Molecular beacon based biosensor for the sequence-specific detection of DNA using DNA-capped gold nanoparticles-streptavidin conjugates for signal amplification

A novel electrochemical biosensor based on signal amplification of Au HFGNs/PnBA-MXene nanocomposite for the detection of miRNA-122 as a biomarker of breast cancer

Cancer is one of the leading causes of death worldwide and a crisis for global health. Breast cancer is the second most common cancer globally. In the perusal, a novel electrochemical biosensor amplified with hierarchical flower-like gold, poly (n-butyl acrylate), and MXene (AuHFGNs/PnBA-MXene) nanocomposite and activated by highly special antisense ssDNA (single-stranded DNA) provide a promising alternative for miRNA-122 detection as a biomarker of breast cancer. The biosensor presented a detection limit of 0.0035 aM (S/N = 3) with a linear range from 0.01 aM to 10 nM. The platform was tried on 20 breast cancer miRNAs extracted from actual serum specimens (10 positives and 10 negatives). Founded on the quantitatively obtained outcomes and statistic analysis (t-test, box-graph, receiver performance characteristic curve, and cut-off amount), the biosensor showed a meaningful discrepancy between the native and positive groups with 100% specificity and 100% sensitivity. While, RT-qPCR showed less specificity and sensitivity (70% specificity, 100% sensitivity) than the proposed biosensor. To assess the quantitative capacity and biosensor detection limit for clinical tests, the biosensor diagnosis performance for continually diluted miRNA extracted from patients was compared to that gained by RT-qPCR results, indicating that the biosensor detection limit was lower than RT-qPCR. ssDNA/AuHFGN/PnBA-MXene/GCE displayed little cross-reaction with other sequences and also showed desirable stability, reproducibility, and specificity and stayed stable until 32 days. As a result, the designed biosensor can perform as a hopeful method for diagnosis applications.

Fabrication strategies and surface tuning of hierarchical gold nanostructures for electrochemical detection and removal of toxic pollutants

The intensive research on the synthesis and characterization of gold (Au) nanostructures has been extensively documented over the last decades. These investigations allow the researchers to understand the relationships between the intrinsic properties of Au nanostructures such as particle size, shape, morphology, and composition to synthesize the Au nano/hybrid nanostructures with novel physicochemical properties. By tuning the properties above, these nanostructures are extensively employed to detect and remove trace amounts of toxic pollutants from the environment. This review attempts to document the achievements and current progress in Au-based nanostructures, general synthetic and fabrication strategies and their utilization in electrochemical sensing and environmental remediation applications. Additionally, the applications of Au nanostructures (e.g., as adsorbents, sensing platforms, catalysts, and electrodes) and advancements in the field of electrochemical sensing of different target analytes (e.g., proteins, nucleic acids, heavy metals, small molecules, and antigens) are summarized. The literature survey concludes the existing methods for the detection of toxic contaminants at various concentration levels. Finally, the existing challenges and future research directions on electrochemical sensing and degradation of toxic contaminants using Au nanostructures are defined.

Adriamycin coated silica microspheres as labels for cancer biomarker alpha-fetoprotein detection

Adriamycin (ADM)-coated silica microspheres as a label for the sensitive detection of a cancer biomarker alpha-fetoprotein (AFP) was reported. Silica microspheres (SiO2 MSs) were employed as the carrier for the immobilization of gold nanoparticles (Au NPs), secondary antibody (Ab2) and ADM (denote: ADM@Au NPs@SiO2 MS/Ab2) as labels. In the presence of AFP, the labels were captured on the surface of the Au NP-reduced graphene oxide (rGO) (Au NP-rGO) nanocomposites to form a sandwich structure vs. the specific recognition of antibody-antigen. In a pH 7.4 phosphate buffer solution, a well-defined peak of ADM at about -0.70 V (vs. SCE) was recorded via differential pulse voltammetry, the peak intensity of which was related to the concentration of AFP. Under optimal experimental conditions, the immunoassay exhibited a wide linear range (0.5 pg mL-1 to 75 ng mL-1) and low limit of detection (0.17 pg mL-1). Further, the immunoassay was evaluated for serum samples, which gave satisfactory results.

Electrochemical Biosensor with Enhanced Antifouling Capability for COVID-19 Nucleic Acid Detection in Complex Biological Media

Biofouling caused by the accumulation of biomolecules on sensing surfaces is one of the major problems and challenges to realize the practical application of electrochemical biosensors, and an effective way to counter this problem is the construction of antifouling biosensors. Herein, an antifouling electrochemical biosensor was constructed based on electropolymerized polyaniline (PANI) nanowires and newly designed peptides for the detection of the COVID-19 N-gene. The inverted Y-shaped peptides were designed with excellent antifouling properties and two anchoring branches, and their antifouling performances against proteins and complex biological media were investigated using different approaches. Based on the biotin-streptavidin affinity system, biotin-labeled probes specific to the N-gene (nucleocapsid phosphoprotein) of COVID-19 were immobilized onto the peptide-coated PANI nanowires, forming a highly sensitive and antifouling electrochemical sensing interface for the detection of COVID-19 nucleic acid. The antifouling genosensor demonstrated a wide linear range (10-14 to 10-9 M) and an exceptional low detection limit (3.5 fM). The remarkable performance of the genosensor derives from the high peak current of PANI, which is chosen as the sensing signal, and the extraordinary antifouling properties of designed peptides, which guarantee accurate detection in complex systems. These crucial features represent essential elements for future rapid and decentralized clinical testing.

