Ternary Electrochemiluminescence Biosensor Based on DNA Walkers and AuPd Nanomaterials as a Coreaction Accelerator for the Detection of miRNA-141

Recent Advances in Electrochemiluminescence Biosensors for MicroRNA Detection

Electrochemiluminescence (ECL) as an analytical technology with a perfect combination of electrochemistry and spectroscopy has received considerable attention in bioanalysis due to its high sensitivity and broad dynamic range. Given the selectivity of bio-recognition elements and the high sensitivity of the ECL analysis technique, ECL biosensors are powerful platforms for the sensitive detection of biomarkers, achieving the accurate prognosis and diagnosis of diseases. MicroRNAs (miRNAs) are crucial biomarkers involved in a variety of physiological and pathological processes, whose aberrant expression is often related to serious diseases, especially cancers. ECL biosensors can fulfill the highly sensitive and selective requirements for accurate miRNA detection, prompting this review. The ECL mechanisms are initially introduced and subsequently categorize the ECL biosensors for miRNA detection in terms of the quenching agents. Furthermore, the work highlights the signal amplification strategies for enhancing ECL signal to improve the sensitivity of miRNA detection and finally concludes by looking at the challenges and opportunities in ECL biosensors for miRNA detection.

Dual-microRNA-Controlled Electrochemiluminescence Biosensor for Breast Cancer Diagnosis and Supplemental Identification of Breast Cancer Metastasis

Breast cancer remains the most frequently diagnosed cancer globally, and the metastasis of this malignancy is the primary cause of mortality in breast cancer patients. Hence, prompt diagnosis and timely detection of metastatic breast cancer are critical for effective therapeutic intervention. Both progression and metastasis of this malignancy are closely associated with aberrant expression of specific microRNAs (miRNAs) and enzymes. To facilitate breast cancer diagnosis and concomitant identification of metastatic breast cancer, we have engineered an innovative electrochemiluminescence (ECL)-based sensing platform integrated with enzyme-free DNA amplification circuits for dual functionality. Specifically, microRNA-21 (miR-21) is employed as a biomarker for breast cancer, and miR-21 induces the quenching of the ECL signal from luminophores via a strategically designed catalytic three-hairpin assembly (CTHA) circuit. Subsequently, miR-105 levels are measured via toehold-mediated strand displacement reactions (TSDR). Here, miR-105 restores the initially quenched ECL signal, enabling the assessment of the metastatic propensity. Our experimental data demonstrate that the devised ECL biosensor offers broad linear detection ranges and low detection limits for both miR-21 and miR-105. Importantly, our novel platform was also successfully validated by using cellular and serum samples. This biosensor not only discriminates breast cancer cell lines MCF-7 and MDA-MB-231 from nonbreast cancer cells like HepG2, TPC-1, and HeLa, but it also distinguishes between malignant MCF-7 and metastatic MDA-MB-231 cells. Consequently, our novel approach holds significant promise for clinical applications and precise cancer screening.

Functionalized nanomaterials-based electrochemiluminescent biosensors and their application in cancer biomarkers detection

To detect a range of trace biomarkers associated with human diseases, researchers have been focusing on developing biosensors that possess high sensitivity and specificity. Electrochemiluminescence (ECL) biosensors have emerged as a prominent research tool in recent years, owing to their potential superiority in low background signal, high sensitivity, straightforward instrumentation, and ease of operation. Functional nanomaterials (FNMs) exhibit distinct advantages in optimizing electrical conductivity, increasing reaction rate, and expanding specific surface area due to their small size effect, quantum size effect, and surface and interface effects, which can significantly improve the stability, reproducibility, and sensitivity of the biosensors. Thereby, various nanomaterials (NMs) with excellent properties have been developed to construct efficient ECL biosensors. This review provides a detailed summary and discussion of FNMs-based ECL biosensors and their applications in cancer biomarkers detection.

