Memory effects on the interfacial characteristics of dioctadecyldimethylammonium bromide monolayers at the air-water interface

The structural and dynamic characteristics of dioctadecyldimethylammonium bromide (DODAB) monolayers on a pure water subphase were investigated by surface film balance, Brewster angle microscopy, and relaxation in area and surface pressure at constant surface pressure and area, respectively. The first compression-expansion cycle of the monolayer is not reversible and the second pi-A compression isotherm deviates to larger molecular areas relative to the first one. At a microscopic level this hysteresis may be assigned to an irreversible hydration of the ammonium groups of DODAB. The morphology and reflectivity of DODAB monolayers during compression and expansion on the monolayer depend on the monolayer history. Bright domains randomly dispersed were observed during compression before collapse. Surprisingly, this random distribution of domains changes into a fractal-like structure during the monolayer expansion in a narrow range of surface pressures. This morphology does not form when the monolayer is previously compressed above the collapse surface pressure. 2D foam-like structure is often observed when the film is expanded at maximum area. Relaxation phenomena in DODAB monolayers are attributed to monolayer reorganization and nucleation of liquid-condensed domains from the liquid-expanded phase. These time-dependent processes are irreversible.     

Electrochemical bisphenol A sensor based on N-doped graphene sheets

Bisphenol A (BPA), which could disrupt endocrine system and cause cancer, has been considered as an endocrine disruptor. Therefore, it is very important and necessary to develop a sensitive and selective method for detection of BPA. Herein, nitrogen-doped graphene sheets (N-GS) and chitosan (CS) were used to prepare electrochemical BPA sensor. Compared with graphene, N-GS has favorable electron transfer ability and electrocatalytic property, which could enhance the response signal towards BPA. CS also exhibits excellent film forming ability and improves the electrochemical behavior of N-GS modified electrode. The sensor exhibits a sensitive response to BPA in the range of 1.0 × 10⁻⁸–1.3 × 10⁻⁶ mol L⁻¹ with a low detection limit of 5.0 × 10⁻⁹ mol L⁻¹ under the optimal conditions. Finally, this proposed sensor was successfully employed to determine BPA in water samples with satisfactory results.     

基于溶剂剥离石墨烯增敏效应的土霉素电化学检测新方法

以N-甲基吡咯烷酮(NMP)为剥离试剂,通过超声剥离石墨制备出了石墨烯纳米片(GS),离心分离后,将GS固体重新分散在较低沸点的N,N-二甲基甲酰胺(DMF)中,经挥发溶剂制备出石墨烯纳米片修饰玻碳电极(GS/GCE)。研究了土霉素的电化学行为,发现在GS/GCE上土霉素的氧化信号得到显著提高。优化了检测条件,建立了一种快速、简便测定土霉素的高灵敏电化学新方法,线性范围为5.0×10-8~1.0×10-6 mol/L,检出限为1.5×10-8 mol/L。将该方法用于尿液样品分析,结果准确。     

Synergetic signal amplification based on electrochemical reduced graphene oxide-ferrocene derivative hybrid and gold nanoparticles as an ultra-sensitive detection platform for bisphenol A

In this paper, a novel electro-active graphene oxide (GO) nanocomposite was firstly prepared by covalently grafted (4-ferrocenylethyne) phenylamine (Fc-NH₂) onto the surface of GO. The synthesized hybridized nanocomposite of GO-Fc-NH₂ coupled with HAuCl₄ simultaneously electrodeposited on the glassy carbon electrodes (GCE) to obtain rGO-Fc-NH₂/AuNPs/GCE. The covalently grafted material of the rGO-Fc-NH₂/AuNPs film can effectively prevent the electron mediator leaking from the electrode surface, which can hold the advantage of both the nanomaterials and electron mediator. By employing the catalysis effect of the nanomaterial and electron mediator coupling with large active surface area and high accumulation capacity of rGO-Fc-NH₂/AuNPs, a synergetic signal amplification platform for ultra-sensitive detection of bisphenol A (BPA) was successfully established. With this novel sensor, the oxidation peak currents of BPA were linearly dependent on the BPA concentrations in the range of 0.005–10 μM with the detection limit of 2 nM. Modification of electron mediators on nanomaterials can greatly enhance the electrochemical performance of the sensors and will provide a new concept for fabricating newly electro-active nanomaterials-based electrochemical biosensors.     