An electrochemical DNA biosensor based on nitrogen-doped graphene nanosheets decorated with gold nanoparticles for genetically modified maize detection

A reliable electrochemical biosensor is reported based on nitrogen-doped graphene nanosheets and gold nanoparticle (Au/N-G) nanocomposites for the event-specific detection of GM maize MIR162. The differential pulse voltammetry response of methylene blue (MB) was chosen to monitor the target DNA hybridization event. Under the optimum conditions, the peak current increased linearly with the logarithm of the concentration of DNA in the range 1.0 × 10^-14 to 1.0 × 10^-8 M, and the detection limit was 2.52 × 10^-15 M (S/N = 3). It is also demonstrated that the DNA biosensor has high selectivity, good stability, and fabrication reproducibility. The biosensor has been effectively applied to detect MIR162 in real samples, showing its potential as an effective tool for GM crop analysis. These results will contribute to the development of new portable transgenic detection systems. Graphical abstract .

A non-spectroscopic optical biosensor for the detection of pathogenic Salmonella Typhimurium based on a stem-loop DNA probe and retro-reflective signaling

The detection of foodborne pathogenic microorganisms is an essential issue in molecular diagnostics. Fluorescence-based assays have been widely utilized in molecular diagnostics because of their ability to detect and measure low analyte concentrations. However, conventional fluorescence-based assays require sophisticated optics systems, such as a specific light source and light filter. To overcome these limitations, we developed an optical sensing system using a retroreflective Janus microparticle (RJP) as a signaling probe. Compared to fluorescent dyes, RJPs have the advantage of not requiring complicated optic systems because they can be observed using visible light without a filter. To confirm that RJPs can be used as a probe for molecular diagnostics, Salmonella was detected using a biotinylated stem-loop DNA probe to capture the target gene DNA and a streptavidin-conjugated RJP (SA-RJP) as the detection molecule. When the target gene DNA was present at the sensing surface where the stem-loop DNA probe was immobilized, the biotinylated stem-loop DNA probe was stretched, exposing biotin, which can react with SA-RJP. Since the amount of exposed biotin increased according to the concentration of the applied target gene DNA, the number of observed RJPs on the sensing surface increased with the concentration of the target gene DNA. Consequently, the concentration of Salmonella could be quantitated by counting the number of observed RJPs. Using this system, Salmonella at concentrations ranging from 0 to 100 nM could be analyzed, with high sensitivity and selectivity, with a limit of detection of 2.48 pM.

Development of magnetic graphene oxide adsorbent for the removal and preconcentration of As(III) and As(V) species from environmental water samples

New-generation adsorbent, Fe3O4@SiO2/GO, was developed by modification of graphene oxide (GO) with silica-coated (SiO2) magnetic nanoparticles (Fe3O4). The synthesized adsorbent was characterized using Fourier transform infrared spectroscopy, X-ray diffractometry, energy-dispersive X-ray spectroscopy, and field emission scanning electron microscopy. The developed adsorbent was used for the removal and simultaneous preconcentration of As(III) and As(V) from environmental waters prior to ICP-MS analysis. Fe3O4@SiO2/GO provided high adsorption capacities, i.e., 7.51 and 11.46 mg g(-1) for As(III) and As(V), respectively, at pH 4.0. Adsorption isotherm, kinetic, and thermodynamic were investigated for As(III) and As(V) adsorption. Preconcentration of As(III) and As(V) were studied using magnetic solid-phase extraction (MSPE) method at pH 9.0 as the adsorbent showed selective adsorption for As(III) only in pH range 7-10. MSPE using Fe3O4@SiO2/GO was developed with good linearities (0.05-2.0 ng mL(-1)) and high coefficient of determination (R (2) = 0.9992 and 0.9985) for As(III) and As(V), respectively. The limits of detection (LODs) (3× SD/m, n = 3) obtained were 7.9 pg mL(-1) for As(III) and 28.0 pg mL(-1) for As(V). The LOD obtained is 357-1265× lower than the WHO maximum permissible limit of 10.0 ng mL(-1). The developed MSPE method showed good relative recoveries (72.55-109.71 %) and good RSDs (0.1-4.3 %, n = 3) for spring water, lake, river, and tap water samples. The new-generation adsorbent can be used for the removal and simultaneous preconcentration of As(III) and As(V) from water samples successfully. The adsorbent removal for As(III) is better than As(V).

Double-stranded probe modified AuNPs for sensitive and selective detection of microRNA 30a in solution and live cell

In this article, we reported a double-stranded DNA probe modified gold nanoparticle used as both “nano-flares” and transfection agents to quantify miR-30a in solution and visualize in live cells.

Reagentless, ratiometric electrochemical DNA sensors with improved robustness and reproducibility

To make the electrochemical DNA sensors (E-sensor) more robust and reproducible, we have now for the first time adapted the techniques of ratiometric analyses to the field of E-sensors. We did this via the simple expedient way of simultaneously using two redox probes: Methylene blue as the reporter of the conformational change, and ferrocene as an internal control. During the conformational transduction, only the distance between the signal probe and the electrode surface undergoes an appreciable change, while the distance between the control probe and the electrode remains relatively constant. This special design has allowed very reliable target recognition, as illustrated in this report using a human T-lymphotropic virus type I gene fragment. The standard deviation between measurements obtained using different electrodes was an order of magnitude less than that obtained using a classic E-sensor, which we prepared as a control. A limit of detection of 25.1 pM was obtained with our new system, with a single mismatch discrimination factor of 2.33 likewise being observed. Additionally, this concept had general applicability, and preliminary data of a "Signal-On" ratiometric E-sensor are also provided. Taken in concert, these results serve to validate the utility of what we believe will emerge as an easily generalized approach to oligonucleotide recognition and sensing.