A molybdenum disulfide@Methylene Blue nanohybrid for electrochemical determination of microRNA-21, dopamine and uric acid

WS2 nanosheets-based electrochemical biosensor for highly sensitive detection of tumor marker miRNA-4484

In this paper, a few-layer WS2 nanosheets-based electrochemical biosensor was fabricated for the highly sensitive detection of breast cancer tumor marker miRNA-4484. Firstly, few-layer WS2 nanosheets were prepared by shear stripping and characterized by SEM, TEM, AFM and UV spectrophotometer. After modification of few-layer WS2 nanosheets on the electrode surface, the miRNA probe was fixed on the few-layer WS2 nanosheets by polycytosine (PolyC). Then short-chain miRNA containing PolyC was used as the blocking agent to close the excess active sites on the surface of WS2 nanosheets to complete the fabrication of the sensor biosensing interface. Finally, the current changes caused by the specific binding of miRNA-4484 to the probe were analyzed by differential pulse voltammetry (DPV). The results showed that the sensor had a good linear relationship for the detection of miRNA-4484 in the concentration range of 1 aM-100 fM, and the detection limit was as low as 1.61 aM. In addition, the electrochemical sensor had excellent selectivity, stability and reproducibility. The artificial sample tests indicated that the developed biosensors have the potential for clinical application in the future.

A dual-blocker aided and dual-label-free electrochemical biosensor based on mbHCR/rGO nanocomplexes for ultrasensitive DNA detection

Heterogeneous electrochemical DNA biosensors have attracted huge attention due to their enhanced signal sensitivity, compared to homogeneous biosensors. However, the high cost of probe labeling and the reduced recognition efficiency associated with current heterogeneous electrochemical biosensors confine their potential applications. In the present work, a dual-blocker assisted and dual-label-free heterogeneous electrochemical strategy based on multi-branched hybridization chain reaction (mbHCR) and reduced graphene oxide (rGO) was fabricated for ultrasensitive detection of DNA. The target DNA could trigger the mbHCR of two DNA hairpin probes, resulting in the generation of multi-branched long chain of DNA duplexes with bidirectional arms. One direction of the multi-branched arms in the mbHCR products were then bound to the label-free capture probe on the gold electrode through multivalent hybridization with enhanced recognition efficiency. The other direction of multi-branched arms in mbHCR product could adsorb rGO via π-π stacking interactions. Two DNA blockers were ingeniously designed to block the binding of excessive H1-pAT on electrode and to prevent the adsorption of rGO by residual unbound capture probes. As a result, with the electrochemical reporter methylene blue selectively intercalated into the long chain of DNA duplex and absorbed on rGO, a remarkable electrochemical signal rise was observed. Thus, a dual-blocker aided and dual-label-free electrochemical strategy for ultrasensitive DNA detection is readily realized with the merit of cost-effective. The as-developed dual-label-free electrochemical biosensor has great potential to be employed in nucleic acid related medical diagnostics.

MicroRNA biosensors for detection of gastrointestinal cancer

Gastrointestinal (GI) cancers are one of the most common causes of cancer-related mortality. The discovery of microRNAs (miRs) and their unique role in cancer and other diseases has prompted the development of highly sensitive molecular diagnostic tools using nanomaterials as sensitive and specific biosensors. Among these, electrochemical biosensors, which are based on a simple and inexpensive design, make them desirable in clinical applications as well as a mass-produced point-of-care device. We review miR-based electrochemical biosensors in GI cancer and examine the use of nanoparticles in the evolving development of miR-based biosensors. Among these, a number of approaches including redox labeled probes, catalysts, redox intercalating agents and free redox indicators are highlighted for use in electrochemical biosensor technology.

