A chemiresistive biosensor based on a layered graphene oxide/graphene composite for the sensitive and selective detection of circulating miRNA-21

Self-powered chip based on exonuclease-driven amplification for portable cancer biomarker detection

Currently, sensitive detection of microRNA (miRNA) in clinical diagnosis remains a challenge consideration of its extremely similar sequences and low concentration characteristics. In this work, a signal-enhanced biosensor constructed for ultra-sensitive miRNA detection based on two-dimensional (2D) transition metal sulfide materials and target induced -DNAzyme cycle and exonuclide-assisted cascade signal amplification strategy. As expected, miRNA-21 concentration has a good linear relationship with open circuit voltage of self-powered biosensor in the range of 1 fM-100 pM, and the detection limit is low as 0.03 fM. The results indicate that 2D materials have great potential in the construction of electrochemical sensors due to their large active surface area, high electron mobility and excellent electrocatalytic performance. In addition, the DNAzyme triggerd by chain substitution reaction can specifically identify the target and amplify the detection signal cyclically. Finally, the self-powered sensing platform with commercial chips, ensuring stable performance and minimal signal fluctuations during long-term continuous monitoring, enabling portable and real-time target monitoring.

Pyrene-Based Metal-Organic Frameworks with Coordination-Enhanced Electrochemiluminescence for Fabricating a Biosensing Platform

Enhancing the electrochemiluminescence (ECL) properties of polycyclic aromatic hydrocarbons (PAHs) is a significant topic in the ECL field. Herein, we elaborately chose PAH derivative luminophore 1,3,6,8-tetrakis(p-benzoic acid)pyrene (H4TBAPy) as the organic ligand to synthesize a new Ru-complex-free ECL-active metal-organic framework Dy-TBAPy. Interestingly, Dy-TBAPy exhibited a more brilliant ECL emission and higher ECL efficiency than H4TBAPy aggregates. On the one hand, TBAPy luminophores were assembled into rigid MOF skeleton via coordination bonds, which not only enlarged the distance between pyrene cores to eliminate the aggregation-caused quenching (ACQ) effect but also obstructed the intramolecular motions of TBAPy to diminish the nonradiative relaxation, thus realizing a remarkable coordination-enhanced ECL. On the other hand, the ultrahigh porosity of Dy-TBAPy was beneficial to the diffusion of electrons, ions, and coreactant (S2O82-) in the skeleton, which efficiently boosted the excitation of interior TBAPy luminophores and led to a high utilization ratio of TBAPy, further improving ECL properties. More intriguingly, the ECL intensity of the Dy-TBAPy/S2O82- system was about 4.1, 87.0-fold higher than those of classic Ru(bpy)32+/TPrA and Ru(bpy)32+/S2O82- systems. Considering the aforementioned fabulous ECL performance, Dy-TBAPy was used as an ECL probe to construct a supersensitive ECL biosensor for microRNA-21 detection, which showed an ultralow detection limit of 7.55 aM. Overall, our study manifests that coordinatively assembling PAHs into MOFs is a simple and practicable way to improve ECL properties, which solves the ACQ issue of PAHs and proposes new ideas for developing highly efficient Ru-complex-free ECL materials, therefore providing promising opportunities to fabricate high-sensitivity ECL biosensors.

A smartphone-assisted electrochemiluminescent biosensor for highly sensitive detection of miRNA-21 based on Ru(bpy)2(L)4+@MOF-5

A smartphone-assisted electrochemiluminescence (ECL) strategy based on Ru(bpy)2(L)4+ as chromophores confined with metal - organic frameworks (Ru(bpy)2(L)4+@MOF-5) for the signal-amplified detection of miRNA-21 was developed. We synthesized a derivative of tris(2,2'-bipyridyl)ruthenium(II) complex (Ru(bpy)2(L)4+) with high charges, which can be loaded into the MOF-5 by strong electrostatic interaction to prevent from leakage. In addition, nucleic acid cycle amplification was used to quench the signal of Ru(bpy)2(L)4+@MOF-5 by ferrocene. This method was applied to detect the concentration of miRNA-21 ranging from 1.0 × 10-14-1.0 × 10-9 M with a low LOD of 7.2 fM. This work demonstrated the construction of a signal quenching strategy ECL biosensor for miRNA using Ru(bpy)2(L)4+@MOF-5 systems and its application in smartphone-assisted ECL detection.

