Enzyme-Free Electrochemical Biosensor Based on Localized DNA Cascade Displacement Reaction and Versatile DNA Nanosheets for Ultrasensitive Detection of Exosomal MicroRNA

Highly Stable and Integrable Graphene/Molybdenum Disulfide Heterojunction Field-Effect Transistor-Based miRNA Biosensor

MicroRNAs (miRNAs) are important noncoding RNA molecules that participate in gene regulation and are widely associated with the occurrence and development of various cancers. Developing rapid, highly sensitive, low-cost, and highly stable miRNA detection methods is of great significance for clinical diagnosis. Field-effect transistors (FETs) based on two-dimensional (2D) materials have been proven to have great potential in the field of miRNA detection due to their label-free, rapid, highly sensitive, low-power, and portable features. However, biosensors based on 2D material FETs require the application of an external gate voltage in solution, which seriously hinders the integration, miniaturization, and signal stability of the devices. This study proposes a graphene-molybdenum disulfide heterojunction (G/MoS2) FET biosensing platform to detect miRNA-21 and miRNA-155 without the need for an external gate voltage. The results demonstrate a detection time of approximately 30 min, a linear response range spanning from 10 fM to 10 nM, and limits of detection of 6.06 fM for miRNA-21 and 2.59 fM for miRNA-155. Through comparative experiments, the biosensor shows excellent selectivity and can distinguish target miRNAs from nontarget miRNAs. The G/MoS2 FET biosensor developed in this study provides a technical platform for miRNA detection and has a broad application prospect, especially in the early diagnosis of diseases and the screening of biomarkers.

CRISPR-Cas12a with split crRNA for the direct and sensitive detection of microRNA

microRNAs (miRNAs) have been identified as potential biomarkers. Despite the prevalence of quantitative PCR in the field of miRNA detection, this technology is encumbered by the complexity of its methodology. This study presents a novel CRISPR/Cas12a-based method for the direct and sensitive detection of miRNA-21 using split crRNA. The system comprises Cas12a protein, crRNA-handle, and activator DNA complementary to the target miRNA. In the presence of the target miRNA, it binds to the activator DNA, forming a duplex. The formed duplex, in conjunction with the crRNA-handle, activates Cas12a's trans-cleavage activity. This leads to cleavage of a fluorescent reporter, generating an enhanced signal. The method enables direct RNA detection without reverse transcription or sample amplification, offering simplicity and efficiency. This method demonstrates high sensitivity with a minimum detectable limit of 5 pM. Furthermore, the method's specificity is substantiated by its capacity to discern point mutations in miRNA. This system has been shown to quantitatively analyse miRNA-21 levels present within serum, as evidenced by the recovery experiment. Therefore, the method's simplicity, stability, and cost-effectiveness render it a powerful tool for nucleic acid detection, with potential for clinical applications.

Enzyme-Free and Triple Sensitivity Amplification for Electrochemical Detection of Exosomal microRNA

Exosomal miRNAs, particularly miRNA-21, are promising cancer biomarkers. Current enzyme-dependent detection methods face challenges, such as environmental limitations and high costs. In contrast, enzyme-independent sensors are highly desirable for on-site, miniaturized, and cost-effective miRNA detection. To address these limitations, we developed a nonenzymatic electrochemical sensor featuring a triple-signal amplification system for ultrasensitive detection of miRNA-21. This sensor utilizes cascade toehold-mediated strand displacement reactions to activate molecular machines triggered by target miRNA, generating biotinylated-and-thiol-modified double-stranded DNA for stable immobilization on a gold electrode. Preprepared biotinylated tetrahedron DNA (TDNA)-mediated hybridization chain reaction probes are then linked to the electrode via streptavidin-biotin binding. This amplification process allows for significant DNA duplex immobilization, with electroactive [Ru(NH3)6]3+ (RuHex) adsorbed onto them, producing a robust electrochemical signal. This approach enables accurate detection of miRNA-21 at concentrations as low as 0.43 fM, with a linear range from 1 fM to 1 nM. Clinical testing demonstrates its potential for cancer diagnostics.

Nanomaterials in gastric cancer: pioneering precision medicine for diagnosis, therapy, and prevention

Gastric cancer (GC) continues to be a major health issue globally due to its high rates of both occurrence and mortality. Despite advancements in treatment, the outlook for those affected remains poor, highlighting the critical need for new diagnostic and treatment methods. Nanotechnology, especially nanoparticles, is emerging as a crucial innovation in cancer care by improving imaging, targeting drug delivery, and enhancing early detection. These nanoparticles are also enhancing the effectiveness of treatments like phototherapy, chemotherapy, and immunotherapy. Notably, they show potential in addressing infections like Helicobacter pylori (H. pylori), which is known to increase the risk of developing GC. This review underscores the pivotal role of nanotechnology in enhancing the integrated management of GC, offering a basis for future advancements in the field.

A novel all-in-one target-powered entropy-driven dynamic DNA networks to regulate the activity of CRISPR/AsCas12a for enhanced DNA detection

BACKGROUND

The non-enzyme autonomous DNA nanodevices have been developed to detect various analytes through the programmability of Watson-Crick base pairing. Nevertheless, by comparison with enzymatic biosensors, the usage of enzyme-free DNA networks to create biosensors for testing low amounts of targets is still subject to the finite number of cycles. Besides, these biosensors still require the incorporation of other amplification strategies to improve the sensitivity, which complicates the detection workflow and lacks of a uniform compatible system to respond to the target in one pot.

RESULTS

Here, we put forward a novel way for rapid and sensitive DNA diagnostic via EDN (entropy-driven dynamic network) coupling with CRISPR/AsCas12a-powered amplification. In the absence of the target, the autonomous hybridization among the substrate and crRNA is kinetically hindered by enclosing complementary regions, which leads to the loss of the activation function of Cas12a. On the contrary, the target initiates the EDN, reconfiguring the activator strand from a duplex to branch construction, which provides a valid means to adjust the hybridization with crRNA, thereby controlling the indiscriminate collateral cleavage activities of the CRISPR/AsCas12a. Compared with the traditional EDN, synergistic activation between the EDN and the CRISPR catalyst could dramatically enhance the detection signal of the target in one pot. Furthermore, the proposed approach provides universal platforms through the rational functional and structural design of DNA assembly modules.

SIGNIFICANCE AND NOVELTY

Overall, this target-triggered EDN switches the activator strand to regulate the activity of AsCas12a (called TERA), which showed nearly one orders of magnitude sensitivity than the conventional Cas12a alone assay, resulting in a devisable universal CRISPR sensing platform that favours the fast, robust and one-pot detection of nucleic molecules.