Electrochemiluminescence resonance energy transfer immunoassay based on a porphyrin metal-organic framework and AuNPs/NSG for the sensitive detection of zearalenone

In this study, a novel electrochemiluminescence resonance energy transfer (ECL-RET) immunoassay was developed for the first time for the detection of zearalenone (ZEN). A porphyrin metal-organic framework (PCN-222), an emerging porphyrin-based ECL luminophore, was prepared by a simple hydrothermal method using tetrakis(4-carboxyphenyl) porphyrin, which has excellent ECL emission as well as good ECL efficiency. Because the ECL emission spectrum of PCN-222 is highly matched to the absorption spectrum of gold nanoparticle-modified graphene oxide (AuNPs/NSG) nanocomposites, they were used as donor-acceptor counterparts in this work for the ECL-RET strategy. Under optimal conditions, the ECL immunosensor showed a sensitive response to ZEN in a wide detection range, with a linearity of 0.0005-1000 ng mL-1 and a detection limit of 0.15 pg mL-1. In addition, the sensor showed good potential for application in the detection of wheat and corn samples, providing a new approach for the detection of mycotoxin-like contaminants such as ZEN in food grains.

Dual-Signal Integrated Aptasensor for Microcystin-LR Detection via In Situ Generation of Silver Nanoclusters Induced by Circular DNA Strand Displacement Reactions

Inspired by the signal accumulation of circular DNA strand displacement reactions (CD-SDRs) and the in situ generation of silver nanoclusters (AgNCs) from signature template sequences, a dual-signal integrated aptasensor was designed for microcystin-LR (MC-LR) detection. The aptamer was programmed to be included in an enzyme-free CD-SDR, which utilized MC-LR as the primer and outputted the H1/H2 dsDNA in a continuous manner according to the ideal state. Ingeniously, H1/H2 dsDNA was enriched with signature template sequences, allowing in situ generation of AgNCs signal probes. To enhance the signal amplification performance, co-reaction acceleration strategies and CRISPR-Cas12a nucleases were invoked. The H1/H2 dsDNA could trigger the incidental cleavage performance of CRISPR-Cas12a nucleases: cis-cleavage reduced signature template sequences for the synthetic AgNCs, while trans-cleavage enabled fluorescence (FL) analysis. Meanwhile, AuPtAg was selected as the substrate material to facilitate the S2O82- reduction reaction for enhancing the electrochemiluminescence (ECL) basal signals. ECL and FL detection do not interfere with each other and have improved accuracy and sensitivity, with limits of detection of 0.011 and 0.023 pmol/L, respectively. This widens the path for designing dual-mode sensing strategies for signal amplification.

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.

A fluorescent sensing platform based on collagen peptides-protected Au/Ag nanoclusters and WS2 for determining collagen triple helix integrity

The unique triple helix structure of collagen plays an important role in its biological properties, and the triple helix integrity is closely correlated with its molecular behavior and biological functions. Nevertheless, there is still a lack of convenient, accurate and practical methods for quantitatively determining collagen triple helix integrity. Herein, we first prepared bovine skin collagen peptide (BSCP)-protected Au/Ag nanoclusters (Au/AgNCs@BSCP) with excellent optical properties, high stability and good biocompatibility, which could adsorb on WS₂ surface leading to fluorescence quenching. Upon the addition of collagen, the interaction of collagen and Au/AgNCs@BSCP led to the detachment of Au/AgNCs@BSCP from the WS₂ surface, causing an increase in the fluorescence signal. Using the difference in the fluorescence recovery of the different samples, we achieved the quantitative determination of collagen triple helix integrity. This developed strategy exhibited excellent accuracy, selectivity, and practicality, thus showing promising potentials in biomedical applications.

Chitosan/luminol/AgNPs nanocomposite for electrochemiluminescent determination of prostate-specific antigen