Activated Glassy Carbon Electrode as an Electrochemical Sensing Platform for the Determination of 4-Nitrophenol and Dopamine in Real Samples

Glassy carbon electrode (GCE) was electrochemically activated using a repetitive cyclic voltammetric technique to develop an activated glassy carbon electrode (AGCE). The developed AGCE was optimized and utilized for the electrochemical assay of 4-nitrophenol (4-NP) and dopamine (DA). Cyclic voltammetry (CV) was employed to investigate the electrochemical behavior of the AGCE. Compared to the bare GCE, the developed AGCE exhibits a significant increase in redox peak currents of 4-NP and DA, which indicates that the AGCE significantly improves the electrocatalytic reduction of 4-NP and oxidation of DA. The electrochemical signature of the activation process could be directly associated with the formation of oxygen-containing surface functional groups (OxSFGs), which are the main reason for the improved electron transfer ability and the enhancement of the electrocatalytic activity of the AGCE. The effects of various parameters on the voltammetric responses of the AGCE toward 4-NP and DA were studied and optimized, including the pH, scan rate, and accumulation time. Differential pulse voltammetry (DPV) was also utilized to investigate the analytical performance of the AGCE sensing platform. The optimized AGCE exhibited linear responses over the concentration ranges of 0.04-65 μM and 65-370 μM toward 4-NP with a lower limit of detection (LOD) of 0.02 μM (S/N = 3). Additionally, the AGCE exhibited a linear responses over the concentration ranges of 0.02-1.0 and 1.0-100 μM toward DA with a lower limit of detection (LOD) of 0.01 μM (S/N = 3). Moreover, the developed AGCE-based 4-NP and DA sensors are distinguished by their high sensitivity, excellent selectivity, and repeatability. The developed sensors were successfully applied for the determination of 4-NP and DA in real samples with satisfactory recovery results.

Sensitive and selective electrochemical determination of uric acid in urine based on ultrasmall iron oxide nanoparticles decorated urchin-like nitrogen-doped carbon

Hypercrosslinked pyrrole was synthesized via the Friedel-Crafts reaction and then carbonized to obtain urchin-like nitrogen-doped carbon (UNC). Ultrasmall iron oxide nanoparticles were then supported on UNC, and the composite was used to prepare an electrochemical sensor for detecting uric acid (UA) in human urine. Fe_xO_y/UNC was characterized and analyzed via scanning electron microscopy, transmission electron microscopy, energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. A glassy carbon electrode (GCE) modified with Fe_xO_y/UNC was used as an electrochemical sensor to effectively identify UA. The electrochemical behavior of the Fe_xO_y/UNC-based UA sensor was studied using differential pulse stripping voltammetry, and the optimal conditions were determined by changing the amount of Fe_xO_y/UNC, pH of the buffer solution, deposition potential, and deposition time. Under optimal conditions, the Fe_xO_y/UNC-based electrochemical sensor detected UA in the range of 2-200 μM, where the limit of detection (LOD) for UA was 0.29 μM. Anti-interference experiments were performed, and the sensor was applied to the actual analysis of human urine samples. Urea, glucose, ascorbic acid, and many cations and anions present at 100-fold concentrations relative to UA did not strongly interfere with the response of the sensor to UA. The Fe_xO_y/UNC electrochemical sensor has high sensitivity and selectivity for uric acid in human urine samples and can be used for actual clinical testing of UA in urine.

Facile fabrication of screen-printed MoS2 electrodes for electrochemical sensing of dopamine

Molybdenum disulfide (MoS₂) screen-printed working electrodes were developed for dopamine (DA) electrochemical sensing. MoS₂ working electrodes were prepared from high viscosity screen-printable inks containing various concentrations and sizes of MoS₂ particles and ethylcellulose binder. Rheological properties of MoS₂ inks and their suitability for screen-printing were analyzed by viscosity curve, screen-printing simulation and oscillatory modulus. MoS₂ inks were screen-printed onto conductive FTO (Fluorine-doped Tin Oxide) substrates. Optical microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDX) analysis were used to characterize the homogeneity, topography and thickness of the screen-printed MoS₂ electrodes. The electrochemical performance was assessed through differential pulse voltammetry. Results showed an extensive linear detection of dopamine from 1 µM to 300 µM (R² = 0.996, sensitivity of 5.00 × 10^-8 A μM^-1), with the best limit of detection being 246 nM. This work demonstrated the possibility of simple, low-cost and rapid preparation of high viscosity MoS₂ ink and their use to produce screen-printed FTO/MoS₂ electrodes for dopamine detection.

