Amperometric detection of microRNA based on DNA-controlled current of a molybdophosphate redox probe and amplification via hybridization chain reaction

Ultrasensitive detection of microRNA-21 by using specific interaction of antimonene with RNA as electrochemical biosensor

MicroRNA exhibits different levels of expression in cancer and can affect the transformation, metastasis, and carcinogenesis of the cancer cell. Herein, we developed a novel kind of electrochemical microRNA biosensor based on two-dimensional nanomaterial of antimonene nano-flakes (AMNFs) and carbon quantum dots (CQDs) which were used as substrating to cadmium ion (Cd²⁺) for specific detection of breast cancer-relevant biomarker-microRNA-21. Compared to graphene, the first principle energetic calculation shows that the AMNFs have completely a stronger force interaction with single strand (ssRNA), due to the antimonene has a more delocalized 5 s/5p orbital. After the addition of complementary microRNA, due to the low adsorption affinity of double-stranded RNA (dsRNA) to antimonene, the hybridized target is easy to desorb from the antimonene interface, and the oxidation peak of metal ions is significantly reduced. Results showed the microRNA-21 concentration can be detected from 100 aM to 1 nM, the limit of detection as low as 21 aM toward microRNA-21, which is 3 times lower than those of the established microRNA biosensors. The unique combination of not be attempted before existing sensing material which has special adsorption properties represents an approach to the detection of breast cancer. And it provides a promising method for early diagnosis, monitoring, and staging of breast cancer.

An amplified fluorescent biosensor for Ag+ detection through the hybridization chain reactions

Ag is widely distributed in nature and it is used in almost all areas of human life. However, due to the widespread use of Ag materials, Ag⁺ pollution seriously threatens the human health and environment. The traditional detection methods for Ag⁺ suffer from disadvantages including high operational cost, complicated operating unit and instrument, and high requirements for professionals. Thus, in this study, a new type of Ag⁺ detection biosensor based on the hybridization signal amplification was designed to overcome these problems. Combining cytosine-Ag⁺-cytosine mismatch structure with the hybridization chain reaction, this biosensor converted the conventional detection signal into the nucleic acid amplification signal, which realized efficient, rapid, sensitive, and specific detection of Ag⁺. The limit-of-detection of this sensor reached 0.69 pM, which is much less than the maximum concentration (0.1 mg L^-1, 927 nM) suggested for drinking water by the World Health Organization, and the maximum concentration (0.05 mg L^-1, 464 nM) suggested by the United States Environmental Protection Agency. This method provides a promising new platform for detecting Ag⁺ concentrations at ultralow levels.

A sensitive electrochemiluminescence DNA biosensor based on the signal amplification of ExoIII enzyme-assisted hybridization chain reaction combined with nanoparticle-loaded multiple probes

An electrochemiluminescence (ECL) DNA biosensor based on ExoIII exonuclease assistance and hybridization chain reaction (HCR) amplification technology has been constructed. ExoIII exonuclease and triple-helix DNA molecular switch are used in detecting a target in circulation. By combining HCR with AuNPs@DNA, a novel signal probe is built, which enables multiple signal amplification and the high-sensitive detection of transgenic rice BT63 DNA. The Fe₃O₄@Au solution is added to a magneto-controlled glassy carbon electrode, and sulfhydryl-modified capture DNA (CP) is immobilized on Fe₃O₄@Au through the Au-S bond. Mercaptoethanol is added to close sites and prevent the nonspecific adsorption of CP on the magnetron glassy carbon electrode. A target DNA is added to a constructed triple-helix DNA molecular centrifuge tube for reaction. Owing to base complementation and the reversible switching of the triple-helix DNA molecular state, the target DNA turns on the triple-helix DNA molecular switch and hybridizes with a long-strand recognition probe (RP) to form a double-stranded DNA (dsDNA). Exonuclease ExoIII is added to specifically recognize and cut the dsDNA and to release the target DNA. The target DNA strand then circulates back completely to open the multiple triple-helix DNA molecular switch, releasing a large number of signal transduction probes (STP). To hybridize with CP, a large amount of STP is added to the electrode. Finally, a AuNPs@DNA signal probe is added to hybridize with STP. H1 and H2 probes are added for the hybridization chain reaction and the indefinite extension of the primer strand on the probe. Then, tris-(bipyridyl)ruthenium(II) is added for ECL signal detection with PBS-tri-n-propylamine as the base solution. In the concentration range 1.0 × 10^-16 to 1.0 × 10^-8 mol/L of the target DNA, good linear relationship was achieved with the corresponding ECL signal. The detection limit is 3.6 × 10^-17 mol/L. The spiked recovery of the rice samples range from 97.2 to 101.5%. The sensor is highly sensitive and has good selectivity, stability, and reproducibility. A novel electrochemiluminescence biosensor with extremely higher sensitivity was prepared for the determination of ultra-trace amount transgenic rice BT63 DNA. The sensitivity was significantly improved by multiple signal enhancements. Firstly, a large number of signal transduction probes are released when the triple-helix DNA molecular switch unlock after recycles assisted by ExoIII exonuclease under target BT63 DNA; and then the signal transduction probes hybridize with the signal probes of AuNPs@(DNA-HCR) produced through hybridization chain reaction. Finally, the signal probes which were embedded with a large amount of electrochemiluminescence reagent produce high luminescence intensity. The detection limit was 3.6 × 10^-17 mol/L, which is almost the most sensitive methods reported.

