Synthesis and characterization of faujasite zeolite membrane for selective enrichment of Arthrobacter sp. in synthetic wastewater.

This paper centers on the preparation and characterization of both a clay support and a faujasite zeolite membrane. Additionally, the study explores the development of bacterial media to assess the performance of these prepared membranes. The faujasite zeolite membrane was created using the hydrothermal method, involving the deposition of a faujasite layer to fine-tune the pore sizes of the clay support. The clay supports were crafted from clay which was sieved to particle size Φ ≤ 63 µm, and compacted with 3.0 wt.% activated carbon, then sintered at 1,000 °C. Distilled water fluxes revealed a decrease from 1,500 L m-2 h-1 to a minimum of 412 L m-2 h-1 after 180 min of filtration. Both membranes were characterized by XRF, XRD, FTIR, adsorption-desorption of nitrogen (N2), and SEM-EDS. PCR technique was used for the identification of the isolated Arthrobacter sp., and the retention of the bacteria on the clay support and the faujasite zeolite membrane were found to be 96 and 99%, respectively. The results showed that the faujasite zeolite membrane passed the clay support due to a narrow pore size of the faujasite zeolite membrane of 2.28 nm compared to 3.55 nm for the clay supports.

Controlled electrochemical surface exfoliation of graphite pencil electrodes for high-performance supercapacitors.

A controlled surface exfoliation method for graphite pencil electrodes using an environmentally friendly, low cost and scalable electrochemical process is reported. A simple direct current power supply in a neutral medium is used for inducing graphene formation on the electrode surface in a controlled manner. The electrochemical properties of the surface exfoliated electrode are characterized, displaying a >300× increase in the electrochemical surface area and >50× decrease in the electrode resistance after exfoliation. The surface graphene layer is characterized using electron microscopy, Raman, infrared, X-ray photoelectron, and energy dispersive X-ray spectroscopies and X-ray diffractometry showing a fully exfoliated surface, formation of surface defects and mild surface graphene oxidation while maintaining an intact graphitic crystal structure. The surface exfoliated electrode is tested as a supercapacitor demonstrating more than 2 orders of magnitude improvement over non-exfoliated electrode in both 3-electrode and 2-electrode setups and achieving a high areal capacitance of ∼54 mF cm-2. The benign nature, low cost, scalability of our controlled surface exfoliation methodology, and its significant impact on the electrochemical properties of the electrode make it very promising for further investigation in various applications such as energy storage and conversion, sensors, and catalysis.

Modified Graphite Pencil Electrode Based on Graphene Oxide-Modified Fe3O4 for Ferrocene-Mediated Electrochemical Detection of Hemoglobin.

This study describes the synthesis of graphene oxide-modified magnetite (rGO/Fe3O4) and its use as an electrochemical sensor for the quantitative detection of hemoglobin (Hb). rGO is characterized by a 2θ peak at 10.03° in its X-ray diffraction, 1353 and 1586 cm-1 vibrations in Raman spectroscopy, while scanning electron microscopy coupled with energy-dispersive spectroscopy of rGO and rGO/Fe3O4 revealed the presence of microplate structures in both materials and high presence of iron in rGO/Fe3O4 with 50 wt %. The modified graphite pencil electrode, GPE/rGO/Fe3O4, is characterized using cyclic voltammetry. Higher electrochemical surface area is obtained when the GPE is modified with rGO/Fe3O4. Linear scan voltammetry is used to quantify Hb at the surface of the sensor using ferrocene (FC) as an electrochemical amplifier. Linear response for Hb is obtained in the 0.1-1.8 µM range with a regression coefficient of 0.995, a lower limit of detection of 0.090 µM, and a limit of quantitation of 0.28 µM. The sensor was free from interferents and successfully used to sense Hb in human urine. Due to the above-stated qualities, the GPE/rGO/Fe3O4 electrode could be a potential competitive sensor for trace quantities of Hb in physiological media.

Multi-functional silver nanoprism-titanium dioxide hybrid nanoarrays for trace-level SERS sensing and photocatalytic removal of hazardous organic pollutants.

