAs expression level into binding events, and the assessment of in situ ncRNAs levels via measurement of the fluorescent signal changes of PAN reporters. Compared to non-amplified methods, the detection limits of PANs are reduced by four orders of magnitude. Using human gastric cancer cell lines as a model system, the PANs-based molecular classifier demonstrates its capacity to measure multiple ncRNAs in living cells and assesses the degree of cell differentiation. This approach can serve as a universal strategy for the classification of cancer cells during malignant transformation and tumor progression.

Dual-responsive 3D DNA nanomachines cascaded hybridization chain reactions for novel self-powered flexible microRNA-detecting platform

The microRNA-21 is closely related to chromatin remodeling and epigenetic regulation. In this work, an efficient double-response 3D DNA nanomachine (DRDN) was assembled by co-immobilizing two different lengths of hairpin DNA on the surface of gold nanoparticles (AuNPs) to capture microRNA-21 (miRNA-21), recycle miRNA-21, and trigger hybridization chain reactions (HCR). This work reports the fabrication of a laser-scribed graphene (LSG) electrode with excellent flexibility and electrical conductivity by laser-scribing commercial polyimide films (PI). The as-proposed self-powered biosensing platform presents significantly increased instantaneous current to in real-time monitor miRNA-21 by a capacitor. The biosensing platform exhibited highly sensitive detection of miRNA-21 with a detection limit of 0.142 fM in the range of 0.5 fM to 1 × 104 fM, and demonstrated high efficiency in the analysis of the tumor markers.

Logic Signal Amplification System for Sensitive Electrochemiluminescence Detection and Subtype Identification of Cancer Cells

Achieving sensitive detection and accurate identification of cancer cells is vital for diagnosing and treating the disease. Here, we developed a logic signal amplification system using DNA tetrahedron-mediated three-dimensional (3D) DNA nanonetworks for sensitive electrochemiluminescence (ECL) detection and subtype identification of cancer cells. Specially designed hairpins were integrated into DNA tetrahedral nanostructures (DTNs) to perform a catalytic hairpin assembly (CHA) reaction in the presence of target microRNA, forming hyperbranched 3D nanonetworks. Benefiting from the "spatial confinement effect," the DNA tetrahedron-mediated catalytic hairpin assembly (DTCHA) reaction displayed significantly faster kinetics and greater cycle conversion efficiency than traditional CHA. The resulting 3D nanonetworks could load a large amount of Ru(phen)32+, significantly enhancing its ECL signal, and exhibit detection limits for both miR-21 and miR-141 at the femtomolar level. The biosensor based on modular logic gates facilitated the distinction and quantification of cancer cells and normal cells based on miR-21 levels, combined with miR-141 levels, to further identify different subtypes of breast cancer cells. Overall, this study provides potential applications in miRNA-related clinical diagnostics.

Proximity hybridization induced molecular machine for signal-on electrochemical detection of α-synuclein oligomers

α-synuclein oligomer is a marker of Parkinson's disease. The traditional enzyme-linked immunosorbent assay for α-synuclein oligomer detection is not conducive to large-scale application due to its time-consuming, high cost and poor stability. Recently, DNA-based biosensors have been increasingly used in the detection of disease markers due to their high sensitivity, simplicity and low cost. In this study, based on the DNAzyme-driven DNA bipedal walking method, we developed a signal-on electrochemical sensor for the detection of α-syn oligomers. Bipedal DNA walkers have a larger walking area and faster walking kinetics, providing higher amplification efficiency compared to conventional DNA walkers. The DNA walker is driven via an Mg2+-dependent DNAzyme, and the binding-induced DNA walker will continuously clamp the MB, resulting in the proliferation of Fc confined near the GE surface. The linear range and limit of detection were 1 fg/mL to 10 pg/mL and 0.57 fg/mL, respectively. The proposed signal-on electrochemical sensing strategy is more selective. It will play a significant role in the sensitive and precise electrochemical analysis of other proteins.

Precise quantification of microRNAs based on proximity ligation of AuNPs-immobilized DNA probes

MiRNAs are critical regulators of target gene expression in many biological processes and are considered promising biomarkers for diseases. In this study, we developed a simple, specific, and sensitive miRNA detection method based on proximity ligation reaction, which is easy to operate. The method uses a pair of target-specific DNA probes immobilized on the same gold nanoparticles (AuNPs), which hybridize to the target miRNA. Hybridization brings the probes close together, allowing the formation of a continuous DNA sequence that can be amplified by Quantitative Real-time PCR (qPCR). This method eliminates the need for complex reverse transcription design and achieves high specificity for discriminating single base mismatches between miRNAs through a simple procedure. This method can sensitively measure three different miRNAs with a detection limit of 20 aM, providing high versatility and sensitivity, even distinguishing single-base variations among members of the miR-200 family with high selectivity. Due to its high selectivity and sensitivity, this method has important implications for the investigation of miRNA biological functions and related biomedical research.

Thermodynamic Allosteric Switch-Actuated 3D DNA Nanomachine for Ultrasensitive Electrochemical/Fluorescent Dual-Mode Biosensing of a Transcription Factor

Herein, we reported an innovative thermodynamic allosteric switch-actuated 3D DNA nanomachine for selective, sensitive, and accurate electrochemical (EC)/fluorescent (FL) dual-mode biosensing of a microphthalmia-associated transcription factor (MITF). The thermodynamic allosteric switch was ingeniously customized as a hairpin probe (HP) that was in dynamic equilibrium but rapidly interconverting conformations. At the "inactive state", the MITF-binding region and the switch part were "sequestered". Upon the introduction of MITF, an MITF-HP complex promptly formed, and the equilibrium of HP thermodynamically inclined from the "inactive state" toward the "active state" conformation. Immediately, the exposed switch on HP effectively actuated the 3D DNA nanomachine and synchronously produced the restriction site for Nb.BbvCI nicking endonuclease. After the autonomous conveying of the 3D DNA nanomachine by means of the high-efficiency circularly nicking endonuclease signal amplification (NESA), not only was MB-S1 in the supernatant used for FL measurements but also MB-SP/MNs/S2 in the precipitate was adapted for EC analysis, significantly improving the utilization of output products derived from the 3D DNA nanomachine. Accordingly, benefiting from the efficient DNA nanomachine signal amplification manner and the self-calibration function of a dual-mode bioassay, the constructed biosensor exhibits superior sensitivity and accuracy for MITF determination.

