Two-dimensional molecular imprinting approach for the electrochemical detection of trinitrotoluene

In this work, we demonstrated a sensitive and selective electrochemical sensing protocol for the detection of TNT prepared from alkanethiols self-assembled on AuNPs modified glassy carbon (GC) electrode with preadsorbed templates of TNT. It demonstrated that the 2D molecular imprinting monolayers (MIMs) can provide a better site accessibility and lower mass-transfer resistance, while the AuNPs can enhance electrode conductivity, facilitate the electron transfer and increase the amount of TNT-imprinted sites. The prepared sensor showed not only high selectivity toward TNT in comparison to other similar nitroaromatic compounds (NACs), but also a wide linear range over TNT concentration from 4.0 × 10⁻⁸ to 3.2 × 10⁻⁶ M with a detection limit of 1.3 × 10⁻⁸ M (S/N = 3). Moreover, the imprinted sensor has been applied to the determination of TNT in spiked environmental water samples and shows promise for fast and sensitive measurement of trace levels of TNT in real samples.     

All fiber-optic sensing of light using side-polished fiber overlaid with photoresponsive liquid crystals

This study presents a highly sensitive, all-fiber sensor for in situ detecting light. A fiber-optic light sensing platform was created by overlaying an in-line side-polished fiber (SPF) with a photoresponsive liquid crystal (P-LC) consisting of an azobenzene dye, a chiral dopant, and a nematic LC. The resulting P-LC overlaid SPF light sensor is sensitive to three different light sources, including 380 nm light emitting diode (LED), mercury lamp, and office ceiling lights. Under the light illumination, the energy of irradiation from short wavelengths of light (<450 nm) initiates the trans-to-cis photoisomerization of azobenzene. The photochemical LC-phase transition induced by the generated cis-moiety of azobenzene changes the refractive index of LC-overlaid side-polished area. Light illumination increased the attenuation of the input laser signal. After turning off the illumination, the attenuation returned to its original value, allowing the fiber-optic light sensor to be reused. The sensitivity of the resulting fiber-optic light sensor was 0.16 dB/(μW/cm²) with a detection limit of 5 μW/cm² and 0.06 dB/lx with a detection limit of 45 lx when a 380 nm LED and office ceiling lights were used as illumination sources, respectively. The detection limit increased from 45 to 12 lx when P-LC containing 20 wt% azobenzene was used as light sensing material. The proposed fiber-based light sensor has potential use in harsh environments, such as severely humid and corrosive environments, which could damage mechanical and electronic light sensors.     

Layer-by-layer self-assembly CdTe quantum dots and molecularly imprinted polymers modified chemiluminescence sensor for deltamethrin detection

A novel chemiluminescence sensor for determination deltamethrin was firstly reported based on CdTe quantum dots and deltamethrin imprinted polymers by layer-by-layer assembly modified on the surface of slide glass, whose shape was the same as the bottom of 96 well micro-plate. The binding characteristic of the imprinted polymers to deltamethrin was evaluated by equilibrium binding experiments and the morphology was studied by scanning electronic microscope. Scatchard analysis was carried out to estimate the binding parameters of the imprinted polymers. The water-soluble TGA-capped CdTe quantum dots were prepared. NaHTe was used as the Te precursor for CdTe quantum dots synthesis. Under the optimum conditions, the chemiluminescence intensity had a linear relationship against the concentration of deltamethrin over the range of 0.053-46.5 μg mL⁻¹ with a lower detection limit of 0.018 μg mL⁻¹. The regression equation was ΔI = 2225 + 107c (c: μg mL⁻¹) with a correlation coefficient of 0.9973. The relative standard deviation was 4.7%. The presented method was applied successfully to the determination of deltamethrin in real samples with satisfactory results.     

