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.     

Hydroxyapatite Nanoparticles Modified Graphite Electrodes for Electrochemical DNA Detection

Hydroxyapatite nanoparticles (HaNP) modified pencil graphite electrodes (PGEs) were developed for the first time in the literature, and accordingly they were applied for electrochemical monitoring of sequence‐selective DNA hybridization. The experimental conditions for HaNP modification of PGE, and DNA hybridization related to Hepatitis B Virus (HBV) DNA sequence were optimized. The microscopic and electrochemical characterization of HaNP‐PGE in contrast to the unmodified one was utilized. Under optimized experimental conditions, the selectivity of HBV DNA probe immobilized biosensor was tested against to non‐complementary (NC), mismatch (MM) sequences and the mixture of target:NC (1 : 1) or target: MM (1 : 1).     

Ionic Liquid Modified Single‐use Electrode Developed for Voltammetric Detection of miRNA‐34a and its Application to Real Samples

The ionic liquid (IL) modified chemically activated (CA) pencil graphite electrodes (PGEs) were developed for label‐free voltammetric detection of miRNA‐34a, and implemented to the real samples. Firstly, the electrochemical characterization of unmodified PGE, CA‐PGE, IL‐PGE and IL‐CA‐PGE was performed by cyclic voltammetry (CV) as well as their DNA binding capacity was studied by electrochemical impedance spectroscopy (EIS) technique. The microscopic characterization of the surface of each electrodes was investigated by scanning electron microscopy (SEM). Differential pulse voltammetry (DPV) technique was used for measuring the oxidation signal of guanine in order to perform a label‐free voltammetric monitoring of a full‐match hybridization specific to miRNA‐34a. The selectivity of biosensor was tested against to miRNA‐155, miRNA‐660 as well as to the mismatch sequence of miRNA‐34a. The further selectivity of this proposed biosensor was studied in the mixture of samples containing miRNA‐34a with other miRNAs (1 : 1). The voltammetric detection of miRNA‐34a was also explored in the artificial serum medium as fetal bovine serum (FBS) and also in total RNA samples isolated from HUH‐7 human hepatocellular carcinoma cell line.     

基于石墨烯化学修饰电极的适体传感器

采用石墨烯(RGO)作载体,凝血酶适体(TBA)作探针,凝血酶为目标蛋白,电化学阻抗谱(EIS)为检测技术,建立了检测蛋白质的新方法。由于RGO可增大电极有效表面积并提高电极表面电子传输速率以及TBA的特异性识别能力,此方法具有较高的灵敏度和良好的选择性。采用本方法检测凝血酶的线性范围为0.3～10 fmol/L,检出限为0.26 fmol/L。本研究将RGO应用于电化学适体传感器,证实了RGO修饰电极在电化学适体传感器领域中潜在的应用价值。     

Impedimetric Aptasensor Based on Disposable Graphite Electrodes Developed for Thrombin Detection

The impedimetric aptasensor for Thrombin (THR) was developed for the first time herein by measuring changes at the charge‐transfer resistance, R_ct upon to protein? aptamer complex formation. After covalent activation of pencil graphite electrode (PGE) surface using covalent agents, amino linked aptamer (APT) was immobilized onto activated PGE surface. Then APT‐THR interaction was explored by electrochemical impedance spectroscopy (EIS). After the optimization of experimental conditions (e.g., APT and THR concentration, immobilization and interaction times), the selectivity of impedimetric aptasensor was tested in the presence of other biomolecules: factor Va and bovine serum albumine (BSA) both in buffer media, or in diluted fetal bovine serum (FBS).     

Nickel and Tungsten Bimetallic Nanoparticles Modified Pencil Graphite Electrode: A High-performance Electrochemical Sensor for Detection of Endocrine Disruptor Bisphenol A

In this work, an economically viable, very low cost, indigenous, ubiquitously available electrochemical sensor based on bimetallic nickel and tungsten nanoparticles modified pencil graphite electrode (NiNP-WNP@PGE) was fabricated for the sensitive and selective detection of bisphenol A (BPA). The NiNP-WNP@PGE sensor was prepared by a facile electrochemical one step co-deposition method. The prepared nanocomposite was morphologically characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray diffraction (XRD), electrochemically by cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The proposed sensor displayed high electrocatalytic activity towards electro-oxidation of BPA with one irreversible peak. The fabricated sensor displayed a wide detection window between 0.025 μM and 250 μM with a limit of detection of 0.012 μM. PGE sensor was successfully engaged for the detection of BPA in bottled water, biological, and baby glass samples.     

