Trace MicroRNA Quantification by Means of Plasmon-Enhanced Hybridization Chain Reaction

Coarse-grained model simulation-guided localized DNA signal amplification probe for miRNA detection

DNA-based enzyme-free signal amplification strategies are widely employed to detect biomarkers in low abundance. To enhance signal amplification, localized DNA reaction units which increases molecular collision probability is commonly utilized. However, the current understanding of the structure-function relationships in localized DNA signal amplification probes is limited, leading to unsatisfied performance. In this study, we introduced a coarse-grained molecular model to simulate the dynamic behavior of two DNA reaction units within a DNA enzyme-free signal amplification circuit called Localized Catalytic Hairpin Assembly (LCHA). We investigated the impact of localized distance and flexibility on reaction performance. The most efficient LCHA probe guided by simulation exhibits sensitivity 28 times greater that of free CHA, with a detection limit of miR-21 reaching 16 pM, while the least effective LCHA probe demonstrated a modest improvement of only 7 times. We successfully employed the optimized probe to differentiate cancer cells from normal cells based on their miR-21 expression levels, showcasing its quantification ability. By elucidating the mechanistic insights and structure-function relationship in our work, we aim to contribute valuable information that can save users' time and reduce costs when designing localized DNA probes. With a comprehensive understanding of how the localization affects probe performance, researchers can now make more informed and efficient decisions during the design process. This work would find broad applications of DNA nanotechnology in biosensing, biocomputing, and bionic robots.

Enhanced DNA Entropy-Driven Circuit by Locked Nucleic Acids and Simulation-Guided Localization

Signal amplification methods based on DNA molecular interactions are promising tools for detecting various biomarkers in low abundance. The entropy-driven circuit (EDC), as an enzyme-free signal amplification method, has been used in detecting and imaging a variety of biomarkers. The localization strategy can effectively increase the local concentration of the DNA reaction modules to improve the signal amplification effect. However, the localization strategy may also amplify the leak reaction of the EDC, and effective signal amplification can be limited by the unclear structure-function relationship. Herein, we utilized locked nucleic acid (LNA) modification to enhance the stability of the localized entropy-driven circuit (LEDC), which suppressed a 94.6% leak signal. The coarse-grained model molecular simulation was used to guide the structure design of the LEDC, and the influence of critical factors such as the localized distance and spacer length was analyzed at the molecular level to obtain the best reaction performance. The sensitivities of miR-21 and miR-141 detected by a simulation-guided optimal LEDC probe were 17.45 and 65 pM, 1345 and 521 times higher than free-EDC, respectively. The LEDC was further employed for the fluorescence imaging of miRNA in cancer cells, showing excellent specificity and sensitivity. This work utilizes LNA and molecular simulations to comprehensively improve the performance of a localized DNA signal amplification circuit, providing an advanced DNA probe design strategy for biosensing and imaging as well as valuable information for the designers of DNA-based probes.

Enhanced fluorescence detection of miRNA by means of Bloch surface wave-based biochips

We report on the use of biochips based on one-dimensional photonic crystals sustaining Bloch surface waves to specifically detect target miRNA that is characteristic of hemorrhagic stroke (miR-16-5p) at low concentration in a buffer solution. The biochips were functionalized with streptavidin and ssDNA oligonucleotides to enable miRNA detection. To discriminate the target miRNA from a non-specific control (miR-101a-3p), we made use of an optical platform developed to work both in label-free and fluorescence detection modes. We demonstrate that the limit of detection provided when operating in the fluorescence mode allows us to specifically detect the target miRNA down to 1 ng mL-1 (140 pM), which matches the recommendations for diagnostic miRNA assays, 5 ng mL-1. The low costs open the way towards the application of these disposable optical biochips based on 1DPC sustaining Bloch surface waves as a promising tool for early disease detection in a liquid biopsy format.