AND Logic Gate-Regulated DNAzyme Nanoflower for Monitoring the Activity of Multiple DNA Repair Enzymes

Despite the progress that has been made in diverse DNA-based nanodevices to in situ monitor the activity of the DNA repair enzymes in living cells, the significance of improving both the sensitivity and specificity has remained largely neglected and understudied. Herein, we propose a regulatable DNA nanodevice to specifically monitor the activity of DNA repair enzymes for early evaluation of cancer mediated by genomic instability. Concretely, an AND logic gate-regulated DNAzyme nanoflower was rationally designed by the self-assembly of the DNA duplex modified with both apurinic/apyrimidinic (AP) site and methyl lesion site. The DNAzyme nanoflower could be reconfigured under the repair of AP sites and O6-methylguanine sites by apurinic/apyrimidinic endonuclease 1 (APE1) and O6-methylguanine methyltransferase (MGMT) to produce a fluorescent signal, realizing the sensitive monitoring of the activity of APE1 and MGMT. Compared to the free DNAzyme duplex, the fluorescent response of the DNAzyme nanoflower increased by 60%, due to the effective enrichment of the DNA probes by the nanoflower structure. More importantly, we have demonstrated that the dual-enzyme activated strategy allows imaging of specific cancer cells in the AND logic gate manner using MCF-7 as a cancer cell model, improving the specificity of cancer cell imaging. This AND logic gate-regulated multifunctional DNAzyme nanoflower provides a simple tool for simultaneously visualizing multiple DNA repair enzymes, holding great potential in early clinical diagnosis and drug discovery.

Proximity hybridization induced bipedal DNA walker for label-free electrochemical detection of apolipoprotein A4 based on DNA meditated Ag nanoparticles growth

Apolipoprotein A4 (Apo-A4) is considered as a prospective molecular biomarker for diagnosis of depression due to its neurosynaptic toxicity. Here, we propose a neighboring hybridization induced catalyzed hairpin assembly (CHA) driven bipedal DNA walker that mediates hybridization of Ag nanoparticles (Ag NPs) with DNA probes for highly sensitive electrochemical quantitative detection of Apo-A4. Driven by CHA, this bipedal DNA walker can spread all over the surface of the sensor, induce the HP1-HP2 double chain structure, make the surface of the sensor negatively charged, and adsorb a large number of Ag ions. After chemical reduction with hydroquinone, the Ag NPs formed provide signal tracers for electrochemical dissolution analysis of the target. The Ag NPs formed by chemical reduction of hydroquinone can provide signal traces for electrochemical stripping analysis of target thrombin. The linear range of this method is from 10 pg mL-1 to 1000 ng mL-1, and the detection limit is 5.1 pg mL-1. This enzyme-free and labeling detection method provides a new strategy for rapid clinical detection of Apo-A4 and accurate identification of depression.

MXene-incorporated C60NPs and Au@Pt with dual-electric signal outputs for accurate detection of Mycobacterium tuberculosis ESAT-6 antigen

Rapid and effective detection of Mycobacterium tuberculosis (MTB) is the crux of minimizing tuberculosis (TB) spread. Consequently, a new electrochemical aptasensor based on dual-signal output for ultrasensitive detection of MTB early secreted antigenic target 6 (ESAT-6) antigen was developed. Especially, a new nanocomposite MXene/C60NPs/Au@Pt was synthesized for signal generation and amplification. In this biosensing architecture, dual independent signal outputs were achieved by coupling the electrochemical redox activity of fullerene nanoparticles (C60NPs) with the effective electrocatalytic activity of Au@Pt nanoparticles. MXene possesses a large specific surface area, allowing densely loaded of these two electroactive materials, further improved sensing capability. In addition, specific ESAT-6 antigen binding aptamers were attached to Au@Pt to create the tracer label. With a typical sandwich format along with the introduction of the gold nanoparticle-loaded molybdenum disulfide (MoS2-Au) as the sensing interface, the limit of detection (LOD) of the proposed aptasensor was 2.88 fg mL-1 (DPV measurement) and 13.50 fg mL-1 (IT measurement), respectively, with a broad linear range of 100 fg mL-1 to 50 ng mL-1. Significantly, it exhibited better specificity and accuracy with a sensitivity of 97.5% and a specificity of 96.7% to distinguish healthy donors, other lung diseases and TB patients compared to commercial ELISA assay, holding a promising prospect in clinical diagnosis.

Constructing DNAzyme-driven three-dimensional DNA nanomachine-mediated paper-based photoelectrochemical device for ultrasensitive detection of miR-486-5p

As a unique class of dynamic nanostructures, biomimetic DNA walking machines that exhibit geometrical complexity and nanometre precision have gained great success in photoelectrochemical (PEC) bioanalysis. Despite certain achievements, the slow reaction kinetics and low processivity severely restrict the amplification efficiency of the DNA walker-mediated biosensors. Herein, by taking advantage of efficient DNA rolling machines, a three-dimensional (3D) DNA nanomachine-mediated paper-based PEC device for speedy ultrasensitive detection of miR-486-5p was successfully constructed. To achieve it, a novel In2S3/SnS2 sensitized heterojunction was firstly in-situ grown on the Au-modified paper fibers and implemented as the photoanode with effective separation of photogenerated carriers to achieve an enhanced initial photocurrent. Subsequently, the copper hexacyanoferrate(II)-modified CuO nanosphere was introduced as a multifunctional signal regulator via the competitive capture of electron donors and photon energy with the photoelectric layer for efficiently quenching the PEC signal. With the introduction of targets, the DNAzyme-driven DNA nanomachine with editable motion modes was gradually activated and it could continuously cleave the tracks DNA labeled quenching probes, finally achieving the recovery of PEC signal. As a proof of concept, the elaborated paper-based PEC device presented a wide linear range from 0.1 fM to 100 pM and a detection limit of 35 aM for miR-486-5p bioassay. This work provides an innovative insight to the exploitation of DNA nanobiotechnology and nucleic acid signal amplification strategy.

