Ag‐CNT Architectures for Attomolar Dopamine Detection and 100‐Fold Fluorescence Enhancements with Cellphone‐Based Surface Plasmon‐Coupled Emission Platform

We report cellphone‐based detection of dopamine with attomolar sensitivity in clinical samples with the use of a surface plasmon‐coupled emission (SPCE) platform. To this end, silver‐coated carbon nanotubes were used as spacer and cavity materials on SPCE substrates to obtain up to 100‐fold fluorescence enhancements. The presence of silver on the carbon nanotubes helped to overcome fluorescence quenching arising due to π–π interactions between the carbon nanotube and rhodamine 6G. The competing adsorption of dopamine versus rhodamine 6G on graphene oxide was utilized to develop this sensing platform.     

Prism‐Based Surface Plasmon Coupled Emission Imaging

A prism‐based surface plasmon coupled emission (SPCE) imaging apparatus with a reverse Kretschmann (RK) configuration was developed and applied to dye‐doped polymer films. Highly polarized, directional and enhanced fluorescence images were obtained. The angular distribution of the SPCE images was in accordance with the validated theoretical calculation performed using Fresnel equation. Prism‐based SPCE imaging combined with microarray technology appears to be a promising platform for rapid and high‐throughput analysis, especially for high‐density arrays. We believe that prism‐based SPCE imaging has potential applications in biochemical research.     

Voltammetric Determination of Urinary 1‐Hydroxypyrene Using Molecularly Imprinted Polymer‐Modified Screen‐Printed Carbon Electrodes

A two step non‐competitive affinity method for the trace determination of 1‐hydroxypyrene (1‐OHP) using a disposable molecularly imprinted polymer (MIP) modified screen‐printed carbon electrode (MIP‐SPCE) has been developed. The MIP was synthesized according to a novel strategy, which is described, and is capable of rebinding the phenolic analyte, 1‐hydroxypyrene (1‐OHP), from high pH aqueous organic media, via ionic interactions. In the first step of our method 1‐OHP was accumulated at the MIP‐SPCE from 35% aqueous methanol containing 0.014 M NaOH and 0.14 M NaCl, at open circuit. In the second step, the resulting SPCE with accumulated 1‐OHP was then transferred to fresh, clean phosphate buffered aqueous methanol, and subjected to cyclic voltammetry (CV) or differential pulse voltammetry (DPV). The latter technique proved to be more sensitive at detecting 1‐OHP, with a limit of detection of 182 nM and a linear range to 125 μM on unmodified electrodes. The possible effects of interference by related phenolic compounds in the MIP‐SPCE of 1‐OHP were investigated. Finally the method was evaluated by carrying out 1‐OHP determinations on spiked human urine samples; the recovery of 1‐OHP was 79.4% and the coefficient of variation was found to be 7.7% (n= 4) using a separate MIP‐SPCE for each determination. Therefore, the performance data suggests that the method is reliable at the concentrations examined in this study. The method was found to be superior to the direct determination of 1‐OHP in human urine by DPV alone, which was greatly affected by interference from uric acid.     

Electrochemical Determination of Pyrogallol at Conducting Poly(3,4‐ethylenedioxythiophene) Film‐Modified Screen‐Printed Carbon Electrodes

The electrochemical oxidation of pyrogallol at electrogenerated poly(3,4‐ethylenedioxythiophene) (PEDOT) film‐modified screen‐printed carbon electrodes (SPCE) was investigated. The voltammetric peak for the oxidation of pyrogallol in a pH 7 buffer solution at the modified electrode occurred at 0.13 V, much lower than the bare SPCE and preanodized SPCE. The experimental parameters, including electropolymerization conditions, solution pH values and applied potentials were optimized to improve the voltammetric responses. A linear calibration plot, based on flow‐injection amperometry, was obtained for 1–1000 µM pyrogallol, and a slope of 0.030 µA/µM was obtained. The detection limit (S/N=3) was 0.63 µM.     

