Voltammetric Detection of Catechol and Dopamine Based on a Supramolecular Composite Prepared from Multifarene[3,3] and Reduced Graphene Oxide

A selective and sensitive modified‐electrode for catechol and dopamine was presented with supramolecular recognition accomplished by making use of the macrocyclic host multifarene[3,3] that was used as a composite with reduced graphene oxide. The morphologies and electrochemical nature of the composite were characterized by atomic force microscopy, transmission electron microscopy, cyclic voltammetry and differential pulse anodic voltammetry. The modified electrode, best operated at a potential around 0.16 V vs. Ag/AgCl, displayed a differential pulse voltammetric response in the linear concentration range of 10–100 nM within a detection limit of 0.51 nM (at S/N=3). It was further applied to detect dopamine (at a working potential of 0.18 V vs. Ag/AgCl) in the linear concentration range of 10–100 nM with a detection limit of 0.62 nM. The modified electrode also exhibited satisfactory results to the determination of dopamine injections. The constructed modified electrode for dopamine detection was investigated in the presence of the interfering substances including glucose, urea and ascorbic acid, indicating a good selectivity.     

基于取代型多酸复合材料的多巴胺电化学检测

本文构建了基于取代型多酸与还原氧化石墨烯（RGO）复合材料的多巴胺电化学传感器. 首先,通过水热法合成了十一钨镍杂多钨硅酸盐K₂H₂SiW₁₁NiO₃₉·xH₂O（SiW₁₁Ni）,利用Hummers法与化学还原法合成了还原氧化石墨烯. 并使用SEM、XRD与FTIR等测试方法对材料进行了表征. 将SiW₁₁Ni与RGO按照一定的比例滴涂在玻碳电极表面,以便成功构建出传感界面（SiW₁₁Ni-RGO/GCE）. 然后,采用电化学阻抗法与循环伏安法等方法研究了传感界面的电化学性质. 优化实验条件后,利用该传感器通过循环伏安法对多巴胺进行定量检测,并且氧化过程展现出较为良好的性能. 其检出限为3.2 μmol·L ^-1（S/N = 3）,灵敏度为9.71 μA·(μmol·L ^-1·cm ^-2) ^-1,线性范围为10 ~ 80 μmol·L ^-1. 同时,所制备的传感器表现出良好的稳定性与抗干扰能力. 该传感器修饰过程简单、成本低、电化学性能良好,为多酸在化学传感领域的应用提供新思路.     

Electrochemical Determination of Dopamine Using a Poly(3,4-Ethylenedioxythiophene)-Reduced Graphene Oxide-Modified Glassy Carbon Electrode

Poly(3,4-ethylenedioxythiophene) was deposited on a reduced graphene oxide-decorated glassy carbon electrode through an electrochemical polymerization. The resulting glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was applied as an electrochemical biosensor for the determination of dopamine in the presence of ascorbic acid and uric acid. The material deposited on glassy carbon electrode was investigated in terms of morphology and structural analysis. The comparison of electrochemical behavior of the glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode with the glassy carbon electrode-graphene oxide, glassy carbon electrode-reduced graphene oxide, and glassy carbon electrode-poly(3,4-ethylenedioxythiophene) electrodes exhibited high electrocatalytic activity for dopamine detection. Electrochemical kinetic parameters of glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene), including the charge transfer coefficient α (0.49) and electron transfer rate constant k_s (1.04), were determined and discussed. The glassy carbon electrode-reduced graphene oxide-poly(3,4-ethylenedioxythiophene) electrode was studied for the determination of dopamine by differential pulse voltammetry and exhibited a linear range from 19.6 to 122.8?µM with a sensitivity of 3.27?µA?µM^?1?cm^?2 and a detection limit of 1.92?µM. The developed biosensor exhibited good selectivity toward dopamine with high reproducibility and stability.     