Rapid and ultrasensitive detection of DNA and microRNA-21 using a zirconium porphyrin metal-organic framework-based switch fluorescence biosensor

Sensitive and accurate detection of nucleic acid biomarkers is critical for early cancer diagnosis, disease monitoring, and clinical treatment. In this study, we developed a switch fluorescence biosensor for simple and high-efficient detection of nucleic acid biomarkers using 6-carboxyfluorescein (FAM)-modified single-stranded DNA (ssDNA) probes (FAM-P1/P2), and zirconium porphyrin metal-organic framework nanoparticles (ZrMOF) acted as fluorescence quencher. FAM-P1/P2 probes were adsorbed on ZrMOF surface because of π-π stacking, hydrogen bonding, and electrostatic interactions. Fluorescence quenching event occurred by fluorescence resonance energy transfer (FRET) and photo-induced electron transfer (PET) processes, thereby achieving the "off" fluorescence status. Once the specific binding was formed between the fluorescence probes and the targets, the rigid double-stranded DNA (dsDNA) structures were released from ZrMOF surface, resulting in the recovery of fluorescence and the "on" status. Because of the superior adsorption ability of ZrMOF toward ssDNA than dsDNA, the switch of fluorescence signals from "off" to "on" allowed rapid and ultrasensitive detection of ssDNA (T1) and microRNA-21 (miR-21) within 30 min. The limit of detection (signal-to-noise ratio = 3) for T1 and miR-21 were 2 fM and 11 aM, respectively. Moreover, the proposed strategy was very simple as it worked by the facile adsorption-quenching-recovery mechanism without difficult and complicated immobilization processes. Also, this biosensor showed an excellent analytical performance in the detection of miR-21 in human serum samples. Therefore, this biosensor might be considered a potential tool for the detection of DNA and miRNA biomarkers in clinical samples.

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

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

A simple electrochemical aptasensor for saxitoxin detection

The combination between the electrochemical sensor and selective specificity of MB modified aptamer(MB-Apt) yielded an electrochemical aptasensor with a high sensitivity and excellent specific recognition ability to STX.

MoS2 Nanoparticle Effects on 80 °C Thermally Stable Water-Based Drilling Fluid

Bentonite-based drilling fluids are used for drilling, where inhibitive fluids are not required. The rheological and the density properties of the drilling fluids are highly affected by high temperature and pressure. Due to high temperature, the clay particles stick together, and the fluid system becomes more flocculated. Poorly designed drilling fluid may cause undesired operational issues such as poor hole cleaning, drill strings sticking, high torque and drag. In this study, the 80 °C thermally stable Herschel Bulkley’s and Bingham plastic yield stresses drilling fluids were formulated based on lignosulfonate-treated bentonite drilling fluid. Further, the impact of a MoS₂ nanoparticle solution on the properties of the thermally stable base fluid was characterized. Results at room temperature and pressure showed that the blending of 0.26 wt.% MoS₂ increased the lubricity of thermally stable base fluid by 27% and enhanced the thermal and electrical conductivities by 7.2% and 8.8%, respectively.

