Electrochemical DNAzyme sensor for lead based on amplification of DNA-Au bio-bar codes

An electrochemical DNAzyme sensor for sensitive and selective detection of lead ion (Pb(2+)) has been developed, taking advantage of catalytic reactions of a DNAzyme upon its binding to Pb(2+) and the use of DNA-Au bio-bar codes to achieve signal enhancement. A specific DNAzyme for Pb(2+) is immobilized onto an Au electrode surface via a thiol-Au interaction. The DNAzyme hybridizes to a specially designed complementary substrate strand that has an overhang, which in turn hybridizes to the DNA-Au bio-bar code (short oligonucleotides attached to 13 nm gold nanoparticles). A redox mediator, Ru(NH3)6(3+), which can bind to the anionic phosphate of DNA through electrostatic interactions, serves as the electrochemical signal transducer. Upon binding of Pb(2+) to the DNAzyme, the DNAzyme catalyzes the hydrolytic cleavage of the substrate, resulting in the removal of the substrate strand along with the DNA bio-bar code and the bound Ru(NH3)6(3+) from the Au electrode surface. The release of Ru(NH3)6(3+) results in lower electrochemical signal of Ru(NH3)6(3+) confined on the electrode surface. Differential pulse voltammetry (DPV) signals of Ru(NH3)6(3+) provides quantitative measures of the concentrations of Pb(2+), with a linear calibration ranging from 5 nM to 0.1 microM. Because each nanoparticle carries a large number of DNA strands that bind to the signal transducer molecule Ru(NH3)6(3+), the use of DNA-Au bio-bar codes enhances the detection sensitivity by five times, enabling the detection of Pb(2+) at a very low level (1 nM). The DPV signal response of the DNAzyme sensor is negligible for other divalent metal ions, indicating that the sensor is highly selective for Pb(2+). Although this DNAzyme sensor is demonstrated for the detection of Pb(2+), it has the potential to serve as a general platform for design sensors for other small molecules and heavy metal ions.     

Electrochemical NO2 sensor using a NiFe1.9Al0.1O4 oxide spinel electrode

A novel solid-state electrochemical sensor using (Sc2O3)0.08(ZrO2)0.92 (ScSZ) electrolyte solid and a NiFe1.9Al0.1O4 oxide spinel electrode was tested for the detection of NO2 at temperatures greater than 700 degrees C for automobile applications. The sensor was found to respond rapidly, reproducibly, and selectively to NO2 at 703 and 740 degrees C. The response time of the sensor was approximately 8 s, and the recovery time was 10 s at both 703 and 741 degrees C. The response of the sensor was highly reproducible to the change in concentration of NO2 and also showed negligible cross-sensitivity to potentially interfering gases such as O2, CO, and CH4 in the gas stream.     

Detection of Nitric Oxide from Living Cells Using Polymeric Zinc Organic Framework‐Derived Zinc Oxide Composite with Conducting Polymer

Sensitive and selective detection of nitric oxide (NO) in the human body is crucial since it has the vital roles in the physiological and pathological processes. This study reports a new type of electrochemical NO biosensor based on zinc‐dithiooxamide framework derived porous ZnO nanoparticles and polyterthiophene‐rGO composite. By taking advantage of the synergetic effect between ZnO and poly(TTBA‐rGO) (TTBA = 3′‐(p‐benzoic acid)‐2,2′:5′,2″‐terthiophene, rGO = reduced graphene oxide) nanocomposite layer, the poly(TTBA‐rGO)/ZnO sensor probe displays excellent electrocatalytic activity and explores to detect NO released from normal and cancer cell lines. The ZnO is immobilized on a composite layer of poly(TTBA‐rGO). The highly porous ZnO offers a high electrolyte accessible surface area and high ion–electron transport rates that efficiently catalyze the NO reduction reaction. Amperometry with the modified electrode displays highly sensitive response and wide dynamic range of 0.019–76 × 10^?6m with the detection limit of 7.7 ± 0.43 × 10^?9m . The sensor probe is demonstrated to detect NO released from living cells by drug stimulation. The proposed sensor provides a powerful platform for the low detection limit that is feasible for real‐time analysis of NO in a biological system.     