Owing to the excellent optoelectronic properties of metal nanoparticle-semiconductor interfaces; hybrid substrates with superior catalytic and sensing properties can be designed. In the present study, we have attempted to evaluate anisotropic silver nanoprisms (SNP) functionalized titanium dioxide (TiO2) particles for multifunctional applications such as SERS sensing and photocatalytic decomposition of hazardous organic pollutants. Hierarchical TiO2/SNP hybrid arrays have been fabricated via facile and low-cost casting techniques. The structural, compositional, and optical characteristics of TiO2/SNP hybrid arrays were well elucidated and correlated to SERS activities. SERS studies revealed that TiO2/SNP nanoarrays possess almost 288 times enhancement compared to bare TiO2 substrates and 2.6 times enhancement than pristine SNP. The fabricated nanoarrays demonstrated detection limits down to 10-12 M concentration levels and lower spot-to-spot variability of âˆ¼ 11%. The photocatalytic studies showed that almost 94 and 86% of rhodamine B and methylene blue were decomposed within 90 min of visible light exposure. Besides, two times enhancement in photocatalytic activities of TiO2/SNP hybrid substrates was also observed than bare TiO2. The highest photocatalytic activity was exhibited by SNP to TiO2 molar ratio of 1.5 × 10-3. The electrochemical surface area and the interfacial electron-transfer resistance were increased with the increment in TiO2/SNP composite load from 3 to 7 wt%. Differential Pulse Voltammetry (DPV) analysis revealed a higher RhB degradation potential of TiO2/SNP arrays than SNP or TiO2. The synthesized hybrids exhibited excellent reusability without any significant deterioration in photocatalytic properties over five successive cycles. TiO2/SNP hybrid arrays were proved to be multiple platforms for sensing and degrading hazardous pollutants for environmental applications.

Graphene nanosheet-sandwiched platinum nanoparticles deposited on a graphite pencil electrode as an ultrasensitive sensor for dopamine.

An ultra-sensitive sensor of dopamine is introduced. The sensor is constructed by encapsulating platinum nanoparticles (PtNPs) between reduced graphene oxide (GR) nanosheets. The sandwiched PtNPs between GR layers acted as a spacer to prevent aggregation and provided a fine connection between the GR nanosheets to provide fast charge transfer. This specific orientation of the GR nanosheets and PtNPs on the graphite pencil electrode (GPE) substantially improved the electrocatalytic activity of the sensor. The synthesized graphene oxide and the fabricated sensor were comprehensively characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, field emission-scanning electron microscopy (FE-SEM), electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and square wave voltammetry (SWV). The value of the charge transfer coefficient (α), apparent heterogeneous electron transfer rate constant (k s), and electroactive surface area for dopamine were found to be about 0.57, 8.99 s-1, and 0.81 cm2, respectively. The developed sensor is highly sensitive towards dopamine, and the detection limit is 9.0 nM. The sensor response is linear for dopamine concentration from 0.06 to 20 µM (R 2 = 0.9991). The behavior of the sensor for dopamine in the presence of a high concentration of l(+) Ascorbic acid and other potential interferents was satisfactory. High recovery percentage between 90% and 105% in the human urine sample, good reproducibility, and facile fabrication of the electrode make it a good candidate for dopamine sensing.

Electron and proton magnetic resonance spectroscopic investigation of anthracene oxidation.

The work reports a method for monitoring anthracene radical-mediated oxidation reactions using electron paramagnetic resonance (EPR) spectroscopy. The formation of anthracene dimer product was well-defined using 1H-NMR and 1H-1H correlation spectroscopy (COSY). Unrestricted 3-21G/B3LYP DFT was used to estimate radical hyperfine spacing (hfs), then to identify the characteristic EPR-spin transitions of anthracene radical intermediate. A detailed investigation of an anthracene oxidation reaction and its possible reaction mechanism in concentrated sulphuric acid is conducted as a model system for polyaromatic hydrocarbons. Peak-to-peak (p2p) intensities of selected EPR-spectral lines were used to evaluate anthracene's oxidation kinetic model. The findings showed that radical intermediate formation is a unimolecular autocatalytic process, dimerization is a pseudo-zero-order reaction, and the latter is the rate-determining step with a half-life of 48 ± 2 min at 25.0 °C.