Electrochemical Oxidation and Sensitive Determination of Pyrogallol at Preanodized Screen‐Printed Carbon Electrodes

In this study, we report a simple, low‐cost and rapid electrochemical sensor based on the anodically pretreated screen‐printed carbon electrodes (SPCE*) for the determination of pyrogallol in pH 7.0 buffer solutions. Cyclic voltammetric studies show that SPCE* lowers overpotentials and improve electrochemical behaviour of pyrogallol, compared to untreated SPCE. All experimental parameters were optimized to improve voltammetric responses; excellent analytical features were achieved by flow‐injection amperometric methods. A linear calibration plot was obtained for 10‐1000 μM pyrogallol with a slope of 0.0562 μA/μM. The detection limit (S/N = 3) was 0.33 μM. Interferences from some inorganic salts and organic compounds were studied. The assay was applied to the determination of pyrogallol in tap water and lake water, respectively.     

Development of Electrochemical Paper‐based Glucose Sensor Using Cellulose‐4‐aminophenylboronic Acid‐modified Screen‐printed Carbon Electrode

The present work describes the fabrication of paper‐based analytical devices (μPADs) by immobilization of glucose oxidase onto the screen printed carbon electrodes (SPCEs) for the electrochemical glucose detection. The sensitivity towards glucose was improved by using a SPCE prepared from homemade carbon ink mixed with cellulose acetate. In addition, 4‐aminophenylboronic acid (4‐APBA) was used as a redox mediator giving a lower detection potential for improvement selectivity. Under optimized condition, the detection limit was 0.86 mM. The proposed device was applied in real samples. This μPAD has many advantages including low sample consumption, rapid analysis method, and low device cost.     

Polymorph‐Dependent Solid‐State Fluorescence and Selective Metal‐Ion‐Sensor Properties of 2‐(2‐Hydroxyphenyl)‐4(3H)‐quinazolinone

2‐(2‐Hydroxy‐phenyl)‐4(3H)‐quinazolinone (HPQ), an organic fluorescent material that exhibits fluorescence by the excited‐state intramolecular proton‐transfer (ESIPT) mechanism, forms two different polymorphs in tetrahydrofuran. The conformational twist between the phenyl and quinazolinone rings of HPQ leads to different molecular packing in the solid state, giving structures that show solid‐state fluorescence at 497 and 511 nm. HPQ also shows intense fluorescence in dimethyl formamide (DMF) solution and selectively detects Zn²⁺ and Cd²⁺ ions at micromolar concentrations in DMF. Importantly, HPQ not only detects Zn²⁺ and Cd²⁺ ions selectively, but it also distinguishes between the metal ions with a fluorescence λ_max that is blue‐shifted from 497 to 420 and 426 nm for Zn²⁺ and Cd²⁺ ions, respectively. Hence, tunable solid‐state fluorescence and selective metal‐ion‐sensor properties were demonstrated in a single organic material.     

Facile Fabrication of Zirconia Modified Screen‐Printed Carbon Electrodes for Electrochemical Sensing of Phosphate

We report here a facile method to immobilize zirconia nanoparticles on a disposable screen‐printed carbon electrode (designated as ZrO₂‐SPCE) for phosphate sensor application. Simply by ultrasonicating a bare SPCE in a ZrO₂ slurry, ZrO₂ nanoparticles can be immobilized effectively on the electrode surface as verified by surface characterization evidences. Using ferricyanide as a redox probe, an increase in the charge transfer resistance (R_ct) of ferricyanide upon adsorption of phosphate on ZrO₂ is used for the determination of phosphate. This ZrO₂‐SPCE phosphate sensor shows a wide linear range up to 1 mM and a detection limit of 1.69 µM (S/N=3). Practical applicability of the ZrO₂‐SPCE is demonstrated by detecting phosphate content in human blood samples.     

Development of an Amperometric Biosensor for β‐N‐Oxalyl‐L‐α,β‐Diaminopropionic Acid (β‐ODAP)

An amperometric method for the determination of the neurotoxic amino acid β‐N‐oxalyl‐L ‐α,β‐diaminopropionic acid (β‐ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulk‐modified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion‐film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/AgCl), flow rate 0.2 mL min^?1, and carrier composition 0.1 mol L^?1 phosphate buffer (pH 7.75). The same conditions were used for the determination of β‐ODAP. The signal was linear within the concentration range 53–855 μmol L^?1 glutamate and 195–1950 μmol L^?1 β‐ODAP. Detection limits (as 3σ value) for both analytes were 9.12 and 111.0 μmol L^?1, respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on‐line use.     