Catalytic Hairpin Assembly-Enhanced Graphene Transistor for Ultrasensitive miRNA Detection

MicroRNAs (miRNAs) have emerged as powerful biomarkers for disease diagnosis and screening. Traditional miRNA analytical techniques are inadequate for point-of-care testing due to their reliance on specialized expertise and instruments. Graphene field-effect transistors (GFETs) offer the prospect of simple and label-free diagnostics. Herein, a GFET biosensor based on tetrahedral DNA nanostructure (TDN)-assisted catalytic hairpin assembly (CHA) reaction (TCHA) has been fabricated and applied to the sensitive and specific detection of miRNA-21. TDN structures are assembled to construct the biosensing interface, facilitating CHA reaction by providing free space and preventing unwanted entanglements, aggregation, and adsorption of probes on the graphene channel. Owing to synergistic effects of TDN-assisted in situ nucleic acid amplification on the sensing surface, as well as inherent signal sensitization of GFETs, the biosensor exhibits ultrasensitive detection of miRNA-21 down to 5.67 × 10-19 M, approximately three orders of magnitude lower than that normally achieved by graphene transistors with channel functionalization of single-stranded DNA probes. In addition, the biosensor demonstrates excellent analytical performance regarding selectivity, stability, and reproducibility. Furthermore, the practicability of the biosensor is verified by analyzing targets in a complex serum environment and cell lysates, showing tremendous potential in bioanalysis and clinical diagnosis.

Recent advances in plasmon-enhanced luminescence for biosensing and bioimaging

Plasmon-enhanced luminescence (PEL) is a unique photophysical phenomenon in which the interaction between luminescent moieties and metal nanostructures results in a marked luminescence enhancement. PEL offers several advantages and has been extensively used to design robust biosensing platforms for luminescence-based detection and diagnostics applications, as well as for the development of many efficient bioimaging platforms, enabling high-contrast non-invasive real-time optical imaging of biological tissues, cells, and organelles with high spatial and temporal resolution. This review summarizes recent progress in the development of various PEL-based biosensors and bioimaging platforms for diverse biological and biomedical applications. Specifically, we comprehensively assessed rationally designed PEL-based biosensors that can efficiently detect biomarkers (proteins and nucleic acids) in point-of-care tests, highlighting significant improvements in the sensing performance upon the integration of PEL. In addition to discussing the merits and demerits of recently developed PEL-based biosensors on substrates or in solutions, we include a brief discussion on integrating PEL-based biosensing platforms into microfluidic devices as a promising multi-responsive detection method. The review also presents comprehensive details about the recent advances in the development of various PEL-based multi-functional (passive targeting, active targeting, and stimuli-responsive) bioimaging probes, highlighting the scope of future improvements in devising robust PEL-based nanosystems to achieve more effective diagnostic and therapeutic insights by enabling imaging-guided therapy.

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.

Reversible Ratiometric Electrochemiluminescence Biosensor Based on DNAzyme Regulated Resonance Energy Transfer for Myocardial miRNA Detection

Myocardial miRNAs in peripheral blood are closely related to the pathogenic process of myocardial infarction. Rapid identification and accurate quantification of myocardial miRNAs are of great significance to clinical interventions for treating cardiovascular lesions. Therefore, a ratiometric electrochemiluminescence (ECL) biosensor integrating DNAzyme with a resonance energy transfer (RET) system was designed to detect myocardial miRNA. The dual-signal system was composed of rA marked substrate strand functionalized CdTe quantum dots (QDs) as reductive-oxidative (R-O) emitters and Cy5-labeled strand-functionalized Ru(bpy)₃²⁺-filled silica nanoparticles (RuSi NPs) as oxidative-reductive (O-R) emitters. In the presence of target miRNA, DNAzyme was activated to cut substrate strands on the CdTe QDs and release triggers for opening hairpin probes. Then, the Cy5 molecule-labeled hairpin DNA on the RuSi NPs was opened to introduce Cy5 molecules and RuSi NPs into the system. The R-O ECL was quenched by ECL-RET between CdTe QDs and Cy5 molecules and the O-R ECL was introduced by the RuSi NPs. In this way, based on the simultaneous changing of the ECL signal, the dual-potential dynamic signal ratiometric ECL sensing platform was developed. By measuring the ratio of O-R ECL signal to R-O ECL signal, the concentration of miRNA-499 was accurately quantified in the range of 10 fM to 10 nM, and the detection limit was as low as 2.44 fM (S/N = 3). This DNAzyme guided dual-potential ratiometric ECL method provides a sensitive and reliable method for myocardial miRNA detection, and it has great potential in clinical diagnosis and treatment.