Molecularly imprinted ligand-exchange recognition assay of DNA by SPR system using guanosine and guanine recognition sites of DNA

Molecular imprinting polymer (MIP) as a recognition element for sensors are increasingly of interest and MIP-SPR have started to appear in the literature. In this study, we have proposed a novel surface imprinting method for DNA recognition and determination by methacryl-amidohistidine-platinum(II) [MAH-Pt(II)] as a new metal-chelating monomer via metal coordination–chelation interactions and guanosine/guanine templates of DNA. The study includes the measurement of binding interaction of molecular imprinted surface plasmon resonance (SPR) sensor via ligand interaction and recognition selectivity studies of guanosine and guanine imprinted polymers with respect to guanine and dsDNA. Adsorption isotherms of adenosine, guanosine, guanine, adenine, ssDNA and dsDNA were plotted and affinity constants for guanosine and guanine imprinted films were also calculated.     

Development of molecularly imprinted electrochemical sensor with titanium oxide and gold nanomaterials enhanced technique for determination of 4-nonylphenol

4-Nonylphenol (4-NP) was reported to affect the health of wildlife and humans through altering endocrine function. A novel electrochemical sensor for sensitive and fast determination of 4-NP was developed. Titanium oxide (TiO₂) nanoparticles and gold nanoparticles (AuNPs) were introduced for the enhancement of electron conduction and sensitivity. 4-NP-imprinted functionalized AuNPs composites with specific binding sites for 4-NP was modified on electrode. The resulting electrodes were characterized by cyclic voltammetry (CV). Rebinding experiments were carried out to determine the specific binding capacity and selective recognition. The linear range was over the range from 4.80 × 10⁻⁴ to 9.50 × 10⁻⁷ mol L⁻¹, with the detection limit of 3.20 × 10⁻⁷ mol L⁻¹ (S/N = 3). The sensor was successfully employed to detect 4-NP in real samples.     

A highly selective triphenylamine-based indolylmethane derivatives as colorimetric and turn-off fluorimetric sensor toward Cu detection by deprotonation of secondary amines

A new triphenylamine-based fluorogenic probe bearing an indolylmethane unit (R1) was developed as a fluorescent chemosensor with high selectivity toward Cu²⁺ over other cations tested. The new probe R1 only sensed Cu²⁺ among heavy and transition metal (HTM) ions in CH₃CN/H₂O (70/30, v/v) solution. The capture of Cu²⁺ by the receptor resulted in deprotonation of the secondary amine conjugated to the triphenylamine, so that the electron-donation ability of the “N” atom would be greatly enhanced; thus sensor showed a 250 nm change in the new absorption band (from 291 nm to 541 nm) and a large colorimetric response, it also exhibited the large decrease in fluorescence intensity at 378 nm and affinity to Cu²⁺ over other cations such as Hg²⁺, Fe³⁺, Pb²⁺, Zn²⁺, Cd²⁺, Ni²⁺, Co²⁺ and Mn²⁺ make this compound a useful chemosensor for Cu²⁺ detection in CH₃CN/H₂O (70/30, v/v) mixture. The probe R1 (c = 1.0 × 10⁻⁶ M) displayed significant fluorescence change and colorimetric change upon addition of Cu²⁺ among the metal ions examined.     

Synthesis of Bi and Gd doped ZnB2O4 for evaluation as potential materials in luminescent display applications

A series of Bi³⁺ and Gd³⁺ doped ZnB₂O₄ phosphors were synthesized with solid state reaction technique. X-ray diffraction technique was employed to study the structure of prepared samples. Excitation and emission spectra were recorded to investigate the luminescence properties of phosphors. The doping of Bi³⁺ or Gd³⁺ with a small amount (no more than 3 mol%) does not change the structure of prepared samples remarkably. Bi³⁺ in ZnB₂O₄ can emit intense broad-band purplish blue light peaking at 428 nm under the excitation of a broad-band peaking at 329 nm. The optimal doping concentration of Bi³⁺ is experimentally ascertained to be 0.5 mol%. The decay time of Bi³⁺ in ZnB₂O₄ changes from 0.88 to 1.69 ms. Gd³⁺ in ZnB₂O₄ can be excited with 254 nm ultraviolet light and yield intense 312 nm emission. The optimal doping concentration of Gd³⁺ is experimentally ascertained to be 5 mol%. The decay time of Gd³⁺ in ZnB₂O₄ changes from 0.42 to 1.36 ms.     