A comprehensive review of the application of Zr-based metal-organic frameworks for electrochemical sensors and biosensors

A family of inorganic-organic hybrid crystalline materials made up of organic ligands and metal cations or clusters is known as metal-organic frameworks (MOFs). Because of their unique stability, intriguing characteristics, and structural diversity, zirconium-based MOFs (Zr-MOFs) are regarded as one of the most interesting families of MOF materials for real-world applications. Zr-MOFs that have the ligands, metal nodes, and guest molecules enclosed show distinct electrochemical reactions. They can successfully and sensitively identify a wide range of substances, which is important for both environmental preservation and human health. The rational design and synthesis of Zr-MOF electrochemical sensors and biosensors, as well as their applications in the detection of drugs, biomarkers, pesticides, food additives, hydrogen peroxide, and other materials, are the main topics of this comprehensive review. We also touch on the current issues and potential future paths for Zr-MOF electrochemical sensor research.

Well plate-based LF-NMR/colorimetric dual-mode homogeneous immunosensor for Vibrio parahaemolyticus detection

A 96-well plate-based low-field nuclear magnetic resonance (LF-NMR)/colorimetric dual-mode homogeneous immunosensor was developed for the detection of pathogen bacteria, using Vibrio parahaemolyticus (VP) as a detection template. The signal unit MNS@Ab2 is graphene oxide (GO) simultaneously loaded with VP antibody and Fe3O4 nanoparticles. A 96-well plate coated with VP antibody captures the target VP, which then binds the signal unit to form the immunocomplex. After acidolysed, Fe3O4 nanoparticles are transformed into Fe3+ and Fe2+, so the non-homogeneous system is transformed into a homogeneous one. The addition of KMnO4 can not only convert Fe2+ into Fe3+ but also provide Mn2+, improving the detection sensitivity. And, colorimetric analysis can be achieved by the quantitative reduction of KMnO4. Under the optimal experimental conditions, the limit of detection was 60 CFU/mL with good selectivity, stability, precision, accuracy, and consistency, providing a simple and reliable detection platform for pathogenic bacteria in food.

Rolling circle amplification assisted CRISPR/Cas12a dual-cleavage photoelectrochemical biosensor for highly sensitive detection of miRNA-21

BACKGROUND

MicroRNA-21 has been determined to be the only microRNA overexpressed in 11 types of solid tumors, making it an excellent candidate as a biomarker for disease diagnosis and therapy. Photoelectrochemical (PEC) biosensors have been widely used for quantification of microRNA-21. However, most PEC biosensing processes still suffer from some problems, such as the difficulty of avoiding the influence of interferents in complex matrices and the false-positive signals. There is a pressing need for establishing a sensitive and stable PEC method to detect microRNA-21.

RESULTS

Herein, a nicking endonuclease-mediated rolling circle amplification (RCA)-assisted CRISPR/Cas12a PEC biosensor was fabricated for ultrasensitive detection of microRNA-21. The p-p type heterojunction PbS QDs/Co3O4 polyhedra were prepared as the quencher, thus the initial PEC signal attained the "off" state. Furthermore, the target was specifically identified and amplified by the RCA process. Then, its product single-stranded DNA S1 activated the cis- and trans-cleavage abilities of CRISPR/Cas12a, leading to almost all of the PbS QDs/Co3O4 polyhedra to leave the electrode surface, the p-n semiconductor quenching effect to be disrupted, and the signal achieving the "super-on" state. This pattern of PEC signal changed from "off" to "on" eliminated the interference of false-positive signals. The proposed PEC biosensor presented a satisfactory linear relationship ranging from 1 fM to 10 nM with a detection limit of 0.76 fM (3 Sb/N).