Electrochemical detection of matrix metalloproteinase-7 using an immunoassay on a methylene blue/2D MoS2/graphene oxide electrode

Methylene blue (MB) adsorption onto a two-dimensional molybdenum disulfide (2D MoS₂)/graphene oxide (GO) nanocomposite sitting on a screen-printed carbon electrode (SPCE) is used to develop a new sensitive label-free electrochemical immunosensor for the detection of matrix metalloproteinase-7 (MMP-7) cancer biomarkers. The 2D MoS₂/GO nanocomposite deposited onto an SPCE provides a large specific surface area, fast electron transfer, and exceptional electrical conductivity. Furthermore, MB adsorbed onto the 2D MoS₂/GO nanocomposite architecture can be used for signal amplification in electrochemical immunosensors. Moreover, an immunosensor platform was fabricated by the adsorption of anti-MMP-7 capture antibodies onto the MB/2D MoS₂/GO nanocomposite surface via electrostatic interactions for the detection of the MMP-7 immunocomplex. Under optimum conditions, the label-free immunosensor exhibits a decrease in the current response for MB corresponding to the MMP-7 concentration. The sensor affords a linear logarithmic range of 0.010-75 ng mL^-1 with a limit of detection (LOD) of 0.007 ng mL^-1. The developed electrochemical immunosensor provides high selectivity, good reproducibility, and excellent stability. Furthermore, the proposed immunosensor can be applied for the detection of MMP-7 in human serum samples with good recovery. Thus, this device can be applied for the early clinical diagnosis of pancreatic and colorectal cancers.

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.

Voltammetric detection of vitamin D employing Au-MoS2 hybrid as immunosensing platform

A voltammetric immunosensor based on molybdenum sulphide (MoS₂) and gold nanoparticles (Au NPs) for the determination of 25-hydroxy vitamin D₃ (25(OH)D₃) is reported. Anti-vit D (Ab-25(OH)D₃) was immobilized onto the cysteamine-modified MoS₂ and Au NPs which were deposited onto a fluoride tin oxide (FTO) electrode (Ab/Cys/Au/MoS₂/FTO). The MoS₂ sheets were prepared by hydrothermal method followed by an in situ growth of Au film onto the MoS₂/FTO surface. Self-assembled monolayer (SAM) of cysteamine was synthesized onto the Au/MoS₂/FTO which acts as a linker to covalently bind Ab-25(OH)D₃. The Ab-25(OH)D₃-immobilized Cys/Au/MoS₂/FTO was used to detect 25(OH)D₃ using differential pulse voltammetry. The electrochemical system provided an anodic peak current at a potential of +0.21 V vs. Ag/AgCl (satd. KCl) of ferricyanide/ferrocyanide redox couple. The detection principle relies on the inhibition of electron transfer at the electrode surface owing to the hindrance caused by the formation of immune complex between Ab-25(OH)D₃ and 25(OH)D₃. The immunosensor shows linear response from 1 pg mL^-1 to 100 ng mL^-1 25(OH)D₃ and a sensitivity of 189 μA [log (pg mL^-1)]^-1 cm^-2 along with a low limit of detection (LOD) of 0.38 pg mL^-1. The immunosensor is highly selective towards 25(OH)D₃ and presented a long shelf life of 28 days. Also, the immunosensor exhibits satisfactory performance towards spiked human serum samples with recovery between 95.1 and 102% (RSD 1.15-3.22%).

"Dual Signal-On" Split-Type Aptasensor for TNF-α: Integrating MQDs/ZIF-8@ZnO NR Arrays with MB-Liposome-Mediated Signal Amplification