A highly sensitive and selective immunoassay for the detection of tetrabromobisphenol A in soil and sediment

Tetrabromobisphenol A is the most widely used brominated flame retardant. A sensitive and selective enzyme-linked immunosorbent assay (ELISA) for the detection of tetrabromobisphenol A was developed. The limit of detection and the inhibition half-maximum concentration of tetrabromobisphenol A in phosphate buffered saline with 10% methanol were 0.05 and 0.87 ng mL⁻¹, respectively. Cross-reactivity values of the ELISA with a set of important brominated flame retardants including tetrabromobisphenol A-bis(2,3-dibromopropylether), 2,2′,6,6′-tetrabromobisphenol A diallyl ether, hexabromocyclododecane, 1,2-bis(pentabromodiphenyl) ethane, 1,2-bis(2,4,6 tribromophenoxy) ethane, bis(2-ethylhexyl)-3,4,5,6-tetrabromophthalate, 2-ethylhexyl-2,3,4,5-tetrabromobenzoate, and polybrominated diphenyl ethers were <0.05%. Concentrations of tetrabromobisphenol A determined by ELISA in the soils from farmlands, the soils from an e-waste recycling site, and the sediments of a canal were in the range of non-detectable–5.6 ng g⁻¹, 26–104 ng g⁻¹ and 0.3–22 ng g⁻¹ dw, respectively, indicating the ubiquitous pollution of tetrabromobisphenol A. The results of this assay for 16 real world samples agreed well with those of the liquid chromatography–tandem mass spectrometry method, indicating this ELISA is suitable for screening of tetrabromobisphenol A in environmental matrices.     

基于还原石墨烯/纳米银复合材料的电化学传感器测定双酚A

石墨烯特有的褶皱层状结构以及银纳米粒子良好的催化性能,使其在电化学方面具有良好的应用潜能.本研究以柠檬酸钠为还原剂,通过水热反应原位制备出还原石墨烯/纳米银复合材料(rGO/AgNPs),用于修饰玻碳电极,研究了双酚A的电化学行为.循环伏安法(CV)和方波伏安法(SWV)的实验结果表明,双酚A可以在rGO/AgNPs修饰电极表面发生快速的氧化还原反应,基于此实现了对双酚A的高灵敏检测.在最优条件下,双酚A的氧化峰电流与其浓度在0.1~40.0μmol/L范围内呈良好的线性关系(r2=0.996),检出限为50.7 nmol/L(S/N=3).将其用于实际环境和塑料样品中双酚A的检测,回收率为91.7%~102.9%.     

A novel sensitive detection platform for antitumor herbal drug aloe-emodin based on the graphene modified electrode

This paper has presented a novel strategy to carry out direct and sensitive determination of antitumor herbal drug aloe-emodin in complex matrices based on the graphene-Nafion modified glassy carbon (GN/GC) electrode. This proposed modified electrode showed good electrochemical response towards aloe-emodin (AE). Compared with the multiwall carbon nanotubes (MWCNTs) modified electrode, the GN/GC electrode has the advantages of higher sensitivity and lower cost. Under the optimized conditions, the calibration curve for AE concentration was linear in the range from 5 nmol/L to 1 μmol/L with the detection limit of 2 nmol/L. In addition, the practical analytical performance of the GN/GC electrode was examined by evaluating the selective detection of AE in natural aloe extracts and human urine samples with satisfied recovery. Therefore, the GN/GC electrode may hold great promise for fast, simple and sensitive detection and biomedical analysis of AE in complex matrices.     