Gas nanosensor design packages based on tungsten oxide: mesocages, hollow spheres, and nanowires

Achieving proper designs of nanosensors for highly sensitive and selective detection of toxic environmental gases is one of the crucial issues in the field of gas sensor technology, because such designs can lead to the enhancement of gas sensor performance and expansion of their applications. Different geometrical designs of porous tungsten oxide nanostructures, including the mesocages, hollow spheres and nanowires, are synthesized for toxic gas sensor applications. Nanosensor designs with small crystalline size, large specific surface area, and superior physical characteristics enable the highly sensitive and selective detection of low concentration (ppm levels), highly toxic NO(2) among CO, as well as volatile organic compound gases, such as acetone, benzene, and ethanol. The experimental results showed that the sensor response was not only dependent on the specific surface area, but also on the geometries and crystal size of materials. Among the designed nanosensors, the nanowires showed the highest sensitivity, followed by the mesocages and hollow spheres-despite the fact that mesocages had the largest specific surface area of 80.9?m(2)?g( - 1), followed by nanowires (69.4?m(2)?g( - 1)), and hollow spheres (6.5?m(2)?g( - 1)). The nanowire sensors had a moderate specific surface area (69.4?m(2)?g( - 1)) but they exhibited the highest sensitivity because of their small diameter (～5?nm), which approximates the Debye length of WO(3). This led to the depletion of the entire volume of the nanowires upon exposure to NO(2), resulting in an enormous increase in sensor resistance.     

A hybrid gas-sensing material based on porous carbon fibers and a TiO2 photocatalyst

The electrode material for a gas sensor was prepared from electrospun carbon fibers. The electrode material was chemically activated to enlarge the gas adsorption sites, and carbon nanotubes (CNTs) were embedded into the polyacrylonitrile-based carbon fibers to enhance their electrical conductivity. TiO₂ was used as an additive to promote NO gas degradation and to improve their response in NO gas sensing. The chemical activation process increased the specific surface area and pore volume of the carbon fibers to values in excess of 2000 m²/g and 1.0 ml/g, respectively. To investigate the photocatalytic effects of the TiO₂ additive, NO gas sensing was conducted in the presence and absence of ultraviolet irradiation. The subsequent results indicate that the response of the sensor was improved due to the TiO₂-photocatalyzed decomposition of NO gas and the subsequent adsorption of HNO₂, NO₂, and HNO₃. The electrical resistance of the sensor was significantly reduced during NO gas sensing due to the electron hopping effect, and highly efficient gas adsorption was observed. In conclusion, a sensitive gas sensor electrode was realized by fabricating a porous material to increase the efficiency of gas adsorption, adding CNTs to improve its electrical conductivity and adding TiO₂ photocatalysts to promote NO decomposition.     

Preparation and characterization of an electrogenerated chemiluminescence sensor by electrochemical grafting of 4-nitrophenyl diazonium salts onto a glass carbon electrode

An ECL sensor was fabricated by immobilization of a tris(2,2'-bipyridyl)ruthenium (II) complex (Ru(bpy)3(2+)) to an amine group-modified GC electrode (NH2-GC electrode). Here, the NH2-GC electrode was prepared by electrochemical reduction of a nitro group-modified GC electrode in 0.1 M KCl ethanol solution under H2 gas, which was followed by electrochemical grafting of 4-nitrophenyl diazonium salts in 0.1 M NBu4BF4 acetonitrile solution onto the GC electrode. The prepared ECL sensor was successfully confirmed via cyclic voltammetry, contact angle, scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and ECL spectrometry. The contact angle for the surface of the GC electrode, NO2-GC electrode, and NH2-GC electrod was 88.4 degrees, 67.4 degrees, and 52.4 degrees, respectively. The stability of the ECL sensor was investigated under continuous cyclic potential scanning for 55 cycles and the ECL intensity remained at 55%. The prepared ECL electrode can be expected to immobilize enzymes for preparation of the ECL biosensor to detect target molecules.     

Carbon nanotube composite coated platinum electrode for detection of Ga(III)

This study demonstrates the application of composite multi-walled carbon nanotube (MWCNT) polyvinylchloride (MWNT-PVC) based on 7-(2-hydroxy-5-methoxybenzyl)-5,6,7,8,9,10-hexahydro-2H benzo [b][1,4,7,10,13] dioxa triaza cyclopentadecine-3,11(4H,12H)-dione ionophore for gallium sensor. The sensor shows a good Nernstian slope of 19.68 ± 0.40 mV/decade in a wide linear range concentration of 7.9 × 10(-7) to 3.2 × 10(-2)M of Ga(NO(3))(3). The detection limit of this electrode is 5.2 × 10(-7)M of Ga(NO(3))(3). This proposed sensor is applicable in a pH range of 2.7-5.0. It has a short response time of about 10s and has a good selectivity over nineteen various metal ions. The practical analytical utility of this electrode is demonstrated by measurement of Ga(III) in river water.     