Synthesis and Spectral Properties of 4‐(2,5‐Dimethoxyphenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO)

An interesting flourophore, 4‐(2,5‐dimethoxyphenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO) was synthesized by mixing an equivalent molar quantity of hippuric acid and 2,5‐dimethoxybenzaldehyde in acetic anhydride in the presence of anhydrous sodium acetate. The absorption and fluorescence characteristics of 4‐(2,5‐dimethoxy‐phenylmethelene)‐2‐phenyl‐5‐oxazolone (DMPO) were investigated in different solvents. DMPO dye exhibits red shift in both absorption and emission spectra as solvent polarity increases, indicating change in the dipole moment of molecules upon excitation due to an intramolecular charge transfer interaction. The fluorescence quantum yield depends strongly on the properties of the solvents, which was attributed to positive and negative solvatokinetic effects. A crystalline solid of DMPO gave strong excimer like emission at 630 nm due to the excitation of molecular aggregates. This is expected from the idealized crystal structure of the dye that belongs to the B‐type class of Steven's Classification. DMPO displayed fluorescence quenching by triethylamine via nonemissive exciplex formation.     

A Simple Method to Tune Up Screen‐Printed Carbon Electrodes Applicable to the Design of Disposable Electrochemical Sensors

We report an easy method to tune up screen‐printed carbon electrodes (SPCEs) for application in fabricating disposable electrochemical sensors. Simply by ultrasonic polishing a bare SPCE in a γ‐Al₂O₃ slurry, the surface roughness was drastically smoothed coupled with a large increase in hydrophilicity. The as‐generated micromorphology on the surface of the SPCE was found to be ideal for the immobilization of catechol to minimize the overpotential in the sensitive detection of nicotinamide adenine dinucleotide (NADH) and hydrazine. Physical characterization by both XPS and AFM studies specify that the adsorption behavior is related to the carbon surface functionalities and the trapping of γ‐Al₂O₃ on the polished‐SPCE.     

Synthesis and Fluorescent Properties of 2‐Arylamino‐5‐(3‐Aryl‐1‐Phenyl‐Pyrazol‐4‐Yl)‐1,3,4‐Thiadiazoles

A series of novel pyrazolyl‐substituted 1,3,4‐thiadiazole derivatives ( 6a‐6d, 7a‐7d, 8a‐8d ) were prepared by cyclization of the intermediate 3‐aryl‐l‐phenyl‐pyrazol‐4‐ylformaldehyde 4′‐phenylthiosemicarbazones with 0.5 M ferric chloride solution. The structures of the new compounds were confirmed by IR, ¹H NMR and elemental analysis. Simultaneously, the compounds were detected by fluorescence spectrophotometer and had preferable fluorescence activity.     

Spectrofluorimetric and Spectrophotometric Determination of Oxamniquine in Pharmaceuticals and Biological Fluids via Derivatization with 4‐Chloro‐7‐Nitrobenzo‐2‐oxa‐1,3‐Diazole (NBD‐Cl)

Spectrophotometric and spectrofluorimetric methods were developed for the determination of oxamniquine (OXM). Both methods are based on coupling with 4‐chloro‐7‐nitrobenzo‐2‐oxa‐1,3‐diazole (NBD‐Cl) in borate buffer of pH 7.6, and the reaction product was measured at 400 nm (Method I). The same product was measured by spectrofluorimetry at 480 nm upon excitation at 400 nm (Method II). The absorbance and the fluorescence intensity were enhanced by addition of sodium dodecyl sulphate (SDS). The absorbance‐concentration plot is rectilinear over the range of 5–25 μg/mL with an LOD of 0.31 μg/mL. The fluorescence‐concentration plot is linear over the range of 0.2–1.2 μg/mL with an LOD of 0.03 μg/mL. Both methods were applied to the analysis of capsules, and the results were in good agreement with those obtained using the official method. The method was applied to spiked human plasma; the mean % recovery (n = 5) is 101.05 ± 1.65. A proposal of the reaction pathway is presented.     