A target-triggered colorimetric sensor for ultrasensitive detection of miRNAs based on self-powered three-dimensional DNA walker

MicroRNAs (miRNAs) play an important role in the process of heart failure (HF) and are emerging biomarkers that can be used for the auxiliary diagnosis of HF. However, it is very challenging to accurately analyze the expression levels of trace miRNAs in complex clinical samples. Here, we developed an enzyme-free colorimetric sensor for the ultrasensitive detection of miRNA-423-5p (HF-associated miRNA) based on three-dimensional DNA walkers constructed from functional nucleic acids and gold nanoparticles (AuNPs). DNAzyme with cleavage activity was specifically activated by miRNA-423-5p to sustainably cleave the substrate, thereby releasing the trigger sequence to initiate the subsequent mismatched catalytic hairpin assembly (MCHA) cycle. Then, as the MCHA cycle proceeded to continuously expose the G-quadruplex (GQ) sequence, the sequence bound with hemin to form a large amount of GQ/hemin DNAzyme on the surface of the AuNPs, which rapidly catalyzed the chromogenic oxidation of 3,3',5,5'-tetramethylbenzidine to yield an amplified colorimetric signal readout. The colorimetric sensor exhibited an ultralow detection limit (32 fM), showed excellent specificity and performed well in serum samples. The sensor was applied to detect miRNA-423-5p in clinical plasma samples from healthy individuals and HF patients, and the results revealed its good clinical application in HF diagnosis. Thus, the developed colorimetric sensor provides a convenient detection tool for early screening and diagnosis of HF, as well as for pathophysiological studies.

Shedding Light on Cellular Secrets: A Review of Advanced Optical Biosensing Techniques for Detecting Extracellular Vesicles with a Special Focus on Cancer Diagnosis

In the relentless pursuit of innovative diagnostic tools for cancer, this review illuminates the cutting-edge realm of extracellular vesicles (EVs) and their biomolecular cargo detection through advanced optical biosensing techniques with a primary emphasis on their significance in cancer diagnosis. From the sophisticated domain of nanomaterials to the precision of surface plasmon resonance, we herein examine the diverse universe of optical biosensors, emphasizing their specified applications in cancer diagnosis. Exploring and understanding the details of EVs, we present innovative applications of enhancing and blending signals, going beyond the limits to sharpen our ability to sense and distinguish with greater sensitivity and specificity. Our special focus on cancer diagnosis underscores the transformative potential of optical biosensors in early detection and personalized medicine. This review aims to help guide researchers, clinicians, and enthusiasts into the captivating domain where light meets cellular secrets, creating innovative opportunities in cancer diagnostics.

Sensitive electrochemical biosensor for rapid detection of sEV-miRNA based turbo-like localized catalytic hairpin assembly

Small extracellular vesicle-associated microRNAs (sEV-miRNAs) have emerged as critical biomarkers for cancer diagnosis, yet the rapid detection of these low-abundance molecules in clinical samples remains a formidable challenge. Herein, a simple turbo-like localized catalytic hairpin assembly (TL-CHA) was proposed for sEV-miR-1246 measurement. This electrochemical sensor achieves dual localization through the ingeniously use of AuNPs and DNA nanowires, which provides rich sites for CHA cascade amplification, significantly enhancing the effective reaction and amplify the detection response. Leveraging this innovative design, this biosensor demonstrated the ability to detect sEV-miRNA at concentrations as low as 5.24 aM in a time frame of 30 min. The precision of the measurements was validated through reverse transcription quantitative polymerase chain reaction. Furthermore, the sensor was used for analyzing plasma samples from gastric cancer patients yielded AUC values of 0.973 for all stages and 0.945 for early stages. This demonstrates the sensor's robust performance in both the staging diagnosis and early screening of gastric cancer. Therefore, this platform has great potential for the clinical cancer diagnosis.

Recent advances in the applications of DNA frameworks in liquid biopsy: A review

Cancer is one of the serious threats to public life and health. Early diagnosis, real-time monitoring, and individualized treatment are the keys to improve the survival rate and prolong the survival time of cancer patients. Liquid biopsy is a potential technique for cancer early diagnosis due to its non-invasive and continuous monitoring properties. However, most current liquid biopsy techniques lack the ability to detect cancers at the early stage. Therefore, effective detection of a variety of cancers is expected through the combination of various techniques. Recently, DNA frameworks with tailorable functionality and precise addressability have attracted wide spread attention in biomedical applications, especially in detecting cancer biomarkers such as circulating tumor cells (CTCs), exosomes and circulating tumor nucleic acid (ctNA). Encouragingly, DNA frameworks perform outstanding in detecting these cancer markers, but also face some challenges and opportunities. In this review, we first briefly introduced the development of DNA frameworks and its typical structural characteristics and advantages. Then, we mainly focus on the recent progress of DNA frameworks in detecting commonly used cancer markers in liquid-biopsy. We summarize the advantages and applications of DNA frameworks for detecting CTCs, exosomes and ctNA. Furthermore, we provide an outlook on the possible opportunities and challenges for exploiting the structural advantages of DNA frameworks in the field of cancer diagnosis. Finally, we envision the marriage of DNA frameworks with other emerging materials and technologies to develop the next generation of disease diagnostic biosensors.

Multiarmed DNA jumper and metal-organic frameworks-functionalized paper-based bioplatform for small extracellular vesicle-derived miRNAs assay

Small extracellular vesicle-derived microRNAs (sEV-miRNAs) have emerged as promising noninvasive biomarkers for early cancer diagnosis. Herein, we developed a molecular probe based on three-dimensional (3D) multiarmed DNA tetrahedral jumpers (mDNA-Js)-assisted DNAzyme activated by Na+, combined with a disposable paper-based electrode modified with a Zr-MOF-rGO-Au NP nanocomplex (ZrGA) to fabricate a novel biosensor for sEV-miRNAs Assay. Zr-MOF tightly wrapped by rGO was prepared via a one-step method, and it effectively aids electron transfer and maximizes the effective reaction area. In addition, the mechanically rigid, and nanoscale-addressable mDNA-Js assembled from the bottom up ensure the distance and orientation between fixed biological probes as well as avoid probe entanglement, considerably improving the efficiency of molecular hybridization. The fabricated bioplatform achieved the sensitive detection of sEV-miR-21 with a detection limit of 34.6 aM and a dynamic range from100 aM to 0.2 µM. In clinical blood sample tests, the proposed bioplatform showed results highly consistent with those of qRT-PCRs and the signal increased proportionally with the NSCLC staging. The proposed biosensor with a portable wireless USB-type analyzer is promising for the fast, easy, low-cost, and highly sensitive detection of various nucleic acids and their mutation derivatives, making it ideal for POC biosensing.