Preparation of Sodalite and Faujasite Clay Composite Membranes and Their Utilization in the Decontamination of Dye Effluents.

The present work describes the deposition of two zeolite films, sodalite and faujasite, by the hydrothermal method to tune the mesopores of clay support, which are prepared from a widely available clay depot from the central region of Morocco (Midelt). The clay supports were prepared by a powder metallurgy method from different granulometries with activated carbon as a porosity agent, using uniaxial compression followed by a sintering process. The 160 µm ≤ Φ ≤ 250 µm support showed the highest water flux compared to the supports made from smaller granulometries with a minimum water flux of 1405 L.m-2·h-1 after a working time of 2 h and 90 min. This support was chosen for the deposition of sodalite (SOM) and faujasite (FAM) zeolite membranes. The X-ray diffraction of sodalite and faujasite showed that they were well crystallized, and the obtained spectra corresponded well with the sought phases. Such findings were confirmed by the SEM analysis, which showed that SOM was crystalized as fine particles while the FAM micrographs showed the existence of crystals with an average size ranging from 0.53 µm to 1.8 µm with a bipyramidal shape and a square or Cubo octahedral base. Nitrogen adsorption analysis showed that the pore sizes of the supports got narrowed to 2.28 nm after deposition of sodalite and faujasite. The efficiencies of SOM and FAM membranes were evaluated by filtration tests of solutions containing methyl orange (MO) using a flow loop, which were developed for dead-end filtration. The retention of methylene orange (MO) followed the order: SOM > FAM > 160 µm ≤ Φ ≤ 250 µm clay support with 55%, 48% and 35%, respectively. Size exclusion was the predominant mechanism of filtration of MO through SOM, FAM, and the support. However, the charge repulsion between the surface of the membrane and the negatively charged MO have not been ruled out. The point of zero charge (pzc) of the clay support, SOM and FAM membrane were pHpzc = 9.4, pHpzc = 10.6, and pHpzc = 11.4, respectively. Filtrations of MO were carried out between pH = 5.5 and pH = 6.5, which indicated that the surface of the membranes was positively charged while MO was negatively charged. The interaction of MO with the membranes might have happened through its vertical geometry.

A new hybrid nanocomposite electrode based on Au/CeO2-decorated functionalized glassy carbon microspheres for the voltammetric sensing of quercetin and its interaction with DNA.

A new hybrid composite containing cerium oxide nanoparticle (CeO2NP) and gold nanoparticle (AuNP)-decorated functionalized glassy carbon microspheres (FGCM) was synthesized (Au/CeO2@FGCM). As a result, an Au/CeO2@FGCM-paraffin oil paste electrode (PE) (Au/CeO2@FGCM-PE) was fabricated and employed for the voltammetric sensing of quercetin (QRT). The structure and surface morphology of Au/CeO2@FGCM were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cyclic voltammetry (CV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS) were employed for the investigation of the electrochemical behavior of Au/CeO2@FGCM-PE. Under the optimum conditions, the SWV oxidation peak current showed linear dependence on the QRT concentration in the range from 48 nM to 1.09 µM. The achieved limits of detection and quantitation were 0.37 nM and 1.22 nM, respectively. Au/CeO2@FGCM-PE was reproducible, sensitive and stable and displayed anti-interference ability for various common interferents. The proposed method was also successfully applied for real sample analysis. The QRT content extracted from natural sources was determined, and satisfactory results were achieved. Furthermore, the interaction of QRT with salmon testes and calf thymus dsDNA (st-DNA and ct-DNA) on Au/CeO2@FGCM-PE was studied by CV and SWV. The corresponding binding constant (K), surface concentration (Γ), and Gibbs free energy (ΔG°) were computed for the free QRT and the bound QRT-dsDNA complex. The calculated K values for the QRT-ct-DNA and QRT-st-DNA complexes were found to be 6.24 × 105 M-1 and 3.63 × 105 M-1, respectively, which revealed that QRT strongly interacted with ct-DNA compared to that with st-DNA. The decreased intensity of the QRT oxidation peak resulting from its interaction with dsDNA provides a chance to use QRT as a new indicator to analyze ct-DNA and st-DNA.