A Cascaded DNA Circuit in Bead Arrays for Quantitative Single-Cell MicroRNA Analysis

Single-cell microRNA (miRNA) analysis helps people understand the causes of diseases and formulate new disease treatment strategies. However, miRNA from a single cell is usually very rare and requires signal amplification for accurate quantification. Here, to amplify the signal, we constructed the cascaded DNA circuits consisting of catalytic hairpin assembly and hybrid chain reaction into the bead array platform, on which the uniformly distributed beads were adopted for miRNA quantification. After exponential signal amplification, a consistent linear correlation between the percentage of fluorescent beads and the copy number of miRNA was detected. The proposed bead array can achieve ultrahigh sensitivity as low as 60 copies of miR-155 and high specificity for distinguishing single nucleotide differences. This method has been successfully applied to the quantitative detection of miRNA in a single cancer cell. The high sensitivity, programmability, and simple workflow of the bead array chip will give a huge advantage in basic and clinical research.

A Deoxyribozyme-Initiated Self-Catalytic DNA Machine for Amplified Live-Cell Imaging of MicroRNA

Functional DNA nanostructures have been widely used in various bioassay fields. Yet, the programmable assembly of functional DNA nanostructures in living cells still represents a challenging goal for guaranteeing the sensitive and specific biosensing utility. In this work, we report a self-catalytic DNA assembly (SDA) machine by using a feedback deoxyribozyme (DNAzyme)-amplified branched DNA assembly. This SDA system consists of catalytic self-assembly (CSA) and DNAzyme amplification modules for recognizing and amplifying the target analyte. The analyte initiates the CSA reaction, leading to the formation of Y-shaped DNA that carries two RNA-cleaving DNAzymes. One DNAzyme can then successively cleave the corresponding substrate and generate numerous additional inputs to activate new CSA reactions, thus realizing a self-catalytic amplification reaction. Simultaneously, the other DNAzyme is assembled as a versatile signal transducer for cleaving the fluorophore/quencher-modified substrate, leading to the generation of an amplified fluorescence readout. By incorporating a flexible auxiliary sensing module, the SDA system can be converted into a universal sensing platform for detecting cancerous biomarkers, e.g., a well-known oncogene microRNA-21 (miR-21). Moreover, the SDA system realized the precise intracellular miR-21 imaging in living cells, which is attributed to the reciprocal amplification property between CSA reactions and DNAzyme biocatalysis. This compact SDA amplifier machine provides a universal and facile toolbox for the highly efficient identification of cancerous biomarkers and thus holds great potential for early cancer diagnosis.

A fluorescent microarray platform based on catalytic hairpin assembly for MicroRNAs detection

The DNA microarray has distinctive advantages of high-throughput and less complicated operations, but tends to have a relatively low sensitivity. Catalytic hairpin assembly (CHA) is one of the most promising enzyme-free, isothermal DNA circuit for high efficient signal amplification. Here, a microarray-based catalytic hairpin assembly (mi-CHA) biosensing method has been developed to detect various miRNAs in a single test simultaneously. The target miRNA can trigger conformational transformations of hairpin-structured DNA probes on the chip surface and lead to the specific signal amplification. A significant advantage of this approach is that each duplex produced by the solid-phase CHA will be immobilized on the certain location of the chip and release fluorescent signal via the universal domain, eliminating the requirement of different fluorophores. This method has manifested a high detection sensitivity of human cancer-associated miRNAs (miR-21 and miR-155) down to 1.33 fM and promised a high specificity to distinguish single-base mismatches. Furthermore, the practicability of this method was demonstrated by analyzing target miRNAs in human serum and cancer cells. The experimental results suggest that the proposed method has high-throughput analytical potential and could be applied to many other clinical diagnosis.