DNA-Based Nanomaterials for Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) are cell-derived nanovesicles comprising a myriad of molecular cargo such as proteins and nucleic acids, playing essential roles in intercellular communication and physiological and pathological processes. EVs have received substantial attention as noninvasive biomarkers for disease diagnosis and prognosis. Owing to their ability to recognize protein and nucleic acid targets, DNA-based nanomaterials with excellent programmability and modifiability provide a promising tool for the sensitive and accurate detection of molecular cargo carried by EVs. In this perspective, recent advancements in EV analysis using a variety of DNA-based nanomaterials are summarized, which can be broadly classified into three categories: linear DNA probes, DNA nanostructures, and hybrid DNA nanomaterials. The design, construction, advantages, and disadvantages of different types of DNA nanomaterials, as well as their performance for detecting EVs are reviewed. The challenges and opportunities in the field of EV analysis by DNA nanomaterials are also discussed.

MnFe@N-CNTs Based Lactate Biomicrochips for Nonintrusive and Onsite Periodontitis Diagnosis

In clinical settings, saliva has been established as a straightforward, noninvasive medium for diagnosing periodontitis. However, the precise diagnosis is often hampered by the absence of a specialized analyzer capable of detecting low concentrations of biomarkers typically found in saliva. In this study, we present a noninvasive, on-site screen-printed biomicrochip specifically engineered for the precise and sensitive quantification of lactate concentrations in saliva, a critical biomarker in the diagnosis of periodontitis. The microchip is constructed using a nanostructured ink formulation that includes MnFe@N-doped carbon nanotubes (MnFe@N-CNTs). These MnFe@N-CNTs exhibit a high degree of graphitization and low electrical resistance, significantly augmenting the electrocatalytic efficiency of the enzymatic reaction of lactate. This results in doubled sensitivity and a detection limit that surpasses those of the current advanced salivary assay methods. Remarkably, within just 30 s, the biomicrochip can quantitatively and precisely measure lactate concentrations in the saliva of 10 patients, which provides valuable insights into the severity of their periodontitis. This biosensor holds excellent potential for large-scale production and could broaden the scope of biomarker recognition, paving the way for the analysis of a wider range of oral diseases.

Nanomaterials in electrochemical nanobiosensors of miRNAs

Nanomaterial-based biosensors have received significant attention owing to their unique properties, especially enhanced sensitivity. Recent advancements in biomedical diagnosis have highlighted the role of microRNAs (miRNAs) as sensitive prognostic and diagnostic biomarkers for various diseases. Current diagnostics methods, however, need further improvements with regards to their sensitivity, mainly due to the low concentration levels of miRNAs in the body. The low limit of detection of nanomaterial-based biosensors has turned them into powerful tools for detecting and quantifying these biomarkers. Herein, we assemble an overview of recent developments in the application of different nanomaterials and nanostructures as miRNA electrochemical biosensing platforms, along with their pros and cons. The techniques are categorized based on the nanomaterial used.

Extracellular vesicles associated microRNAs: Their biology and clinical significance as biomarkers in gastrointestinal cancers

Gastrointestinal (GI) cancers, including colorectal, gastric, esophageal, pancreatic, and liver, are associated with high mortality and morbidity rates worldwide. One of the underlying reasons for the poor survival outcomes in patients with these malignancies is late disease detection, typically when the tumor has already advanced and potentially spread to distant organs. Increasing evidence indicates that earlier detection of these cancers is associated with improved survival outcomes and, in some cases, allows curative treatments. Consequently, there is a growing interest in the development of molecular biomarkers that offer promise for screening, diagnosis, treatment selection, response assessment, and predicting the prognosis of these cancers. Extracellular vesicles (EVs) are membranous vesicles released from cells containing a repertoire of biological molecules, including nucleic acids, proteins, lipids, and carbohydrates. MicroRNAs (miRNAs) are the most extensively studied non-coding RNAs, and the deregulation of miRNA levels is a feature of cancer cells. EVs miRNAs can serve as messengers for facilitating interactions between tumor cells and the cellular milieu, including immune cells, endothelial cells, and other tumor cells. Furthermore, recent years have witnessed considerable technological advances that have permitted in-depth sequence profiling of these small non-coding RNAs within EVs for their development as promising cancer biomarkers -particularly non-invasive, liquid biopsy markers in various cancers, including GI cancers. Herein, we summarize and discuss the roles of EV-associated miRNAs as they play a seminal role in GI cancer progression, as well as their promising translational and clinical potential as cancer biomarkers as we usher into the area of precision oncology.

Exploring the Versatility of Exosomes: A Review on Isolation, Characterization, Detection Methods, and Diverse Applications

Extracellular vesicles (EVs) are crucial mediators of intercellular communication and can be classified based on their physical properties, biomolecular structure, and origin. Among EVs, exosomes have garnered significant attention due to their potential as therapeutic and diagnostic tools. Exosomes are released via fusion of multivesicular bodies on plasma membranes and can be isolated from various biofluids using methods such as differential ultracentrifugation, immune affinity capture, ultrafiltration, and size exclusion chromatography. Herein, an overview of different techniques for exosome characterization and isolation, as well as the diverse applications of exosome detection, including their potential use in drug delivery and disease diagnosis, is provided. Additionally, we discuss the emerging field of exosome detection by sensors, which offers an up-and-coming avenue for point-of-care diagnostic tools development. Overall, this review aims to provide a exhaustive and up-to-date summary of the current state of exosome research.

Multicomponent synthesis of pyrido[2,3-b]pyrazine derivatives: electrochemical DNA sensing, nonlinear optical properties and biological activity

We synthesized novel pyrido[2,3-b]pyrazin based heterocyclic compounds (4-7) and their chemical structures were ascertained by spectral techniques (NMR, FT-IR). Besides experimental investigation, density functional theory (DFT) computations with B3LYP/6-31G(d,p) level of theory were executed to obtain spectroscopic and electronic properties. Nonlinear optical (NLO) properties, frontier molecular orbitals (FMOs), UV-visible, vibrational analysis, natural bond orbitals (NBOs), transition density matrix (TDM) and density of states (DOS) analyses of molecules (4-7) were accomplished at B3LYP/6-31G (d,p) level. Global reactivity parameters (GRPs) were correlated with the band gap (Egap) values; compound 7 with lower Egap (3.444 eV), exhibited smaller value of hardness (1.722 eV) with greater softness value (0.290 eV-1). The dipole moment (μ), average polarizability 〈α〉, first (βtot) and second 〈γ〉 hyper-polarizabilities were calculated for compounds (4-7). Compound 7 showed less Egap, highest absorption wavelength and remarkable NLO response. The highest 〈α〉, βtot and 〈γ〉 values for compound 7 were observed as 3.90 × 10-23, 15.6 × 10-30 and 6.63 × 10-35 esu, respectively. High NLO response revealed that pyrido[2,3-b]pyrazin based heterocyclic compounds had very remarkable contributions towards NLO technological applications. Further compounds (4-7) are utilized for the first time in electrochemical sensing of DNA, in vitro antioxidant and antiurease activity.