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.

New trends in the development of electrochemical biosensors for the quantification of microRNAs

MicroRNAs (miRNAs) are non-coding regulatory RNAs that play an important role in RNA silencing and post-transcriptional gene expression regulation. Since their dysregulation has been associated with Alzheimer disease, cardiovascular diseases and different types of cancer, among others, miRNAs can be used as biomarkers for early diagnosis and prognosis of these diseases. The methods commonly used to quantify miRNAs are, in general, complex, costly, with limited application for point-of-care devices or resource-limited facilities. Electrochemical biosensors, mainly those based on nanomaterials, have emerged as a promising alternative to the conventional miRNA detection methods and have paved the way to the development of sensitive, fast, and low-cost detection systems. This review is focused on the most relevant contributions performed in the field of electrochemical miRNAs biosensors between 2017 and the beginning of 2020. The main contribution of this article is the critical discussion of the different amplification strategies and the comparative analysis between amplified and non-amplified miRNA electrochemical biosensing and between the different amplification schemes. Particular emphasis was given to the importance of the nanostructures, enzymes, labelling molecules, and special sequences of nucleic acids or analogues on the organization of the different bioanalytical platforms, the transduction of the hybridization event and the generation the analytical signal.

Dually enhanced homogenous synthesis of molybdophosphate by hybridization chain reaction and enzyme nanotags for the electrochemical bioassay of carcinoembryonic antigen

A magnetic bead (MB)-based sandwich biorecognition reactions is combined with a gold nanoprobe-induced homogenous synthesis of molybdophosphate to develop a novel bioassay method for the electrochemical detection of the tumor biomarker of carcinoembryonic antigen (CEA). The nanoprobe is prepared through the specific loading of numerous alkaline phosphatase (ALP)-functionalized gold nanoparticles (Au NPs) on a double-stranded DNA (dsDNA) produced by the CEA aptamer-triggered hybridization chain reaction (HCR). Both the large amounts of PO₄^3- produced by the ALP catalytic hydrolysis of pyrophosphate and the phosphate backbones of dsDNA can react with the added MoO₄^2- to generate electroactive molybdophosphates. So, the gold nanoprobe was used for signal tracing of the sandwich bioassay of CEA at a constructed antibody-functionalized MB platform. The sensitive electrochemical measurement of molybdophosphate produced from the quantitatively captured nanoprobes at a carbon nanotube-modified electrode (measured at about 0.12 V vs. Ag/AgCl, 3 M KCl) enabled the convenient signal transduction of the method. Due to the dually enhanced synthesis of molybdophosphate by the HCR and multi-enzyme Au NP nanotags, this method shows a wide linear range from 0.05 pg mL^-1 to 10 ng mL^-1 along with a low detection limit of 0.027 pg mL^-1. In addition, the MB-based biorecognition reaction and the homogeneous synthesis of molybdophosphate are much convenient in manipulations. These excellent performances decide the extensive application potentials of the method. Graphical abstract A magnetic bead-based bioassay method was simply developed for the electrochemical detection of carcinoembryonic antigen. The dually enhanced homogenous synthesis of molybdophosphate by hybridization chain reaction (HCR) and enzyme nanotags and the sensitive electrochemical measurement of molybdophosphate at a carbon nanotube (CNT)-electrode enable ultrasensitive signal transduction of the method.

