Silica-nanoparticle-based interface for the enhanced immobilization and sequence-specific detection of DNA.

Colloid Au-enhanced DNA immobilization for the electrochemical detection of sequence-specific DNA

This research aims to develop DNA chip array without an indicator. We fabricated microelectrode array by photolithography technology. Several DNA probes were immobilized on an electrode. Then, indicator-free target DNA was hybridized by an electrical force and measured electrochemically. Cyclic-voltammograms (CVs) showed a difference between DNA probe and mismatched DNA in an anodic peak. Immobilization of probe DNA and hybridization of target DNA could be confirmed by fluorescent. This indicator-free DNA chip microarray resulted in the sequence-specific detection of the target DNA quantitatively ranging from <TEX>$10^{-18}\;M\;to\;10^{-5}$</TEX> M in the buffer solution. This indicator-free DNA chip resulted in a sequence-specific detection of the target DNA.

Hybridization chain reaction amplification for highly sensitive fluorescence detection of DNA with dextran coated microarrays

Photoluminescence and light reflectance properties of silica and titania nanoparticles (NPs) in two bilayer configurations were studied. In the first configuration, Titania and Silica NPs monolayers were deposited on a silicon wafer, the Titania NPs monolayer was the one in contact with the wafer and silica NPs was the top monolayer. The second configuration consisted in Silica NPs bilayer. The periodic monolayers were deposited by the spin coating technique. The concentration of colloidal suspension of NPs and their distribution over the surface were controlled by the revolutions per minute (rpm) during spin coating deposition. A set of samples were annealed with increments of 10 minutes, ranging from 0 min (i.e. not annealed) to 60 min. As well other samples were annealed during 2 and 3 hours, at 1,100 °C. The bilayers were characterized using several techniques as Fourier Transform Infrared Spectroscopy (FTIR), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), reflectance and photoluminescence (PL) measurements. For the first configuration, our results shown that for short annealing time the PL emission increased 6 times with respect to the non annealed sample. However, the light reflected by the first configuration is lower than the one reflected by the second configuration. These results can be attractive for light emitting devices as well as for absorbing layers on crystalline silicon solar cells.

We report on a highly sensitive chemiluminescence (CL) assay for the detection of specific DNA sequence, where streptavidin-modified polystyrene microspheres (PS–SA) coupled with hybridization chain reaction (HCR) were employed as dual amplification platform. Briefly, a “sandwich-type” detection strategy was proposed in our design, which involved capture probe DNA immobilized on the surface of carboxyl-terminated magnetic beads (MB) and the reporter DNA combined with the HCR trigger immobilized on the surface of PS–SA. After that, two hairpin-type monomers were added to initiate the HCR. In the detection system, CL signal was obtained via the instantaneous derivatization reaction between 3,4,5-trimethoxylphenylglyoxal (TMPG) and guanine bases in the target and the HCR complex binding on the magnetic beads. As compared to traditional sandwich type (capture/target/reporter) assays, this dual-amplified strategy for sequence-specific DNA detection showed better specificity, lower detection limit and wider linear response range (linear range of 0.01 fmol–10 pmol and a low detection limit of 5 amol). Moreover, this approach could be easily extended to detect a wide range of specific DNA sequences by modification of the hybridization region. We believe this simple technique will present a significant step towards early diagnoses of diseases.

Ultrasensitive SERS detection of Bacillus thuringiensis special gene based on Au@Ag NRs and magnetic beads

Label-free electrochemical detection of cancer biomarkers DNA and anti-p53 at tin oxide quantum dot-gold-DNA nanoparticle modified electrode

Methods for the fluorescent detection of specific sequences of double strand DNA in homogeneous solution may be useful in the field of human genetics. A series of hairpin polyamides with tetramethyl rhodamine (TMR) attached to an internal pyrrole ring were synthesized, and the fluorescence properties of the polyamide-fluorophore conjugates in the presence and absence of duplex DNA were examined. We observe weak TMR fluorescence in the absence of DNA. Addition of >/=1:1 match DNA affords a significant fluorescence increase over equimolar mismatch DNA for each polyamide-TMR conjugate. Polyamide-fluorophore conjugates offer a new class of sensors for the detection of specific DNA sequences without the need for denaturation. The polyamide-dye fluorescence-based method can be used to screen in parallel the interactions between aromatic ring pairs and the minor groove of DNA even when the binding site contains a non-Watson-Crick DNA base pair. A ranking of the specificity of three polyamide ring pairs-Py/Py, Im/Py, and Im/Im-was established for all 16 possible base pairs of A, T, G, and C in the minor groove. We find that Im/Im is an energetically favorable ring pair for minor groove recognition of the T.G base pair.