An all-in-one enzymatic DNA network based on catalytic hairpin assembly for label-free and highly sensitive detection of APE1

Apurinic/apyrimidinic endonuclease 1 (APE1), identified as a prospective cancer biomarker, plays a vital role in the occurrence and progression of cancer cell lines and impacts on genome stability. However, conventional approaches typically rely on the interactions between the antigen and antibody, limiting their utility for qualitative assessments of APE1 expression. Herein, an all-in-one enzymatic DNA network (EDN) assay with catalytic hairpin assembly for label-free and ultrasensitive detection of APE1 has been developed. In this work, the blocking strand can inhibit the initiator by obstructing the complementary region, preventing the hairpin from hybridizing in the absence of APE1 targets. While the presence of targets can activate the unlocking of the initiator, which can trigger the catalytic hairpin reaction, and increase the fluorescent signal. Under optimal conditions, the developed sensing method can detect the target APE1 down to 4.78 × 10-6 U mL-1 with a wide linear range from 5 × 10-6 U mL-1 to 30 U mL-1. This strategy has also been successfully applied to the analysis of complicated biological samples compared to ELISA, demonstrating its potential applications in biochemical and molecular biology research as well as clinical diagnostics. Overall, benefiting from the high amplification efficiency, this strategy has successfully and simply detected low-abundance APE1 without additional enzyme isolation steps, presenting great potential for clinical detection applications.

A novel biosensor based on tetrahedral DNA nanostructure and terminal deoxynucleotidyl transferase-assisted amplification strategy for fluorescence analysis of uracil-DNA glycosylase activity

Tetrahedral DNA nanostructure (TDN), as a classical bionanomaterial, which not only has excellent structural stability and rigidity, but also possesses high programmability due to strict base-pairs complementation, is widely used in various biosensing and bioanalysis fields. In this study, we first constructed a novel biosensor based on Uracil DNA glycosylase (UDG) -triggered collapse of TDN and terminal deoxynucleotidyl transferase (TDT)-induced insertion of copper nanoparticles (CuNPs) for fluorescence and visual analysis of UDG activity. In the presence of the target enzyme UDG, the uracil base modified on the TDN were specifically identified and removed to produce an abasic site (AP site). Endonuclease IV (Endo.IV) could cleave the AP site, making the TDN collapse and generating 3'-hydroxy (3'-OH), which were then elongated under the assistance of TDT to produce poly (T) sequences. Finally, Copper (II) sulfate (Cu²⁺) and l-Ascorbic acid (AA) were added to form CuNPs using poly (T) sequences as templates (T-CuNPs), resulting in a strong fluorescence signal. This method exhibited good selectivity and high sensitivity with a detection limit of 8.6 × 10^-5 U/mL. Moreover, the strategy has been successfully applied to the screening of UDG inhibitors and the detection of UDG activity in complex cell lysates, which means that it has promising applications in clinical diagnosis and biomedical research.

Three-Dimensional CHA-HCR System Using DNA Nanospheres for Sensitive and Rapid Imaging of miRNA in Live Cells and Tissues

Isothermal, enzyme-free amplification techniques, such as the hybridization chain reaction (HCR) and catalytic hairpin assembly (CHA), have gained increasing attention for miRNA analysis. However, current methodological challenges, including slow kinetics, low amplification efficiency, difficulties in efficient cellular internalization of DNA probes, and concerns regarding the intracellular stability of nucleic acids, need to be addressed. To this end, we propose a novel strategy for sensitive miRNA detection based on a three-dimensional (3D) CHA-HCR system. This system comprises two DNA nanospheres, named DS-13 and DS-24, which are functionalized with CHA and HCR hairpins. Target miR-21 initiates CHA between the two nanospheres, thereby activating downstream HCR and bringing cyanine 3 (Cy3) and cyanine 5 (Cy5) into proximity. The 3D CHA-HCR process leads to the formation of large DNA aggregates and the generation of fluorescence resonance energy transfer signals. In this strategy, the employment of a cascaded reaction and spatial confinement effect improve sensitivity and kinetics, while the use of DNA nanocarriers facilitates cellular delivery and protects nucleic acid probes. The experimental results in vitro, in living cells, and in clinical tissue samples demonstrated the desirable sensing performance. Collectively, this approach holds promise as a valuable tool for cancer diagnosis and biomedical research.

Artificial intelligence in theranostics of gastric cancer, a review

Gastric cancer (GC) is one of the commonest cancers with high morbidity and mortality in the world. How to realize precise diagnosis and therapy of GC owns great clinical requirement. In recent years, artificial intelligence (AI) has been actively explored to apply to early diagnosis and treatment and prognosis of gastric carcinoma. Herein, we review recent advance of AI in early screening, diagnosis, therapy and prognosis of stomach carcinoma. Especially AI combined with breath screening early GC system improved 97.4 % of early GC diagnosis ratio, AI model on stomach cancer diagnosis system of saliva biomarkers obtained an overall accuracy of 97.18 %, specificity of 97.44 %, and sensitivity of 96.88 %. We also discuss concept, issues, approaches and challenges of AI applied in stomach cancer. This review provides a comprehensive view and roadmap for readers working in this field, with the aim of pushing application of AI in theranostics of stomach cancer to increase the early discovery ratio and curative ratio of GC patients.

miRNAs as Predictors of Barrier Integrity

The human body has several barriers that protect its integrity and shield it from mechanical, chemical, and microbial harm. The various barriers include the skin, intestinal and respiratory epithelia, blood-brain barrier (BBB), and immune system. In the present review, the focus is on the physical barriers that are formed by cell layers. The barrier function is influenced by the molecular microenvironment of the cells forming the barriers. The integrity of the barrier cell layers is maintained by the intricate balance of protein expression that is partly regulated by microRNAs (miRNAs) both in the intracellular space and the extracellular microenvironment. The detection of changes in miRNA patterns has become a major focus of diagnostic, prognostic, and disease progression, as well as therapy-response, markers using a great variety of detection systems in recent years. In the present review, we highlight the importance of liquid biopsies in assessing barrier integrity and challenges in differential miRNA detection.