A Laser Reduced Graphene Oxide Grid Electrode for the Voltammetric Determination of Carbaryl

Laser-reduced graphene oxide (LRGO) on a polyethylene terephthalate (PET) substrate was prepared in one step to obtain the LRGO grid electrode for sensitive carbaryl determination. The grid form results in a grid distribution of different electrochemically active zones affecting the electroactive substance diffusion towards the electrode surface and increasing the electrochemical sensitivity for carbaryl determination. Carbaryl is electrochemically irreversibly oxidized at the secondary amine moiety of the molecule with the loss of one proton and one electron in the pH range from 5 to 7 by linear scan voltammetry (LSV) on the LRGO grid electrode with a scan rate of 300 mV/s. Some interference of the juice matrix molecules does not significantly affect the LSV oxidation current of carbaryl on the LRGO grid electrode after adsorptive accumulation without applied potential. The LRGO grid electrode can be used for LSV determination of carbaryl in fruit juices in the concentration range from 0.25 to 128 mg/L with LOD of 0.1 mg/L. The fabrication of the LRGO grid electrode opens up possibilities for further inexpensive monitoring of carbaryl in other fruit juices and fruits     

Preparation of Molecularly Imprinted Electrochemical Sensor for Detection of Vincristine Based on Reduced Graphene Oxide/Gold Nanoparticle Composite Film

An innovative molecularly imprinted electrochemical sensor was fabricated based on reduced graphene oxide (RGO) and gold nanocomposite (Au) for rapid detection of vincristine (VCR). The RGO‐Au composite membrane was obtained via direct one‐step electrodeposition technique of graphene oxide (GO) and chloroauric acid (HAuCl₄) on the surface of a glassy carbon electrode (GCE) by means of cyclic voltammetry (CV) in the potential range between ?1.5 and 0.6 V in phosphate buffer solution (PBS) of pH 9.18, which is capable of effectively utilizing its superior electrical conductivity, larger specific surface area due to its synergistic effect between RGO and Au. The molecularly imprinted polymers (MIPs) were synthesized on the RGO‐Au modified glassy carbon electrode surface with VCR as the template molecular, methyl acrylic acid (MAA) as the functional monomer, and ethylene glycol maleic rosinate acrylate (EGMRA) as a cross‐linker. The performance of the sensor was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) in detail. Under the optimum conditions, the fabricated sensor exhibited a linear relationship between oxidation peak current and VCR concentration over the range of 5.0×10^?8–5.0×10^?6 mol·L ^minus;1 with a correlation coefficient of 0.9952 and a detection limit (S/N=3) of 2.6×10^minus;8 mol·L^minus;1. The results indicated that the imprinted polymer films exhibited an excellent selectivity for VCR. The imprinted sensor was successfully used to determine VCR in real samples with recoveries of 90% –120% by using the standard addition method.     

Prussian Blue/Reduced Graphene Oxide Composite for the Amperometric Determination of Dopamine and Hydrogen Peroxide

Prussian blue has significant application for the construction of electrochemical biosensors. In this work, Prussian blue-reduced graphene oxide modified glass carbon electrodes were successfully fabricated using electrochemical deposition. The high surface area of graphene oxide enhanced the deposition of Prussian blue and the resulting electrocatalytic activity. Infrared spectroscopy and scanning electron microscopy showed that the relatively porous Prussian blue was on the surface of reduced graphene oxide. Cyclic voltammetry showed that Prussian blue-coated reduced graphene oxide composite films improved electron transfer compared to Prussian blue films. The Prussian blue-reduced graphene oxide composite film provided higher response for the reduction of hydrogen peroxide and the oxidation of dopamine compared with the Prussian blue film due to synergistic effects between the reduced graphene oxide and Prussian blue particles. The sensitivity of the electrode was 0.1617 µA µM^?1 cm^?2. The linear dynamic range extended from 0.5 µM to 0.7 mM dopamine with a limit of detection equal to 125 nM. This work provided a versatile strategy for the design and construction of sensitive amperometric sensors with robust electrocatalytic behavior.     