Reduced Graphene Oxide Nanocomposite Modified Electrodes for Sensitive Detection of Ciprofloxacin

The synthesis of novel nanocomposites with great sensing enhancement has played an important role in analytical chemistry, especially in the electrochemical detection of drug molecules. In this work, we report a wet chemical method for the preparation of a gold nanoparticle coated β‐cyclodextrin functionalized reduced graphene oxide nanocomposite. A number of different analytical techniques including ultraviolet‐visible spectroscopy, fourier transform infrared spectroscopy, scanning electron microscope and energy dispersive X‐ray spectroscopy were employed to characterize the as‐synthesized nanocomposite. With excellent electrocatalytic properties and high supramolecular recognition ability, the as‐synthesized nanocomposite was used to modify a glassy carbon electrode surface for the sensitive determination of ciprofloxacin using voltammetric technique. The current response of ciprofloxacin on the nanocomposite modified electrode was greatly enhanced compared to that on the bare and other modified electrodes. Using differential pulse voltammetry, the oxidation peak currents increased linearly with the ciprofloxacin concentrations in the range between 0.01 to 120 μM with a detection limit of 2.7 nM. The electrochemical testing results showed good stability and reproducibility. Therefore, the nanocomposite could be a potential candidate for the development of electrochemical sensors for sensitive and selective determination of ciprofloxacin or similar drugs in the future.     

化学改性氧化石墨烯交联的聚酰亚胺气凝胶

聚酰亚胺(PI)气凝胶是一类密度低、机械性能好、隔热性能优异的多孔材料, 通常使用昂贵的化学交联剂进行交联. 氧化石墨烯(GO)是近年来广受关注的用于聚合物增强的纳米功能填料. 以前报道的PI/GO 复合材料多是纤维或膜的形式. 为了获得PI/GO 复合气凝胶, 本文采用化学改性氧化石墨烯(m-GO)替代1,3,5-三(4-氨基苯氧基)苯(TAB)等常规的交联剂, 使之与4,4'-二氨基二苯基醚(ODA)和3,3',4,4'-联苯四羧酸二酐(BPDA)反应, 制得了m-GO交联的PI 气凝胶. GO的化学改性通过其与过量ODA在水热条件下反应实现. 通过扫描电子显微镜(SEM)研究了PI/m-GO气凝胶的微观结构. 分别通过氮气吸脱附测试、热重分析和热线法研究了m-GO对气凝胶的孔特性、热稳定性和热导率的影响. 测试结果表明, 所获得的PI/m-GO气凝胶保持了高的孔隙率、热稳定性和绝热性. 压缩测试结果显示, 与采用1.8% (质量分数, w)的TAB进行交联的PI 气凝胶相比,仅用0.6% (w)的m-GO交联所获得的气凝胶具有更高的比杨氏模量(杨氏模量/密度)、比屈服强度(屈服强度/密度)和更小的体积收缩率.     

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。     

还原氧化石墨烯改性少层剥离石墨增强石墨基钾离子电池负极稳定性

钾在石墨中嵌入电位较低,因此石墨负极可使钾离子电池具有较高的能量密度,是一种理想的钾离子电池负极材料。然而,石墨嵌钾后的体积膨胀率高达60%,导致钾离子电池的循环稳定性较差。此外,钾嵌入石墨层间的动力学过程缓慢,制约了钾离子电池倍率性能的提升。在本工作中,我们用还原氧化石墨烯(rGO)包覆剥离石墨(EG),得到一种具有协同效应的层状复合材料。一方面,以少层的EG代替石墨可以减少由于钾的嵌入/脱嵌所引起的体积膨胀和内部应力;另一方面,外层rGO可以避免EG的堆叠,这有利于加速动力学过程并在钾化/去钾化过程中稳定结构。当复合材料所用EG和GO的质量比为1 : 1时,其性能达到最优,在50 mA·g^-1的电流密度下能够提供443 mAh·g^-1的比容量;在电流密度为800 mA·g^-1时,比容量为190 mAh·g^-1,保持率为42.9%。相同测试条件下,纯EG和rGO的容量保持率仅为14.2%和27.2%。测试结果说明EG-1/rGO-1复合材料在比容量和倍率性能两个方面得到了提升。     

Carbon Nanotubes Modified Graphite Electrodes for Monitoring of Biointeraction Between 6‐Thioguanine and DNA

In this present study, single‐walled carbon nanotubes (SWCNT) modified disposable pencil graphite electrodes (SWCNT‐PGEs) were developed for the electrochemical monitoring of anticancer drug, and its interaction with double stranded DNA (dsDNA). Under this aim, SWCNT‐PGEs were applied for the first time in the literature to analyse of 6‐Thioguanine (6‐TG), and also to investigate its interaction with DNA by voltammetric and impedimetric methods. The surface morphologies of PGE and SWCNT‐PGE were explored using scanning electron microscopy (SEM) and electrochemical characterization of unmodified/modified electrodes was performed by cyclic voltammetry (CV). Experimental parameters; such as, the concentration of 6‐TG and its interaction time with dsDNA were optimized by using differential pulse voltammetry (DPV). Additionally, the interaction of 6‐TG with dsDNA was studied in case of different interaction times by electrochemical impedance spectroscopy (EIS) in contrast to voltammetric results. The detection limit of 6‐TG was found to be 0.25 μM by SWCNT‐PGE.     