Research progress in the detection of common foodborne hazardous substances based on functional nucleic acids biosensors

With the further improvement of food safety requirements, the development of fast, highly sensitive, and portable methods for the determination of foodborne hazardous substances has become a new trend in the food industry. In recent years, biosensors and platforms based on functional nucleic acids, along with a range of signal amplification devices and methods, have been established to enable rapid and sensitive determination of specific substances in samples, opening up a new avenue of analysis and detection. In this paper, functional nucleic acid types including aptamers, deoxyribozymes, and G-quadruplexes which are commonly used in the detection of food source pollutants are introduced. Signal amplification elements include quantum dots, noble metal nanoparticles, magnetic nanoparticles, DNA walkers, and DNA logic gates. Signal amplification technologies including nucleic acid isothermal amplification, hybridization chain reaction, catalytic hairpin assembly, biological barcodes, and microfluidic system are combined with functional nucleic acids sensors and applied to the detection of many foodborne hazardous substances, such as foodborne pathogens, mycotoxins, residual antibiotics, residual pesticides, industrial pollutants, heavy metals, and allergens. Finally, the potential opportunities and broad prospects of functional nucleic acids biosensors in the field of food analysis are discussed.

Dual-layer 3D DNA nanostructure: The next generation of ultrafast DNA nanomachine for microRNA sensing and intracellular imaging

The working efficiency of traditional 3D DNA nanomachines is extremely restricted due to the complex DNA components modified on nanoparticles in the same spatial height. Herein, an ultrafast dual-layer 3D DNA nanomachine (UDDNM) based on catalytic hairpin assembly (CHA) was developed by assembling two different lengths of hairpin DNA on the surface of gold nanoparticles, the long hairpin 1 (H1), to capture the trigger, and the short hairpin 2 (H2), as the signal probe, to recycle the trigger. Compared to the traditional single-layer 3D DNA nanomachine, the dual-layer 3D DNA nanostructure greatly enhances the effective collision between trigger and targeted DNA probe, H1, since the H1 located in outer layer would react with the trigger, inhibiting the invalid collision between the trigger and residual DNA component, H2, and remarkably decreasing the steric hindrance associated with the nucleic acids layer around the nanoparticles. Especially, when the distance of two layers was fixed at 3 nm, the corresponding UDDNM could accomplish the overall reaction only in 3 min with a dramatically high initial rate of up to 5.93 × 10-7 M s-1, which was at least 5-fold beyond that of the typical single-layer 3D DNA nanomachines. As a proof of concept, the described UDDNM was successfully applied in ultrasensitive fluorescence detection and sensitive intracellular imaging of miRNA-21. Consequently, our strategy, based on the creation of dual-layer 3D DNA nanostructure, may create a new approach to designing the next generation of DNA nanomachine and has enormous potential for applications in bio-analysis, logic gate operations, and clinical diagnoses.

Self-accelerated DNA walker mediated electrochemical biosensor for rapid and ultrasensitive detection of microRNA

Herein, we developed a novel three-dimensional (3D) self-accelerated DNA walker (SADW) which progressively expedite walking rate by unlocking the more walking arm continuously in walker process to construct electrochemical biosensor for ultrasensitive detection of microRNA. Particularly, we skillfully introduced a target analogue sequence in the double-loop hairpin, which could be released in the walking process of SADW, then rapidly activating more silenced walking strands to achieve the continuous self-acceleration, resulting in the expedited reaction rate. Surprisingly, the average reaction rate of SADW was quite higher than that of traditional 3D self-circulating DNA walkers (DW) under pretty low target miRNA concentration, which is ascribed to the outstanding acceleration process of the SADW, readily conquering the major predicaments of DW in detecting target with traces concentration: slow reaction rate and low sensitivity. This way, the elaborated SADW is favorably applied in the ultrasensitive and rapid detection of miRNA-21 in tumor cancer cell lysates with a detection limit down to 5.81 aM which was far from lower than the detection limit of DW. This approach develops the novel generation of widespread strategy for the applications in clinic diagnose, biosensing assay, and DNA nanobiotechnology.

The Dual-Response-Single-Amplification Fluorescent Nanomachine for Tumor Imaging and Gastric Cancer Diagnosis

Gastric cancer (GC) is one of the most common tumors worldwide and is the leading cause of tumor-related mortality. Traditional biomarkers and screening methods cannot meet the clinical demands. There is an urgent need for highly sensitive diagnostic markers as well as accurate quantification methods for early gastric cancer (EGC) screening. Here a dual-target cooperatively responsive fluorescent nanomachine by the innovative application of two targets─responsive strand migration system with a single-amplification-cycle element was developed for the simultaneous detection of GC biomarkers miR-5585-5p and PLS3 mRNA, which were selected by next-generation sequencing and RT-qPCR. It was also an RNA extraction-free, PCR-free, and nonenzymatic biosensor to achieve tumor cell imaging and serum diagnosis. Requiring only a 20 μL serum sample and 20 min incubation time, the nanomachine achieved an ultrasensitive detection limit of fM level with a broad linear range from fM to nM. More importantly, a higher AUC value (0.884) compared to the clinically used biomarker CA 72-4 was obtained by the nanomachine to distinguish GC patients successfully. Notably, for the key concerns of diagnosis of EGC patients, the nanomachine also achieved a satisfactory AUC value of 0.859. Taken together, this work has screened and obtained multiple biomarkers and developed a fluorescent nanomachine for combination diagnosis of GC, providing an ingenious design of a functionalized DNA nanomachine and a feasible strategy for the transformation of serum biomarkers into clinical diagnosis.

Electrochemiluminescence detection of miRNA-21 based on dual signal amplification strategies: Duplex-specific nuclease -mediated target recycle and nicking endonuclease-driven 3D DNA nanomachine

DNA nanomachines have shown potential application in the construction of various biosensors. Here, an electrochemiluminescence biosensor for the sensitive detection of miRNA-21 were reported based on three-dimensional (3D) DNA nanomachine and duplex-specific nuclease (DSN)-mediated target recycle amplification strategy. First, the bipedal DNA walkers were obtained by DSN-mediated digestion reaction initiated by target miRNA-21.3D DNA tracks were prepared by modifying Fe₃O₄ magnetic beads (MBs) with ferrocene-labeled DNA (Fc-DNA). The produced DNA walkers autonomously moved along 3D DNA tracks powered by nicking endonuclease. During the movement, ferrocene-labeled DNA was cleaved, resulting in large amounts of Fc-labeled DNA fragments away from the MBs surface. Finally, the liberated Fc-labeled DNA fragments were dropped on the C-g-C₃N₄ modified electrode surface, leading to the quenching of C-g-C₃N₄ electrochemiluminescence (ECL). Benefiting from the dual amplification strategy of 3D DNA nanomachine and DSN-mediated target recycling, the developed ECL biosensor exhibited an excellent performance for miRNA-21 detection with a wide linear range of 10 fM to 10 nM and a low detection limit of 1.0 fM. This work offers a new thought for the application of DNA walkers in the construction of various biosensors.