A sensitive electrochemical chlorophenols sensor based on nanocomposite of ZnSe quantum dots and cetyltrimethylammonium bromide

In this work, a very sensitive and simple electrochemical sensor for chlorophenols (CPs) based on a nanocomposite of cetyltrimethylammonium bromide (CTAB) and ZnSe quantum dots (ZnSe–CTAB) through electrostatic self-assembly technology was built for the first time. The composite of ZnSe–CTAB introduced a favorable access for the electron transfer and gave superior electrocatalytic activity for the oxidation of CPs than ZnSe QDs and CTAB alone. Differential pulse voltammetry (DPV) was used for the quantitative determination of the CPs including 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and pentachlorophenol (PCP). Under the optimum conditions, the peak currents of the CPs were proportional to their concentrations in the range from 0.02 to 10.0 μM for 2-CP, 0.006 to 9.0 μM for 2,4-DCP, and 0.06 to 8.0 for PCP. The detection limits were 0.008 μM for 2-CP, 0.002 μM for 2,4-DCP, and 0.01 μM for PCP, respectively. The method was successfully applied for the determination of CPs in waste water with satisfactory recoveries. This ZnSe–CTAB electrode system provides operational access to design environment-friendly CPs sensors.     

Ultrasensitive electrochemical immunoassay for carcinoembryonic antigen based on three-dimensional macroporous gold nanoparticles/graphene composite platform and multienzyme functionalized nanoporous silver label

Three-dimensional macroporous gold nanoparticles/graphene composites (3D-AuNPs/GN) were synthesized through a simple two-step process, and were used to modify working electrode sensing platform, based on which a facile electrochemical immunoassay for sensitive detection of carcinoembryonic antigen (CEA) in human serum was developed. In the proposed 3D-AuNPs/GN, AuNPs were distributed not just on the surface, but also on the inside of graphene. And this distribution property increased the area of sensing surface, resulting in capturing more primary antibodies as well as improving the electronic transmission rate. In the presence of CEA, a sandwich-type immune composite was formed on the sensing platform, and the horseradish peroxidase-labeled anti-CEA antibody (HRP-Ab₂)/thionine/nanoporous silver (HRP-Ab₂/TH/NPS) signal label was captured. Under optimal conditions, the electrochemical immunosensor exhibited excellent analytical performance: the detection range of CEA is from 0.001 to 10 ng mL⁻¹ with low detection limit of 0.35 pg mL⁻¹ and low limit of quantitation (LOQ) of 0.85 pg mL⁻¹. The electrochemical immunosensor showed good precision, acceptable stability and reproducibility, and could be used for the detection of CEA in real samples. The proposed method provides a promising platform of clinical immunoassay for other biomolecules     

氧化石墨烯量子点对鸡卵清蛋白递送-免疫增强佐剂效力评估

利用改进的Hummers法氧化鳞片石墨,获得富含羟基和羧基的氧化石墨烯量子点(GOQDs)。通过透射电子显微镜、X射线衍射、红外光谱及拉曼光谱测试表征其理化性质。此外,利用鸡卵清蛋白(OVA)作为模式抗原,构筑GOQDs/OVA纳米疫苗并评估其载量、安全性、免疫效力等。结果显示,GOQDs/OVA纳米疫苗直径在5nm左右,具有高度的水分散性和稳定性。其对OVA的最大负载量约为 500mg·g^-1,在pH=5.5和7.4环境下24 h的释放率分别为74.65%和56.93%,表现出pH刺激响应释放性能。当GOQDs浓度在500μg·mL^-1以下时,不会引起溶血、细胞损伤、重要组织发生病变等现象。免疫后,与 OVA单独免疫对照组相比,GOQDs/OVA纳米疫苗可以诱导产生高水平的免疫球蛋白G(IgG)、免疫球蛋白G1(IgG1)及免疫球蛋白G2a(IgG2a)抗体,提高白细胞介素(IL)-1β、IL-2、IL-4和IL-6、肿瘤坏死因子-α(TNF-α)和γ干扰素(IFN-γ)的分泌,同时促进脾中辅助性(CD4⁺)和细胞毒性(CD8⁺)T淋巴细胞百分比的增加。     