Label-free fluorometric detection of microRNA using isothermal rolling circle amplification generating tandem G-quadruplex

MicroRNAs (miRNAs) play an important role in various biological processes and have been regarded as promising diagnostic biomarkers for solid tumors in the field of clinical diagnostics. In this study, we developed a simple label/quencher-free fluorometric system for sensitive and selective miRNA detection using isothermal gene amplification such as rolling circle amplification generating tandem G-quadruplex DNA structures (GQ-RCA). The closed-circular dumbbell-shaped padlock DNA was designed to be complementary to its corresponding target miRNA. In the presence of the target miRNA, a long stretch of ssDNA with tandem G-quadruplex sequence repeats was readily generated by RCA, initiated by phi29 DNA polymerase through DNA synthesis priming at the 3'-OH of the target miRNA annealed to the padlock DNA. The RCA product harboring tandem G-quadruplex was monitored with fluorophore Thioflavin T (ThT) that emits strong fluorescence only when it intercalates into the G-quadruplex. The GQ-RCA assay enabled us to detect miRNA as low as 4.9 fM with a linear range from 25.6 fM to 80 pM within 0.5 h. In addition, our system was applied to the miRNA samples present in human plasma, showing its potential use in the clinical diagnosis of cancer.

Nanoplasmon-enhanced drop-screen for high throughput single-cell nucleocytoplasmic miRNA profiling

Cell nucleocytoplasmic profiles of microRNAs (miRNAs) are critical to determining a single cell's essential functionalities, such as cellular transcription, nucleus export and degradation, which gives a comprehensive view of cellular processes. Despite the importance of addressing nucleocytoplasmic heterogeneity, the challenge of high-throughput screening remains. Although a droplet-based approach was developed for single-cell miRNA assays, the challenge of quantifying miRNA with high sensitivity to indicate nucleocytoplasmic heterogeneity remains. In this study, a nanoplasmon-enhanced droplet screening platform was developed to quantify single-cell nucleocytoplasmic heterogeneity with the high sensitivity of 0.1 nM. Droplet screening and multiplexed plasmonic assays are synergistic: droplet screening is used to isolate single cells for high-throughput screening, while enhanced nanoplasmonic assays are conducted to precisely determine different types of miRNAs, addressing the cell nucleocytoplasmic profile. Here, two nucleic acid-functionalized plasmonic nanosensors, silver nanoparticles functionalized with designed sequences to target miRNAs, are synthesized. After the targets are bound, competitive formation of sensor-target hybrids interferes with plasmonic coupling between the nanoparticles, decreasing a fluorescence signal and thus enabling high-sensitivity single-cell miRNA quantification. Using the fluorescence signal change as a readout allows continuous-flow measurement to provide a single-cell nucleocytoplasmic profile in a high-throughput manner (∼100 cells per minute) for effective quantitative cell biology.

Construction of an ultrasensitive electrochemical sensing platform for microRNA-21 based on interface impedance spectroscopy

A hybridization chain reaction (HCR) amplification-based electrochemical impedimetric biosensor is fabricated for the quick, sensitive, and specific detection of miRNA-21 (miR-21) via monitoring of electrode interfacial property changes in real-time. Two sequences of H1 and H2 are adopted to trigger HCR amplification. A large amount of linear DNA concatemer are formed which could change the interfacial properties of the electrode. Interfacial charge transfer resistance difference (R_ct) is probed via electrochemical impedance spectroscopy (EIS) and Randles equivalent circuit. After amplifying via HCR, oligonucleotides with negatively charged repelling [Fe(CN)₆]^3-/4- ions can form a spatial blockage. HCR amplification strategy markedly enhanced the electrochemical signal with a limit of detection (LOD) down to 4.63 fM (S/N = 3). This strategy exhibited excellent selectivity for three different miRNAs: miR-199a, miR-141, and miR-155. Moreover, results show that the proposed method can be applied to miR-21 detection in the total RNA extracted from five cells. This work presents an enzyme-free and label-free EIS nucleic acid sensor for sensitively and selectively detecting miR-21, offering a promising approach in early diseases diagnosis.