Free‐Radical‐Promoted Conversion of Graphite Oxide into Chemically Modified Graphene

The preparation of chemically modified graphene (CMG) generally involves the reduction of graphite oxide (GO) by using various reducing reagents. Herein, we report a free‐radical‐promoted synthesis of CMG, which does not require any conventional reductant. We demonstrated that the phenyl free radical can efficiently promote the conversion of GO into CMG under mild conditions and produces phenyl‐functionalized CMG. This pseudo‐“reduction” process is attributed to a free‐radical‐mediated elimination of the surface‐attached oxygen‐containing functionalities. This work illustrates a new strategy for preparing CMG that is alternative to the conventional means of chemical reduction. Furthermore, the phenyl‐functionalized graphene shows an excellent performance as an electrode material for lithium‐battery applications.     

Electrochemical Detection of Activated Protein C Using an Aptasensor Based on PAMAM Dendrimer Modified Pencil Graphite Electrodes

Electrochemical aptasensing of APC was carried out using PAMAM dendrimer modified pencil graphite electrodes (PGEs) for the first time herein. Poly(amidoamine) dendrimer having 16 succinamic acid surface groups (generation 2, G2‐PS) modified PGEs were developed, and then were utilized for APC monitoring using differential pulse voltammetry, electrochemical impedance spectroscopy and cyclic voltammetry. The selectivity of single‐use aptasensor was tested against to other proteins; BSA and THR as well as to the affinity of APC binding to different DNA aptamer, or oligonucleotide. Voltammetric APC detection was also explored in a diluted fetal bovine serum resulting with a detection limit DL as 1.5 µg/mL.     

Simultaneous,Selective and Highly Sensitive Voltammetric Determination of Lead,Cadmium, and Zinc via Modified Pencil Graphite Electrodes

Pencil graphite electrode (PGE) modified with MWCNT and Bi³⁺ (MWCNT/Bi/PGE) was utilized in simultaneous analysis of Pb²⁺, Cd²⁺, and Zn²⁺. Surface and electrochemical characteristics of MWCNT/Bi/PGE were investigated via SEM, cyclic voltammetry, electrochemical impedance spectroscopy, and FTIR measurements. Even though modification with MWCNT did not improve the electroactive surface area, it significantly decreased the charge transfer resistance. Furthermore, modification with Bi³⁺ significantly increased the sensitivity. Finally, MWCNT/Bi/PGE exhibited the highest sensitivity and reproducibility compared to PGE and PGE modified with only MWCNT. MWCNT/Bi/PGE provided LOD values of 0.27, 0.43, and 1.63 μg L⁻¹, and linear ranges of 1–80, 5–80, and 10–80 μg L⁻¹ for Pb²⁺, Cd²⁺, and Zn²⁺, respectively. Proposed modification method offers effective electroanalytical performance with low time consumption and cost for the analyst.     

Copper Oxide – Graphite Composite Electrodes: Application to Nitrite Sensing

A simple method for the modification of carbon powder with copper oxides is presented. Carbon powder is impregnated with copper(II) nitrate by stirring carbon powder in copper(II) nitrate solution for 1 hour and subsequently thermally treated at 823 K. The modified carbon powder was characterized using electrochemical and spectroscopic techniques. The existence of both copper(I) and copper(II) oxides have been established. The copper oxide modified carbon powder was used for preparation of composite electrodes, and the electrochemical and electrocatalytic behavior of the resulting composite electrodes was studied. The copper oxide modified carbon powder – epoxy composite electrodes showed a high electrocatalytic activity for the nitrite detection in aqueous media, with the detection limit comparable or lower than detection limits obtained with other electrochemical sensors.     

Applications of Chemically Modified Electrodes to Analysis of Metal Ions

Abstract

A carbon paste electrode containing chemically modified graphite has been fabricated and applied to the analysis of silver ion in aqueous media. Utilizing complexation and subsequent precipitation steps, it is shown that one can preconcentrate and then analyze for metal ions at low concentrations using these electrodes.     