Previously, we reported the application of micromachined silicon nanotweezers (SNT) integrated with a comb-drive actuator and capacitive sensors for capturing and mechanical characterization of DNA bundles. Here, we demonstrate direct DNA amplification on such a MEMS structure with subsequent electrical and mechanical characterization of a single stranded DNA (ssDNA) bundle generated between the tips of SNT via isothermal rolling circle amplification (RCA) and dielectrophoresis (DEP). An in situ generated ssDNA bundle was visualized and evaluated via electrical conductivity (I-V) and mechanical frequency response measurements. Colloidal gold nanoparticles significantly enhanced (P < 0.01) the electrical properties of thin ssDNA bundles. The proposed technology allows direct in situ synthesis of DNA with a predefined sequence on the tips of a MEMS sensor device, such as SNT, followed by direct DNA electrical and mechanical characterization. In addition, our data provides a "proof-of-principle" for the feasibility of the on-chip label free DNA detection device that can be used for a variety of biomedical applications focused on sequence specific DNA detection.

Rapid, sequence-specific DNA detection is essential for applications in medical diagnostics and genetic screening. Electrical biosensors that use immobilized nucleic acids are especially promising in these applications because of their potential for miniaturization and automation. Current DNA detection methods based on sequencing by synthesis rely on optical readouts; however, a direct electrical detection method for this technique is not available. We report here an approach for direct electrical detection of enzymatically catalyzed DNA synthesis by induced surface charge perturbation. We discovered that incorporation of a complementary deoxynucleotide (dNTP) into a self-primed single-stranded DNA attached to the surface of a gold electrode evokes an electrode surface charge perturbation. This event can be detected as a transient current by a voltage-clamp amplifier. Based on current understanding of polarizable interfaces, we propose that the electrode detects proton removal from the 3'-hydroxyl group of the DNA molecule during phosphodiester bond formation.

In the present study, the basalt fibers (BFs) were treated with hybrid sizings consisting silane coupling agent (3‐Glycidoxypropyl)trimethoxysilane, and silicon dioxide nanoparticles (SNPs). Using acetone washing and heat treatment, the commercial sizing previously on the BFs was removed. Next, the fibers were dip‐coated, and silanes condensed on the surface of the fibers. Fiber samples were characterized using thermogravimetric analysis (TGA), atomic force microscopy (AFM), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The test findings demonstrate that acetone extraction was an effective way to remove sizings. The AFM analysis and SEM micrographs demonstrate that SNP and silane particles were dispersed uniformly across the fiber surface. The single fiber tensile testing results indicated that the deposition of hybrid sizings enhanced the fibers strength. Because of the better adhesion between the fiber and epoxy, the hybrid sizings also improved the flexural strength by 22.28% and the interlaminar shear strength by 20.75%.Highlights Hybrid sizings (silanes and nano‐particles) on the basalt fiber surface. Characterization of the sizings and understanding of surface morphology. Hybrid sizings resulted in better tensile strength. Failure mechanisms of the fibers were observed using fractography. The effect of hybrid sizing on ILSS and flexural properties was observed.

An ionic liquid supported CeO2 nanoshuttles–carbon nanotubes composite as a platform for impedance DNA hybridization sensing

Effect of glassy carbon, gold, and nickel electrodes on nickel electrocrystallization in an industrial electrolyte

The application of natural materials films for the surface modification of glassy carbon and gold electrodes to enhance their selective sense in the electrochemical detection of organic and inorganic species is a major challenge. In this study, gliadin was extracted from wheat flour and, for the first time, applied as a novel biocompatible permselective modifier film on gold and glassy carbon electrodes for the electrochemical detection of various compounds. The structure and surface morphology of the extracted gliadin were investigated by Fourier transform infrared (FT-IR) spectroscopy and atomic force microscopy (AFM) techniques. AFM and scanning electron microscopy (SEM) showed that porous structures with high nanometric roughness were present in gliadin membranes prepared from the casting solution of gliadin in ethanol. Compared to hydrophobic ions, the capacitance (C) values of electrical double layers of gliadin film modified electrodes for hydrophilic ions were very high. The findings of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) proved high performance of gliadin membrane as permselectcive film for nominated cationic compounds with fast electrochemical kinetics responses in aqueous solutions (PBS, pH = 7). This behavior was verified by circulating solutions containing model compounds from a home-made continuous cell equipped with gliadin-modified polyamide membranes.

Electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), and photon polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) were employed to investigate the formation of alamethicin pores in negatively charged bilayers composed of a mixture of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and egg-PG floating at gold (111) electrode surfaces modified by self-assembled monolayers of 1-thio-β-d-glucose (β-Tg). The EIS data showed that the presence of alamethicin decreases the membrane resistivity by about 1 order of magnitude. PM-IRRAS measurements provided information about the tilt angles of peptide helical axis with respect to the bilayer normal. The small tilt angles obtained for the peptide helical axis prove that the alamethicin molecules were inserted into the DMPC/egg-PG membranes. The tilt angles decreased when negative potentials were applied, which correlates with the observed decrease in membrane resistivity, indicating that ion pore formation is assisted by the transmembrane potential. Molecular resolution AFM images provided visual evidence that alamethicin molecules aggregate forming hexagonal porous 2D lattices with periodicities of 2.0 ± 0.2 nm. The pore formation by alamethicin in the negatively charged membrane was compared with the interaction of this peptide with a bilayer formed by zwitterionic lipids. The comparison of these results showed that alamethicin preferentially forms ion translocating pores in negatively charged phospholipid membranes.