SIGNIFICANCE AND NOVELTY

With innovatively synthesized PbS QDs/Co3O4 polyhedra as the effective quencher for PEC signal, the CRISPR/Cas12a dual-cleavage PEC biosensor possessed excellent selectivity, stability and repeatability. Furthermore, the detection of various miRNAs can be realized by changing the relevant base sequences in the constructed PEC biosensor. It also provides a powerful strategy for early clinical diagnosis and biomedical research.

Target-initiated triplex signal amplification cascades for non-label and sensitive fluorescence sensing of microRNA

The aberrant expression of microRNAs (miRs) in cells is closely linked to the initiation and progression of various diseases. Sensitive monitoring of their level is hence vital for biomedical research and disease diagnosis. Herein, a highly sensitive and non-label fluorescence sensor based on multiple recycling signal amplification cascades is constructed for the detection of miR-21 in human sera. The presence of miR-21 initiates the primer-fueled target recycling process for the generation of many primer/hairpin templates for the subsequent auto-cycling primer extension (APE) amplification cycles, which result in the formation of lots of long-stem hairpins. The enzyme-based cleavage of such hairpins via polymerization/excision cycles further leads to the generation of abundant G-quadruplex strands, which associate with the thioflavin T (ThT) dye to emit remarkably magnified fluorescence for detecting miR-21 in the range of 1 pM-100 nM with a 0.32 pM detection limit without labeling the probes. Besides, the proposed assay can selectively discriminate miR-21 against other control molecules and realize the sensing of low levels of miR-21 in diluted sera. With features of high sensitivity via the triplex signal amplification cycles and simplicity in a non-label homogeneous manner, our miR sensing protocol can be a robust means for detecting various nucleic acids for the early diagnosis of diseases.

A highly sensitive and robust electrochemical biosensor for microRNA detection based on PNA-DNA hetero-three-way junction formation and target-recycling catalytic hairpin assembly amplification

Robust and sensitive methods for the detection of microRNAs (miRNAs) are crucial in the clinical diagnosis of cancers. In this study, a novel electrochemical biosensor with high sensitivity for miRNA-21 detection is developed, which relies on the formation of a peptide nucleic acid (PNA)-DNA hetero-three-way junction (H3WJ) and target-recycling catalytic hairpin assembly (CHA) amplification. The electroneutral PNA probes are initially immobilized onto a gold electrode to construct the sensor. Upon introduction of miRNA-21, target-recycling CHA is initiated, resulting in abundant double-stranded CHA products. Subsequently, association between the PNA probes and these products leads to the formation of PNA-DNA H3WJs. Consequently, the electrode surface is densely populated with numerous electroactive Ferrocene (Fc) groups, resulting in a significantly amplified current response for highly sensitive detection of miRNA-21 at concentrations as low as 0.15 fM. This approach demonstrates remarkable specificity towards target miRNAs and can be utilized for quantitative monitoring of miRNA-21 expression in human cancer cells. More importantly, the sensor exhibits exceptional stability and shows a significant reduction in background noise during miRNA detection, making this method a highly promising sensing platform for monitoring various miRNA biomarkers to facilitate the diagnosis of diverse cancers.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Self-powered dual-mode sensing strategy based on graphdiyne and DNA nanoring for sensitive detection of tumor biomarker

MicroRNA-21 (miRNA-21) is currently the only known oncogenic miRNA that is upregulated in almost all malignant tumors and exhibits a broad spectrum of tumor recognition characteristics. It holds significant value in the early diagnosis, malignant degree assessment, and prognostic evaluation of tumors. In this study, a novel dual-mode self-powered sensing platform is developed using Au nanoparticles/graphdiyne as the electrode substrate and combined with DNA nanoring for highly sensitive and specific detection of miRNA-21. The DNA nanoring structure, which is easy to prepare and contains multiple recognition sites, induces significant electrochemical/colorimetric signal responses of the signaling molecule methylene blue. Under optimal conditions, the linear ranges of the electrochemical and colorimetric detection modes of this self-powered sensor are 0.1 fM-100 pM and 0.1 fM-10 nM, respectively, with the detection limits of 35.1 aM and 61.6 aM (S/N=3). This strategy provides a new reference for the sensitive detection of microRNA and has immense potential for application in the screening and detection of clinical nucleic acid diseases.