A green, environmentally friendly protocol was developed for ultrasensitive and highly specific recognition of prostate-specific antigen (PSA) based on the ECL effect of luminol supported by chitosan-silver nanoparticles (CS/AgNPs) nanocomposites. The transducing surface was fabricated through two consecutive electrodeposition steps of gold nanoparticles (AuNPs) and chitosan (CS)-AgNPs-luminol electrochemiluminophore onto the glassy carbon electrode. In addition to an appropriate desirable biocompatibility, the electrochemical synthesis presents low-cost preparation and ultrafast determination opportunity. AgNPs play a linking role to attach luminol, as an ECL agent to the CS support via donor-acceptor bonds between Ag atoms with NH groups of luminol and CS. Also, AgNPs can amplify the ECL intensity as a consequence of their excellent specific surface area and conductivity. To enhance the performance of the nanobiosensor, AuNPs were also used due to their high-specific surface area and excellent affinity toward amine groups of CS. Based on this high-performance analysis strategy, ultrasensitive screening of PSA was attained with a desirable limit of detection of 0.6 ng mL^-1 and a broad linear range between 1 pg mL^-1 and 10 ng⋅mL^-1 (R²=0.994). Approximately, the same results were recorded for the analysis of the unprocessed serum samples of patients with prostate cancer at different stages. This research provided significant insight into electrografting methods to construct ECL transducers for clinical monitoring of PSA and other tumor biomarkers in the clinical setting.

Controllable Three-Dimensional DNA Nanomachine-Mediated Electrochemical Biosensing Platform for Rapid and Ultrasensitive Detection of MicroRNA

In this work, a high-efficiency controllable three-dimensional (3D) DNA nanomachine (CDNM) was reasonably developed by regulating the diameter of the core and the length of the DNAzyme cantilever, which acquired greater amplification efficiency and speedier walking rate than traditional 3D DNA nanomachines with gold nanoparticles as the cores and DNAzymes as the walking arms. Significantly, once the target miRNA-21 existed, a large number of silent DNAzymes on the CDNM could be activated by enzyme-free-target-recycling amplification (EFTRA) to achieve fast cleavage and walking on the biosensor surface under the interaction of Mg²⁺. Impressively, when the diameter of the core was 40 nm and the length of the DNAzyme cantilever was 5 nm (15 bp), the CDNM could complete the reaction process in 60 min that was at least twice shorter than those of conventional DNA nanomachines. Moreover, the designed electrochemical biosensor successfully detected target miRNA-21 at an ultrasensitive level with a wide response range (100 aM to 1 nM) and a low detection limit (33.1 aM). Therefore, the developed CDNM provides a new idea for exploring functional DNA nanomachines in the field of biosensing for applications.

Hijacking the self-replicating machine of bacteriophage for PCR-based cascade signal amplification in detecting SARS-CoV-2 viral marker protein in serum

In this work, the nucleic acid detection of SARS-Cov-2 is extended to protein markers of the virus, utilizing bacteriophage. Specifically, the phage display technique enables the main protease of SARS-Cov-2 to control the self-replication of m13 phage, so that the presence of the viral protease can be amplified by phage replication as the first round of signal amplification. Then, the genome of replicated phage can be detected using polymer chain reaction (PCR), as the second round of signal amplification. Based on these two types of well-established biotechnology, the proposed method shows satisfactory sensitivity and robustness in the direct serum detection of the viral protease. These results may point to clinical application in the near future.

Covalent organic framework linked with amination luminol derivative as enhanced ECL luminophore for ultrasensitive analysis of cytochrome c

Cytochrome c (cyt c) plays a critical role in mitochondrial respiratory chain, whose absence is detrimental to electron transport and reduce adenosine triphosphate. For ultrasensitive detection of cyt c, sheet-like covalent organic frameworks (COFs) were prepared by orderly accumulation of 1,3,5-benzenetricarboxaldehyde (BTA) and p-phenylenediamine (PDA), and further grafted with N-(4-aminobutyl)-N-ethylisoluminol (ABEI) - an electrochemiluminescence (ECL) emitter. Specifically, the morphology and structure of the COFs-ABEI were mainly characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis, and X-ray photoelectron spectroscopy (XPS). In parallel, the optical properties of the emitter were certified by UV-vis absorbance spectroscopy, Fourier infrared spectroscopy (FTIR), fluorescence (FL), and ECL measurements, showing 2.25-time enhanced ECL efficiency over pure ABEI, coupled by illustrating the interfacial electron transport mechanism. On the above foundation, a label-free "signal off" ECL biosensor was constructed by virtue of the specific immune recognition between the aptamer of the target cyt c with its capture DNA (cDNA) anchored on the biosensing platform, exhibiting a wider linear range of 1.00 fg mL^-1-0.10 ng mL^-1 (R² = 0.998) and a lower limit of detection (LOD) down to 0.73 fg mL^-1. This work offers some constructive guidelines for sensitive bioassays of disease-related biomarkers in the clinical field.