Synthesis, characterization and electrochemical properties of some biologically important indole-based-sulfonamide derivatives.

A new series of indole-based-sulfonamide derivatives (A1-A8) was synthesized by treating 5-fluoro-1H-indole-3-carbohydrazide with different aryl-sulfonyl chloride in the presence of pyridine. All synthesized derivatives (A1-A8) were characterized by different analytical methods. The electrochemical behavior of these compounds (A1-A8) was investigated in detail using cyclic voltammetry (CV) and square wave voltammetry (SWV) at the pencil graphite electrode (PGE). In the present study, the redox behavior of all derivatives varies due to the nature of substitutions in the indole sulfonamide moiety. Various fundamental electrochemical parameters, including the standard heterogeneous rate constants (ks), and the electroactive surface coverage (Г) were calculated from the obtained CVs. The obtained results shed light on the understanding of structure-activity relationships of this class of compounds.

Exploring efficacy of indole-based dual inhibitors for α-glucosidase and α-amylase enzymes: In silico, biochemical and kinetic studies.

α-Glucosidase and α-amylase are enzymes which are associated with diabetic II. These enzymes break macromolecules of sugar into monosugar molecules which is soluble in body, hence increase the sugar level in blood. There is need to develop economical and save inhibitors to prevent them from breaking sugar macromolecules to soluble molecules which will control the level of sugar in blood. Therefore, we synthesized indole-based derivatives (1-18) and evaluated as dual inhibitor for α-glucosidase and α-amylase. These chemical scaffolds were built with variation in aryl ring which were found active with good to moderate activity for α-glucosidase having IC50 value ranging from 13.99 ± 0.10 to 59.09 ± 0.30 µM when compared with standard acarbose with IC50 of 11.29 ± 0.10 µM; for α-amylase IC50 value ranging from 13.14 ± 0.10 to 58.99 ± 0.30 µM when compared with the standard acarbose with IC50 of 11.12 ± 0.10 µM. Structure activity relationship (SAR) has been established for all compounds. Enzymatic kinetic study and molecular docking study have been carried out to investigate the binding interactions α-glucosidase and α-amylase enzyme.

Synthesis, in vitro urease inhibitory potential and molecular docking study of Benzimidazole analogues.

Despite of many diverse biological activities exhibited by benzimidazole scaffold, it is rarely explored for the urease inhibitory potential. For that purpose, benzimidazole analogues 1-19 were synthesized and screened for in vitro urease inhibitory potential. Structures of all synthetic analogues were deduced by different spectroscopic techniques. All analogues revealed inhibition potential with IC50 values of 0.90 ±â€¯0.01 to 35.20 ±â€¯1.10 µM, when compared with the standard thiourea (IC50 = 21.40 ±â€¯0.21 µM). Limited SAR suggested that the variations in the inhibitory potentials of the analogues are the result of different substitutions on phenyl ring. In order to rationalize the binding interactions of most active compounds with the active site of urease enzyme, molecular docking study was conducted.

Potent In Vitro and In Vivo Anticancer Activity of New Bipyridine and Bipyrimidine Gold (III) Dithiocarbamate Derivatives.