Light‐driven and aggregation‐induced emission from side‐chain azoindazole polymers

The well‐defined azoindazole‐containing homopolymer, poly(6‐{6‐[(4‐dimethylamino) phenylazo]‐indazole}‐hexyl methacrylate) (PDHMA), and amphiphilic diblock copolymer, poly({6‐[6‐(4‐dimethylamino)phenylazo]‐indazole}‐hexyl methacrylate)‐b‐poly(2‐(dimethylamino)ethylmethacrylate) (PDHMA_m‐b‐PDMAEMA_n), were successfully prepared via reversible addition‐fragmentation chain transfer polymerization technique. The homopolymer and amphiphilic diblock copolymer in CH₂Cl₂ exhibited intense fluorescence emission accompanied by trans–cis photoisomerization of azoindazole group under UV irradiation. The experiment results indicated that the intense fluorescence emission may be attributed to an inhibition of photoinduced electron transfer of the cis form of azoindazole. On the other hand, the intense fluorescence emission of amphiphilic diblock copolymers in water‐tetrahydrofuran mixture was observed, which increased with the volume ratio of water in the mixed solvent. The self‐aggregation behaviors of three amphiphilic diblock copolymers were examined by transmission electron microscopy, laser light scattering, and UV–vis spectra. The restriction of intramolecular rotation of the azoindazole groups in aggregates was considered as the main cause of aggregation‐induced fluorescence emission. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Fluorescence Detection of Microcapsule‐Type Self‐Healing,Based on Aggregation‐Induced Emission

An extrinsic self‐healing coating system containing tetraphenylethylene (TPE) in microcapsules was monitored by measuring aggregation‐induced emission (AIE). The core healing agent comprised of methacryloxypropyl‐terminated polydimethylsiloxane, styrene, benzoin isobutyl ether, and TPE was encapsulated in a urea‐formaldehyde shell. The photoluminescence of the healing agent in the microcapsules was measured that the blue emission intensity dramatically increased and the storage modulus also increased up to 10⁵ Pa after the photocuring. These results suggested that this formulation might be useful as a self‐healing material and as an indicator of the self‐healing process due to the dramatic change in fluorescence during photocuring. To examine the ability of the healing agent to repair damage to a coating, a self‐healing coating containing embedded microcapsules was scribed with a razor. As the healing process proceeded, blue light fluorescence emission was observed at the scribed regions. This observation suggested that self‐healing could be monitored using the AIE fluorescence.

     

Asymmetrical Fluorene[2,3‐b]benzo[d]thiophene Derivatives: Synthesis,Solid‐State Structures,and Application in Solution‐Processable Organic Light‐Emitting Diodes

A series of novel asymmetrical fused compounds containing the backbone of fluorene[2,3‐b]benzo[d]thiophene (FBT) were effectively synthesized and fully characterized. Single‐crystal X‐ray studies demonstrated that the length of the substituent side chains greatly affects the solid‐state packing of the obtained fused compounds. DFT, photophysical, and electrochemical studies all showed that the FBTs have large band gaps, low‐lying HOMO energy levels, and therefore good stability toward oxidation. Moreover, the substituents strongly influence the fluorescence properties of the resulting FBT derivatives. The di‐n‐hexyl compound exhibits intense fluorescence in solution with the highest quantum yield of up to 91 %. Solution‐processed green phosphorescent organic light‐emitting diodes with the di‐n‐butyl derivative as the host material exhibited a maximum brightness of 14 185 cd m^?2 and a luminescence efficiency of 12 cd A^?1.     