The "How" and "Where" Behind the Functionalization of Graphene Oxide by Thiol-ene "Click" Chemistry

Graphene oxide (GO) is a 2D nanomaterial with unique chemistry due to the combination of sp2 hybridization and oxygen functional groups (OFGs) even in single layer. OFGs play a fundamental role in the chemical functionalization of GO to produce GO-based materials for diverse applications. However, traditional strategies that employ epoxides, alcohols, and carboxylic acids suffer from low control and undesirable side reactions, including by-product formation and GO reduction. Thiol-ene "click" reaction offers a promising and versatile chemical approach for the alkene functionalization (-C=C-) of GO, providing orthogonality, stereoselectivity, regioselectivity, and high yields while reducing by-products. This review examines the chemical functionalization of GO via thiol-ene "click" reactions, providing insights into the underlying reaction mechanisms, including the role of radical or base catalysts in triggering the reaction. We discuss the "how" and "where" the reaction takes place on GO, the strategies to avoid unwanted side reactions, such as GO reduction and by-product formation. We anticipate that multi-functionalization of GO via the alkene groups will enhance GO physicochemical properties while preserving its intrinsic chemistry.

An overview of biochemical technologies for the cancer biomarker miR-21 detection

In recent years, the incidence of cancer has continuously increased, in which various miRNAs have been proposed as biomarkers for the early screening of cancer patients. As a consequence, the development of accurate methods for miRNA quantification has become a major research challenge worldwide. As one of the first discovered oncogenic miRNAs, microRNA-21 (miR-21) has been highlighted for its critical role in cancers. This review describes the main techniques currently available for miR-21 detection, compares the differences of the methods and the amplification strategies, and provides an overview of the state of knowledge in the field.

Prospects of microbial-engineering for the production of graphene and its derivatives: Application to design nanosystms for cancer theranostics

Cancer is known as one of the leading causes of morbidity and fatality, currently faced by our society. The prevalence of cancer related dieses is rapidly increasing around the world. To reduce the mortality rates, early diagnosis and subsequent treatment of cancer in timely manner is quite essential. Advancements have been made to achieve effective theranostics strategies to tackle cancerous dieses, yet very challenging to overcome this issue. Recently, advances made in the field of nanotechnology have shown tremendous potential for cancer theranostics. Different types of nanomaterials have been successfully employed to develop sophisticated diagnosis and therapy techniques. In this context, graphene and its derivatives e.g. graphene oxide (GO) and reduced graphene oxide (RGO) have been investigated as promising candidates to design graphene-based nanosystems for the diagnosis and therapeutic purpose. Further, to synthesize graphene and its derivatives different types of physicochemical methods are being adopted. However, each method has its own advantage and disadvantages. In this reference, among diverse biological methods, microbial technique can be one of the most promising and eco-friendly approach for the preparation of graphene and its derivatives, particularly GO and RGO. In this review, we summarize studies performed on the preparation of graphene and its derivatives following microbial routes meanwhile focus has been made on the preparation method and the possible mechanism involved therein. Thereafter, we have discussed applications of graphene and its derivatives to developed advanced nanosystem that can be imperative for the cancer theranostics. Results of recent studies exploring applications graphene based nanosystem for the preparation of different types of biosensors for early diagnosis; advanced therapeutic approaches by designing drug delivery nanosystems along with multifunctionality (e.g cancer imaging, drug delivery, photodynamic and photo thermal therapy) in cancer theranostics have been discussed. Particularly, emphasis has been given on the preparation techniques of graphene based nanosystems, being employed in designing of biosensing platforms, drug delivery and multifunctional nanosystems. Moreover, issues have been discussed on the preparation of graphene and its derivatives following microbial technique and the implementation of graphene based nanosystems in cancer theranostics.