Highly Effective Detection of Exosomal miRNAs in Plasma Using Liposome-Mediated Transfection CRISPR/Cas13a

Exosomal miRNAs play a critical role in cancer biology and could be potential biomarkers for cancer diagnosis. However, due to the low abundance of miRNAs in the exosomes, recognizing and detecting disease-associated exosomal miRNAs in an easy-to-operate way remain a challenge. Herein, we used a liposome-mediated membrane fusion strategy (MFS) to transfect CRISPR/Cas13a into exosomes, termed MFS-CRISPR, directly measuring exosomal miRNAs in plasma. Using the MFS-CRISPR platform for detection of the exosomal miR-21, we achieve a linear range spanning four orders of magnitude (10⁴-10⁸ particles/mL) and the method is able to detect the exosomal miR-21 in as low as 1.2 × 10³ particles/mL. The liposome-mediated MFS could confine fluorescent signals in fused vesicles, which can be used for exosome heterogeneity analysis. Moreover, MFS-CRISPR assay was evaluated by measuring clinical samples, and the difference of miR-21 expression of breast cancer patients and healthy donors was significant. Because of high sensitivity and simplicity, the proposed method could have promising clinical potential for cancer diagnosis and treatment monitoring.

Electrochemical biosensors in exosome analysis; a short journey to the present and future trends in early-stage evaluation of cancers

The tumor microenvironment consists of a multiplicity of cells such as cancer cells, fibroblasts, endothelial cells, and immune cells within the specific parenchyma. It has been indicated that cancer cells can educate other cells within the tumor niche in a paracrine manner by the release of nano-sized extracellular vesicles namely exosomes (Exo), resulting in accelerated tumor mass growth. It is suggested that exosomal cargo with remarkable information can reflect any changes in metabolic and proteomic profiles in parent tumor cells. Therefore, exosomes can be touted as prognostic, diagnostic, and therapeutic elements with specific biomarkers in patients with different tumor types. Despite the advantages, conventional exosome separation and purification protocols are time-consuming and laborious with low abnormal morphology and purity rate. During the last decades, biosensor-based modalities, as emerging instruments, have been used to detect and analyze Exo in biofluids. Due to suitable specificity, sensitivity, and real-time readout, biosensors became promising approaches for the analysis of Exo in in vitro and in vivo settings. The inherent advantages and superiority of electrochemical biosensors in the determination of tumor grade based on exosomal cargo and profile were also debated. Present and future challenges were also discussed related to the application of electrochemical biosensors in the clinical setting. In this review, the early detection of several cancer types associated with ovaries, breast, brain, colon, lungs, T and B lymphocytes, liver and rare types of cancers were debated in association with released exosomes.

Combining bioinspired nanochannels with ferrocene doped MoS2 nanoplates: Application to ratiometric electrochemical detection of let-7a

Sensitive and accurate detection of tumor suppressor genes is vastly important to the related therapeutic research. Herein, a ratiometric electrochemical method for let-7a detection was established by integrating a ferrocene (Fc) doped MoS₂ nanoplates modified electrode into the nanochannels-based biosensing platform. The ratiometric signal was developed by the redox current of methylene blue (MB) which reflects the target recognition occurred into the nanochannels and the redox current of Fc which corrects the slight signal deviation caused by some analyte-independent factors. And thus, the ratio of peak current of MB and Fc (I_MB/I_Fc) measured at differential pulse voltammogram varied precisely with the increment of the concentration of let-7a incubated in the bioinspired nanochannels. The strategy of spherical DNAzyme induced deposition in nanochannels was utilized to further amplify the signal. Under optimal conditions, a wide linear dynamic range of 50 aM to 10 pM spanning five orders of magnitude was obtained. The developed electrochemical method, with attomole level of detection limit, was successfully applied to the determination of let-7a in human serum and tumor cells. The study not only offers a new route for reliable nucleic acid detection, but also provides an excellent opportunity to extend the application of the two-dimensional transition-metal dichalcogenides.

The self-powered electrochemical biosensing platform with multi-amplification strategy for ultrasensitive detection of microRNA-155

A self-powered biosensor (SPB) was constructed for the ultra-sensitive detection of microRNA-155 (miR-155) by combining a capacitor/enzymatic biofuel cell (EBFC), a strategy of rolling circle amplification (RCA) and a digital multimeter (DMM). The experimental results show that the sensitivity of the assembled EBFC-SPB can reach 15.85 μA/pM with the action of matching capacitor, which is 513% of that without capacitor (3.09 μA/pM). This achieves the first signal amplification. Furthermore, when the target miR-155 triggers RCA, electrons are continuous generated and flow to the biocathode through the external circuit to catalyze the reduction of oxygen and release [Ru(NH₃)₆]³⁺ electron acceptor. This achieves the second signal amplification. Finally, DMM is used to convert the signal into instantaneous current and amplify it for real-time reading. This achieves the third signal amplification. Therefore, the limit of detection (LOD) of the developed biosensor is as low as 0.17 fM (S/N = 3), and the linear range is between 0.5 fM and 10,000 fM, indicating that the EBFC-SPB has a broad application prospect for cancer marker of miR-155 with ultrasensitive detection.

In situ detection of exosomal RNAs for cancer diagnosis

Exosomes are considered as biomarkers reflecting the physiological state of the human body. Studies have revealed that the expression levels of specific exosomal RNAs are closely associated with certain cancers. Thus, detection of exosomal RNA offers a new avenue for liquid biopsy of cancers. Many exosomal RNA detection methods based on various principles have been developed, and most of the methods detect the extracted RNAs after lysing exosomes. Besides complex and time-consuming extraction steps, a major drawback of this approach is the degradation of the extracted RNAs in the absence of plasma membrane and cytosol. In addition, there is considerable loss of RNAs during their extraction. In situ detection of exosomal RNAs can avoid these drawbacks, thus allowing higher diagnostic reliability. In this paper, in situ detection of exosomal RNAs was systematically reviewed from the perspectives of detection methods, transport methods of the probe systems, probe structures, signal amplification strategies, and involved functional materials. Furthermore, the limitations and possible improvements of the current in situ detection methods for exosomal RNAs towards the clinical diagnostic application are discussed. This review aims to provide a valuable reference for the development of in situ exosomal RNA detection strategies for non-invasive diagnosis of cancers. STATEMENT OF SIGNIFICANCE: Certain RNAs have been identified as valuable biomarkers for some cancers, and sensitive detection of cancer-related RNAs is expected to achieve better diagnostic efficacy. Currently, the detection of exosomal RNAs is receiving increasing attention due to their high stability and significant concentration differences between patients and healthy individuals. In situ detection of exosomal RNAs has greater diagnostic reliability due to the avoidance of RNA degradation and loss. However, this mode is still limited by some factors such as detection methods, transport methods of the probe systems, probe structures, signal amplification strategies, etc. This review focuses on the progress of in situ detection of exosomal RNAs and aims to promote the development of this field.