Electrochemical Investigation of Gold Based Screen Printed Electrodes: An Application for a Seafood Toxin Detection

Although commercial screen-printed electrodes (SPEs) are used extensively for biosensor purposes nowadays, detailed studies on characterization are still limited. In this study, the surface of the gold-based screen-printed electrode (SPGE) was carefully modified with self-assembly-monolayer through an optimized immobilization procedure. The key physical and chemical properties with regeneration capacity of the developed biosensors were assessed by various characterization techniques. Then SPGE was used to determine its sensitivity, limit of detection (LOD) and limit of quantification (LOQ) for a toxin substance of domoic acid in seafood that has become more common and rising concern of marine wildlife and seawater pollution. LOD in phosphate buffered saline (PBS) and cell culture media were obtained as 2.93 ng mL⁻¹ and 4.28 ng mL⁻¹, respectively. The reduced sensitivity for antibody-based biosensors in the cell culture medium was probably due to interaction of nonspecific compounds with DA in the culture medium compared to the much less complex environment of PBS. In addition, the regeneration capacity has been found very limited due to inherent heterogeneity and low robustness. This study can be used for the main challenges with the design requirements of commercial SPE-based biosensors to provide a detailed perspective for further toxicity studies.     

Polymer/Iron Oxide Nanoparticle Modified Glassy Carbon Electrodes for the Enhanced Detection of Epinephrine

Novel electrochemical sensors for epinephrine (EP) based on a glassy carbon electrode (GCE) modified with a redox polymer film and iron (III) oxide nanoparticles (Fe₂O₃NP) have been developed. Two redox polymers‐poly(brilliant cresyl blue) (PBCB) and poly(Nile blue) (PNB), and two different architectures‐polymer/Fe₂O₃/GCE and Fe₂O₃/polymer/GCE were investigated. The electrochemical oxidation of epinephrine at the modified electrodes was performed by differential pulse voltammetry (DPV), in pH 7 electrolyte, and the analytical parameters were determined. The results show enhanced performance, more sensitive responses and lower detection limits at the modified electrodes, compared to other electrochemical epinephrine sensors reported in the literature. The best voltammetric response with the lowest detection limit was obtained for the determination of epinephrine at PBCB/Fe₂O₃/GCE. The novel sensors are reusable, with good reproducibility and stability, and were successfully applied to the determination of epinephrine in commercial injectable adrenaline samples.     

Chemically Modified Electrodes for Recessed Microelectrode Array

Chemical modifications on recessed microelectrode array, achieved via electrodeposition techniques are reported here. Silicon-based gold microelectrode arrays of 10 μm microband and microdisc array were selected and functionalised using sol-gel and nanoporous gold (NPG) respectively. For electrochemically assisted self-assembly (EASA) formati6154on of sol-gel, electrode surface was first pre-treated with a self-assembled partial monolayer of mercaptopropyltrimethoxysilane (MPTMS) before transferring it into the sol containing cetyltrimethyl ammonium bromide (CTAB)/tetraethoxysilane (TEOS):MPTMS (90:10) precursors. A cathodic potential is then applied. It was found that larger current densities were required in ensuring successful film deposition when moving from macro- to micro- dimensions. For NPG modification, a chemical etching process called dealloying was employed. NPG of three different thicknesses have been successfully deposited. All the modified and functionalized microelectrode arrays were characterized by both optical (SEM) and electrochemical analysis (cyclic voltammetry and impedance spectroscopy). An increase in surface area and roughness has been observed and such will benefit for future sensing application.     

Interfacial Capacitance of Graphene Oxide Films Electrodes: Fundamental Studies on Electrolytes Interface Aiming (Bio)Sensing Applications

The understanding of bidimensional materials dynamics and its electrolyte interface equilibrium, such as graphene oxide (GO), is critical for the development of a capacitive biosensing platform. The interfacial capacitance (C_i) of graphene-based materials may be tuned by experimental conditions such as pH optimization and cation size playing key roles at the enhancement of their capacitive properties allowing their application as novel capacitive biosensors. Here we reported a systematic study of C_i of multilayer GO films in different aqueous electrolytes employing electrochemical impedance spectroscopy for the application in a capacitive detection system. We demonstrated that the presence of ionizable oxygen-containing functional groups within multilayer GO film favors the interactions and the accumulation of cations in the structure of the electrodes enhancing the GO C_i in aqueous solutions, where at pH 7.0 (the best condition) the C_i was 340 μF mg⁻¹ at −0.01 V vs Ag/AgCl. We also established that the hydrated cation radius affects the mobility and interaction with GO functional groups and it plays a critical role in the Ci, as demonstrated in the presence of different cations Na⁺=640 μF mg⁻¹, Li⁺=575 μF mg⁻¹ and TMA⁺=477 μF mg⁻¹. As a proof-of-concept, the capacitive behaviour of GO was explored as biosensing platform for standard streptavidin-biotin systems. For this system, the C_i varied linearly with the log of the concentration of the targeting analyte in the range from 10 pg mL⁻¹ to 100 ng mL⁻¹, showing the promising applicability of capacitive GO based sensors for label-free biosensing.