A multifunctional plasmonic chip for bacteria capture, imaging, detection, and in situ elimination for wound therapy

A multifunctional plasmonic gold chip has been constructed for early diagnosis and highly effective killing of bacteria, which is critical for human health. The chip features high bacterial capture efficiency, plasmon-enhanced fluorescence (PEF) and surface-enhanced Raman scattering (SERS) and can act as a highly sensitive sensor for dual-mode bacteria imaging and detection (down to 102 CFU mL-1) with good reliability and accuracy. The developed assay can distinguish Gram-positive S. aureus bacteria from Gram-negative E. coli bacteria, providing valuable information for therapy. Importantly, the chip presents excellent photothermal antibacterial activity (98%) and can inactivate both Gram-positive and Gram-negative bacteria in situ. Furthermore, the chip was used to effectively promote the wound healing process in bacteria infected mice in vivo, showing great potential for antibacterial applications.

Homogeneous multiplexed digital detection of microRNA with ligation-rolling circle amplification

MicroRNA was transformed into a DNA nanoflower ball by LRCA reaction for homogeneous multiplexed digital detection using flow cytometry.

Detection of microRNA using enzyme-assisted amplifying and DNA-templated silver nanoclusters signal-off fluorescence bioassay

A Simple and fast analysis strategy of fluorescence quenching based on DNA-templated silver nanoclusters was developed for detection of miR-122 related to diseases such as human liver. We used Exo III to cleave the silver cluster template and assist in the DNA-RNA complex cycle. When the target is absent, the silver cluster template remains intact, and DNA-AgNCs are generated under the action of AgNO₃/NaBH₄, producing a strong background fluorescence signal. Once the target is added, the site of the Exo III occurs after a series of hybridization cycles, the Exo III acts, the template DNA is continuously hydrolyzed, and the fluorescence intensity of the system is significantly reduced. By comparing the changes in the fluorescence signal, we found that this strategy has good sensitivity and the detection limit is as low as 84.0 pM. The strategy also has excellent discriminating ability and good selectivity, it can provide a persuasive reference for the early diagnosis of liver cancer and hepatitis.

Lighting Up Fluorescent Silver Clusters via Target-Catalyzed Hairpin Assembly for Amplified Biosensing

Isothermal enzyme-free nucleic acid circuits have been developed for carrying out diverse functions ranging from dictate biocomputing to amplified biosensing. Catalytic hairpin assembly (CHA), the catalyzed cross-opening of two hairpin substrates by an initiator, has attracted increasing attention because of its facile design and high amplification capacity. The complex labeling and frequent photobleaching of a conventional fluorescent CHA biosensor still remains a challenge that needs to be solved. Herein, we constructed a new label-free and enzyme-free isothermal CHA lighting up AgNCs strategy for amplified nucleic acid assay by integrating the interfacially and spatially sensitive feature of DNA-templated fluorescent silver nanoclusters (DNA-AgNCs) and the high signal amplification capability of the CHA circuit. In this strategy, one polyguanine-grafted hairpin and the other AgNCs-capturing hairpin were engineered as assembly constitutes, which were kinetically impeded from cross-hybridizations without target. However, in the presence of target, the CHA-catalyzed assembly of two functional hairpins was successively progressed and concomitantly accompanied by an efficient accommodation of AgNCs to the polyguanine-elongated dsDNA product, leading to highly efficient AgNCs-lighting up and to the generation of an amplified fluorescence signal. As a simple mix-and-detect strategy, the isothermal enzyme-free CHA-mediated lighting up AgNCs (CHA-AgNCs) system provided a facile visualization way for amplified detection of DNA with a detection limit of 20 pM, which was comparable to or even better than some enzyme-involved amplification methods. The homogeneous CHA-AgNCs system can be used as a general sensing platform and be easily adapted for analyzing other biologically important analytes, for example, microRNA (miRNA), by introducing the sensing module consisting of an auxiliary hairpin through an easy-to-integrate procedure. By taking advantage of the signal amplification features of CHA and the robust AgNCs-lighting up procedure, we anticipate that the CHA-lighting up AgNCs system can provide an important tool for biomedicine and bioimaging applications and thus should hold great promise in clinical diagnoses and treatment fields.