We synthesized eight new bipyridine and bipyrimidine gold (III) dithiocarbamate-containing complexes (C1-C8) and tested them in a panel of human cancer cell lines. We used osteosarcoma (MG-63), lung (A549), prostate (PC3 and DU145), breast (MCF-7), ovarian (A2780 and A2780cis, cisplatin- and doxorubicin-resistant), and cervical (ME-180 and R-ME-180, cisplatin resistant) cancer cell lines. We found that C2, C3, C6, and C7 were more cytotoxic than cisplatin in all cell lines tested and overcame cisplatin and doxorubicin resistance in A2780cis and R-ME-180 cells. In the PC3 prostate cancer cell line, the gold (III) complex C6 ([Au2(BPM)(DMDTC)2]Cl4) induced apoptosis and double-stranded DNA breaks, modified cell cycle phases, increased Reactive Oxigen Species (ROS) generation, and reduced thioredoxin reductase and proteasome activities. It inhibited PC3 cell migration and was more cytotoxic against PC3 cells than normal human adipose-derived stromal cells. In mice bearing PC3 tumor xenografts, C6 reduced tumor growth by more than 70% without causing weight loss. Altogether, our results demonstrate the anticancer activity of these new gold (III) complexes and support the potential of C6 as a new agent for prostate cancer treatment.

A hybrid nanocomposite of CeO2-ZnO-chitosan as an enhanced sensing platform for highly sensitive voltammetric determination of paracetamol and its degradation product p-aminophenol.

For the determination of paracetamol (PAR) and its primary degradation product (p-aminophenol, PAP) a highly selective electrochemical sensor was fabricated. A glassy carbon microspheres paste electrode (GCMPE) was modified with a CeO2-ZnO-chitosan hybrid nanocomposite (CeO2-ZnO-CS) which was characterized by X-ray diffraction and transmission electron microscopy. The CeO2-ZnO-CS/GCMPE was characterized by scanning electron microscopy, and cyclic voltammetry. The modified GCMPE exhibits excellent electrocatalytic activity for the determination of PAR and PAP separately or simultaneously, typically at working potentials of 0.38 and 0.09 V vs. Ag/AgCl. The square wave voltammetric response in solutions of near-neutral pH value increases linearly in the 20 nM to 1.8 µM PAR concentration range, and the lower LOD is 0.86 nM. The sensor is shown to enable the determination of PAR even in the presence of a 180-fold excess of PAP. PAR and PAP can also be simultaneously determined, and the LODs for PAR and PAP are 0.98 nM and 9.5 nM, respectively. The results agreed well with data obtained using other electrodes. The sensor is reproducible and stable over eight weeks, and interference by biologically essential compounds is negligible. The method was applied to the determination of PAR in pharmaceutical formulations and in spiked blood serum and urine samples. The relative standard deviations ranged from 97.5 to 102.0%.

Trace Determination of Hg(II) in Human Saliva Using Disposable Electrochemically Pretreated Graphite Pencil Electrode Surfaces.

An electrochemically pretreated graphite pencil electrode (PGPE) was designed to assay trace levels of Hg(II) in human saliva. The GPE was pretreated in 0.1 mol/L nitric acid by cycling the potential between -1.6 and -0.6 V for 60 cycles at a scan rate of 50 mV/s. The effects of pretreatment conditions, including media constituents, pH, and various electrochemical techniques and parameters, were analyzed and optimum conditions determined. Square wave anodic stripping voltammetry (SWASV) was used for the determination of Hg(II). The calibration curve obtained under optimum conditions showed that the linear range of the PGPE was from 10.0 × 10-9 mol/L to 175.0 × 10-9 mol/L with a detection limit of 3.0 × 10-9 mol/L (S/N = 3). Relative to non-pretreated GPE surfaces, electrochemical pretreatment improved the electrochemical performance of GPE surfaces in detecting Hg(II). The present analytical method was used to measure Hg(II) released from dental amalgam in human saliva.

New bipyridine gold(III) dithiocarbamate-containing complexes exerted a potent anticancer activity against cisplatin-resistant cancer cells independent of p53 status.