多巴胺在电沉积石墨烯修饰碳分子线电极上的电化学测定

以分子线二苯乙炔为修饰剂和粘合剂制备了一种新型的碳糊电极-碳分子线电极(CMWE),并以其为基底电极采用电化学还原法将石墨烯(GR)沉积到CMWE表面得到电沉积石墨烯修饰碳分子线电极(GR/CMWE)。考察了多巴胺(DA)在该修饰电极上的电化学行为。实验结果显示DA在GR/CMWE上出现了1对峰形良好的氧化还原峰,与裸电极相比,该氧化还原峰的电流增大,峰电位差减小,表明修饰电极对DA的电化学反应有催化作用。在最佳实验条件下峰电流与DA浓度在8.0×10-7~2.0×10-3mol/L范围内呈良好的线性关系,检出限(3σ)为2.55×10-7mol/L。将该电极用于多巴胺注射液样品的检测,结果满意。     

石墨烯修饰电极分子印迹电化学传感器的研制及其对多巴胺的测定

以石墨烯为电极增敏材料,多巴胺印迹聚合物为特异性识别材料,采用滴涂法组装石墨烯修饰电极的分子印迹电化学传感器。考察了pH值、石墨烯浓度、印迹聚合物浓度对传感器的影响,优化的实验条件为:pH 7.0,石墨烯浓度为0.5g/L,印迹聚合物浓度为20g/L。实验表明,该印迹传感器对多巴胺的响应电流远大于非印迹电极,同时该印迹传感器对多巴胺具有较好的选择性,检测范围为2.0×10-7～1.0×10-4mol/L,检出限(S/N=3)为6.8×10-8mol/L。该传感器用于盐酸多巴胺注射液的测定,其回收率为98%～105%。     

有序介孔碳/石墨烯/镍泡沫的制备及其对多巴胺的高灵敏度和高选择性检测

柔性生物传感器在可穿戴电子设备中有着广泛的应用前景. 为了获得柔性电化学多巴胺传感器,作者在本工作中首先在镍泡沫表面通过化学气相沉积生长石墨烯,随后通过高温碳化嵌段共聚物与酚醛树脂在石墨烯表面共组装形成的薄膜制备了有序介孔碳/石墨烯/镍泡沫（OMC/G/Ni）复合材料. 其中,镍泡沫可以为复合材料提供具有高导电性和良好柔韧性的金属骨架,而具有垂直排列介孔阵列的有序介孔碳层为复合材料提供了高的电活性表面积,且有利于活性位点的暴露. 值得注意的是,夹在有序介孔碳层和镍泡沫之间的石墨烯极大地增强了各组分之间的相容性,有利于进一步提升复合材料的电化学性能. 作为电化学传感器中的工作电极,OMC/G/Ni体现出优异的多巴胺检测能力. 不但具有宽的线性检测范围（0.05 ~ 58.75 μmol·L^-1）和低检测限（0.019 μmol·L^-1）,还具有良好的选择性、重现性和稳定性. 此外,OMC/G/Ni在弯曲状态下依旧能够保持对多巴胺的高检测能力,证明了其在柔性生物传感器中的应用潜力.     

An electrochemical sensor based on molecularly imprinted polydopamine coated on reduced graphene oxide for selective detection of ornidazole

The electrochemical sensing of ornidazole (OR) was achieved with a highly selective sensor fabricated by a combination of an electrochemically reduced graphene oxide (ERGO) and molecularly imprinted polydopamine (PDA). The sensor (OR-imp@PDA/ERGO/GCE) was synthesized by electrochemical polymerization of dopamine (DA) on ERGO modified glassy carbon electrode (GCE). The analytical response of the sensor changed linearly with OR concentration varying from 1.5 × 10⁻⁹ M to 1.0 × 10⁻⁸ M and 1.0 × 10⁻⁸ M to 2.0 × 10⁻⁷ M, and the detection limit was defined as 1.1 × 10⁻⁹ M. The proposed sensor ensured the highly sensitive detection of OR concentration because of the advantages of ERGO and molecularly imprinted PDA.     