Cobalt nanoparticles anchored to porous silicon as a novel modifier for the construction of enzyme‐free hydrogen peroxide screen‐printed sensor

In this work, a screen‐printed carbon electrode (SPCE) was modified with a cobalt/porous silicon (Co@PSi) nanocomposite powder to develop a nonenzymatic sensor for the detection of hydrogen peroxide. The Co@PSi nanocomposite was synthesized through the chemical reaction between silicon powder in a HF/HNO₃ solution and cobalt cations. In this process, cobalt nanoparticles were anchored on the porous silicon. The structure and morphology of the synthesized nanocomposite were investigated by X‐ray diffraction, Fourier transform infrared spectroscopy, X‐ray photoemission spectroscopy, energy dispersive X‐ray spectroscopy, and field‐emission scanning electron microscopy. The constructed nonenzymatic, screen‐printed sensors based on the Co@PSi nanocomposite showed perfect electrocatalytic oxidation response to hydrogen peroxide over the range 1–170 and 170–3,770 μmol/L with the limit of detection of 0.8 μmol/L. In addition, the Co@PSi‐SPCE sensor exhibited good selectivity for the determination of H₂O₂ in the presence of common interfering species including glucose, ascorbic acid, uric acid, dopamine, nitrate, and nitrite ions. The constructed electrochemical sensor was successfully used for the determination of H₂O₂ in real samples.     

Determination of Parathion‐methyl in Vegetables by Fluorescent‐Labeled Molecular Imprinted Polymer

A novel sensor for the determination of parathion‐methyl based on couple grafting of functional molecular imprinted polymers (MIPs) was fabricated which is developed by anchoring the MIP layer on surfaces of silica particles embedded CdSe quantum dots by surface imprinting technology. The synthesized molecular imprinted silica nanospheres (CdSe@SiO₂@MIP) allow a high selectivity and sensitivity of parathion‐methyl via fluorescence intensity decreasing when the MIP material rebinding the parathion‐methyl molecule. Compared with the MIP fabricated in traditional method, the template of parathion‐methyl was easier to remove from the CdSe@SiO₂@MIP imprinted material. Under optimal conditions, the fluorescence intensity of parathion‐methyl at the imprinted sensor was detected by spectrofluorophotometer. The relative fluorescence intensity of CdSe@SiO₂@MIP decreased linearly with the increasing concentration of parathion‐methyl ranging from 0.013 mg·kg⁻¹ to 2.63 mg·kg⁻¹ with a detection limit (3δ) of 0.004 mg·kg⁻¹ (S/N=3), which is lower than the MIP in tradition. The imprinted film sensor was applied to detect parathion‐methyl in vegetable samples without the interference of other organophosphate pesticides and showed a prosperous application in the field of food safety.     

3,14‐Bis(p‐nitrophenyl)‐17,17‐dipentyltetrabenzo[a,c,g,i]‐fluorene: A New Fluorophore Displaying Both Remarkable Solvatochromism and Crystalline‐Induced Emission

A series of 17,17‐dialkyl‐3,14‐diaryltetrabenzofluorenes were efficiently prepared by using Suzuki–Miyaura cross‐coupling reactions of the corresponding 3,14‐dibromo derivatives. Studies of the unique fluorescence properties of these compounds showed that they display intense blue to yellow fluorescence with high quantum yields in the solution state and blue to orange fluorescence with moderate quantum yields in the solid state. In addition, the fluorescence wavelength of the bis(p‐nitrophenyl) derivative is remarkably solvent‐dependent in a manner that correlates with the solvent polarity parameter E_T(30). The results of density function theory calculations suggest that the intramolecular charge‐transfer character of the HOMO–LUMO transition is responsible for the large solvent effect. Moreover, addition of water to a tetrahydrofuran (THF) solution of this compound leads to quenching of the yellow fluorescence owing to an increase in the solvent polarity. However, when the amount of water fraction exceeds 70 %, a new fluorescence band appears at the same orange‐red emission wavelength as that of the solid‐state fluorescence. This observation suggests the occurrence of a crystallization‐induced emission (CIE) phenomenon in highly aqueous THF.     

Electroanalytical Sensor Based on Unmodified Screen‐Printed Carbon Electrode for the Determination of Levo‐Thyroxine

The electrochemical behaviour of thyroxine (T₄) is analysed using the disposable screen‐printed carbon electrode (SPCE) in the neutral phosphate buffer solution with cyclic voltammetric technique. The Differential Pulse Voltammetry and Chronoamperometry were employed for sensing of T₄. The lowest detection limit of 3 nM was obtained from the differential pulse voltammetric method without preconditioning. The Density Functional Theoretical study of T₄ was performed to elucidate the mechanism of oxidation. The analysis of the commercial pharmaceutical samples indicates the validity of the proposed method.