Shell-Isolated Nanoparticle-Enhanced Phosphorescence

The emerging field of plasmonics has promoted applications of optical technology, especially in plasmon-enhanced spectroscopy (PES). However, in plasmon-enhanced fluorescence (PEF), "metal loss" could significantly quench the fluorescence during the process, which dramatically limits its applications in analysis and high-resolution imaging. In this report, silver core silica shell-isolated nanoparticles (Ag@SiO₂ NPs or SHINs) with a tunable thickness of shell are used to investigate the interactions between NPs and emitters by constructing coupling and noncoupling modes. The plasmonic coupling mode between Ag@SiO₂ NPs and Ag film reveals an exceeding integrating spectral intensity enhancement of 330 and about 124 times that of the radiative emission rate acceleration for shell-isolated nanoparticle enhanced phosphorescence (SHINEP). The experimental findings are supported by theoretical calculations using the finite-element method (FEM). Hence, the SHINEP may provide a novel approach for understanding the interaction of plasmon and phosphorescence, and it holds great potential in surface detection analysis and singlet-oxygen-based clinical therapy.

A hybridization chain reaction amplification strategy for fluorescence imaging of human telomerase activity in living cells

A hybridized chain reaction (HCR)-based biosensing method has been developed for the imaging detection of intracellular telomerase activity. The telomerase-targeting responder-transmitter DNA complex (HPT) consisting of telomerase primer sequence (HP) and a HCR initiator (trigger) is transfected into cell plasma. In the presence of telomerase, HPT can be recognized and extended, producing plenty of triggers which initiate HCR amplification reaction. Finally, a long nicked dsDNA with a lot of outstretched single chains was formed by hybridizing with Q of the reporter complex, generating an enhanced fluorescence signal. The developed biosensing approach can be used for the detection of telomerase activity in cell lysate with the detection limit of 578 cells/100 μl. In addition, this strategy has been successfully applied not only for the sensitive and specific imaging of telomerase activity in living cells but also for comparing of telomerase activity among different cell lines. Therefore, the method might become a potential alternative tool for telomerase-related cancer diagnosis and therapy in medical research and early clinical diagnosis.

Plasmonic molecular assays: Recent advances and applications for mobile health

Plasmonics-based biosensing assays have been extensively employed for biomedical applications. Significant advancements in use of plasmonic assays for the construction of point-of-care (POC) diagnostic methods have been made to provide effective and urgent health care of patients, especially in resourcelimited settings. This rapidly progressive research area, centered on the unique surface plasmon resonance (SPR) properties of metallic nanostructures with exceptional absorption and scattering abilities, has greatly facilitated the development of cost-effective, sensitive, and rapid strategies for disease diagnostics and improving patient healthcare in both developed and developing worlds. This review highlights the recent advances and applications of plasmonic technologies for highly sensitive protein and nucleic acid biomarker detection. In particular, we focus on the implementation and penetration of various plasmonic technologies in conventional molecular diagnostic assays, and discuss how such modification has resulted in simpler, faster, and more sensitive alternatives that are suited for point-of-use. Finally, integration of plasmonic molecular assays with various portable POC platforms for mobile health applications are highlighted.

Optical nano-biosensing interface via nucleic acid amplification strategy: construction and application

Modern optical detection technology plays a critical role in current clinical detection due to its high sensitivity and accuracy. However, higher requirements such as extremely high detection sensitivity have been put forward due to the clinical needs for the early finding and diagnosing of malignant tumors which are significant for tumor therapy. The technology of isothermal amplification with nucleic acids opens up avenues for meeting this requirement. Recent reports have shown that a nucleic acid amplification-assisted modern optical sensing interface has achieved satisfactory sensitivity and accuracy, high speed and specificity. Compared with isothermal amplification technology designed to work completely in a solution system, solid biosensing interfaces demonstrated better performances in stability and sensitivity due to their ease of separation from the reaction mixture and the better signal transduction on these optical nano-biosensing interfaces. Also the flexibility and designability during the construction of these nano-biosensing interfaces provided a promising research topic for the ultrasensitive detection of cancer diseases. In this review, we describe the construction of the burgeoning number of optical nano-biosensing interfaces assisted by a nucleic acid amplification strategy, and provide insightful views on: (1) approaches to the smart fabrication of an optical nano-biosensing interface, (2) biosensing mechanisms via the nucleic acid amplification method, (3) the newest strategies and future perspectives.