Polymer single-nanowire optical sensors

We report highly versatile nanosensors using polymer single nanowires. On the basis of the optical response of waveguiding polymer single nanowires when exposed to specimens, functionalized polymer nanowires are used for humidity sensing with a response time of 30 ms and for NO 2 and NH 3 detection down to subparts-per-million level. The compact and flexible sensing scheme shown here may be attractive for very fast detection in physical, chemical, and biological applications with high sensitivity and small footprint.     

Gas-sensing properties of catalytically modified WO/sub 3/ with copper and vanadium for NH/sub 3/ detection

Ammonia gas detection by pure and catalytically modified WO/sub 3/-based gas sensors was analyzed. Sensor response of pure tungsten oxide to NH/sub 3/ was unsatisfactory, probably due to the unselective oxidation of ammonia into NO/sub x/. Copper and vanadium were introduced in different concentrations and the resulting material was annealed at different temperatures in order to improve the sensing properties for NH/sub 3/ detection. The introduction of Cu and V as catalytic additives improved the sensor response to NH/sub 3/. Possible reaction mechanisms of NH/sub 3/ over these materials are discussed. Sensor responses to other gases like NO/sub 2/ or CO and interference of humidity on ammonia detection were also analyzed so as to choose the best sensing element.     

A highly selective lead-sensitive electrode with solid contact based on ionic liquid

A new polyvinylchloride membrane sensor for Pb(2+) with solid contact based on ionic liquid has been prepared. The electrode shows a Nernstian response for lead ions over a wide concentration range (1×10(-8) to 1×10(-1) mol L(-1)) and the slope of 29.8 mV/decade. The limit of detection is 4.3×10(-9) mol L(-1). It has a fast response time of 5-7 s and can be used for 4 months without any divergence in potential. The proposed sensor is not pH sensitive in the range 3.5-7.3 and shows a very good discriminating ability towards Pb(2+) ion in comparison with some alkali, alkaline earth, transition and heavy metal ions. It was successfully applied as an indicator electrode in potentiometric titration of lead ions with K(2)CrO(4) and for direct determination of Pb(2+) ions in real sample solution.     

Acoustic wave-based sensors using mode conversion in periodic gratings

Using periodic gratings etched into the surface of a piezoelectric plate, surface acoustic waves (SAW) can be converted into bulk waves and vice versa with high efficiency. If parallel grating structures are fabricated on opposite surfaces of a piezoelectric plate, a SAW also can be directed from one surface to the other. Using such structures, acoustic wave-based sensors can be designed that utilize SAW for the detection of chemical analytes on an electrode-free surface, i.e., the back surface. As a result, spurious sensor response and electrode aging that may occur when a chemical analyte comes in contact with the transducers are minimized. The design principles of these grating-based SAW sensors are explained, and the mass sensitivity is investigated using chemical vapor deposited thin polymer films, a type of material used in many practical chemical sensor applications. Experimental results are presented for the detection of nitrogen dioxide (NO(2 )) in sub-ppm concentrations.     

MWCNT-polymer composites as highly sensitive and selective room temperature gas sensors

Multi-walled carbon nanotubes (MWCNTs)-polymer composite-based hybrid sensors were fabricated and integrated into a resistive sensor design for gas sensing applications. Thin films of MWCNTs were grown onto Si/SiO(2) substrates via xylene pyrolysis using the chemical vapor deposition technique. Polymers like PEDOT:PSS and polyaniline (PANI) mixed with various solvents like DMSO, DMF, 2-propanol and ethylene glycol were used to synthesize the composite films. These sensors exhibited excellent response and selectivity at room temperature when exposed to low concentrations (100 ppm) of analyte gases like NH(3) and NO(2). The effect of various solvents on the sensor response imparting selectivity to CNT-polymer nanocomposites was investigated extensively. Sensitivities as high as 28% were observed for an MWCNT-PEDOT:PSS composite sensor when exposed to 100 ppm of NH(3) and - 29.8% sensitivity for an MWCNT-PANI composite sensor to 100 ppm of NO(2) when DMSO was used as a solvent. Additionally, the sensors exhibited good reversibility.     