氧化石墨烯量子点对鸡卵清蛋白递送-免疫增强佐剂效力评估

利用改进的Hummers法氧化鳞片石墨,获得富含羟基和羧基的氧化石墨烯量子点(GOQDs)。通过透射电子显微镜、X射线衍射、红外光谱及拉曼光谱测试表征其理化性质。此外,利用鸡卵清蛋白(OVA)作为模式抗原,构筑GOQDs/OVA纳米疫苗并评估其载量、安全性、免疫效力等。结果显示,GOQDs/OVA纳米疫苗直径在5 nm左右,具有高度的水分散性和稳定性。其对OVA的最大负载量约为500 mg·g^-1,在pH=5.5和7.4环境下24 h的释放率分别为74.65%和56.93%,表现出pH刺激响应释放性能。当GOQDs浓度在500 μg·mL^-1以下时,不会引起溶血、细胞损伤、重要组织发生病变等现象。免疫后,与OVA单独免疫对照组相比,GOQDs/OVA纳米疫苗可以诱导产生高水平的免疫球蛋白G(IgG)、免疫球蛋白G1(IgG1)及免疫球蛋白G2a(IgG2a)抗体,提高白细胞介素(IL)-1β、IL-2、IL-4和IL-6、肿瘤坏死因子-α(TNF-α)和γ干扰素(IFN-γ)的分泌,同时促进脾中辅助性(CD4⁺)和细胞毒性(CD8⁺)T淋巴细胞百分比的增加。     

Electrochemical sensor based on f-SWCNT and carboxylic group functionalized PEDOT for the sensitive determination of bisphenol A

A simple,sensitive,and reliable method for the voltammetric determination of bisphenol A(BPA) by using carboxylic group functionalized single-walled carbon nanotubes(f-SWCNT)/carboxylic-functionalized poly(3,4-ethylenedioxythiophene)(PC4) complex modified glassy carbon electrode(GCE) has been successfully developed.The electrochemical behavior of BPA at the surface of the modified electrode is investigated by electrochemical techniques.The cyclic voltammetry results show that the as-prepared electrode exhibits strong catalytic activity toward the oxidation of BPA with a well-defined anodic peak at 0.623 V in PBS(0.1 mol/L,pH 7.0).The surface morphology of the 3D network of composite film is beneficial for the adsorption of analytes.Under the optimized conditions,the oxidation peak current is proportional to BPA concentration in the range between 0.099 and 5.794 μmol/L(R~2 = 0.9989),with a limit of detection of 0.032 μmol/L(S/N = 3).The enhanced performance of the sensor can be attributed to the excellent electrocatalytic property of/-SWCNT and the extraordinary conductivity of PC4.Furthermore,the proposed modified electrode displays high stability and good reproducibility.The good result on the voltammetric determination of BPA also indicates that the asfabricated modified electrode will be a good candidate for the electrochemical determination and analysis of BPA.     

A solid-state electrochemiluminescence sensing platform for detection of adenosine based on ferrocene-labeled structure-switching signaling aptamer

A solid-state electrochemiluminescence sensing platform based on ferrocene-labeled structure-switching signaling aptamer (Fc-aptamer) for highly sensitive detection of small molecules is developed successfully using adenosine as a model analyte. Such special sensing platform included two main parts, an electrochemiluminescence (ECL) substrate and an ECL intensity switch. The ECL substrate was made by modifying the complex of Au nanoparticle and Ruthenium (II) tris-(bipyridine) (Ru(bpy)₃²⁺-AuNPs) onto Au electrode. An anti-adenosine aptamer labeled by ferrocene acted as the ECL intensity switch. A short complementary ssDNA for the aptamer was applied to hybridizing with the aptamer, yielding a double-stranded complex of the aptamer and the ssDNA on the electrode surface. The introduction of adenosine triggered structure switching of the aptamer. As a result, the ssDNA was forced to dissociate from the sensing platform. Such structural change of the aptamer resulted in an obvious ECL intensity decrease due to the increased quenching effect of Fc to the ECL substrate. The analytic results were sensitive and specific.     