Enhanced room temperature response of SnO2 thin film sensor loaded with Pt catalyst clusters under UV radiation for LPG

The room temperature response characteristics of SnO₂ thin film sensor loaded with platinum catalyst clusters are investigated for LPG under the exposure of ultraviolet radiation. The SnO₂-Pt cluster sensor structures have been prepared using rf sputtering. Combined effect of UV radiation exposure (λ = 365 nm) and presence of Pt catalyst clusters (10 nm thick) on SnO₂ thin film sensor surface is seen to lead to an enhanced response (4.4 × 10³) for the detection of LPG (200 ppm) at room temperature whereas in the absence of UV illumination a comparable response (∼5 × 10³) could be obtained but only at an elevated temperature of 220 °C. The present study therefore investigates the effect of UV illumination on LPG sensing characteristics of SnO₂ sensors loaded with Pt clusters of varying thickness values. Results indicate the possibility of utilizing the sensor structure with novel dispersal of Pt catalyst clusters on SnO₂ film surface for efficient detection of LPG at room temperature under the illumination of UV radiations.     

Detection of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) by displacement of antibodies

A molecular layer with low non-specific binding enabling determination of low concentrations of 3,4-methylenedioxymethamphetamine (MDMA) by the displacement of antibodies has been developed. Antibody Fab′-fragments at various concentrations have been site-directly immobilised on gold and intercalated with a hydrophilic non-ionic polymer that reduces non-specific binding. Bovine serum albumin conjugated with MDMA and various concentrations of anti-MDMA antibodies were bound to the layer. The amount of conjugates and antibodies bound was dependent on the amount of Fab′-fragments in the layer. Antibodies were also bound to the conjugates physisorbed directly onto the gold surface and in mixtures with the polymer or with a lipoamide. A high displacement of antibodies was observed by surface plasmon resonance (SPR) on interaction of MDMA with the different layers in buffer solution. No displacement could, however, be observed in saliva with the pure conjugate layer because of a high non-specific binding of proteins. When the conjugates were coupled to the surface through the antibody Fab-fragment/polymer layer, MDMA concentrations as low as 0.02 ng mL⁻¹ (0.14 nM) could easily be detected in buffer. In diluted saliva the lowest limit of detection was 0.4 ng mL⁻¹ enabling determination of drugs from saliva with a cut-off concentration of 2 ng mL⁻¹. The molecular layer of antibody Fab′-fragments and polymer thus shows great potential for binding conjugates and antibodies that can be displaced on the interaction with very low concentrations of small-sized molecules. A low non-specific binding is guaranteed by the presence of the hydrophilic polymer.     

Effect of thickness of platinum catalyst clusters on response of SnO2 thin film sensor for LPG

This paper reports the sensing response characteristics of rf-sputtered SnO₂ thin films (90 nm thick) loaded with platinum catalyst cluster of varying thickness (2-20 nm) for LPG detection. The enhanced response (5 × 10³) was obtained for 200 ppm LPG with the presence of 10 nm thin and uniformly distributed Pt catalyst clusters on the surface of SnO₂ thin film at a relatively low operating temperature (220 °C). The high response for LPG is shown to be primarily due to the enhanced catalytic activity for adsorbed oxygen on the surface of SnO₂ thin film besides the spill over mechanism at elevated temperature.     

On the reproducibility of field-measured reflectance factors in the context of vegetation studies

This paper describes a study aimed at quantifying uncertainty in field measurements of vegetation canopy hemispherical conical reflectance factors (HCRF). The use of field spectroradiometers is common for this purpose, but the reliability of such measurements is still in question. In this paper we demonstrate the impact of various measurement uncertainties on vegetation canopy HCRF, using a combined laboratory and field experiment employing three spectroradiometers of the same broad specification (GER 1500). The results show that all three instruments performed similarly in the laboratory when a stable radiance source was measured (NEΔL < 1 mW m⁻² sr⁻¹ nm⁻¹ in the range of 400-1000 nm). In contrast, field-derived standard uncertainties (u = SD of 10 consecutive measurements of the same surface measured in ideal atmospheric conditions) significantly differed from the lab-based uncertainty characterisation for two targets: a control (75% Spectralon panel) and a cropped grassland surface. Results indicated that field measurements made by a single instrument of the vegetation surface were reproducible to within ± 0.015 HCRF and of the control surface to within ± 0.006 HCRF (400-1000 nm (± 1σ)). Field measurements made by all instruments of the vegetation surface were reproducible to within ± 0.019 HCRF and of the control surface to within ± 0.008 HCRF (400-1000 nm (± 1σ)). Statistical analysis revealed that even though the field conditions were carefully controlled and the absolute values of u were small, different instruments yielded significantly different reflectance values for the same target. The results also show that laboratory-derived uncertainty quantities do not present a useful means of quantifying all uncertainties in the field. The paper demonstrates a simple method for u characterisation, using internationally accepted terms, in field scenarios. This provides an experiment-specific measure of u that helps to put measurements in context and forms the basis for comparison with other studies.     

