One DNA circle capture probe with multiple target recognition domains for simultaneous electrochemical detection of miRNA-21 and miRNA-155

Electrochemical biosensors for measurement of colorectal cancer biomarkers

Colorectal cancer (CRC) is associated with one of the highest rates of mortality among cancers worldwide. The early detection and management of CRC is imperative. Biomarkers play an important role in CRC screening tests, CRC treatment, and prognosis and clinical management; thus rapid and sensitive detection of biomarkers is helpful for early detection of CRC. In recent years, electrochemical biosensors for detecting CRC biomarkers have been widely investigated. In this review, different electrochemical detection methods for CRC biomarkers including immunosensors, aptasensors, and genosensors are summarized. Further, representative examples are provided that demonstrate the advantages of electrochemical sensors modified by various nanomaterials. Finally, the limitations and prospects of biomarkers and electrochemical sensors in detection are also discussed. Graphical abstract.

Highly Stable Covalent Organic Framework Nanosheets as a New Generation of Electrochemiluminescence Emitters for Ultrasensitive MicroRNA Detection

A pyrene-based sp² carbon-conjugated covalent organic framework (COF) nanosheet (Py-sp²c-CON) with strong and stable electrochemiluminescence (ECL) emission was constructed by C═C polycondensation of tetrakis(4-formylphenyl)pyrene (TFPPy) and 2,2'-(1,4-phenylene)diacetonitrile, which was employed as a highly efficient ECL emitter to fabricate an ECL biosensor for the first time. The Py-sp²c-CON exhibited higher ECL intensity and efficiency than those of TFPPy, bulk Py-sp²c-COF, and imine-linked pyrene COF, not only because the pyrene luminophores and aggregation-induced emissive luminogens (cyano-substituted phenylenevinylene) were topologically linked into Py-sp²c-CON, which greatly increased the immobilization amount of luminophores and decreased the aggregation-caused quenching effect and nonradiative transition but also because the porous ultrathin structure of Py-sp²c-CON effectively shortened transport distances of an electron, ion, and co-reactant (S₂O₈^2-), which made more ECL luminophores be activated and thus efficiently increased the utilization ratio of luminophores. More interestingly, when Bu₄NPF₆ was introduced into the Py-sp²c-CON/S₂O₈^2- system as a co-reaction accelerator, the ECL signal of Py-sp²c-CON was further amplified. As expected, the average ECL intensity of the Py-sp²c-CON/S₂O₈^2-/Bu₄NPF₆ system was about 2.03, 5.76, 24.31, and 190.33-fold higher than those of Py-sp²c-CON/S₂O₈^2-, Py-sp²c-COF/S₂O₈^2-, TFPPy/S₂O₈²,^- and imine-linked pyrene COF/S₂O₈^2- systems. Considering these advantages, the Py-sp²c-CON/S₂O₈^2-/Bu₄NPF₆ system was employed to prepare an ECL biosensor for microRNA-21 detection, which exhibited a broad linear response (100 aM to 1 nM) and a low detection limit (46 aM). Overall, this work demonstrated that sp² carbon CONs can be directly used as a high-performance ECL emitter, thus expanding the application scope of COFs and opening a new horizon to develop new types of ECL emitters.

Advances in multiplexed techniques for the detection and quantification of microRNAs

MicroRNA detection is currently a crucial analytical chemistry challenge: almost 2000 papers were referenced in PubMed in 2018 and 2019 for the keywords "miRNA detection method". MicroRNAs are potential biomarkers for multiple diseases including cancers, neurodegenerative and cardiovascular diseases. Since miRNAs are stably released in bodily fluids, they are of prime interest for the development of non-invasive diagnosis methods, such as liquid biopsies. Their detection is however challenging, as high levels of sensitivity, specificity and robustness are required. The analysis also needs to be quantitative, since the aim is to detect miRNA concentration changes. Moreover, a high multiplexing capability is also of crucial importance, since the clinical potential of miRNAs probably lays in our ability to perform parallel mapping of multiple miRNA concentrations and recognize typical disease signature from this profile. A plethora of biochemical innovative detection methods have been reported recently and some of them provide new solutions to the problem of sensitive multiplex detection. In this review, we propose to analyze in particular the new developments in multiplexed approaches to miRNA detection. The main aspects of these methods (including sensitivity and specificity) will be analyzed, with a particular focus on the demonstrated multiplexing capability and potential of each of these methods.