聚多巴胺/多壁碳纳米管/玻璃碳电极上多巴胺的电分析

基于多巴胺（DA）在多壁碳纳米管（MWCNTs）修饰玻璃碳（GC）电极上的电聚合,制得聚多巴胺(PDA)/MWCNTs/GC电极,并对该修饰电极进行了电化学阻抗谱 (EIS)和循环伏安法(CV)表征。 在该修饰电极上,DA呈现良好的电化学行为。在pH=7.4磷酸缓冲溶液中其氧化电流显著高于在裸电极上的响应,且能有效地抑制2.0 mmol/L抗坏血酸(AA)或K4Fe(CN)6的直接电化学响应,表明MWCNTs可增敏信号,且阳离子选择透过性PDA膜可抑制阴离子的电化学干扰。 采用CV实验检测DA,DA氧化的半微分伏安峰高(ipa-sd)与多巴胺浓度在0.08～1.76 μmol/L范围内呈线性关系,在无抗坏血酸和有0.5 mmol/L抗坏血酸共存时的线性回归方程分别为ipa-sd(μA/s1/2)=0.107+0.405c(μmol/L)（r2=0.986）和ipa-sd(μA/s1/2)=0.628+0.649c(μmol/L)(r2=0.992),检测限均为8.0×10-8 mol/L(S/N=3)。 该法用于盐酸多巴胺注射液中多巴胺的快速测定,结果满意。     

Systematic Comparison of Graphene Materials for Supercapacitor Electrodes

A comparison of the performance of graphene-based supercapacitors is difficult, owing to the variety of production methods used to prepare the materials. To the best of our knowledge, there has been no systematic investigation into the effect of the graphene production method on the supercapacitor performance. In this work, we compare graphene produced through several routes. This includes anodic and cathodic electrochemically exfoliated graphene, liquid phase exfoliated graphene, graphene oxide, reduced graphene oxide, and graphene nanoribbons. Graphene oxide exhibited the highest capacitance of approximately 154 F g⁻¹ in 6 M KOH at 0.5 A g⁻¹ attributed to oxygen functional groups giving an additional pseudocapacitance and preventing significant restacking; however, the capacitance retention was poor, owing to the low conductivity. In comparison, the anodic electrochemically exfoliated graphene exhibited a capacitance of approximately 44 F g⁻¹, the highest of the ‘pure’ graphene materials, which all exhibited superior capacitance retention, owing to their higher conductivity. The cyclability of all of the materials, with the exception of reduced graphene oxide (70 %), was found to be greater than 95 % after 10 000 cycles. These results highlight the importance of matching the graphene production method with a specific application; for example, graphene oxide and anodic electrochemically exfoliated graphene would be best suited for high energy and power applications, respectively.     

Treated Screen Printed Electrodes Based on Electrochemically Reduced Graphene Nanoribbons for the Sensitive Voltammetric Determination of Dopamine in the Presence of Uric Acid

In this research, the graphene oxide nanoribbons (GONRs) were substantially synthesized by the oxidative longitudinal unzipping of the multi‐walled carbon nanotubes (MWCNTs). Then, a direct electrochemical technique was employed for reducing GONRs adsorbed on the screen printed carbon electrode (SPCE). Electrochemical reduction effectively eliminated the oxygen‐containing groups in the GONRs and produced the electrochemically reduced graphene nanoribbons (ERGNRs). Field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were employed to characterize the materials. The modified SPCE with ERGNRs (ERGNRs/SPCE) displayed acceptable electrocatalytic characteristics towards the oxidation of dopamine (DA) and uric acid (UA) and applied to the simultaneous determination of these two analytes. ERGNRs/SPCE has a peak potential difference of 245 mV between DA and UA. The anodic peak currents of DA and UA were linear within the concentration ranges between 0.5 and 300.0 μM and 1.0 to 400.0 μM in phosphate buffer (pH=7.0) respectively. The detection limit of the technique for DA is 0.15 μM (S/N=3) and for UA is 0.3 μM (S/N=3). The proposed approach has been applied to the determination of DA and UA in real samples and generated acceptable outputs.     