Synthesis, characteristics and luminescent properties of a new europium(III) organic complex applied in near UV LED

A novel indane based β-diketone with trifluorobutane in the contraposition, 5-acetylindane-4,4,4-trifluorobutane-1,3-dione (HAITFBD) and its europium(III) ternary complex, Eu(AITFBD)₃phen, were designed and synthesized, where phen was 1,10-phenanthroline. The complex was characterized by IR, UV-visible, thermogravimetric analysis (TGA) and photoluminescence (PL) spectroscopy in details. The results show that the Eu(III) complex exhibits high thermal stability, wide and strong excitation bands from 300 nm to 425 nm when monitored at 611 nm, which matches well with the 380 nm-emitting InGaN chips. The complex exhibits intense red emission under excitation of near UV light due to the f-f transitions of the central Eu³⁺ ion. Based on the emission spectrum, the CIE chromaticity coordinates of the LED are calculated as x = 0.63 and y = 0.34, which is suitable to be used as an efficient red phosphor in fabrication of white LEDs. The fluorescence lifetime and the luminescence quantum yield were also measured. The lowest triplet state energy of the primary ligand AITFBD was measured to be 17,730 cm⁻¹, higher than that of the lowest excitation state energy level of the central Eu³⁺ ion, ⁵D₀, and this suggests that the photoluminescence of the complex is a ligand-sensitized luminescence process (antenna effect). Finally, a bright red light-emitting diode was fabricated by coating the Eu(AITFBD)₃phen complex onto a 380 nm-emitting InGaN chip. All the results indicate that Eu(AITFBD)₃phen can be applied as a red component for fabrication of near ultraviolet-based white light-emitting diodes.     

Leu-Phe分子印迹预组装体系热力学平衡的计算模拟

使用Gaussian03软件研究以Leu-Phe为模板,甲基丙烯酸为功能单体,乙二醇二甲基丙烯酸酯为交联剂,三氟乙酸为助溶剂的分子印迹预组装体系.计算了功能单体、助溶剂和交联剂加入量对各种模板复合物浓度的影响,进而确定了Leu-Phe分子印迹聚合物的合成条件.按条件合成聚合物后考察其识别性能,并结合计算模拟和实验结果解释实验现象.计算模拟可能有助于合成高特异性和亲和性分子印迹聚合物,探讨了分子印迹聚合物的分子识别机理.     

Enantioselective molecular imprinting polymer coated QCM for the recognition of l-tryptophan

A new quartz crystal microbalance (QCM) sensor that provides enantioselectivity to tryptophan enantiomers, with a high selectivity and sensitivity, was fabricated by the use of the molecularly imprinted polymers (MIPs) as the artificial biomimetic recognition material. Non-covalent molecular imprinting polymers were synthesized using acrylamide (AM) and trimethylolpropane trimethacrylate (TRIM) as a functional monomer and a cross-linking agent, respectively. The preparation of the thin permeable film coatings on QCM surface is described as well as the results and discussion on the sensitivity and selectivity of the coatings to tryptophan enatiomers under different conditions. The sensor was able to discriminate between the l- and d-tryptophan enantiomers in citric acid buffer solutions owing to the enantioselectivity of the imprinted sites. The detection limit is 8.8 μM. The influence of the cross-linking agent concentration on the sensitivity and selectivity of the fabricated polymer films was investigated and optimized. The enantionmeric composition of l- and d-tryptophan enantiomer mixtures can be determined by measuring the frequency shifts of the sample. The characteristics of the thiol monolayer and MIP film on the surface of the QCM were studied by atomic force microscopy (AFM).     