Dual-probe fluorescent biosensor based on T7 exonuclease-assisted target recycling amplification for simultaneous sensitive detection of microRNA-21 and microRNA-155

Effective and simultaneous monitoring of the abnormal expression of certain microRNAs (miRNAs), especially for miRNA-21 and miRNA-155, can indicate drug resistance in lung cancer. In this work, T7 exonuclease (T7 Exo)-assisted target recycling amplification coupled with the extensive fluorescence quenching of graphene oxide (GO) was designed for the simultaneous detection of miRNA-21 and miRNA-155 using FAM- and ROX-labeled single-strand DNA probes. Through this method, the variable emission intensities of FAM and ROX caused by the introduction of miRNA-21 and miRNA-155, respectively, were obtained with high sensitivity. The method exhibited excellent analytical performance for simultaneous detection of miRNA-21 and miRNA-155 without cross-interference. The linear range was from 0.005 nM to 5 nM over three orders of magnitude, with detection limits as low as 3.2 pM and 4.5 pM for miRNA-21 and miRNA-155, respectively. Furthermore, the recovery (92.49-103.67%) and relative standard deviation (RSD < 4.8%) of the standard addition test of miRNA-21 and miRNA-155 in human plasma suggested the potential for drug resistance warning in clinical practice via this simple strategy. A homogeneous T7 Exo-assisted signal amplification combined with GO quenching platform was developed for accurate, sensitive and simultaneous analysis of miRNA-21 and miRNA-155 for drug resistance warning in lung cancer. This simple method exhibited a wide linear range and low LODs for miR-21 and miR-155.

Simple Tripedal DNA Walker Prepared by Target-Triggered Catalytic Hairpin Assembly for Ultrasensitive Electrochemiluminescence Detection of MicroRNA

In contrast to common DNA walkers, multipedal DNA walkers exhibit larger walking area and faster walking kinetics and provide increased amplification efficiency. Consequently, they have received a considerable amount of attention in biosensing. However, most of them are synthesized by immobilizing multiple DNA walking strands on the surface of Au nanoparticles, which is tedious and time-consuming. Simple preparation of multipedal DNA walkers remains a challenge. Herein, we adopted a simple enzyme-free target-triggered catalytic hairpin assembly (CHA) circuit to synthesize a tripedal DNA walker. By walking on a DNA track-functionalized electrode, a sensitive electrochemiluminescence DNA nanomachine biosensor was constructed for sensing miRNA-21. The DNA walker was powered by toehold-mediated strand displacement; the whole process did not need the assistance of enzymes, thus avoiding tedious procedures and enzyme degradation under unfavorable environmental conditions. Specifically, a superior detection limit of 4 aM and a broad linear range of 10 aM to 1 pM were achieved. This CHA-tripedal DNA walker biosensor was then applied for the detection of miRNA-21 in human serum and showed high selectivity and excellent reproducibility, demonstrating its practical application in bioanalysis. In particular, the Y-shaped tripedal DNA walker comes from the DNA circuit, which makes the approach ideally suited for biosensing of small nucleic acid targets.

Surface plasmon resonance imaging-based biosensor for multiplex and ultrasensitive detection of NSCLC-associated exosomal miRNAs using DNA programmed heterostructure of Au-on-Ag

Exosomal miRNAs are potential tumor biomarkers for early diagnosis of non-small cell lung cancer (NSCLC). Herein, a surface plasmon resonance imaging (SPRi)-based biosensor was developed for simultaneous detection of multiplex NSCLC-associated exosomal miRNAs in a clinical sample using Au-on-Ag heterostructure and DNA tetrahedral framework (DTF). Exosomal miRNAs are captured by various DTF probes immobilized on the gold array chip. Subsequently, single-stranded DNA (ssDNA) functionalized silver nanocube (AgNC) hybridizes with the captured exosomal miRNAs and then the ssDNA-coated Au nanoparticles assembled on the surface of AgNC, forming Au-on-Ag heterostructures as essential labels to realize amplified SPR response. With the aid of DNA programmed Au-on-Ag heterostructure and DTF, the SPRi-based biosensor exhibits wide detection range from 2 fM to 20 nM, ultralow limit of detection of 1.68 fM, enhanced capture efficiency, and improved antifouling capability. Furthermore, the biosensor enables accurate discrimination of NSCLC patients based on detection results of exosomal miRNAs. Overall, this developed biosensor is a promising tool for multiplex exosomal miRNAs detection, providing a new possibility for early diagnosis of NSCLC.