Exosomal MicroRNA Profiling

Exosomes are extracellular vesicles, which have the ability to convey various types of cargo between cells. Lately, a great amount of interest has been paid to exosomal microRNAs (miRNAs), since much evidence has suggested that the sorting of miRNAs into exosomes is not an accidental process. It has been shown that exosomal miRNAs (exo-miRNAs) are implicated in a variety of cellular processes including (but not limited to) cell migration, apoptosis, proliferation, and autophagy. Exosomes can play a role in cardiovascular diseases and can be used as diagnostic biomarkers for several diseases, especially cancer. Tremendous advances in technology have led to the development of various platforms for miRNA profiling. Each platform has its own limitations and strengths that need to be understood in order to use them properly. In the current review, we summarize some exo-miRNAs that are relevant to exo-miRNA profiling studies and describe new methods used for the measurement of miRNA profiles in different human bodily fluids.

Analysis and Biomedical Applications of Functional Cargo in Extracellular Vesicles

Extracellular vesicles (EVs) can facilitate essential communication among cells in a range of pathophysiological conditions including cancer metastasis and progression, immune regulation, and neuronal communication. EVs are membrane-enclosed vesicles generated through endocytic origin and contain many cellular components, including proteins, lipids, nucleic acids, and metabolites. Over the past few years, the intravesicular content of EVs has proven to be a valuable biomarker for disease diagnostics, involving cancer, cardiovascular diseases, and central nervous system diseases. This review aims to provide insight into EV biogenesis, composition, function, and isolation, present a comprehensive overview of emerging techniques for EV cargo analysis, highlighting their major technical features and limitations, and summarize the potential role of EV cargos as biomarkers in disease diagnostics. Further, progress and remaining challenges will be discussed for clinical diagnostic outlooks.

A domino-like localized cascade toehold assembly amplification-based DNA nanowire for microRNA imaging in living cells

High sensitivity and specificity imaging of miRNA in living cells plays an important role in understanding miRNA-related regulation and pathological research. Localized DNA circuits have shown good performance in reaction rate and sensitivity and have been proposed for sensitive imaging of miRNA in living cells. However, most reported localized DNA circuits have a high risk of derailment or a limited loading rate capacity, which hinder their further application. To solve these issues, we herein developed a domino-like localized cascade toehold assembly (LCTA) amplification-based DNA nanowire to achieve highly sensitive and highly specific imaging of miRNAs in living cells by using DNA nanowires as reactant delivery vehicles and confining both reactant probes in a compact space. The LCTA is constructed by interval hybridization of DNA double-stranded probe pairs to a DNA nanowire with multiplex footholds generated by alternating chain hybridization. Due to the localized effect, the LCTA showed high reaction kinetics and sensitivity, and the method could detect miRNAs as low as 51 pM. The LCTA was proven to be able to accurately distinguish the miRNA expression difference between normal cells and cancer cells. In particular, the developed LCTA could be used to construct an OR logic gate to simultaneously image the total amount of multiple miRNAs in living cells. We believe that the developed LCTA can be an effective intracellular nucleic acid imaging tool and can promote the development of nucleic acid-related clinical disease diagnosis and DNA logical sensors.

Recent Advances in Exosomal miRNA Biosensing for Liquid Biopsy

As a noninvasive detection technique, liquid biopsy plays a valuable role in cancer diagnosis, disease monitoring, and prognostic assessment. In liquid biopsies, exosomes are considered among the potential biomarkers because they are important bioinformation carriers for intercellular communication. Exosomes transport miRNAs and, thus, play an important role in the regulation of cell growth and function; therefore, detection of cancer cell-derived exosomal miRNAs (exo-miRNAs) gives effective information in liquid biopsy. The development of sensitive, convenient, and reliable exo-miRNA assays will provide new perspectives for medical diagnosis. This review presents different designs and detection strategies of recent exo-miRNA assays in terms of signal transduction and amplification, as well as signal detection. In addition, this review outlines the current attempts at bioassay methods in liquid biopsies. Lastly, the challenges and prospects of exosome bioassays are also considered.

Electrochemical nano-sensing interface for exosomes analysis and cancer diagnosis

Exosomes are a class of the nanosized extracellular vesicles, which have emerged as representative liquid biopsy biomarkers. To date, the electrochemical nanosensors are of great significance in the exosome detection with the advantages of easy operation, high accuracy and reliable repeatability. Especially, the growing field of nano interface has provided the electrochemical sensing platforms for the accurate exosomes analysis. The incorporation of multiple nanomaterials can take advantages and synergistic properties of functional units. So, based on the integration of with nanomaterial-based signal transduction and specific biorecognition, the nano-sensing interface provides excellent electrochemical features owing to rapid mass transport and excellent conductivity. The nano-sensing interface with a wide variety of morphologies and structure also provides the large active surface area for the immobilization of bio-capturing agents. Furthermore, through the design of nanostructured electrode array, the efficiency of transducer can be greatly improved. It should be noticed that the elaboration of a proper sensor requires the profound knowledge of the nano-sensing interface. Therefore, this article presents a review of the recent advance in exosomes detection based on the electrochemical nano-sensing interface, including electrochemical analysis principles, exosome sensing mechanisms, nano-interface construction strategies, as well as the typical diagnosis application. In particular, the article is focused on the exploration of the various electrochemical sensing performance of nano-interface in the exosome detection. We have also prospected the future trend and challenge of the electrochemical nano-sensing interface for exosomes analysis in clinical cancer diagnosis.