A chemiresistive biosensor for detection of cancer biomarker in biological fluids using CVD-grown bilayer graphene

A chemiresistive biosensor is described for simple and selective detection of miRNA-21. We developed chemical vapor deposition (CVD) and low-damage plasma treatment (LDPT)-treated bilayer graphene composite of graphene oxide/graphene (GO/GR) for the determination of a reliable biomarker. We have successfully overcome the self-limiting growth mechanism by using CVD method to grow more than one layer of graphene on copper foil. In addition, LDPT can be used to form GO/GR structures for chemiresistive biosensor applications. Due to the direct formation of BLGR (bilayer graphene), the coupling between graphene layers is theoretically superior to that of stacked BLGR, which is also confirmed by the blue shift of the characteristic peak of graphene in Raman spectroscopy. The shift is about double compared with that of stacked BLGR. Based on the results, the limit of detection for the target miRNA-21 was calculated to be 5.20 fM and detection rage is calculated as 100 fM to 10 nM, which is obviously better performance. Compared with previous work, this chemiresistive biosensor has good selectivity, and stability towards detection of miRNA-21. The ability to detect miRNA-21 in different biological fluids was almost identical to that in pH 7.4 phosphate-buffered saline (PBS). Thus, the proposed bilayer GO/GR of modified chemiresistive biosensor may potentially be applied to detect cancer cells in clinical examinations.

A novel conductive nanocomposite-based biosensor for ultrasensitive detection of microRNA-21 in serum, using methylene blue as mediator

MicroRNA-21 (miRNA-21) is a common biomarker with high expression in breast tumors. Therefore, sensitive detection of miRNA-21 is of great significance for clinical breast tumor diagnosis. A TH/rGO/CMK-3/AuNPs nanocomposite is composed of thionine (TH), reduced graphene oxide (rGO), ordered mesoporous carbon (CMK-3), and gold nanoparticles (AuNPs), which help to increase the specific surface area of a glassy carbon electrode (GCE) and to amplify the DPV signal. Meanwhile, methylene blue (MB) was combined with the capture probe guanine and absorbed by the composite material to mediate the differential pulse voltammetry (DPV) of the obtained miRNA biosensor. The current response decreased with increasing miRNA-21 concentration under optimal conditions. The biosensor responds to miRNA-21 in the 0.1fM-1 pM concentration range, and the detection limit (LOD) was 0.046 fM. Moreover, human serum samples were effectively detected utilizing the miRNA-21 biosensor with satisfactory results.

MiR-21 regulating PVT1/PTEN/IL-17 axis towards the treatment of infectious diabetic wound healing by modified GO-derived biomaterial in mouse models

BACKGROUND

Diabetic foot ulcer (DFU), persistent hyperglycemia and inflammation, together with impaired nutrient and oxygen deficiency, can present abnormal angiogenesis following tissue injury such that these tissues fail to heal properly. It is critical to design a new treatment method for DFU patients with a distinct biomechanism that is more effective than current treatment regimens.

METHOD

Graphene oxide (GO) was combined with a biocompatible polymer as a kind of modified GO-based hydrogel. The characterization of our biomaterial was measured in vitro. The repair efficiency of the biomaterial was evaluated in the mouse full-skin defect models. The key axis related to diabetic wound (DW) was identified and investigated using bioinformatics analyses and practical experiments.

RESULT

In the study, we found that our modified GO-based wound dressing material is a promising option for diabetic wound. Secondly, our biomaterial could enhance the secretion of small EVs (sEVs) with more miR-21 by adipose-derived mesenchymal stem cells (AD-MSCs). Thirdly, the PVT1/PTEN/IL-17 axis was found to be decreased to promote DFU wound healing by modifying miR-21 with the discovery of PVT1 as a critical LncRNA by bioinformatics analysis and tests.

CONCLUSION

These findings could aid in the development of clinical care strategies for DFU wounds.

Sensitive detection of microRNAs using polyadenine-mediated fluorescence spherical nucleic acids and a microfluidic electrokinetic signal amplification chip