Lanthanide Recognition: Monitoring of Praseodymium(III) by a Novel Praseodymium(III) Microsensor Based on N′-(Pyridin-2-Ylmethylene)Benzohydrazide

In this work, for the first time, we introduce a highly selective and sensitive praseodymium(III) microsensor. Npsila-(pyridin-2-ylmethylene)benzohydrazide (PBH) was used as a membrane-active component to prepare a highly sensitive Pr(III)-selective polymeric membrane microelectrode. The electrode exhibits a Nernstian response toward Pr(III) ions over a very wide concentration range (1.0 times 10^-3 -1.0 times 10^-8 M), with a detection limit of 7.0 times 10^-9 M (~1 ng/ml). It has a very fast response time in the whole concentration range (~10 s). The proposed microelectrode can be used for at least six weeks without any considerable divergence in potentials. The proposed membrane sensor revealed very good selectivity toward Pr(III) ions over a wide variety of other metal ions including common alkali, alkaline earth and, specially, lanthanide ions. It could be used in the pH range of 3.0-8.5. The Pr(III) microelectrode was used as an indicator electrode for the titration of 20 ml of a 1.0 times 10^-6 M Pr(III) ions with a 1.0 times 10^-4 M EDTA.     

Improved planar amperometric nitric oxide sensor based on platinized platinum anode. 1. Experimental results and theory when applied for monitoring NO release from diazeniumdiolate-doped polymeric films

An improved miniature amperometric nitric oxide sensor design with a planar sensing tip (ranging from 150 microm to 2 mm in diameter) is reported. The sensor is fabricated using a platinized platinum anode and a Ag/AgCl cathode housed behind a microporous poly(tetrafluoroethylene) (PTFE; Gore-tex) gas-permeable membrane. Platinization of the working platinum electrode surface dramatically improves the analytical performance of the sensor by providing approximately 10-fold higher sensitivity (0.8-1.3 pA/nM), approximately 10-fold lower detection limit (< or =1 nM), and extended (at least 3-fold) stability (>3 d) compared to sensors prepared with bare Pt electrodes. These improvements in performance arise from increasing the kinetics and lowering the required potential for the 3-electron oxidation of NO to nitrate, relative to that observed using a nonplatinized working electrode. The outer porous PTFE membrane provides complete selectivity for NO over nitrite ions (up to 10 mM nitrite). The new sensor is applied for surface measurements of NO released from diazeniumdiolate-loaded silicone rubber films (SR-DACA-6/N(2)O(2)). The effects of sensor size (for sensor dimensions of 0.15-, 1-, and 2-mm o.d.) and the distance of the sensor from the surface of the NO-emitting polymer film are investigated via experiments as well as theoretical calculations. A significant analyte trapping effect is demonstrated, the degree of which depends on the sensor size and its distance from the surface. It is further demonstrated that surface NO concentrations for fresh SR-DACA-6/N(2)O(2) loaded films are also influenced by the polymer film thickness, with thicker films generating higher surface concentrations of NO.     

Selective voltammetric determination of norepinephrine in the presence of acetaminophen and tryptophan on the surface of a modified carbon nanotube paste electrode

A new electrochemical sensor for the determination of norepinephrine (NE), acetaminophen (AC) and tryptophan (TRP) is described. The sensor is based on carbon paste electrode (CPE) modified with 5-mino-3′,4′-dimethyl-biphenyl-2-ol (5ADB) and takes the advantages of carbon nanotubes (CNTs), which makes the modified electrode highly sensitive for the electrochemical detection of these compounds. Under the optimum pH of 7.0, the oxidation of NE occurs at a potential about 170 mV less positive than that of the unmodified CPE. Also, square wave voltammetry (SWV) was used for the simultaneous determination of NE, AC and TRP at the modified electrode.     

In vivo electrochemical detection of nitric oxide in tumor-bearing mice

Interest in elucidating the mechanisms of action of various classes of anticancer agents and exploring the pathways of the induced-nitric oxide (NO) release provides an impetus to conceive a better designed approach to locally detect NO in tumors, in vivo. We report here on the first use of an electrochemical sensor that allows the in vivo detection of NO in tumor-bearing mice. In a first step, we performed the electrochemical characterization of a stable electroactive probe, K4Fe(CN)6, directly injected into the liquid microenvironment especially created around the electrode in the tumor. Second, the ability of the inserted electrode system to detect the presence of NO itself in the tumoral tissue was achieved by using the chemically modified Pt/Ir electrode as NO sensor and two NO donor molecules: diethylammonium (Z)-1-(N,N-diethylamino)diazen-1-ium 1,2-diolate (DEA-NONOate) and (Z)-1-[N-(2-aminopropyl)-N-(2-ammonio propyl)amino]diazen-1-ium 1,2-diolate (PAPA-NONOate). These two NO donor molecules allowed proving the electrochemical detection of (i) directly injected exogenous NO phosphate buffer solution into the tumor (decomposed DEA-NONOate) and (ii) biomimetically induced endogeneous release of NO in the tumoral tissue, upon injection of PAPA-NONOate into the tumor. This approach could be applied to the in vivo study of candidate anticancer drugs acting on the NO pathways.     