Effect of Graphene Characteristics on Morphology and Performance of Composite Noble Metal-Reduced Graphene Oxide SERS Substrate

Graphene/noble metal substrates for surface enhanced RAMAN scattering (SERS) possess synergistically improved performance, due to the strong chemical enhancement mechanism accounted to graphene and the electromagnetic mechanism raised from the metal nanoparticles. However, only the effect of noble metal nanoparticles characteristics on the SERS performance was studied so far. In attempts to bring a light to the effect of quality of graphene, in this work, two different graphene oxides were selected, slightly oxidized GOS (20%) with low aspect ratio (1000) and highly oxidized (50%) GOG with high aspect ratio (14,000). GO and precursors for noble metal nanoparticles (NP) simultaneous were reduced, resulting in rGO decorated with AgNPs and AuNPs. The graphene characteristics affected the size, shape, and packing of nanoparticles. The oxygen functionalities actuated as nucleation sites for AgNPs, thus GOG was decorated with higher number and smaller size AgNPs than GOS. Oppositely, AuNPs preferred bare graphene surface, thus GOS was covered with smaller size, densely packed nanoparticles, resulting in the best SERS performance. Fluorescein in concentration of 10⁻⁷ M was detected with enhancement factor of 82 × 10⁴. This work demonstrates that selection of graphene is additional tool toward powerful SERS substrates.     

三维还原氧化石墨烯/聚苯胺复合材料的制备及其超级电容性能

以制备的氧化石墨凝胶和聚苯胺纳米线为原料, 将二者按一定的质量比进行混合超声分散, 再以混合分散液为前驱体采用一步水热法制备得到三维还原氧化石墨烯(RGO)/聚苯胺(PANI) (RGP)复合材料, 采用扫描电镜(SEM), 透射电镜(TEM), X射线衍射(XRD), 傅里叶变换红外(FT-IR)光谱, X射线光电子能谱(XPS)和电化学测试等分析研究了复合材料的形貌、结构和超级电容性能. 结果表明, 复合材料既保持了还原氧化石墨烯的基本形貌, 又能使聚苯胺较好地镶嵌在还原氧化石墨烯的网状结构中; 且当氧化石墨与聚苯胺的质量比为1:1时复合材料在0.5 A·g^-1电流密度下比电容可高达758 F·g^-1, 即使在大电流密度(30 A·g^-1)下其比容量仍高达400 F·g^-1,在1A·g^-1电流密度下循环1000次后比容量保持率为86%, 表现出了良好的倍率性能和循环稳定性, 其超级电容性能远优于单纯的还原氧化石墨烯和聚苯胺, 其优异的超级电容性能可归咎于二者的相互协同作用.     

Injectable Graphene Oxide/Graphene Composite Supramolecular Hydrogel for Delivery of Anti-Cancer Drugs

Injectable hydrogels have attracted a lot of attention in drug delivery, however, their capacity to deliver water-insoluble or hydrophobic anti-cancer drugs is limited. Here, we developed injectable graphene oxide/graphene composite supramolecular hydrogels to deliver anti-cancer drugs. Pluronic F-127 was used to stabilize graphene oxide (GO) and reduced graphene oxide (RGO) in solution, which was mixed with α-cyclodextrin (α-CD) solution to form hydrogels. Native hydrogel was used as control. GO or RGO slightly shortened gelation time. The storage and loss moduli of the hydrogels were tracked by dynamic force measurement. The storage modulus of GO or RGO composite hydrogels was larger than that of the native hydrogel. Hydrogels were unstable in solution and eroded gradually. GO or RGO in Pluronic F-127 solution could potentially improve the solubility of the water-insoluble anti-cancer drug camptothecin (CPT), especially with large drug-loaded CPT amount. Drug release behaviors from solutions and hydrogels were characterized. The nanocomponents (GO or RGO) were able to bind more drug molecules either for CPT or for doxorubicin hydrochloride (DXR) in solution. Therefore, GO or RGO composite hydrogel could potentially enable better controlled and gentler drug release (for both CPT and DXR) than native hydrogel.     