The identification of tumor-related microRNAs (miRNAs) exhibits excellent promise for the early diagnosis of cancer and other bioanalytical applications. Therefore, we developed a sensitive and efficient biosensor using polyadenine (polyA)-mediated fluorescent spherical nucleic acid (FSNA) for miRNA analysis based on strand displacement reactions on gold nanoparticle (AuNP) surfaces and electrokinetic signal amplification (ESA) on a microfluidic chip. In this FSNA, polyA-DNA biosensor was anchored on AuNP surfaces via intrinsic affinity between adenine and Au. The upright conformational polyA-DNA recognition block hybridized with 6-carboxyfluorescein-labeled reporter-DNA, resulting in fluorescence quenching of FSNA probes induced by AuNP-based resonance energy transfer. Reporter DNA was replaced in the presence of target miRNA, leading to the recovery of reporter-DNA fluorescence. Subsequently, reporter-DNAs were accumulated and detected in the front of with Nafion membrane in the microchannel by ESA. Our method showed high selectivity and sensitivity with a limit of detection of 1.3 pM. This method could also be used to detect miRNA-21 in human serum and urine samples, with recoveries of 104.0%–113.3% and 104.9%–108.0%, respectively. Furthermore, we constructed a chip with three parallel channels for the simultaneous detection of multiple tumor-related miRNAs (miRNA-21, miRNA-141, and miRNA-375), which increased the detection efficiency. Our universal method can be applied to other DNA/RNA analyses by altering recognition sequences.

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FSNA assisted microfluidic chip was developed for miRNAs detection.

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Three different miRNAs were detected simultaneously.

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The excellent sensitivity and specificity were displayed toward miRNAs.

Rapid electrochemical detection of MiRNA-21 facilitated by the excellent catalytic ability of Pt@CeO2 nanospheres

Pt@CeO2 nanospheres (NSs) were first synthesized by simply mixing Ce(NO3)3 and K2PtCl4 under the protection of pure argon at 70 °C for 1 h, which exhibited excellent catalytic ability toward hydrogen peroxide (H2O2). An electrochemical biosensor was successfully developed using Pt@CeO2 NSs as a capture probe for the ultra-sensitive and fast detection of miRNA-21, a new type of biomarker for disease diagnostics, especially for cancer. During the step-by-step construction process of the RNA sensor, Pt@CeO2 NSs were functionalized with streptavidin (SA) to obtain SA-Pt@CeO2 NSs through amide bonds. Gold nanoparticles (Au NPs) were electrodeposited on the surface of the glassy carbon electrode to improve the transmission capacity of electrons and provided Au atoms for fixing the thiolated capture probe (SH-CP) with a hairpin structure on the electrode via forming Au-S bonds. The target miRNA-21 specifically hybridized with SH-CP and opened the hairpin structure to form a rigid duplex so as to activate the biotin at the end of the capture probe. SA-Pt@CeO2 NSs were thus specially attached to the electrode surface through the biotin-streptavidin affinity interaction, finally leading to the significant signal amplification. The ultra-sensitive and rapid detection of miRNA-21 was finally realized as expected benefiting from the excellent catalytic ability of Pt@CeO2 NSs toward H2O2 in a wide linear concentration range from 10 fM to 1 nM with the detection limit as low as 1.41 fM. The results achieved with this new RNA sensor were quite satisfactory during the blood sample analysis.

Structure and function encoding of a bidirectional activatable synergetic DNA machine for speeded and ultrasensitive determination of microRNAs

This work describes the unique design of a bidirectional activatable synergetic DNA machine (BAS-DNA machine) for speeded and ultrasensitive determination of microRNA-21 (miR-21), a well-known biomarker for biomedical research and early diagnosis of lung cancer. The BAS-DNA machine is composed by a pair of track strands (Track 1 and Track 2) encoding with two regions in the opposite direction for miR-21 recognition. Introduction of miR-21 can hybridize either with Track 1 or with Track 2 to activate the BAS-DNA machine with a synergistic effect for speeded amplifying the fluorescence signal. Moreover, compared with common DNA machine with only one switch for exogenous target recognition, the BAS-DNA machine with two switches for miR-21 binding allows the speeded and strong operation of the autonomous strand scission, replication, and displacement on Track 1 and Track 2 simultaneously. This behavior makes the BAS-DNA machine powerful for ultrasensitive, specific, and fast screening of miR-21 even from real biological samples, and the fluorescence signal was found to be linear from 1 pM to 10 nM with a detection limit of 703.6 fM. We envision this BAS-DNA machine with its superior assay performance will provide a new avenue for simple, sensitive, and affordable biomedical assays.