Stimulus-responsive strategy based on MnO2 nanosheet-modified mesoporous silica nanoprobes for accurate multiple mRNAs detection

Fluorescence detection of multiple mRNAs has attracted great attention for disease diagnosis. In this work, a stimulus-responsive strategy for highly sensitive and accurate multiple mRNAs detection was proposed. This stimulus-responsive detection system was prepared by mesoporous silica nanoparticles (MSN), manganese dioxide (MnO₂) nanosheets, and DNA probes. DNA probes were loaded into the pores of MSN, which were closed with MnO₂ nanosheets. In the presence of glutathione (GSH) and target mRNAs, MnO₂ nanosheets were degraded by GSH, resulting in the release of DNA probes. These DNA probes hybridized to the corresponding target mRNA, thereby changing the fluorescence intensity of fluorophores of DNA probes, which could achieve the quantification of target mRNA. This system could simultaneously detect survivin mRNA and Thymidine kinase 1 mRNA at low background levels with relative limits of detection of 0.9 nM and 0.7 nM, respectively. Moreover, this assay has been successfully applied to detect multiple mRNAs with adequate anti-interference ability in the biological sample.

A photoelectrochemical biosensor based on ZnIn2S4@AuNPs coupled with circular bipedal DNA walker for signal-on detection of circulating tumor DNA

The circulating tumor DNA (ctDNA) is a crucial cancer marker, its sensitive monitoring is useful for early diagnose and therapy of tumor-related diseases. Herein, a bipedal DNA walker with multiple recognition sites is designed through the transition of dumbbell-shaped DNA nanostructure to realize the dual amplification of the signal and achieve ultrasensitive photoelectrochemical (PEC) detection of ctDNA. Initially, the ZnIn₂S₄@AuNPs is obtained by combining the drop coating method with electrodeposition method. When the target is present, the dumbbell-shaped DNA structure transforms into an annular bipedal DNA walker that can walk unrestrictedly on the modified electrode. After the cleavage endonuclease (Nb.BbvCI) was added to the sensing system, the ferrocene (Fc) on the substrate is released from the electrode surface, and the transfer efficiency of photogenerated electron-hole pairs is extremely improved, enabling the "signal on" testing of ctDNA. The detection limit of the prepared PEC sensor is 0.31 fM, and the recovery of actual samples varied between 96.8 and 103.6% with an average relative standard deviation of about 8%. Meaningfully, the prepared PEC biosensor with an innovative bipedal DNA walker has potential application value for ultrasensitive detection of other nucleic acid-related biomarker.

Programmable Nanostructures Based on Framework-DNA for Applications in Biosensing

DNA has been actively utilized as bricks to construct exquisite nanostructures due to their unparalleled programmability. Particularly, nanostructures based on framework DNA (F-DNA) with controllable size, tailorable functionality, and precise addressability hold excellent promise for molecular biology studies and versatile tools for biosensor applications. In this review, we provide an overview of the current development of F-DNA-enabled biosensors. Firstly, we summarize the design and working principle of F-DNA-based nanodevices. Then, recent advances in their use in different kinds of target sensing with effectiveness have been exhibited. Finally, we envision potential perspectives on the future opportunities and challenges of biosensing platforms.

Advances in electrochemiluminescence luminophores based on small organic molecules for biosensing

Electrochemiluminescence (ECL) has several advantages, such as a near-zero background signal, high sensitivity, wide dynamic range, simplicity, and is widely used for sensing, imaging, and single cell analysis. ECL luminophores are the key factors in the performance of various applications. Among various luminophores, small organic luminophores exhibit many intriguing features including good biocompatibility, facile modification, well-defined molecular structure, and sustainable raw materials, making small organic luminophores attractive for the use in the ECL field. Although many great achievements have been made in the synthesis of new small organic luminophores, solving various challenges, and expanding new applications, there are almost no comprehensive reviews on small organic ECL luminophores. In this review, we briefly introduce the advantages and emission mechanisms of small organic ECL luminophores, summarize the main types, molecular characteristics, and ECL properties of most existing small organic ECL luminophores, and present the important applications and design principles in sensors, imaging, single cell analysis, sterilization, and other fields. Finally, the challenges and outlook of organic ECL luminophores to be popularized in biosensing applications are also discussed.

High-Efficiency 3D DNA Walker Immobilized by a DNA Tetrahedral Nanostructure for Fast and Ultrasensitive Electrochemical Detection of MiRNA

Herein, by directly limiting the reaction space, an ingenious three-dimensional (3D) DNA walker (IDW) with high walking efficiency is developed for rapid and sensitive detection of miRNA. Compared with the traditional DNA walker, the IDW immobilized by the DNA tetrahedral nanostructure (DTN) brings stronger kinetic and thermodynamic favorability resulting from its improved local concentration and space confinement effect, accompanied by a quite faster reaction speed and much better walking efficiency. Once traces of target miRNA-21 react with the prelocked IDW, the IDW could be largely activated and walk on the interface of the electrode to trigger the cleavage of H2 with the assistance of Mg²⁺, resulting in the release of amounts of methylene blue (MB) labeled on H2 from the electrode surface and the obvious decrease of the electrode signal. Impressively, the IDW reveals a conversion efficiency as high as 9.33 × 10⁸ in 30 min with a much fast reaction speed, which is at least five times beyond that of typical DNA walkers. Therefore, the IDW could address the inherent challenges of the traditional DNA walker easily: slow walking speed and low efficiency. Notably, the IDW as a DNA nanomachine was utilized to construct a sensitive sensing platform for rapid miRNA-21 detection with a limit of detection (LOD) of 19.8 aM and realize the highly sensitive assay of biomarker miRNA-21 in the total RNA lysates of cancer cell. The strategy thus helps in the design of a versatile nucleic acid conversion and signal amplification approach for practical applications in the areas of biosensing assay, DNA nanotechnology, and clinical diagnosis.