Versatile Electrochemiluminescence Biosensing Platform Based on DNA Nanostructures and Catalytic Hairpin Assembly Signal Amplification

Achieving rapid and highly sensitive detection of biomarkers is crucial for disease diagnosis and treatment. Here, a highly sensitive and versatile dual-amplification electrochemiluminescence (ECL) biosensing platform was constructed for target detection based on DNA nanostructures and catalyzed hairpin assembly (CHA). Specifically, when the target DNA was present, it would hybridize with the auxiliary strands (D1 and D2) to form an I-shaped nanostructure, which in turn triggered the subsequent catalytic hairpin assembly reaction to generate plenty of double-stranded DNA complexes (H1-H2). The resulting double-stranded complex could be trapped on the electrode surface and adsorbed the ECL signal probe Ru(phen)₃²⁺.We found that the I-shaped nanostructure-triggered CHA reaction had higher amplification efficiency compared with traditional CHA amplification. Thus, a sensitive "signal-on" ECL biosensor was constructed for target DNA detection with a detection limit of 1.09 fM. Additionally, by combining the binding properties of C-Ag⁺-C with an elaborately designed "Ag⁺-helper" probe, the proposed strategy could be immediately utilized for the highly sensitive and selective detection of silver ions, demonstrating the versatility of the developed biosensing platform. This strategy provided a new approach with potential applications in disease diagnosis and environmental monitoring.

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.

An electrochemiluminescence immunosensor based on ABEI-GO-AgNPs as a double-amplified luminophore for the ultra-sensitive detection of prostate-specific antigen

A sandwich electrochemiluminescence (ECL) immunosensor based on an N-(4-aminobutyl)-N-ethylisoluminol-graphene oxide-Ag nanoparticle (ABEI-GO-AgNPs) complex and cysteine silver nanowires (AgCysNWs) was prepared to detect prostate-specific antigen (PSA). Our results showed that an ECL signal probe, ABEI-GO-AgNPs, with an ultrahigh specific surface area, favorable catalytic properties, and electrical conductivity was prepared by a one-step synthesis method. ABEI-GO-AgNPs with good biocompatibility immobilized secondary antibody (Ab₂) via AgN bonds. Furthermore, AgCysNWs containing many -COOH groups were prepared and used to enrich primary antibody (Ab₁), which could be used as an affinity probe for the selective capture of PSA. Lastly, through layer-by-layer assembly, we established an ECL immunosensing platform for the sensitive detection of PSA. Under the optimized conditions, the designed ECL immunosensor showed promising sensitivity and selectivity for the detection of PSA in the linear range of 5.5 × 10^-7-5.5 ng/mL, with a detection limit of 1.2 × 10^-7 ng/mL. The constructed ECL sensing platform possessed good specificity, reproducibility, and stability and could detect PSA in actual human serum samples.

A Versatile Electrochemical Biosensor for the Detection of Circulating MicroRNA toward Non-Small Cell Lung Cancer Diagnosis

Circulating microRNAs (miRNAs) can be used as noninvasive biomarkers and are also found circulating in body fluids such as blood. Dysregulated miRNA expression is associated with many diseases, including non-small cell lung cancer (NSCLC), and the miRNA assay is helpful in cancer diagnosis, prognosis, and monitoring. In this work, a versatile electrochemical biosensing system is developed for miRNA detection by DNAzyme-cleavage cycling amplification and hybridization chain reaction (HCR) amplification. With cleavage by Mn²⁺ targeted DNAzyme, DNA-walker can move along the predesigned DNA tracks and contribute to the transduction and enhancement of signals. For the electrochemical process, the formation of multiple G-quadruplex-incorporated long double-stranded DNA (dsDNA/G-quadruplex) structures is triggered through HCR amplification. The introduction of G-quadruplex allows sensitive measurement of miRNA down to 5.68 fM with good specificity. Furthermore, by profiling miRNA in the NSCLC cohort, this designed strategy shows high efficiency (area under the curve (AUC) of 0.879 using receiver operating characteristic (ROC) analysis) with the sensitivity of 80.0% for NSCLC early diagnosis (stage I). For the discrimination of NSCLC and benign disease, the assay displays an AUC of 0.907, superior to six clinically-acceptable protein tumor markers. Therefore, this platform holds promise in clinical application toward NSCLC diagnosis and prognosis.