还原氧化石墨烯/金纳米修饰电极在新冠病毒检测中的应用

研究使用电化学沉积法在丝网印刷碳电极表面制备了还原氧化石墨烯和金纳米颗粒,构建了一种用于新冠病毒检测的石墨烯电化学传感器。通过扫描电子显微镜(SEM)和相应的电化学方法对纳米复合材料在电极表面的成功修饰进行了表征分析。并采用差分脉冲伏安法对传感器的性能进行检测,实验构建的电化学传感器具有良好的灵敏度,该传感器检线性范围为10_-10^-10_-6^mol/L,具有良好的重复性和特异性。     

氧化石墨烯水热还原前后的发光光谱

分别采用改进Hummers方法和水热还原法制备了氧化石墨烯(GO)和还原氧化石墨烯(RGO)。 GO和RGO经透射电子显微镜(TEM)、紫外-可见吸收光谱(UV-Vis)、红外光谱(IR)、荧光发射和激发光谱(PL、PLE)等技术手段进行了表征。 荧光发射光谱显示,氧化石墨烯(GO)在可见光的激发下可以得到波长在600~800 nm范围内的宽谱近红外荧光。 通过比较氧化石墨烯水热还原前后的光谱变化,发现氧化石墨烯近红外荧光起源于氧化石墨烯的表面含氧基团,如C=O、COOH。 近红外荧光穿透性好、对生物组织损坏小,非常适合于生物成像,预示着氧化石墨烯在生物成像方面的应用潜力。     

Chitosan/Nitrogen Doped Reduced Graphene Oxide Modified Biosensor for Impedimetric Detection of microRNA

The development of a low‐cost and disposable biosensor platform for the sensitive and rapid detection of microRNAs (miRNAs) is of great interest for healthcare, pharmaceuticals, and medical science. We designed an impedimetric biosensing platform using Chitosan (CHIT)/nitrogen doped reduced graphene oxide (NRGO) conductive composite to modify the surface of pencil graphite electrodes (PGE) for the sensitive detection of miRNAs. An initial optimisation protocol involved investigation of the effect of NRGO concentration and miR 660 DNA probe concentration on the response of the modified electrode. After the optimization protocol, the sequence‐selective hybridization between miR 660 DNA probe and its RNA target was evaluated by measuring changes on charge transfer resistance, R_ct values. Moreover, the selectivity of impedimetric biosensor was tested in the presence of non‐complementary miRNA (NC) sequences, such as miR 34a and miR 16. The hybridization process was examined both in phosphate buffer (PBS) and in PBS diluted fetal bovine serum (FBS:PBS) solutions. The biosensor demonstrated a detection limit of 1.72 μg/mL in PBS and 1.65 μg/mL in FBS:PBS diluted solution. Given the easy, quick and disposable attributes, the proposed conductive nanocomposite biosensor platform shows great promise as a low‐cost sensor kit for healthcare monitoring, clinical diagnostics, and biomedical devices.     

部分还原氧化石墨烯/二氧化钛复合材料的水热合成及其光催化活性

采用水热法以Hummers氧化法制备的氧化石墨和钛酸四丁酯为原料制备了部分还原的氧化石墨烯/二氧化钛(RGO/TiO₂)复合光催化剂, 并研究了该复合材料在可见光以及紫外光下对亚甲基蓝的光催化降解活性.结果表明, 通过改变反应温度和氧化石墨加入量可以调控TiO₂的晶相组成及其在复合材料中的分散性; 在水热反应过程中氧化石墨烯发生了部分还原; 所制备的RGO/TiO₂复合材料的可见光和紫外光催化活性均高于纯TiO₂; 部分还原的氧化石墨烯在复合材料中担当载体和电子受体, 同时可以使TiO₂的初始吸收边向可见光区域红移, 增强了TiO₂在可见光区域的吸收, 能有效提高对目标污染物的吸附性和光催化降解活性.