Ultrasensitive Electrochemiluminescence Biosensor Based on 2D Co3O4 Nanosheets as a Coreaction Accelerator and Highly Ordered Rolling DNA Nanomachine as a Signal Amplifier for the Detection of MicroRNA

A novel ultrasensitive electrochemiluminescence (ECL) biosensor was constructed using two-dimensional (2D) Co₃O₄ nanosheets as a novel coreaction accelerator of the luminol/H₂O₂ ECL system for the detection of microRNA-21 (miRNA-21). Impressively, coreaction accelerator 2D Co₃O₄ nanosheets with effective mutual conversion of the Co²⁺/Co³⁺ redox pair and abundant active sites could promote the decomposition of coreactant H₂O₂ to generate more superoxide anion radicals (O₂^•-), which reacted with luminol for significantly enhancing ECL signals. Furthermore, the trace target miRNA-21 was transformed into a large number of G-wires through the strand displacement amplification (SDA) process to self-assemble the highly ordered rolling DNA nanomachine (HORDNM), which could tremendously improve the detection sensitivity of biosensors. Hence, on the basis of the novel luminol/H₂O₂/2D Co₃O₄ nanosheet ternary ECL system, the biosensor implemented ultrasensitive detection of miRNA-21 with a detection limit as low as 4.1 aM, which provided a novel strategy to design an effective ECL emitter for ultrasensitive detection of biomarkers for early disease diagnosis.

Self-assembly of DNA nanospheres with controllable size and self-degradable property for enhanced antitumor chemotherapy

Controllable size, self-degradability and targeting property are important for a precise improvement of anticancer effects and reduction of side effects of drug vehicles. Here, a series of DNA nanospheres with controllable size and self-degradation ability were constructed through the hybridization of two i-motif strands and two linker strands for targeted cancer therapy. DNA nanospheres with different sizes were fabricated by regulating the linker sequence, and their pH-responsive self-degradation property was realized by the introduction of the i-motif strand. Moreover, the ZY11 aptamer was introduced to endow the DNA nanospheres with targeting property toward SMMC-7721 cancer cells. The results revealed that the appropriate size of DNA nanospheres (80 nm) highly promoted the internalization by mammalian cells. The results of DLS, AFM and CD spectra showed that the DNA nanospheres were stable in a physiological environment but they self-degraded in a slightly acidic environment due to the existence of the i-motif strand. Moreover, the fluorescence of DOX@AP-NSs2 was triple at pH = 5.0 than at pH = 7.4, which further confirmed the pH-responsive drug release performance. The above results proved that the use of DOX@AP-NSs2 is a promising approach to accelerate the rapid release of drugs into the tumors and avoid drug leakage into the normal tissue. The results at a cellular level and in vivo confirmed the pH-responsive targeted antitumor effect. Hence, the novel DNA nanospheres with controllable size and self-degradable property represent a potential tool for targeted drug delivery and cancer therapy.

Aluminum(III)-Based Organic Nanofibrous Gels as an Aggregation-Induced Electrochemiluminescence Emitter Combined with a Rigid Triplex DNA Walker as a Signal Magnifier for Ultrasensitive DNA Assay

Due to effective tackling of the problems of aggregation-caused quenching of traditional ECL emitters, aggregation-induced electrochemiluminescence (AIECL) has emerged as a research hotspot in aqueous detection and sensing. However, the existing AIECL emitters still encounter the bottlenecks of low ECL efficiency, poor biocompatibility, and high cost. Herein, aluminum(III)-based organic nanofibrous gels (AOGs) are used as a novel AIECL emitter to construct a rapid and ultrasensitive sensing platform for the detection of Flu A virus biomarker DNA (fDNA) with the assistance of a high-speed and hyper-efficient signal magnifier, a rigid triplex DNA walker (T-DNA walker). The proposed AOGs with three-dimensional (3D) nanofiber morphology are assembled in one step within about 15 s by the ligand 2,2':6',2″-terpyridine-4'-carboxylic acid (TPY-COOH) and cheap metal ion Al³⁺, which demonstrates an efficient ECL response and outstanding biocompatibility. Impressively, on the basis of loop-mediated isothermal amplification-generated hydrogen ions (LAMP-H⁺), the target-induced pH-responsive rigid T-DNA walker overcomes the limitations of conventional single or duplex DNA walkers in walking trajectory and efficiency due to the entanglement and lodging of leg DNA, exhibiting high stability, controllability, and walking efficiency. Therefore, AOGs with excellent AIECL performance were combined with a CG-C⁺ T-DNA nanomachine with high walking efficiency and stability, and the proposed "on-off" ECL biosensor displayed a low detection limit down to 23 ag·μL^-1 for target fDNA. Also, the strategy provided a useful platform for rapid and sensitive monitoring of biomolecules, considerably broadening its potential applications in luminescent molecular devices, clinical diagnosis, and sensing analysis.

Programmable mismatch-fueled high-efficiency DNA signal amplifier

Herein, by introducing mismatches, a high-efficiency mismatch-fueled catalytic multiple-arm DNA junction assembly (M-CMDJA) with high-reactivity and a high-threshold is developed as a programmable DNA signal amplifier for rapid detection and ultrasensitive intracellular imaging of miRNA. Compared with traditional nucleic acid signal amplification (NASA) with a perfect complement, the M-CMDJA possesses larger kinetic and thermodynamic favorability owing to the more negative reaction standard free energy (ΔG) as driving force, resulting in much higher efficiency and rates. Once traces of the input initiator react with the mismatched substrate DNA, it could be converted into amounts of output multiple-arm DNA junctions via the M-CMDJA as the functional DNA conversion nanodevice. Impressively, the mismatch-fueled catalytic four-arm DNA junction assembly (M-CFDJA) exhibits high conversion efficiency up to 1.05 × 108 in 30 min, which is almost ten times more than those of conventional methods. Therefore, the M-CMDJA could easily address the challenges of traditional methods: slow rates and low efficiency. In application, the M-CFDJA as a DNA signal amplifier was successfully used to develop a biosensing platform for rapid miRNA detection with a LOD of 6.11 aM and the ultrasensitive intracellular imaging of miRNA, providing a basis for the next-generation of versatile DNA signal amplification methods for ultimate applications in DNA nanobiotechnology, biosensing assay, and clinical diagnoses.