A ratiometric electrochemical DNA-biosensor for detection of miR-141

A sensitive biosensor for the detection of miR-141 has been constructed. The DNA-biosensor is prepared by first immobilizing the thiolated methylene blue-labeled hairpin capture probe (MB-HCP) on two-layer nanocomposite film graphene oxide-chitosan@ polyvinylpyrrolidone-gold nanourchin modified glassy carbon electrode. We used the hematoxylin as an electrochemical auxiliary indicator in the second stage to recognize DNA hybridization via the square wave voltammetry (SWV) responses that record the accumulated hematoxylin on electrode surfaces. The morphology and chemical composition of nanocomposite was characterized using TEM, FE-SEM, and FT-IR techniques. The preparation stages of the DNA-biosensor were screened by electrochemical impedance spectroscopy and cyclic voltammetry. The proposed DNA-biosensor can distinguish miR-141 from a non-complementary and mismatch sequence. A detection limit of 0.94 fM and a linear range of 2.0 -5.0 × 10⁵ fM were obtained using SWV for miR-141 detection. The working potential for methylene blue and hematoxylin was -0.28 and + 0.15 V vs. Ag/AgCl, respectively. The developed biosensor can be successfully used in the early detection of non-small cell lung cancer (NSCLC) by directly measuring miR-141 in human plasma samples. This novel DNA-biosensor is of promise in early sensitive clinical diagnosis of cancers with miR-141 as its biomarker.

Sensitive Electrochemiluminescence Biosensor Based on the Target Trigger Difference of the Electrostatic Interaction between an ECL Reporter and the Electrode Surface

The discrepancy of the electrostatic interaction of negatively charged signal molecules to long and short DNA strands of the modified electrode surface has been used for the first time to the develop an electrochemiluminescence (ECL) biosensor for human papillomavirus 16 (HPV 16) DNA detection. The short single-stranded capture probe (CP) was modified first on the surface of the gold electrode, which only has a small amount of negative charge. The electrostatic interaction between the negatively charged tris(2,2'-bipyridyl) ruthenium(II) chloride hexahydrate-doped SiO₂ nanoparticles (Ru@SiO₂ NPs) and CP is weak, hence Ru@SiO₂ NPs easily diffuse to the surface of the electrode to generate a strong ECL signal. Hybrid chain reaction (HCR) amplification products (long strand dsDNA) were prepared in homogeneous solution in advance. When the target was present, the dsDNA can be connected on the electrode surface and cause the enhancement of the negative charge on the electrode surface. Owing to electrostatic interaction and steric hindrance, Ru@SiO₂ NPs are difficult to diffuse to the electrode surface, resulting in a significantly reduced ECL signal. The decrease of ECL signal is linearly correlated with the logarithm of the HPV concentration under optimal conditions, with the detection range being 0.1 fM -5 pM with a limit of 1.41 aM. This innovative methodology expands the application of electrostatic interaction in ECL sensing, but can also easily develop biosensors for detecting other targets by changing the DNA sequence used in this strategy.

Metal-organic framework nanoreactor-based electrochemical biosensor coupled with three-dimensional DNA walker for label-free detection of microRNA