Effect of electron transport layer engineering based on blue phosphorescent organic light-emitting diodes

A main requirement for achieving high efficiency in organic light-emitting diodes (OLEDs) is that all charges and electrically generated excitons should be employed for emission. We fabricated blue phosphorescent OLEDs with four types electron transporting layers, which were doped with lithium quinolate (Liq) from 0% to 10%. A series of blue devices consisted of indium tin oxide (ITO, 180 nm)/4,4-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (NPB, 50 nm)/N,N′-dicarbazolyl-3,5-benzene (mCP, 10 nm)/iridium(III)bis[(4,6-di-fluoropheny)-pyridinato-N,C²] picolinate (FIrpic) doped in mCP (8%, 30 nm)/1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi, 20 nm)/TPBi mixed with Liq (20 nm)/Liq (2 nm)/aluminum (Al, 100 nm). The blue OLED doped with 5% Liq, which demonstrated a maximum luminous efficiency and external quantum efficiency of 17.64 cd/A and 8.78%, respectively, were found to be superior to the other blue devices.     

Impedimetric immunosensor for electronegative low density lipoprotein (LDL) based on monoclonal antibody adsorbed on (polyvinyl formal)-gold nanoparticles matrix

Monoclonal antibodies (MAb) have been commonly applied to measure LDL in vivo and to characterize modifications of the lipids and apoprotein of the LDL particles. The electronegative low density lipoprotein (LDL⁻) has an apolipoprotein B-100 modified at oxidized events in vivo. In this work, a novel LDL⁻ electrochemical biosensor was developed by adsorption of anti-LDL⁻ MAb on an (polyvinyl formal)-gold nanoparticles (PVF-AuNPs)-modified gold electrode. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the recognition of LDL⁻. The interaction between MAb-LDL⁻ leads to a blockage in the electron transfer of the [Fe(CN)₆]⁴⁻/K₄[Fe(CN)₆]³⁻ redox couple, which may could result in high change in the electron transfer resistance (R_CT) and decrease in the amperometric responses in CV analysis. The compact antibody-antigen complex introduces the insulating layer on the assembled surface, which increases the diameter of the semicircle, resulting in a high R_CT, and the charge transferring rate constant κ⁰ decreases from 18.2 × 10⁻⁶ m/s to 4.6 × 10⁻⁶ m/s. Our results suggest that the interaction between MAb and lipoprotein can be quantitatively assessed by the modified electrode. The PVF-AuNPs-MAb system exhibited a sensitive response to LDL⁻, which could be used as a biosensor to quantify plasmatic levels of LDL⁻.     

An assessment of the black ocean pixel assumption for MODIS SWIR bands

Recent studies show that an atmospheric correction algorithm using shortwave infrared (SWIR) bands improves satellite-derived ocean color products in turbid coastal waters. In this paper, the black pixel assumption (i.e., zero water-leaving radiance contribution) over the ocean for the Moderate Resolution Imaging Spectroradiometer (MODIS) SWIR bands at 1240, 1640, and 2130 nm is assessed for various coastal ocean regions. The black pixel assumption is found to be generally valid with the MODIS SWIR bands at 1640 and 2130 nm even for extremely turbid waters. For the MODIS 1240 nm band, however, ocean radiance contribution is generally negligible in mildly turbid waters such as regions along the U.S. east coast, while some slight radiance contributions are observed in extremely turbid waters, e.g., some regions along the China east coast, the estuary of the La Plata River. Particularly, in the Hangzhou Bay, the ocean radiance contribution at the SWIR band 1240 nm results in an overcorrection of atmospheric and surface effects, leading to errors of MODIS-derived normalized water-leaving radiance at the blue reaching ~ 0.5 mW cm^− 2 μm^− 1 sr^− 1. In addition, we found that, for non-extremely turbid waters, i.e., the ocean contribution at the near-infrared (NIR) band < ~ 1.0 mW cm^− 2 μm^− 1 sr^− 1, there exists a good relationship in the regional normalized water-leaving radiances between the red and the NIR bands. Thus, for non-extremely turbid waters, such a red-NIR radiance relationship derived regionally can possibly be used for making corrections for the regional NIR ocean contributions without using the SWIR bands, e.g., for atmospheric correction of ocean color products derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS).     