Light responsive nucleic acid for biomedical application

Nucleic acids are widely used in biomedical applications because of their programmability and biocompatibility. The light responsive nucleic acids have attracted wide attention due to their remote control and high spatiotemporal resolution. In this review, we summarized the latest developments in biomedicine of light responsive molecules. The molecules which confer light responsive properties to nucleic acids were summarized. The binding sites of molecules to nucleic acids, the induced structural changes, and functional regulation of nucleic acids were reviewed. Then, the biomedical applications of light responsive nucleic acids were listed, such as drug delivery, biosensing, optogenetics, gene editing, etc. Finally, the challenges were discussed and possible future directions of light-responsive nucleic acids were proposed.

Electrochemiluminescence Systems for the Detection of Biomarkers: Strategical and Technological Advances

Electrochemiluminescence (ECL)-based sensing systems rely on light emissions from luminophores, which are generated by high-energy electron transfer reactions between electrogenerated species on an electrode. ECL systems have been widely used in the detection and monitoring of diverse, disease-related biomarkers due to their high selectivity and fast response times, as well as their spatial and temporal control of luminance, high controllability, and a wide detection range. This review focuses on the recent strategic and technological advances in ECL-based biomarker detection systems. We introduce several sensing systems for medical applications that are classified according to the reactions that drive ECL signal emissions. We also provide recent examples of sensing strategies and technologies based on factors that enhance sensitivity and multiplexing abilities as well as simplify sensing procedures. This review also discusses the potential strategies and technologies for the development of ECL systems with an enhanced detection ability.

Enhanced Electrochemiluminescence of Graphitic Carbon Nitride by Adjustment of Carbon Vacancy for Supersensitive Detection of MicroRNA

Herein, a supersensitive biosensor was constructed by using graphitic carbon nitride with a carbon vacancy (V_C-g-C₃N₄) as an efficient electrochemiluminescence (ECL) emitter for detection of microRNA-21 (miRNA-21). Impressively, V_C-g-C₃N₄ could be prepared by formaldehyde (HCHO)-assisted urea ploycondensation, and the concentration of the carbon vacancy could be controlled by adjusting the dosage of HCHO to improve the ECL performance, in which the carbon vacancy could improve the charge carrier transfer to enhance the conductivity and it also could be used as an electron trap to prevent electrode passivation and facilitate the adsorption of coreactant S₂O₈^2- to accelerate its reduction. Compared with original g-C₃N₄, the introduction of carbon vacancies resulted in a significant enhancement of the ECL efficiency of V_C-g-C₃N₄. With the aid of improved cascade strand displacement amplification (IC-SDA), the ECL biosensor realized sensitive detection of miRNA-21 with a low detection limit of 3.34 aM. This successful strategy promoted the development of g-C₃N₄ in the ECL field to construct the sensitive biosensor for molecular and disease diagnoses.

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.

Versatile Electrochemical Biosensor Based on the Target-Controlled Capture and Release of DNA Nanotubes for the Ultrasensitive Detection of Multiplexed Biomarkers

Herein, an ultrasensitive and versatile electrochemical biosensor was developed through the target-controlled capture and release of signal probe-loaded DNA nanotube for the ultrasensitive detection of two different types of cancer-related biomarkers, microRNA-21 (miRNA-21) and glutathione (GSH). In this system, target 1 (miRNA-21) first triggered duplex-specific nuclease (DSN)-assisted recycle amplification to generate numerous disulfide-linked DNA strands (DL), which could effectively capture DNA nanotube to immobilize methylene blue (MB) to produce remarkable electrochemical signals and achieve the ultrasensitive detection of miRNA-21 with a detection limit down to 32.6 aM. Furthermore, in the presence of target 2 (GSH), the electrochemical signal was significantly reduced by a thiol-disulfide bond exchange reaction on DL to release MB-immobilized DNA nanotubes away from the sensing interface, which enabled the sensitive analysis of GSH with a detection limit of 0.379 nM. Impressively, this strategy could achieve ultrasensitive detection of different types of biomarkers to prominently lessen false-positive responses from the current sensing methods toward a single biomarker or the same type of biomarker and remarkably heighten the accuracy and precision of early cancer diagnosis. Meanwhile, the proposed electrochemical biosensor made it possible to realize the regenerative analysis of targets over four times without extra fuel, which could conspicuously improve the analytical efficiency compared with that of traditional biosensing assays. As a result, this study might open up novel insights to design a versatile and multifunctional sensing platform and encourage deeper exploration for detecting different types of biomarkers in the fields of early disease diagnosis and biochemical research.

Aptasensor for Mycobacterium tuberculosis antigen MPT64 detection using anthraquinone derivative confined in ordered mesoporous carbon as a new redox nanoprobe

Rapid and sensitive tuberculosis (TB) diagnoses remain big challenges to current detection tools. In this work, a sensitive electrochemical aptasensor was constructed for the determination of Mycobacterium tuberculosis antigen MPT64 using a new redox nanoprobe. We found that anthraquinone derivative, anthraquinone-2-carboxylic acid (AQCA), a redox mediator, could be confined in ordered mesoporous carbon material of CMK-3. Due to the large loading amount of AQCA, as well as the confined space and electron transfer promotion effect of CMK-3, the obtained AQCA/CMK-3 nanohybrid with mass ratio of 2:1 showed excellent electroactivity and was employed as a new redox nanoprobe for signal amplification for the first time. Additionally, urchin-like Ce-MOFs were used to load a large amount of deposited gold nanocrystals (dep-Au), leading to dense immobilization of capture probe. The proposed electrochemical aptasensor for MPT64 detection showed a good linear relationship in the range from 100 fg/mL to 10 ng/mL with a low detection limit of 67.6 fg/mL. Besides, the aptasensor was utilized to detect MTP64 in human serum samples for TB diagnosis and presented satisfactory results.

Emerging Approaches for Enabling RNAi Therapeutics

RNA interference (RNAi) is a primitive evolutionary mechanism developed to escape incorporation of foreign genetic material. siRNA has been instrumental in achieving the therapeutic potential of RNAi by theoretically silencing any gene of interest in a reversible and sequence-specific manner. Extrinsically administered siRNA generally needs a delivery vehicle to span across different physiological barriers and load into the RISC complex in the cytoplasm in its functional form to show its efficacy. This review discusses the designing principles and examples of different classes of delivery vehicles that have proved to be efficient in RNAi therapeutics. We also briefly discuss the role of RNAi therapeutics in genetic and rare diseases, epigenetic modifications, immunomodulation and combination modality to inch closer in creating a personalized therapy for metastatic cancer. At the end, we present, strategies and look into the opportunities to develop efficient delivery vehicles for RNAi which can be translated into clinics.