Hand-powered centrifugal microfluidic platform inspired by the spinning top for sample-to-answer diagnostics of nucleic acids

Point-of-care (POC), sample-to-answer and electricity-free nucleic acid diagnostic tools are vital for health care and disease control in resource-limited settings where centralized medical facilities or even electric power may remain unreliable. Inspired by one of the oldest recognizable toys, the spinning top, here we report a fully hand-powered centrifugal microfluidic platform for the diagnostics of pathogenic bacteria. Assay procedures such as zeolite-based purification of nucleic acids, loop-mediated isothermal amplification (LAMP) and visual detection of fluorescence signals are integrated into a single microfluidic disc. A simple pull-out operation of the top rack of the customized centrifuge initiates high-speed rotation of the disc, resulting in efficient actuation and mixing of preloaded sample/reagent fluids. This microfluidic platform enables the simultaneous detection of six kinds of pathogenic bacteria within a small disc in an electricity-free manner, showing great promise in sample-to-answer nucleic acid detection in remote settings.

Rapid and label-free fluorescence bioassay for microRNA based on exonuclease III-assisted cycle amplification

A new assay for the rapid and simple detection of microRNA based on G-quadruplex and Exonuclease III (ExoIII) dual signal amplification was constructed.

Dual Amplification Fluorescence Assay for Alpha Fetal Protein Utilizing Immunohybridization Chain Reaction and Metal-Enhanced Fluorescence of Carbon Nanodots

As an emerging fascinating fluorescent nanomaterial, carbon nanodots (CDs) have attracted much attention owing of their unique properties such as small size, antiphotobleaching, and biocompatibility. However, its use in biomedical analysis is limited because of its low quantum yield. Herein, we constructed a dual amplification fluorescence sensor by incorporating immunohybridization chain reaction (immuno-HCR) and metal-enhanced fluorescence (MEF) of CDs for the detection of alpha fetal protein (AFP). The immunoplasmonic slide and detection antibodies-conjugated oligonucleotide initiator are served to capture and probe AFP molecules, respectively. Then, CD-tagged hairpin nucleic acids were introduced to trigger the HCR, in which the hairpin nucleic acid and oligonucleotide initiator are complementary. The interaction between CDs and the gold nanoisland film greatly improves the radiative decay rate, increases the quantum yield, and enhances the fluorescence emission of the CDs. Furthermore, the HCR provides secondary amplification of fluorescence intensity. Therefore, the MEF-capable immunohybridization reactions provide obvious advantages and result in exceptional sensitivity. In addition, the sandwich immunoassay method offers high specificity. The results show a wide linearity between the fluorescence intensity and AFP concentration over 5 orders of magnitude (0.0005-5 ng/mL), and the detection limit reaches as low as 94.3 fg/mL. This method offers advantages of high sensitivity and reliability, wide detection range, and versatile plasmonic chips, thus presenting an alternative for the technologies in biomedical analysis and clinical applications.

Ultrasensitive microRNA-21 detection based on DNA hybridization chain reaction and SYBR Green dye

It is extremely important for quantifying trace microRNAs in the biomedical applications. In this study, an ultrasensitive, rapid and efficient label-free fluorescence method was proposed and applied for detecting microRNA-21 in serum of gastric cancer patients based on DNA hybridization chain reaction (HCR). DNA H1 and DNA H2 were designed and used as hairpin probes, the HCR was proceeded in the presence of target microRNAs. Amounts of SYBR Green І dyes were used as signal molecules to intercalate long DNA concatemers from HCR, which guaranteed the model of label-free fluorescence and strong fluorescence density. The detection method showed a wide linear region from 1 fM to 10⁵ fM, and the limit of detection was 0.2554 fM (at S/N = 3) for microRNAs. The results showed that this method had an excellent specificity and reproducibility. Furthermore, the label-free fluorescence strategy exhibited a sensitive response to microRNA-21 in real serum samples of gastric cancer patients and the results obtained were in accordance with reference method (R² = 0.994). Overall, the proposed strategy could be satisfactory for rapid, ultrasensitive and efficient detection of microRNA-21, and held great potentials in clinic diagnosis of gastric cancer.