MXene-MoS2 heterostructure collaborated with catalyzed hairpin assembly for label-free electrochemical detection of microRNA-21

Abnormal expression of microRNAs is greatly associated with the occurrence of various cancer types, revealing great potential of microRNA as biomarkers for cancer diagnosis and prognosis. Herein, a MXene-MoS₂ heterostructure enhancing electrochemical biosensor coupled with catalytic hairpin assembly (CHA) amplification approach for label-free determination of microRNA-21 (miR-21) was successfully assembled. In particular, the unique micro-nano heterostructure with large specific area and favorable electroconductivity exhibited the ability of excellent confinement effect. Thus, rendered the MXene-MoS₂ heterostructure the ability to trigger more target recycling reaction, giving new vitality to the traditional CHA amplification method. Meanwhile, thionine (Thi) and gold nanoparticles (AuNPs) were anchoring at the surface of MXene-MoS₂ heterostructure, respectively, empowered the sensor the capability of capture probes fixation and miR-21 label-free determination. When numerous electronegative double-stranded DNA generated, the electron transfer was greatly hindered, resulting in signal decrease. Accordingly, the design denoted a broad dynamic range from 100 fM to 100 nM and a detection limit of about 26 fM, comparable or lower than previous reported methods for miR-21 detection. Furthermore, the sensing platform supplied satisfactory selectivity, reproducibility and stability towards the miR-21 detection. The real sample determination also showed a promising performance under clinical circumstance. Finally, from the clinical standpoint, the proposed biosensor is a considerable platform toward early disease detection and monitoring.

Overcoming Aggregation-Induced Quenching by Metal-Organic Framework for Electrochemiluminescence (ECL) Enhancement: Zn-PTC as a New ECL Emitter for Ultrasensitive MicroRNAs Detection

Polycyclic aromatic hydrocarbons (PAHs) as traditional electrochemiluminescence (ECL) luminophores have been widely applied in the analysis field. However, their ECL intensity and efficiency are still limited due to the aggregation-induced quenching (ACQ) effect of PAHs. Hence, to overcome this limitation, we put forward a new strategy to increase the ECL intensity and efficiency by eliminating the ACQ effect of PAHs through the coordinative immobilization of PAHs within metal-organic frameworks (MOFs). As anticipated, the proof-of-concept experiment indicated that the coordinative immobilization of perylene-3,4,9,10-tetracarboxylate (PTC) into a Zn-PTC MOF could distinctly increase the ECL intensity and efficiency compared with H₄PTC aggregates and H₄PTC monomers. The reason for the ECL enhancement of Zn-PTC was that the immobilization of PTC within the MOF effectively amplified the distance between perylene rings of PTC ligands and thus eliminated the ACQ effect. Furthermore, the PTC into Zn-PTC was stacked in an edge-to-edge mode to form J-aggregation, which was also conducive to ECL enhancement. On the basis of the excellent ECL performance, we utilized Zn-PTC as a new ECL emitter combined with exonuclease III-stimulated target cycling and DNAzyme-assisted cycling dual amplification strategies to construct an ECL sensor for microRNA-21 detection, which had a wide signal response (100 aM to 100 pM) with a detection limit of 29.5 aM. Overall, this work represents a new and convenient method to overcome the ACQ effect of PAHs and boost the ECL performance, which opens a new horizon for developing high-performance ECL materials, thus offering more opportunities for building highly sensitive ECL biosensors.

A Microfluidic Chip-Based MRS Immunosensor for Biomarker Detection via Enzyme-Mediated Nanoparticle Assembly

Conventional immunoassay methods have their common defects, such as tedious processing steps and inadequate sensitivity, in detecting whole blood. To overcome the above problems, we report a microfluidic chip-based magnetic relaxation switching (MRS) immunosensor via enzyme-mediated nanoparticles to simplify operation and amplify the signal in detecting whole blood samples. In the silver mirror reaction with catalase (CAT) as the catalyst, H2O2 can effectively control the production of Ag NPs. The amount of Ag NPs formed further affects the degree of aggregation of magnetic nanoparticles (MNPS), which gives rise to the changes of transverse relaxation time (T2). Both sample addition and reagent reaction are carried out in the microfluidic chip, thereby saving time and reagent consumption. We also successfully apply the sensor to detect alpha-fetoprotein (AFP) in real samples with a satisfied limit of detection (LOD = 0.56 ng/ml), which is superior to the conventional ELISA.