Three-in-One System Based on Multi-Path Nucleic Acid Amplification for Bioanalysis of Pre-miRNA/miRNA and Dicer Activity

Today, a lot of attention is being paid to the pre-miRNAs/miRNAs or activity of Dicer due to their important functions in various physiological processes. Especially, the intrinsic relationship among these associated targets is of significant importance for more in-depth research on the mechanism of disease formation and early diagnosis. Herein, a strategy for simultaneous bioanalysis of miRNAs/pre-miRNAs and Dicer enzyme based on the self-designed multi-path nucleic acid amplification technology was proposed. Typically, in the presence of pre-miRNA-155, it can hybridize with Helper to generate a structure with two new toeholds, one of which could react with H1, H2, and H3, performing a modified CHA reaction with obvious fluorescence responses of FAM, and another of which could hybridize with H4, H5, and H6 to construct the [H4-H5-H6]_n DNA nanosphere with obvious fluorescence responses of Cy5. Similarly, miRNA-155 could just hybridize with H1, H2, and H3 to generate the same modified CHA reaction with obvious fluorescence responses of FAM. Due to the successful multi-path nucleic acid amplification, the proposed bioanalysis strategy could be successfully employed for miRNA-155 and pre-miRNA-155 analysis in the range from 500 pM to 100 nM and 1 to 300 nM, respectively. The proposed strategy could be applied to explore another inter-related nucleic acid relationship also, providing great potential in bioanalysis of various nucleic acids.

Recent progress in nanomaterial-based bioelectronic devices for biocomputing system

Bioelectronic devices have received the massive attention because of their huge potential to develop the core electronic components for biocomputing system. Up to now, numerous bioelectronic devices have been reported such as biomemory and biologic gate by employment of biomolecules including metalloproteins and nucleic acids. However, the intrinsic limitations of biomolecules such as instability and low signal production hinder the development of novel bioelectronic devices capable of performing various novel computing functions. As a way to overcome these limitations, nanomaterials have the great potential and wide applicability to grant and extend the electronic functions, and improve the inherent properties from biomolecules. Accordingly, lots of nanomaterials including the conductive metal, graphene, and transition metal dichalcogenide nanomaterials are being used to develop the remarkable functional bioelectronic devices like the multi-bit biomemory and resistive random-access biomemory. This review discusses the nanomaterial-based superb bioelectronic devices including the biomemory, biologic gates, and bioprocessors. In conclusion, this review will provide the interdisciplinary information about utilization of various novel nanomaterials applicable for biocomputing system.

Dual-Engine Powered Paper Photoelectrochemical Platform Based on 3D DNA Nanomachine-Mediated CRISPR/Cas12a for Detection of Multiple miRNAs

This work proposed a novel double-engine powered paper photoelectrochemical (PEC) biosensor based on an anode-cathode cooperative amplification strategy and various signal enhancement mechanisms, which realized the monitoring of multiple miRNAs (such as miRNA-141 and miRNA-21). Specifically, C₃N₄ quantum dots (QDs) sensitized ZnO nanostars and BiOI nanospheres simultaneously to construct a composite photoelectric layer that amplified the original photocurrent of the photoanode and photocathode, respectively. Through the independent design and partition of a flexible paper chip to functionalize injection holes and electrode areas, the bipolar combination completed the secondary upgrade of signals, which also provided biological reaction sites for multitarget detection. With the synergistic participation of a three-dimensional (3D) DNA nanomachine and programmable CRISPR/Cas12a shearing tool, C₃N₄ QDs lost their attachment away from the electrode surface to quench the signal. Moreover, electrode zoning significantly reduced the spatial cross talk of related substances for multitarget detection, while the universal trans-cleavage capability of CRISPR/Cas12a simplified the operation. The designed PEC biosensor revealed excellent linear ranges for detection of miRNA-141 and miRNA-21, for which the detection limits were 5.5 and 3.4 fM, respectively. With prominent selectivity and sensitivity, the platform established an effective approach for trace multitarget monitoring in clinical applications, and its numerous pioneering attempts owned favorable reference values.

Aromaticity-Enhanced pH-Responsive Electrochemiluminescence of Cyclopentadienols

Due to significantly tackling the problems of aggregation-caused quenching and water insolubility, aggregation-induced emission electrochemiluminescence (AIE-ECL) has emerged as a research highlight in aqueous detection and sensing. Herein, we reported a series of cyclopentadienols featuring excellent AIE-ECL properties on the basis of an enhanced aromaticity strategy. In detail, substituents profoundly determined ECL emission by affecting the characteristic absorption peak intensity ratio in UV-vis spectra and lowest unoccupied molecular orbital (LUMO)-highest occupied molecular orbital (HOMO) energies. It was found that 1,2,3,4,5-pentafluorophenyl cyclopentadienol (PFCD) containing an electron-withdrawing fluorine substituent, the maximum R/B band ratio, and a smaller LUMO-HOMO band gap demonstrated the best ECL performance. Meanwhile, such an AIE-ECL system displayed a wide response range toward pH (4-12) with a good linear relationship. Our research not only enriched polycyclic aromatic hydrocarbon-based AIE-ECL systems but also established an efficient pH sensor in the aqueous phase.

Construction of Multiple Logic Circuits Based on Allosteric DNAzymes

In DNA computing, the implementation of complex and stable logic operations in a universal system is a critical challenge. It is necessary to develop a system with complex logic functions based on a simple mechanism. Here, the strategy to control the secondary structure of assembled DNAzymes’ conserved domain is adopted to regulate the activity of DNAzymes and avoid the generation of four-way junctions, and makes it possible to implement basic logic gates and their cascade circuits in the same system. In addition, the purpose of threshold control achieved by the allosteric secondary structure implements a three-input DNA voter with one-vote veto function. The scalability of the system can be remarkably improved by adjusting the threshold to implement a DNA voter with 2n + 1 inputs. The proposed strategy provides a feasible idea for constructing more complex DNA circuits and a highly integrated computing system.