Amplified impedimetric aptasensor based on gold nanoparticles covalently bound graphene sheet for the picomolar detection of ochratoxin A

An amplified electrochemical impedimetric aptasensor for ochratoxin A (OTA) was developed with picomolar sensitivity. A facile route to fabricate gold nanoparticles covalently bound reduced graphene oxide (AuNPs–rGO) resulted in a large number of well-dispersed AuNPs on graphene sheets with tremendous binding sites for DNA, since the single rGO sheet and each AuNP can be loaded with hundreds of DNA strands. An aptasensor with sandwich model was fabricated which involved thiolated capture DNA immobilized on a gold electrode to capture the aptamer, then the sensing interface was incubated with OTA at a desired concentration, followed by AuNPs–rGO functionalized reporter DNA hybridized with the residual aptamers. By exploiting the AuNPs–rGO as an excellent signal amplified platform, a single hybridization event between aptamer and reporter DNA was translated into more than 10⁷ redox events, leading to a substantial increase in charge-transfer resistance (R_ct) by 7∼ orders of magnitude compared with that of the free aptamer modified electrode. Such designed aptasensor showed a decreased response of R_ct to the increase of OTA concentrations over a wide range of 1 pg mL⁻¹–50 ng mL⁻¹ and could detect extremely low OTA concentration, namely, 0.3 pg mL⁻¹ or 0.74 pM, which was much lower than that of most other existed impedimetric aptasensors. The signal amplification platform presented here would provide a promising model for the aptamer-based detection with a direct impedimetric method.     

Electrochemical deoxyribonucleic acid biosensor based on carboxyl functionalized graphene oxide and poly-l-lysine modified electrode for the detection of tlh gene sequence related to vibrio parahaemolyticus

A carboxyl functionalized graphene oxide (GO-COOH) and electropolymerized ploy-l-lysine (PLLy) modified glassy carbon electrode (GCE) was fabricated and used for the construction of an electrochemical deoxyribonucleic acid (DNA) biosensor. The NH₂ modified probe ssDNA sequences were immobilized on the surface of GO-COOH/PLLy/GCE by covalent linking with the formation of amide bonds, which was stable and furthur hybridized with the target ssDNA sequence. Differential pulse voltammetry (DPV) was used to monitor the hybridization events with methylene blue as electrochemical indicator, which gave a sensitive reduction peak at −0.287 V (vs. SCE). Under the optimal conditions the reduction peak current was proportional to the concentration of tlh gene sequence in the range from 1.0 × 10⁻¹² to 1.0 × 10⁻⁶ mol L⁻¹ with a detection limit as 1.69 × 10⁻¹³ mol L⁻¹ (3σ). The polymerase chain reaction products of tlh gene from oyster samples were detected with satisfactory results, indicating the potential application of this electrochemical DNA sensor.     

A disposable electrochemical sensor for the determination of indole-3-acetic acid based on poly(safranine T)-reduced graphene oxide nanocomposite

A disposable electrochemical sensor for the determination of indole-3-acetic acid (IAA) based on nanocomposites of reduced graphene oxide (rGO) and poly(safranine T) (PST) was reported. The sensor was prepared by coating a rGO film on a pre-anodized graphite electrode (AGE) through dipping-drying and electrodepositing a uniform PST layer on the rGO film. Scanning electron microscopic (SEM) and infrared spectroscopic (IR) characterizations indicated that PST-rGO formed a rough and crumpled composite film on AGE, which exhibited high sensitive response for the oxidation of IAA with 147-fold enhancement of the current signal compared with bare AGE. The voltammetric current has a good linear relationship with IAA concentration in the range 1.0 × 10⁻⁷-7.0 × 10⁻⁶ M, with a low detection limit of 5.0 × 10⁻⁸ M. This sensor has been applied to the determination of IAA in the extract samples of several plant leaves and the recoveries varied in the range of 97.71-103.43%.     

A Study on the Electrochemical and Electrochemiluminescent Behavior of Homogentisic Acid at Carbon Electrodes