A signal-on fluorescence-based strategy for detection of microRNA-21 based on graphene oxide and λ exonuclease-based signal amplification

MicroRNA (miRNA) expression is perturbed in various diseases. Herein, we have aimed to develop a novel and rapid fluorescence-based assay for detecting microRNA-21 (miR-21) activity based on FAM molecular signal amplification and graphene oxide (GO) quenching. In this system, a single stranded DNA (ssDNA) with a phosphate group at the 5'-end is labeled with a FAM molecular label at the 3'-end. In the presence of miR-21, this ssDNA forms a DNA/RNA duplex, which is cleaved by λ exonuclease (λ-exo), releasing FAM and resulting in fluorescence signal amplification at 530 nm. However, the DNA/RNA duplex is not generated in the absence of miR-21, which impedes λ-exo cleavage; subsequently, GO quenches the fluorescence intensity. The results show a detection limit of 0.02 nM and a wide linear range of 0.02-5 nM. The high sensitivity and easy operability of this assay can be applied for detecting miR-21 during clinical diagnosis of certain diseases and in biological research.

Graphene/Silver Nanowires/Graphene Sandwich Composite for Stretchable Transparent Electrodes and Its Fracture Mechanism

Polycrystalline graphene grown by chemical vapor deposition (CVD) is characterized by line defects and disruptions at the grain boundaries and nucleation sites. This adversely affects the stretchability and conductivity of graphene, which limits its applications in the field of flexible, stretchable, and transparent electrodes. We demonstrate a composite electrode comprised of a graphene/silver nanowires (AgNWs)/graphene sandwich structure on a polydimethylsiloxane substrate to overcome this limitation. The sandwich structure exhibits high transparency (>90%) and excellent conductivity improvement of the graphene layers. The use of AgNWs significantly suppresses the conductivity loss resulting from stretching. The mechanism of the suppression of the conductivity loss was investigated using scanning electron microscopy, atomic force microscopy, and lateral force microscopy. The results suggest that the high surface friction of the sandwich structure causes a sliding effect between the graphene layers would produce low crack or hole formation to maintain the conductivity. In addition to acting as conductive layers, the top and bottom graphene layers can also protect the AgNWs from oxidation, thereby enabling maintenance of the electrical performance of the electrodes over a prolonged period. We also confirmed the applicability of the sandwich structure electrode to the human body, such as on the wrist, finger, and elbow.

Development of Flow Cytometric Assay for Detecting Papillary Thyroid Carcinoma Related hsa-miR-146b-5p through Toehold-Mediated Strand Displacement Reaction on Magnetic Beads

In this work, a simple enzyme-free flow cytometric assay (termed as TSDR-based flow cytometric assay) has been developed for the detection of papillary thyroid carcinoma (PTC)-related microRNA (miRNA), hsa-miR-146b-5p with high performance through the toehold-mediated strand displacement reaction (TSDR) on magnetic beads (MBs). The complementary single-stranded DNA (ssDNA) probe of hsa-miR-146b-5p was first immobilized on the surface of MB, which can partly hybridize with the carboxy-fluorescein (FAM)-modified ssDNA, resulting in strong fluorescence emission. In the presence of hsa-miR-146b-5p, the TSDR is trigged, and the FAM-modified ssDNA is released form the MB surface due to the formation of DNA/RNA heteroduplexes on the MB surface. The fluorescence emission change of MBs can be easily read by flow cytometry and is strongly dependent on the concentration of hsa-miR-146b-5p. Under optimal conditions, the TSDR-based flow cytometric assay exhibits good specificity, a wide linear range from 5 to 5000 pM and a relatively low detection limit (LOD, 3σ) of 4.21 pM. Moreover, the practicability of the assay was demonstrated by the analysis of hsa-miR-146b-5p amounts in different PTC cells and clinical PTC tissues.