A Novel Ratiometric Electrochemical Biosensor Using Only One Signal Tag for Highly Reliable and Ultrasensitive Detection of miRNA-21

Herein, a novel ratiometric electrochemical biosensor with methylene blue (MB) as the only one signal tag was proposed for highly reliable and ultrasensitive detection of microRNA-21 (miRNA-21) under the assistance of an intelligent target-induced dual signal amplification (T-DSA). First, a small amount of target miRNA-21 could produce abundant mimic targets DNA S1 and Zn²⁺ through target-induced recycle and acid dissolution, respectively. Then, S1 triggered rolling circle amplification (RCA) to generate functional DNA nanospheres (DSP) encoded by DNAzyme and substrate sequence for loading numerous signal tag MB with a remarkable electrochemical signal (signal on), and the Zn²⁺ cofactor mediated the nonviolent DNAzyme-catalyzed cleavage of DSP to sharply release MB with obviously reduced electrochemical responses (signal off). Impressively, our strategy could controllably load and release the only signal tag MB through the well-designed DSP to effectively avoid the false positive responses caused by the non-ideal upright state of DNA probes connected to electrodes in traditional distance-dependent signal adjustment ratiometric strategies with two different signal tags. Meanwhile, with the aid of innovative T-DSA recycle and RCA-produced functional DSP, the detection sensitivity of this sensing platform was significantly improved. As a result, the proposed biosensor successfully realized highly reliable and ultrasensitive detection of miRNA-21 with a detection limit down to 26.7 aM, which shows exceptional promise in biological analysis and medical diagnosis.

miRNA-Guided Imaging and Photodynamic Therapy Treatment of Cancer Cells Using Zn(II)-Protoporphyrin IX-Loaded Metal-Organic Framework Nanoparticles

An analytical platform for the selective miRNA-21-guided imaging of breast cancer cells and miRNA-221-guided imaging of ovarian cancer cells and the selective photodynamic therapy (PDT) of these cancer cells is introduced. The method is based on Zn(II)-protoporphyrin IX, Zn(II)-PPIX-loaded UiO-66 metal-organic framework nanoparticles, NMOFs, gated by two hairpins H_i/H_j through ligation of their phosphate residues to the vacant Zr⁴⁺-ions associated with the NMOFs. The hairpins are engineered to include the miRNA recognition sequence in the stem domain of H_i, and in the H_i and H_j, partial locked stem regions of G-quadruplex subunits. Intracellular phosphate-ions displace the hairpins, resulting in the release of the Zn(II)-PPIX and intracellular miRNAs open H_i, and this triggers the autonomous cross-opening of H_i and H_j. This activates the interhairpin hybridization chain reaction and leads to the assembly of highly fluorescent Zn(II)-PPIX-loaded G-quadruplex chains. The miRNA-guided fluorescent chains allow selective imaging of cancer cells. Moreover, PDT with visible light selectively kills cancer cells and tumor cells through the formation of toxic reactive oxygen species.

Electrospun nanofibers modified with zeolitic imidazolate framework-8 for electrochemiluminescent determination of terbutaline

For the first time it is demonstrated that zeolitic imidazolate framework-8 electrospun nanofibers (ZIF-8 NF) could serve as electrochemiluminescence (ECL) accelerator for the facile detection of terbutaline residual. A novel ECL sensor for the determination of terbutaline was fabricated based on ZIF-8 NF. The ZIF-8 NF were successfully prepared according to electrospinning and in-situ growth method. First, chitosan was modified on the surface of the electrode, and then the ZIF-8 NF was modified onto the upper layer of the chitosan. Taking advantages of chitosan and ZIF-8 NF in conductivity and electrocatalysis, the modified electrode presents obvious ECL phenomenon in 0.2 M PBS solution (pH 10.0) containing 0.025 M luminol. After the addition of terbutaline, ECL intensity decreased significantly, and the decreasing value showed a linear relationship with the logarithm of terbutaline concentration. The linear range was from 2.0 × 10^-10 to 2.0 × 10^-5 M, and the detection limit was 1.41 × 10^-11 M (3σ/m). The method had high sensitivity, good stability, and good applicability to actual pork samples.

Programmable High-Speed and Hyper-Efficiency DNA Signal Magnifier

Herein, a programmable dual-catalyst hairpin assembly (DCHA) for realizing the synchronous recycle of two catalysts is developed, displaying high reaction rate and outstanding conversion efficiency beyond traditional nucleic acid signal amplifications (NASA). Once catalyst I interacts with the catalyst II, the DCHA can be triggered to realize the simultaneous recycle of catalysts I and II to keep the highly concentrated intermediate product duplex I-II instead of the steadily decreased one in typical NASA, which can accomplish in about only 16 min and achieves the outstanding conversion efficiency up to 4.54 × 108 , easily conquering the main predicaments of NASA: time-consuming and low-efficiency. As a proof of the concept, the proposed DCHA as a high-speed and hyper-efficiency DNA signal magnifier is successfully applied in the rapid and ultrasensitive detection of miRNA-21 in cancer cell lysates, which exploits the new generation of universal strategy for the applications in biosensing assay, clinic diagnose, and DNA nanobiotechnology.

Target-Activated, Light-Actuated Three-Dimensional DNA Walker Nanomachine for Amplified miRNA Detection

Accurate analysis of microRNA (miRNA) is promising for elucidation of cancer processes and therapeutic effects. In this study, we reported a new target-activated, light-actuated three-dimensional (3D) DNA walker on gold nanoparticles for sensitive detection of miRNA using pyrene-incorporated DNAzyme analogues. In this design, the target miRNA activated the 3D DNA walker system to releases the walking arm. Then, under ultraviolet light irradiation, the pyrene DNAzyme on the walking arm would consecutively cleave the disulfide bonds of substrate strands and recover the fluorescence signal, thus achieving the amplified miRNA detection. The sophisticated design of the light-actuated 3D DNA walker was systematically investigated. Furthermore, this strategy could also be employed for miRNA analysis in serum samples with satisfactory reproducibility. Notably, the proposed light-actuated 3D DNA walker-based technique eliminated the need of enzymes, cofactors, and RNA backbones, thereby significantly improving the stability and efficiency. Overall, the light-actuated 3D DNA walker-based strategy enabled facile, sensitive, and specific detection of miRNA and provided new perspectives in diagnostics.