Electrochemical Biosensors for Detection of MicroRNA as a Cancer Biomarker: Pros and Cons

Cancer is the second most fatal disease in the world and an early diagnosis is important for a successful treatment. Thus, it is necessary to develop fast, sensitive, simple, and inexpensive analytical tools for cancer biomarker detection. MicroRNA (miRNA) is an RNA cancer biomarker where the expression level in body fluid is strongly correlated to cancer. Various biosensors involving the detection of miRNA for cancer diagnosis were developed. The present review offers a comprehensive overview of the recent developments in electrochemical biosensor for miRNA cancer marker detection from 2015 to 2020. The review focuses on the approaches to direct miRNA detection based on the electrochemical signal. It includes a RedOx-labeled probe with different designs, RedOx DNA-intercalating agents, various kinds of RedOx catalysts used to produce a signal response, and finally a free RedOx indicator. Furthermore, the advantages and drawbacks of these approaches are highlighted.

Homogeneous electrochemical biosensor for microRNA based on enzyme-driven cascaded signal amplification strategy

Infectious diseases are a long-standing and severe global public health problem. The rapid diagnosis of infectious diseases is an urgent need to solve this problem. MicroRNA (miRNA) plays an important role in the intervention of some infectious diseases and is expected to become a potential biomarker for the diagnosis and prognosis of infectious diseases. It is of great significance to develop rapid and sensitive methods for detecting miRNA for effective control of infectious diseases. In this study, a simple and highly sensitive homogeneous electrochemical method for microRNAs using enzyme-driven cascaded signal amplification has been developed. In the presence of target miRNA, the reaction system produced plenty of MB-labeled single-nucleotide fragments (MB-MF) containing a few negative charges, which can diffuse to the negative surface of the ITO electrode easily, so an obvious electrochemical signal enhancement was obtained. Without the target, MB-HP contains a relatively large amount of negative charges due to the phosphates on the DNA chain, which cannot be digested by the enzyme and cannot diffuse freely to the negatively charged ITO electrode, so only a small signal was detected. The enhanced electrochemical response has a linear relationship with the logarithm of miRNA concentration in the range of 10 fM to 10 nM and the limit of detection as low as 3.0 fM. Furthermore, the proposed strategy showed the capability of discriminating single-base mismatch and performed eligibly in the analysis of miRNA in cell lysates, exhibiting great potential for disease diagnosis and biomedical research. Graphical abstract.

A Novel Biosensor Based on Molybdenum Disulfide (MoS2 ) Modified Porous Anodic Aluminum Oxide Nanochannels for Ultrasensitive microRNA-155 Detection

Artificial photoresponsive nanochannels have attracted widespread attention because of their capacity to achieve ion transport through light modulation. Herein, a biosensor for ultrasensitive miRNA-155 detection is devised based on molybdenum disulfide (MoS₂ ) modified porous anodic aluminum oxide (AAO) photoresponsive nanochannels by atomic layer deposition (ALD). According to the optimized experimental results, when the cycles of ALD, the wavelength, and the power of the excitation laser are 70 cycles, 450 nm, and 80 mW, respectively, the most supreme photocurrent performance of these photoresponsive nanochannels are obtained. AAO nanochannels modified with MoS₂ can work as a photoelectrochemical (PEC) biosensor by generating photoexcitation current; what is more, the high channel density in AAO can magnify the ion current signal response effectively by aggrandizing the flux of electroactive species. By using AAO photoresponsive nanochannels with an average diameter of 150 nm as PEC biosensor, an ultrasensitive detection record ranging from 0.01 fM to 0.01 nM with a detection limit of 3 aM can be achieved. This work not only proposes a simple method for manufacturing semiconductor photoresponsive nanochannels, but also exhibits great potential in the ultrasensitive detection of biomolecules.