Design of a DOPC-MoS2/AuNP hybrid as an organic bed with higher amplification for miR detection in electrochemical biosensors

The liposome-based biosensors are used for detection of nucleic acids and proteins as organic beds which are biocompatible tools for point of care tests, but their lack of sensitivity has been challenging. Therefore, designing a proper strategy is vital to increase the sensitivity of the target in diagnostic tests. In this study, for the first time, we use a combination of cationic DOPC liposome (dioleoylphosphatidylcholine) with MoS₂ to enhance the sensitivity of liposomal sensors clearly. The electrochemical measurements are performed between potentials at - 0.4 V and + 0.4 V with 1 mM [Fe(CN)₆]^-3/-4. At first, we construct the DOPC/MoS₂ hybrid (as a mineral/organic bed) to promote higher electrochemical behavior than DOPC liposome (as organic bed). In this research, adding AuNP can cause attachment with both the DOPC and MoS₂. Therefore, the electrochemical reactions are enhanced accordingly to provide more positions for attaching the probes on the AuNP. So our DOPC-MoS₂/AuNP hybrid can detect miR-21 with high sensitivity (LOD = 10 aM) because of attachment of miR-21 to MoS₂/AuNP in addition to DOPC/AuNP. This sensor has also high specificity and repeatability as a biocompatible sensor, which can be used in point of care tests and transduction instruments.

Aptamer based determination of the cancer biomarker HER2 by using phosphate-functionalized MnO2 nanosheets as the electrochemical probe

The authors report a sensitive electrochemical aptamer-based assay for the cancer biomarker human epidermal growth factor receptor-2 (HER2). It is based on the use of MnO₂ nanosheets that were functionalized with phosphate and a HER2 binding aptamer and serve as the electrochemical probe. The assay follows a sandwich protocol. A peptide that can specifically recognize HER2 was immobilized on a gold electrode for the capture of HER2. Then, the functionalized MnO₂ nanosheets were linked to the electrode via the binding between HER2 and HER2 aptamer on the MnO₂ nanosheets. The reaction of phosphate and aptamer on the MnO₂ nanosheets with molybdate leads to the formation of redox-active molybdophosphate. This results in dual signal amplification. The generated electrochemical current was measured at 0.22 V (vs. Ag/AgCl). The assay allows HER2 to be determined in the 0.1 to 500 pg·mL^-1 concentration range, and the detection limit is as low as 0.05 pg·mL^-1. The assay was successfully applied for the detection of HER2 in spiked human serum samples. Graphical abstract Electrochemical detection of breast cancer biomarker human epidermal growth factor receptor-2 (HER2) is reported utilizing phosphate ions and aptamer functionalized MnO₂ nanosheet as probe.

Electrochemical determination of the activity and inhibition of telomerase based on the interaction of DNA with molybdate

An ultrasensitive electrochemical sensor is described for the determination of the activity of telomerase. It is based on a DNA-generated current that is due to the reaction of the phosphate groups on DNA with molybdate to form a redox-active molybdophosphate. A telomerase substrate primer was first immobilized on a gold electrode. In the presence of telomerase and deoxyribonucleoside triphosphates (dNTPs), the primer can be extended with repetitive nucleotide sequences (TTAGGG). The subsequent reaction of the sensor with molybdate results in the enhancement of electrochemical current intensity due to an increased amount of nucleotides on the electrode. Sensitivity can be further improved by introducing a hairpin probe that partially hybridizes with the repetitive TTAGGG sequence and further enhances the amount of DNA on the electrode. The biosensor, best operated at 0.2 V (vs. Ag/AgCl) shows a linear response to telomerase activity from 1×10² to 10⁷ Hela cells mL^-1. The assay was applied to the detection of telomerase activity in HeLa cancer cells treated with the anticancer drug epigallocatechin gallate, and the results indicate that it holds great potential in anticancer drug screening. Graphical abstract Schematic presentation of an ultrasensitive electrochemical sensor for the determination of telomerase activity based on DNA generated electrochemical current. dNTPs in the scheme represents deoxyribonucleoside triphosphates.

Photoelectrochemical biosensor for microRNA detection based on multiple amplification strategies

A photoelectrochemical biosensor is described for sensitive detection of microRNA-162a. A multiple amplification strategy is employed that involves (a) isothermal strand displacement polymerase reaction; (b) terminal deoxynucleotidyl transferase-mediated extension, (c) amplification of streptavidin-coated gold nanoparticles, and (d) biotin functionalized alkaline phosphatase. Graphite-like C₃N₄ (g-C₃N₄) nanosheets were used as photoactive material. By using these amplification strategies, the detection limit is as low as 0.18 fM of microRNA, and the photocurrent increases linearly with the concentration of microRNA-162a in the range from 0.5 fM to 1 pM. The method was successfully applied to quantify the expression level of microRNA-162a in total RNA extracted from the leaves of maize seedlings after incubation with the chemical mutagen ethyl methanesulfonate. The results confirmed the applicability of the method to the analysis of practical biological samples. Graphical Abstract Schematic of a photoelectrochemical microRNA assay based on a multiple amplification strategy involving (a) isothermal strand displacement polymerase reaction; (b) terminal deoxynucleotidyl transferase-mediated extension,