We synthesized, characterized and tested in a panel of cancer cell lines, nine new bipyridine gold(III) dithiocarbamate-containing complexes. In vitro studies demonstrated that compounds 1, 2, 4, 5, 7 and 8 were the most cytotoxic in prostate, breast, ovarian cancer cell lines and in Hodgkin lymphoma cells with IC50 values lower than the reference drug cisplatin. The most active compound 1 was more active than cisplatin in ovarian (A2780cis and 2780CP-16) and breast cancer cisplatin-resistant cells. Compound 1 determined an alteration of the cellular redox homeostasis leading to increased ROS levels, a decrease in the mitochondrial membrane potential, cytochrome-c release from the mitochondria and activation of caspases 9 and 3. The ROS scavenger NAC suppressed ROS generation and rescued cells from damage. Compound 1 resulted more active in tumor cells than in normal human Mesenchymal stromal cells. Gold compounds were active independent of p53 status: exerted cytotoxic effects on a panel of non-small cell lung cancer cell lines with different p53 status and in the ovarian A2780 model where the p53 was knocked out. In conclusion, these promising results strongly indicate the need for further preclinical evaluation to test the clinical potential of these new gold(III) complexes.

Synthesis, characterization and theoretical calculations of (1,2-diaminocyclohexane)(1,3-diaminopropane)gold(III) chloride complexes: in vitro cytotoxic evaluations against human cancer cell lines.

The gold(III) complexes of the type (1,2-diaminocyclohexane)(1,3-diaminopropane)gold(III) chloride, [(DACH)Au(pn)]Cl3, [where DACH = cis-, trans-1,2- and S,S-1,2-diaminocyclohexane and pn = 1,3-diaminopropane] have been synthesized and characterized using various spectroscopic and analytical techniques including elemental analysis, UV-Vis and FTIR spectroscopy; solution as well as solid-state NMR measurements. The solid-state (13)C NMR shows that 1,2-diaminocyclohexane (1,2-DACH) and 1,3-diaminopropane (pn) are strongly bound to the gold(III) center via N donor atoms. The stability of the mixed diamine ligand gold(III) was checked by UV-Vis spectroscopy and NMR measurements. The molecular structure of compound 1 (containing cis-1,2-DACH) was determined by X-ray diffraction analysis. The structure of 1 consists of [(cis-DACH)Au(pn)](3+) complex ion and chloride counter ions. Each gold atom in the complex ion adopts a distorted square-planar geometry. The structural details and relative stabilities of the four possible isomers of the complexes were also estimated at the B3LYP/LANL2DZ level of theoretical calculations. The computational study demonstrates that trans- conformations are slightly more stable than the cis- conformations. The antiproliferative effects and cytotoxic properties of the mixed ligand gold(III) complexes were evaluated in vitro on human gastric SGC7901 and prostate PC3 cancer cells using MTT assay. The antiproliferative study of the gold(III) complexes on PC3 and SGC7901 cells indicate that complex 3 (containing 1S,2S-(+)-1,2-(DACH)) is the most effective antiproliferative agent. The IC50 data reveal that the in vitro cytotoxicity of complex 3 against SGC7901 cancer cells manifested similar and very pronounced cytotoxic effects with respect to cisplatin. Moreover, the electrochemical behavior, and the interaction of complex 3 with two well-known model proteins, namely, hen egg white lysozyme and bovine serum albumin is also reported.

Adsorptive stripping voltammetry of antibiotics rifamycin SV and rifampicin at renewable pencil electrodes.

Adsorptive stripping voltammetry of antibiotics of rifamycin SV (RSV) and rifampicin (RIF) was investigated by cyclic voltammetry and differential pulse voltammetry using a renewable pencil graphite electrode (PGE). The nature of the oxidation process of RSV and RIF taking place at the PGE was characterized. The results show that the determination of highly sensitive oxidation peak current is the basis of a simple, accurate and rapid method for quantification of RSV and RIF in bulk forms, pharmaceutical formulations and biological fluids by differential pulse adsorptive stripping voltammetry (DPASV). Factors influencing the trace measurement of RSV and RIF at PGE are assessed. The limits of detection for the determination of RSV and RIF in bulk forms are 6.0 × 10(-8) mol/L and 1.3 × 10(-8) mol/L, respectively. Moreover, the proposed procedure was successfully applied to assay both RSV and RIF in pharmaceutical formulations and in biological fluids. The capability of the proposed procedure for simultaneous assay of antibiotics RSV-isoniazid and RIF-isoniazid was achieved. The statistical analysis and calibration curve data for trace determination of RSV and RIF are reported.