An Amperometric Solid State NO Sensor Using a LaGaO3 Electrolyte for Monitoring Exhaust Gas

A LaGaO₃-based electrochemical sensor in the amperometric mode was demonstrated as highly sensitive to NO in the temperature range 500-700°C. Sensor performance was found dependent on the Ni doping of LaGaO₃. Using optimized electrode materials, highest sensitivity was achieved as high as 2409 µ A/decade (at 550°C) when Ni doping to electrolyte was 7 mol%. The selectivity of the sensor was found very high to NO with respect to the typical coexisting gases in the exhaust environment. The sensing principle was observed to follow the mixed potential behavior.     

A highly sensitive chemical gas detecting transistor based on highly crystalline CVD-grown MoSe<Subscript>2</Subscript> films

Layered semiconductors with atomic thicknesses are becoming increasingly important as active elements in high-performance electronic devices owing to their high carrier mobilities,large surface-to-volume ratios,and rapid electrical responses to their surrounding environments.Here,we report the first implementation of a highly sensitive chemical-vapor-deposition-grown multilayer MoSe2 field-effect transistor (FET) in a NO2 gas sensor.This sensor exhibited ultra-high sensitivity (S =ca.1,907 for NO2 at 300 ppm),real-time response,and rapid on-off switching.The high sensitivity of our MoSe2 gas sensor is attributed to changes in the gap states near the valence band induced by the NO2 gas absorbed in the MoSe2,which leads to a significant increase in hole current in the off-state regime.Device modeling and quantum transport simulations revealed that the variation of gap states with NO2 concentration is the key mechanism in a MoSe2 FET-based NO2 gas sensor.This comprehensive study,which addresses material growth,device fabrication,characterization,and device simulations,not only indicates the utility of MoSe2 FETs for high-performance chemical sensors,but also establishes a fundamental understanding of how surface chemistry influences carrier transport in layered semiconductor devices.     

A chemically-responsive nanojunction within a silver nanowire

The formation of a nanometer-scale chemically responsive junction (CRJ) within a silver nanowire is described. A silver nanowire was first prepared on glass using the lithographically patterned nanowire electrodeposition method. A 1-5 nm gap was formed in this wire by electromigration. Finally, this gap was reconnected by applying a voltage ramp to the nanowire resulting in the formation of a resistive, ohmic CRJ. Exposure of this CRJ-containing nanowire to ammonia (NH(3)) induced a rapid (<30 s) and reversible resistance change that was as large as ΔR/R(0) = (+)138% in 7% NH(3) and observable down to 500 ppm NH(3). Exposure to water vapor produced a weaker resistance increase of ΔR/R(0,H(2)O) = (+)10-15% (for 2.3% water) while nitrogen dioxide (NO(2)) exposure induced a stronger concentration-normalized resistance decrease of ΔR/R(0,NO(2)) = (-)10-15% (for 500 ppm NO(2)). The proposed mechanism of the resistance response for a CRJ, supported by temperature-dependent measurements of the conductivity for CRJs and density functional theory calculations, is that semiconducting p-type Ag(x)O is formed within the CRJ and the binding of molecules to this Ag(x)O modulates its electrical resistance.     

Hybrid fluorometric flow analyzer for ammonia

We describe a robust, highly sensitive instrument for the determination of ambient ammonia. The instrument uses two syringe pumps to handle three liquids. The flow configuration is a hybrid between traditional flow injection (FI) and sequential injection (SI) schemes. This hybrid flow analyzer spends approximately 87% of its time in the continuous flow FI mode, providing the traditional FI advantages of high baseline stability and sensitivity. The SI fluid handling operation in the remaining time makes for flexibility and robustness. Atmospheric ammonia is collected in deionized water by a porous membrane diffusion scrubber at 0.2 L/min with quantitative collection efficiency, derivatized on-line to 1-sulfonatoisoindole, and measured by fluorometry. In the typical range for ambient ammonia (0-20 ppbv), response is linear (r2 = 0.9990) with a S/N = 3 limit of detection of 135 pptv (15 nM for 500 microL of injected NH4+(aq)) with an inexpensive light emitting diode photodiode-based detector. Automated operation in continuously repeated, 8-min cycles over 9 days shows excellent overall precision (n = 1544 p(NH)3 = 5 ppbv, RSD = 3%). Precision for liquid-phase injections is even better (n = 1520, [NH4+(aq)] = 2.5 microM, RSD = 2%). The response decreases by 3.6% from 20 to 80% relative humidity.