The electrochemical oxidation and electrochemiluminescent behavior of homogentisic acid (HGA) has been studied in aqueous solutions over a wide pH range by linear sweep voltammetry, cyclic voltammetry, chronocoulometry at a glassy carbon electrode, by controlled potential electrolysis at a large area spectroscopic graphite electrode, and by spectroelectrochemistry at an optically transparent drilled holes graphite (DHG) electrode in a thin‐layer cell. The studies reveal that the electrochemical oxidation of HGA at carbon electrodes is a reversible process involving two‐electron, two‐proton transfer. In addition to the electrochemical oxidation, the chemical oxidation of HGA by dissolved oxygen was investigated by spectroscopic method combined with voltammetry. It was revealed that HGA is fairly stable in strongly acidic media but readily oxidized by dissolved oxygen in alkaline media giving rise to 1,4‐benzoquinone‐2‐acetic acid, the same product as that of electrooxidation of HGA. This oxidation product is stable in acidic, neutral and weakly alkaline media, but can further degrade in strongly alkaline media yielding oxalate as the final product. The electrochemiluminescent mechanism of HGA in the presence of Ru(bpy)₃²⁺ at a glassy carbon electrode was also investigated in detail, based on which a sensitive ECL method for determination of HGA was developed, and the detection limit was 3.0×10^?8 mol L^?1.     

Analysis of tryptophan at nmoll(-1) level based on the fluorescence enhancement of terbium-gadolinium-tryptophan-sodium dodecyl benzene sulfonate system

It is found that Tb³⁺ can react with tryptophan (Trp) and sodium dodecyl benzene sulfonate (SDBS), and emits the intrinsic fluoresence of Tb³⁺. The fluorescence intensity can be enhanced by La³⁺, Gd³⁺, Lu³⁺, Sc³⁺ and Y³⁺, among which Gd³⁺ has the greatest enhancement. This is a new co-luminescence system. The studies indicate that in the Tb-Gd-Trp-SDBS system, there is both Tb-Trp-SDBS and Gd-Trp-SDBS complexes, and they aggregate together and form a large congeries. The fluorescence enhancement of the Tb-Gd-Trp-SDBS system is considered to originate from intramolecular and intermolecular energy transfers, and the energy-insulating sheath effect of Gd-Trp-SDBS complex.Under the optimum conditions, the enhanced intensity of fluorescence is in proportion to the concentration of Trp in the range from 4×10⁻⁸ to 4×10⁻⁵ mol l⁻¹. The detection limit is 10⁻⁹ mol l⁻¹. The proposed method is one of the most sensitive fluoremetries of Trp.     

Electrochemical Aptasensor for the Determination of Ochratoxin A at the Au Electrode Modified with Ag Nanoparticles Decorated with Macrocyclic Ligand

An electrochemical aptasensor for ochratoxin A (OTA) detection has been developed on the base of a gold electrode covered with electropolymerized neutral red and silver nanoparticles obtained by chemical reduction with macrocyclic ligands bearing catechol fragments. Thiolated aptamers against OTA were covalently attached to silver nanoparticles via Ag? S bonding. The interaction with OTA induced the conformational switch of the aptamer, which caused increase of the charge transfer resistance measured by EIS in the presence of ferricyanide ions. The LOD achieved (0.05 nM) was comparable to other electrochemical aptasensors employing sophisticated assembling technique and enzyme amplification of the signal. The aptasensor was validated in spiked beer samples. The recovery of the OTA determination was found to be 66.3±14.1 % for light beer and 64.3±1.8 % for dark beer.     

Electrochemical piezoelectric quartz crystal impedance study on the interaction between concanavalin A and glycogen at Au electrodes

The carbohydrate research has emerged as a "new frontier" in chemical/biological field. The binding of lectin with carbohydrate is one of the important courses of life activities. The report studies concanavalin A (Con A)-glycogen interaction on gold electrode surfaces by electrochemical piezoelectric quartz crystal impedance (EPQCI) method. The piezoelectric quartz crystal (PQC) parameters, resonant frequency shift (Deltaf(0)) and the motional resistance change (DeltaR(1)), and the electrochemical impedance (EI) parameters, electrolyte resistance change (DeltaR(s)) and the double layer capacitance change (DeltaC(s)), were measured and discussed simultaneously. Two methods were adopted for measuring the Con A-glycogen association. Based on EPQCI measurement during Con A reaction with glycogen adsorbed on Au electrode, association constant K(a) and the amount of the binding sites s calculated are 1.48 x 10(6) M(-1) and 4.09, respectively. Based on single PQC measurement of glycogen reaction with Con A assembled on Au electrode, K(a) was estimated to be 1.26 x 10(6) M(-1).