Ultrasensitive and accurate detection of biomarkers in serum is of great importance for disease diagnosis and treatment. So far, the commonly used single-mode signal suffers from certain instinct drawbacks that restrict assay performances. Herein, we report the proof-of-concept fabrication of a split-type photoelectrochemical (PEC) and electrochemical (EC) dual-modal aptasensor for ultrasensitively tracing tumor necrosis factor-α, a noteworthy biological biomarker with essential clinical importance. By smart integrating molybdenum disulfide QDs/zeolitic imidazolate framework-8@ZnO nanorod arrays with a methylene blue-liposome-mediated signal amplification strategy, "dual signal-on" detection is accomplished based on a sandwich reaction of the target with aptamer-anchored carboxyl magnetic beads and an aptamer-confined MB liposome. Linear ranges of 5 fg/mL-5 μg/mL (detection limit 1.46 fg/mL) for PEC and 10 fg/mL-0.5 μg/mL (detection limit 6.14 fg/mL) for EC are obtained, respectively. An independent signal transduction mechanism supports the accuracy improvement, and a separate biological process from a translator enables convenient fabrication, short-time consumption, wider linearity, as well as outstanding reproducibility and stability in practical application. This work presents a universal bioassay route with prospects in biomedical and related areas.

Recent trends in application of nanomaterials for the development of electrochemical microRNA biosensors

The biology of the late twentieth century was marked by the discovery in 1993 of a new class of small non-coding ribonucleic acids (RNAs) which play major roles in regulating the translation and degradation of messenger RNAs. These small RNAs (18-25 nucleotides), called microRNAs (miRNAs), are implied in several biological processes such as differentiation, metabolic homeostasis, or cellular apoptosis and proliferation. The discovery in 2008 that the presence of miRNAs in body fluids could be correlated with cancer (prostate, breast, colon, lung, etc.) or other diseases (diabetes, heart diseases, etc.) has made them new key players as biomarkers. Therefore, miRNA detection is of considerable significance in both disease diagnosis and in the study of miRNA function. Until these days, more than 1200 miRNAs have been identified. However, traditional methods developed for conventional DNA does not apply satisfactorily for miRNA, in particular due to the low expression level of these miRNA in biofluids, and because they are very short strands. Electrochemical biosensors can provide this sensitivity and also offer the advantages of mass fabrication, low-cost, and potential decentralized analysis, which has wide application for microRNAs sensing, with many promising results already reported. The present review summarizes some newly developed electrochemical miRNA detection methods.

Signal-off photoelectrochemical determination of miRNA-21 using aptamer-modified In2O3@Cu2MoS4 nanocomposite

In₂O₃@Cu₂MoS₄ nanocomposite with superior photoelectrochemical (PEC) performance is used for the first time as a photoactivity material, and a signal-off PEC biosensing platform for miRNA detection has been successfully constructed. Firstly, the Cu₂MoS₄ nanosheets are synthesized by a hydrothermal method, and then, the homogeneous In₂O₃ nanoparticles (In₂O₃ NPs) are synthesized by calcination in the air. The In₂O₃@Cu₂MoS₄ nanocomposite is constructed with the Cu₂MoS₄ nanosheets as matrix and In₂O₃ NPs as sensitizer through a layer-by-layer assembly strategy. The nanocomposite with a tight interface and the matched band structure restrains the electron-hole pair recombination. Under visible light (400-700 nm), the nanocomposite exhibits a strong initial signal. With the catalyzed hairpin assembly, dozens of PbS quantum dots (QDs) are introduced on the surface of an electrode, significantly reducing the photocurrent of n-type In₂O₃@Cu₂MoS₄. Since PbS QDs can compete with the nanocomposite for light energy and electron donors, the signal decreased. Under optimal conditions, the biosensor manifests a broad linear range (1 fM-1 nM) and a low detection limit of about 0.57 fM, at a working potential of 0 V (vs. Ag/AgCl). The recovery of spiked human serum is between 94.0 and 102%, and the relative standard deviation (RSD) is between 1.3 and 2.7%. Therefore, the as-fabricated biosensor exhibits a potential for the determination of miRNA-21 in practical applications.Graphical abstract The In₂O₃@Cu₂MoS₄ nanocomposite owns a strong anode photocurrent signal, which can be used as a photoactive material to construct a "signal-off" biosensor for the detection of miRNA in non-enzymatically catalyzed hairpin assembly (CHA) reaction.

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.