Gold nanoparticle-modified graphite pencil electrode for the high-sensitivity detection of hydrazine.

A novel gold nanoparticle-modified graphite pencil electrode (AuNP-GPE) is prepared just by immersing a bare GPE in AuNP solution, followed by heating for 15 min. The bare and modified GPEs are characterized by FE-SEM imaging and cyclic voltammetry. The AuNP-GPEs showed excellent electrocatalytic activities with respect to hydrazine oxidation, with good reproducibility. To reduce the quantification and detection limits, and increase the hydrazine sensitivity, the pH and square wave voltammetry parameters are optimized. A square wave voltammetry study as a function of the hydrazine concentration showed that the AuNP-GPE detector's quantification limit was 100 nmol L(-1) hydrazine, much lower than the value obtained using amperometry (10 µmol L(-1)). The limits of detection (at 3σ) for hydrazine sensing at AuNP-GPEs using square wave voltammetry and amperometry were 42 nmol L(-1) and 3.07 µmol L(-1). Finally, the modified electrode was used to determine the hydrazine concentration in drinking water, and satisfactory results are obtained. This simple, rapid, low-cost method for fabricating a modified electrode is an attractive approach to the development of new sensors.

Visual detection of single-base mismatches in DNA using hairpin oligonucleotide with double-target DNA binding sequences and gold nanoparticles.

We describe a hairpin oligonucleotide (HO) with double-target DNA binding sequences in the loop and 11-base in the stem for visual detection of single-base mismatches (SBM) in DNA with highly specificity. The thiol-modified HO was immobilized on gold nanoparticle (Au-NP) surface through a self-assembling process. The strategy of detecting SBM depends on the unique molecular recognition properties of HO to the perfect-matched DNA and SBM to generate different quantities of duplex DNA on the Au-NP surface, which are captured on the test zone of lateral flow test strip via the DNA hybridization reaction between the duplex DNA and preimmobilized DNA probe. Accumulation of Au-NPs produces the characteristic red bands, enabling visual detection of SBM. It was found that the ability of HO to differentiate perfect-matched DNA and SBM was increased dramatically by incorporating double-target DNA binding sequences in the loop of HO. The signal ratio between perfect-matched DNA and SBM was up to 28, which is much higher than that of conventional HO or molecular beacon. The approach was applied to detect the mutation sites, Arg142Cys and Gly529Ile, of transglutaminase 1 gene in autosomal recessive congenital ichthyosis. The results presented here show that the new HO is a potential molecular recognition probe for the future development of nucleic acid-based biosensors and bioassays. The approach can be used for point-of-care diagnosis of genetic diseases and detecting infectious agents or warning against bio-warfare agents.

Aptamer-functionalized gold nanoparticles as probes in a dry-reagent strip biosensor for protein analysis.

The highly specific molecular recognition properties of aptamers are combined with the unique optical properties of gold nanoparticles for the development of a dry-reagent strip biosensor that enables qualitative (visual)/quantitative detection of protein within minutes. A model system comprising thrombin as an analyte and a pair of aptamer probes is used to demonstrate the proof-of-concept on the conventional lateral flow test strip. The assay avoids the multiple incubation and washing steps performed in most current aptamer-based protein analyses. Although qualitative tests are realized by observing the color change of the test zone, quantitative data are obtained by recording the optical responses of the test zone with a portable "strip reader". The response of the biosensor is linear over the range of 5-100 nM of thrombin with a detection limit of 2.5 nM (S/N = 3). By comparing the analytical performances of the aptamer-based strip biosensor with the antibody-based strip sensor, we can demonstrate that aptamers are equivalent or superior to antibodies in terms of specificity and sensitivity, respectively. The sensor was used successfully for detection of thrombin in human plasma samples. It shows great promise for use of aptamer-functionalized gold nanoparticle probes in dry-reagent strip biosensors for point-of-care or in-field detection of proteins.