MoS2 Quantum Dots as New Electrochemiluminescence Emitters for Ultrasensitive Bioanalysis of Lipopolysaccharide

Cd-based semiconductor quantum dots (QDs) with size-tunable luminescence and high quantum yield have become the most promising electrochemiluminescence (ECL) emitters. However, their unavoidable biotoxicity limited their applications in bioassays. Here, the nontoxic and economical MoS₂ QDs prepared by chemical exfoliation from the bulk MoS₂ were first investigated as new ECL emitters, and then the possible luminescence mechanism of MoS₂ QDs was studied using ECL-potential curves and differential pulse voltammetry (DPV) methods in detail. With MoS₂ QDs as the ECL emitters and triethylamine (TEA) as the efficient coreactant, a practical and label-free aptasensor for lipopolysaccharide (LPS) detection was constructed based on aptamer recognition-driven target-cycling synchronized rolling circle amplification. Comparing to conventional stepwise reactions, this target-cycling synchronized rolling circle amplification achieved more efficient signal amplification and simpler operation. The developed assay for LPS detection demonstrated a wide linear range of 0.1 fg/mL to 50 ng/mL with limit of detection down to 0.07 fg/mL. It is worth mentioning that MoS₂ QDs with stable ECL emission exhibited a great application potential in ECL bioanalysis and imaging as a new type of excellent emitter candidates.

Building Electromagnetic Hot Spots in Living Cells via Target-Triggered Nanoparticle Dimerization

Electromagnetic hot spots of surface-enhanced Raman scattering have been extensively employed for bioanalysis in solution or on a substrate, but building hot spots in living systems for probing targets of interest has not been achieved yet because of the complex and dynamic physiological environment. Herein, we show that a target-programmed nanoparticle dimerization can be combined with the background-free Raman reporters (alkyne, C≡C; nitrile, C≡N) for multiplexed imaging of microRNAs (miRNAs) in living cells. The in situ formation of plasmonic dimers results in an intense hot spot, thus dramatically enhancing the Raman signals of the reporters residing in the hot spot. More significantly, the reporters exhibit single nonoverlapping peaks in the cellular Raman-silent region (1800-2800 cm^-1), thus eliminating spectral unmixing and background interference. A 3D Raman mapping technique was harnessed to monitor the spatial distribution of the dimers and thus the multiple miRNAs in cells. This approach could be extended to probe other biomarkers of interest for monitoring specific pathophysiological events at the live-cell level.

Liposome-encoded magnetic beads initiated by padlock exponential rolling circle amplification for portable and accurate quantification of microRNAs

In this work, we propose a strategy for glucoamylase-encapsulated liposome-encoded magnetic beads initiated by padlock exponential rolling circle amplification (P-ERCA) for portable and accurate quantification of miRNA by using a glucometer (GM) for readout.

Can nanotechnology improve cancer diagnosis through miRNA detection?

miRNAs are key regulators of gene expression, and alterations in their expression levels correlate with the onset and progression of cancer. Although miRNAs have been proposed as biomarkers for cancer diagnosis, their application in routine clinical praxis is yet to come. Current quantification strategies have limitation, and there is a great interest in developing innovative ones. Since a few years, nanotechnology-based approaches for miRNA quantification are emerging at fast pace but there is urgent need to go beyond the proof-of-concept stage. Nanotechnology will have a strong impact on cancer diagnosis through miRNA detection only if it is demonstrated that the newly developed approaches are indeed working on ‘real-world’ samples under standardized conditions.