Analyte selective response in solution-deposited tetrabenzoporphyrin thin-film field-effect transistor sensors

Organic thin film transistor (OTFT) chemical sensors rely on the specific electronic structure of the organic semiconductor (OSC) film for determining sensor stability and response to analytes. The delocalized electronic structure is influenced not only by the OSC molecular structure, but also the solid state packing and film morphology. Phthalocyanine (H₂Pc) and tetrabenzoporphyrin (H₂TBP) have similar molecular structures but different film microstructures when H₂Pc is vacuum deposited and H₂TBP is solution deposited. The difference in electronic structures is evidenced by the different mobilities of H₂TBP and H₂Pc OTFTs. H₂Pc has a maximum mobility of 8.6 × 10⁻⁴ cm² V⁻¹ s⁻¹ when the substrate is held at 250 °C during deposition and a mobility of 4.8 × 10⁻⁵ cm² V⁻¹ s⁻¹ when the substrate is held at 25 °C during deposition. Solution deposited H₂TBP films have a mobility of 5.3 × 10⁻³ cm² V⁻¹ s⁻¹, which is consistent with better long-range order and intermolecular coupling within the H₂TBP films compared to the H₂Pc films. Solution deposited H₂TBP also exhibits a textured film morphology with large grains and an RMS roughness 3-5 times larger than H₂Pc films with similar thicknesses. Despite these differences, OTFT sensors fabricated from H₂TBP and H₂Pc exhibit nearly identical analyte sensitivity and analyte response kinetics. The results suggest that while the interactions between molecules in the solid state determine conductivity, localized interactions between the analyte and the molecular binding site dominate analyte binding and determine sensor response.     

A new acridine derivative as a highly selective ‘off-on’ fluorescence chemosensor for Cd in aqueous media

A new acridine fluoroionophore containing two diethanolamine ligands, 4,5-bis(N,N-di (2-hydroxyethyl)iminomethyl)acridine (BHIA), was designed and synthesized based on the fluorophore-spacer-receptor format. And its fluorescent sensing behavior towards metal ions was investigated in buffered aqueous media. The presence of Cd²⁺ induces the formation of a 1:1 ligand/metal complex at neutral pH, which exhibits enhanced emission at 454 nm. The fluorescence intensity is linear with the Cd²⁺ concentration in the range of 1.0 × 10⁻⁶ to 3.0 × 10⁻⁵ M (R = 0.9967). Experimental results show a low interference response towards other metal ions. The selective switch-on fluorescence response of BHIA to Cd²⁺ makes it suitable for sensing of Cd²⁺ in aqueous solution. The detection limit is 1.3 × 10⁻⁷ M. Moreover, the results indicated that BHIA was a reversible chemosensor for Cd²⁺, which makes it attractive for sensing applications.     

Satellite and surface-based remote sensing of Saharan dust aerosols

The spatial and temporal characteristics of dust aerosols and their properties are assessed from satellite and ground-based sensors. The spatial distribution of total column aerosol optical depth at 550 nm (AOD) from the Moderate Resolution Imaging SpectroRadiometer (MODIS) coupled with top of atmosphere Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes are examined from the Terra satellite over the Atlantic Ocean. These data are then compared with AOD from two Aerosol Robotic Network (AERONET) ground-based sun photometer measurement sites for nearly six years (2000-2005). These two sites include Capo Verde (CV) (16°N, 24°W) near the Saharan dust source region and La Paguera (LP) (18°N, 67°W) that is downwind of the dust source regions. The AOD is two to three times higher during spring and summer months over CV when compared to LP and the surrounding regions. For a unit AOD value, the instantaneous TOA shortwave direct radiative effect (DRE) defined as the change in shortwave flux between clear and aerosol skies for CV and LP are − 53 and − 68 Wm^− 2 respectively. DRE for LP is likely more negative due to fall out of larger particles during transport from CV to LP. However, separating the CERES-derived DRE by MODIS aerosol effective radii was difficult. Satellite and ground-based dust aerosol data sets continue to be useful to understand dust processes related to the surface and the atmosphere.