An Ultrasensitive Electrochemical Biosensor Integrated by Nicking Endonuclease-Assisted Primer Exchange Reaction Cascade Amplification and DNA Nanosphere-Mediated Electrochemical Signal-Enhanced System for MicroRNA Detection

Specific and sensitive microRNAs (miRNAs) detection is essential to early cancer diagnosis. The development of these technologies including functional nuclease-mediated target amplification and DNA nanotechnology possesses tremendous potential for the high-performance detection of miRNAs in the accurate diagnosis of disease. In this study, we have established an ultrasensitive electrochemical biosensor by combining nicking endonuclease-assisted primer exchange reaction (PER) cascade amplification with a DNA nanosphere (DNS)-mediated electrochemical signal-enhanced system for the detection of miRNA-21 (miR-21). The cascade amplification is initiated by a nicking endonuclease that can cleave specific DNA substrates and highly amplify translation of the target to single-stranded DNA fragments (sDNA). Then, the PER cascade is powered by strand-displacing polymerase and generates a large amount of nascent single-stranded connector DNA (cDNA) via sDNA triggering of the dumbbell probe (DP), thus achieving the cascade amplification of the target. Finally, the DNS loaded with plenty of electroactive substances can be captured on the electrode via cDNA for further enhancing the electrochemical signal and highly sensitive detection of miR-21. The proposed electrochemical biosensor exhibits a wide detection range of 1 aM to 0.1 nM and a low detection limit of 0.58 aM. The excellent selectivity allows the biosensor to discriminate miR-21 from other miRNAs, even the one base-mismatched sequence. Moreover, the practicability of the biosensor is investigated by analyzing miR-21 in human serum and cancer cell lysate. Therefore, our proposed nicking endonuclease-assisted PER cascade amplification strategy provides a powerful platform for the early detection of miRNA-related disease and molecular diagnosis.

Scalable Printing of Prussian Blue Analogue@Au Edge-Rich Microcubes as Flexible Biosensing Microchips Performing Ultrasensitive Sucrose Fermentation Monitoring

Sucrose is one of the most applied carbon sources in the fermentation process, and it directly determines the microbial metabolism with its concentration fluctuation. Meanwhile, sucrose also plays a key role of a protective agent in the production of biological vaccines, especially in the new mRNA vaccines for curing COVID-19. However, rapid and precise detection of sucrose is always desired but unrealized in industrial fermentation and synthetic biology research. In order to address the above issue, we proposed an ultrasensitive biosensor microchip achieving accurate sucrose recognition within only 12 s, relying on the construction of a Prussian blue analogue@Au edge-rich (PBA@AuER) microarchitecture. This special geometric structure was formed through exactly inducing the oriented PBA crystallization toward a certain plane to create more regular and continuous edge features. This composite was further transformed to a screen-printed ink to directly and large-scale fabricate an enzymatic biosensor microchip showing ultrahigh sensitivity, a wide detection range, and a low detection limit to the accurate sucrose recognition. As confirmed in a real alcohol fermentation reaction, the as-prepared microchip enabled us to accurately detect the sucrose and glucose concentrations with outstanding reusability (more than 300 times) during the whole process through proposing a novel analytical strategy for the binary mixture substrate system.

Carbon Electrodes with Gold Nanoparticles for the Electrochemical Detection of miRNA 21-5p

Extracellular vesicles are involved in many physiological and pathological activities. They transport miRNAs to recipient cells during their role in intercellular communication, making them emerging biomarkers of many diseases. Interest in exosomal miRNAs has grown after they have shown numerous advantages as biomarkers for diagnosis, prognosis, and evaluation of cancer treatment. This work describes the development of a biosensor for the detection of 21-5p miRNA in human serum using screen-printed carbon electrodes modified with gold nanoparticles fabricated in situ, an innovative approach to avoid the use of more expensive gold substrates that provide better analytical outputs. The several variables involved in the assembly of the biosensor were optimized by univariant mode. Under the best conditions, the biosensor showed a linear response from 0.010 fM to 10 pM, with a limit of detection (LOD) of 4.31 aM. The sensitivity was 0.3718 relative Ω per decade concentration in buffered saline solutions, and the standard deviation of the blank is 2.94 Ω. A linear response was also obtained when human serum samples were tested with miRNA 21-5p. Interference from similar miRNA and miss-match miRNA sequences was evaluated and good selectivity for miRNA 21-5p was observed. Overall, the device proposed is an alternative approach to gold substrates, which typically result in more sensitive systems and lower LODs, which compares favorably to current gold-based biosensors for the targeted miRNA. This design may be further extended to other nucleic acids.

Sensitive fluorescent detection of exosomal microRNA based on enzymes-assisted dual-signal amplification

The analysis of microRNAs (miRNAs) in exosomes offers significant information for a rapid and non-invasive diagnosis of cancer. However, the clinical utility of miRNAs as biomarkers is often hampered by their low abundance in exosomes. Herein, we develop a dual-signal amplification biosensor for the sensitive detection of exosomal miRNA-21 (miR-21). In the presence of a cognate target, it hybridizes with a biotin-modified capture probe (Cp) to form a DNA-RNA heteroduplex that serves as a substrate for duplex-specific nuclease (DSN). With the assistance of DSN, the Cps are enzymatically hydrolyzed and numerous DNA catalysts are released, leading to the first signal amplification. After magnetic isolation, the DNA catalyst remaining in the supernatant triggers a strand displacement reaction based on the nicking-assisted reactant recycling strategy, without depleting the reactants, to implement the second signal amplification. Using this dual-signal amplification concept, our biosensor achieves a limit of detection of miR-21 of 0.34 fM, with a linear range of 0.5-100 fM. The receiver operating characteristic curve generated during clinical sample analysis indicates that the exosomal miR-21 outperforms serum carcinoembryonic antigen in discriminating between patients with gastric cancer (GC) and patients with precancerous (PC) lesions (area under the curve: 0.89 versus 0.74, n = 40). Moreover, the proposed biosensor exhibits an 83.9% accuracy in classifying patients with GC or PC lesions and healthy donors using a confusion matrix. Furthermore, patients with GC with or without metastases are discriminated using the proposed biosensor. Our technology may expand the applications of DNA-based biosensor-enabled cancer diagnostic tools.

Sensitive, Highly Stable, and Anti-Fouling Electrode with Hexanethiol and Poly-A Modification for Exosomal microRNA Detection

It remains a huge challenge to integrate the sensitivity, stability, reproducibility, and anti-fouling ability of electrochemical biosensors for practical applications. Herein, we propose a self-assembled electrode combining hexanethiol (HT), poly-adenine (poly-A), and cholesteryl-modified DNA to meet this challenge. HT can tightly pack at the electrode interface to form a hydrophobic self-assembled monolayer (SAM), effectively improving the stability and signal-to-noise ratio (SNR) of electrochemical detection. Cholesteryl-modified DNA was immobilized at the electrode through the hydrophobic interaction with HT to avoid the competition between the SAM and the DNA probe on the gold site. Thus, the assembly efficiency and uniformity of the DNA probe as well as the detection reproducibility were increased remarkedly. Poly-A was added on the HT assembled electrode to occupy the unreacted sites of gold to further enhance the anti-fouling ability. The combination of HT and poly-A allows the electrode to ensure favorable anti-fouling ability without sacrificing the detection performance. On this basis, we proposed a dual-signal amplification electrochemical biosensor for the detection of exosomal microRNAs, which showed excellent sensitivity with a detection limit down to 1.46 aM. Importantly, this method has been successfully applied to detect exosomal microRNA-21 in cells and human serum samples, proving its potential utility in cancer diagnosis.