MicroRNAs (miRNAs), serving as the regulators for gene expression and cellular function, have emerged as the important biomarkers for diagnosis of cancers. In this study, a label-free electrochemical biosensing platform equipped with metal-organic frameworks (MOFs)-based nanoreactors has been developed by coupling three-dimensional (3D) DNA walker for amplification detection of miRNA. The MOF-based nanoreactors are constructed via the encapsulation of GOx in zeolitic imidazolate framework-8 (ZIF-8) driven by the rapid GOx-triggered nucleation of ZIF-8 with high catalytic activity, which also contributes to preserve the biological activity of GOx even in harsh environments. The gold nanoparticles (AuNPs) are further loaded on the surface of ZIF-8 by electrostatic adsorption, which can be used to not only anchor the orbit of 3D DNA walker by Au-S covalent bond but also promote the electron transfer on electrode interface. In the presence of target miRNA-21, the 3D DNA walker is initiated, resulting in the recycling of targets and the immobilization of numerous fuel DNAs with G-quadruplex/hemin complex on the nanoreactors spontaneously. As a result, a cascade catalysis reaction is triggered in the confined space of ZIF-8 nanoreactors, where the H₂O₂ as an intermediate is generated with the oxidization of glucose catalyzed by GOx and subsequently decomposed by G-quadruplex/hemin HRP-mimicking DNAzyme for the further oxidation of ABTS to obtain a differential pulse voltammetry (DPV) signal. Under the optimal conditions, the proposed electrochemical biosensor exhibits an excellent performance for amplification detection of miRNA-21 in the dynamic working range from 0.1 nM to 10 μM with a detection limit of 29 pM, which opens a new way for clinical analysis of miRNAs and early diagnosis of cancers.

Toehold-mediated strand displacement coupled with single nanoparticle dark-field microscopy imaging for ultrasensitive biosensing

Highly sensitive detection of biomarkers is essential for disease prevention and early diagnosis. Herein, a highly sensitive strategy was proposed for microRNA-21 (miRNA-21) detection by the incorporation of programmable toehold-mediated strand displacement (TMSD) and dark-field microscopy imaging. Firstly, efficient and specific TSMD was carried out via hybridization between the substrate strand (Sub) and two short probe strands (P1, P2). Then, miRNA-21 could specifically hybridize with Sub due to the toehold that existed on its tail, which triggered the amplification with the help of the assist strands, and forming a large number of Sub-assist double-stranded DNA (dsDNA). This process realized the targeted highly specific recognition of miRNA-21 and the amplification of the trace target to high-output dsDNA. Additionally, as glucose oxidase (Gox) was modified on the end of the assist strands in advance, hydrogen peroxide was generated after adding glucose to the system, which further etched gold-silver core-shell nanocubes (Au@Ag NCs). As a result, the size of Au@Ag NCs decreased and the scattering intensity reduced simultaneously. The scattering intensity reduction value of Au@Ag NCs has a linear relationship with miRNA-21 concentration in the range of 1.0 to 100.0 fM with a limit of detection of 1.0 fM. Finally, the proposed method has been successfully demonstrated for the determination of miRNA-21 in lung cancer cell A549 lysate.

Ratiometric electrochemical detection of miRNA based on DNA nanomachines and strand displacement reaction

MicroRNAs (miRNAs) play an important role in regulating gene expression in cells. Abnormal expression of miRNAs has been associated with a variety of diseases. A ratiometric electrochemical method for miRNA detection based on DNA nanomachines and strand displacement reaction was developed. Signal probe with ferrocene label and reference probe with methylene blue label were immobilized on gold nanoparticle (AuNP)-coated magnetic microbeads (AuNP-MMBs). The miRNA triggers the strand displacement reaction and forms a duplex with the protect probe, releasing one end of the DNA walker (DW); the released DW hybridizes with the ferrocene (Fc)-labeled signal probe. The signal probe detached from AuNP-MMBs upon cleavage of the Nb.BbvCI enzyme. The oxidation peak of MB moieties on the reference probe remains unchanged and the signals of Fc moieties on the signal probe are inversely proportional to the concentrations of miRNA. The ratio between Fc moieties at 0.35 V and MB moieties at -0.22 V (vs. Ag/AgCl) was used to quantify the expression level of miRNA with a detection limit down to 0.12 fM. The ratiometric assay possesses a strong ability to eliminate interference from environmental changes, thus offering the high selectivity of miRNA from the complexed biosystems, holding great significance for miRNA sensing. A ratiometric assay with high selectivity of miRNA has been developed based on DNA nanomachines and strand displacement reaction.

A glucose/O2 biofuel cell integrated with an exonuclease-powered DNA walker for self-powered sensing of microRNA

With the aid of an exonuclease-powered DNA walker, the amount of glucose oxidase immobilized on the bioanode can be facilely tailored by varying the concentration of microRNA-141, so a glucose/O₂ biofuel cell is employed as a self-powered sensor for sensitive and selective detection of microRNA-141.