DNA Logic Nanodevices for the Sequential Imaging of Cancer Markers through Localized Catalytic Hairpin Assembly Reaction

Monitoring tumor biomarkers is crucial for cancer diagnosis, progression monitoring, and treatment. However, identifying single or multiple biomarkers with the same spatial locations can cause false-positive feedback. Herein, we integrated the DNA tetrahedron (DT) structures with logic-responsive and signal amplifying capability to construct transmembrane DNA logic nanodevices (TDLNs) for the in situ sequential imaging of transmembrane glycoprotein mucin 1 (MUC1) and cytoplasmic microRNA-21 (miR-21) to cell identifications. The TDLNs were developed by encoding two metastable hairpin DNAs (namely, H1 and H2) in a DT scaffold, in which the triggering toeholds of H1 for miR-21 were sealed by the MUC1-specific aptamer (MUC1-apt). The TDLNs not only had the function of signal amplification owing to the localized catalytic hairpin assembly (CHA) reaction through spatial constraints effect of DT structures but also performed an AND logic operation to output a green Cy3 signal in MCF-7 cells, where MUC1 protein and miR-21 were simultaneously expressed. These results showed that the newly developed TDLNs have better molecular targeting and recognition ability so as to be easily identify cell types and diagnose cancer early.

Dispersion-to-localization of catalytic hairpin assembly for sensitive sensing and imaging microRNAs in living cells from whole blood

Localized DNA circuits have shown good performance regarding reaction rate and sensitivity for sensing intracellular microRNAs (miRNAs). However, these methods reported recently require large kinds of DNA strands and suffer from low signal-to-background (S/B) ratio, which hinder their clinical application. To circumvent these issues, we herein developed a novel strategy for sensitive sensing and imaging miRNAs in living cells based on dispersion-to-localization of catalytic hairpin assembly (DL-CHA). This strategy consists of only three classes of DNA strands (two hairpins and a linker strand), which largely reduces sequence design complexity. Additionally, owing to the unique engineering of the substrate transformation from dispersion to localization, the DL-CHA exhibits not only minimal background leakage but also intensive signal amplification, thus significantly improving the S/B ratio. In particular, the simple sensing method is capable of imaging miRNAs in cells from clinical blood samples for the diagnosis of breast cancer. Therefore, this work provides a powerful tool for intracellular molecules detection and gives a much broader design space for constructing high-performance DNA circuits.

Spatial Confinement-Derived Double-Accelerated DNA Cascade Reaction for Ultrafast and Highly Sensitive In Situ Monitoring of Exosomal miRNA and Exosome Tracing

Exosomal microRNAs (miRNAs) are reliable biomarkers of disease progression, allowing for non-invasive detection. However, detection of exosomal miRNAs in situ remains a challenge due to low abundance, poor permeability of the lipid bilayers, and slow kinetics of previous methods. Herein, an accelerated DNA nanoprobe was implemented for fast, in situ monitoring of miRNA in exosomes by employing a spatial confinement strategy. This nanoprobe not only detects miRNA in exosomes but also distinguishes tumor exosomes from those derived from normal cells with high accuracy, paving the way toward exosomal miRNA bioimaging and disease diagnosis. Furthermore, the fast response allows for this nanoprobe to be successfully utilized to monitor the process of exosomes endocytosis, making it also a tool to explore exosome biological functions.

A Photoresponsive and Metal-Organic Framework Encapsulated DNA Tetrahedral Entropy-Driven Amplifier for High-Performance Imaging Intracellular MicroRNA

The further development of high-performance fluorescent biosensors to image intracellular microRNAs is beneficial to cancer medicine. By virtue of the need for enzymes and hairpin DNA probes, the entropy-driven reaction-assisted signal amplification strategy has shown an enormous potential to accomplish this task. Nevertheless, this good option still meets with poor biostability, low cell uptake efficiency, and unsatisfactory accuracy. On the basis of these challenges, we put forward here a battery of solving pathways. First, the straight DNA probes are anchored onto the vertexes of dual DNA tetrahedrons, and thus the enzyme resistance of the whole sensing system is observably enhanced. A metal-organic framework (ZIF-8 nanoparticle), which can be effectively dissociated into a weakly acidic environment, then is employed as an additional delivery vehicle to encapsulate such a DNA tetrahedron sustained biosensor and finally bring about a more efficient endocytosis. Last, a kind of photocleavage-linker triggered photoresponsive manner is incorporated to achieve an exceptional precise target identification, by which the biosensor can only be initiated under the irradiation of an externally mild 365 nm ultraviolet light source. In accordance with the above efforts, worthy assay performance toward microRNA-196a has given rise to this newly constructed biosensor, whose sensitivity is down to 2.7 pM and also able to distinguish single-base variation. Beyond that, the amplifier can work as a powerful imaging toolbox to accurately determine the targets in living cells, providing a promising intracellular sensing platform.

Ratiometric Fluorescent Biosensor Based on Forster Resonance Energy Transfer between Carbon Dots and Acridine Orange for miRNA Analysis

The expression level of miRNA is highly correlated with the pathological process of malignant tumors. Therefore, the abnormal expression of miRNA in serum is considered as reliable evidence for the existence of tumor cells. Here, a ratiometric fluorescent biosensor based on the Forster resonance energy transfer between fluorophores is proposed for detecting colorectal cancer-specific miRNA (miR-92a-3p). The miRNA in serum was first isolated by carboxyl-modified SiO2 microspheres. Then, the addition of miRNA to the detection system resulted in the distance change between the donor acridine orange (AO) and the acceptor fluorescent carbon dots (CDs), which made the fluorescence signal change. The physicochemical properties, especially the fluorescence characteristics of CDs and AO, which enabled the ratiometric fluorescence detection, were comprehensively studied. The ratiometric fluorescent biosensor could detect miRNA in the concentration range of 1-9 nM and showed a detection limit of 0.14 nM. Moreover, the ratiometric fluorescent biosensor exhibited high selectivity for the target miRNA. The validity of the ratiometric fluorescent biosensor was also verified using the serum sample, demonstrating its potential for enzyme-free miRNA analysis.