Immobilization and electrochemical behavior of gold nanoparticles modified leukemia K562 cells and application in drug sensitivity test

A new strategy for immobilization of tumor cells on electrode surface and accelerating electron transfer between electrode and the immobilized cells was proposed to study the electrochemical behavior of cells and the effect of antitumor drug on cell viability. The leukemia K562 cells immobilized in a microporous cellulose membrane were firstly modified with colloidal gold nanoparticles to retain efficiently the activity of immobilized living tumor cells and promote electron transfer between electroactive centers of the cells and the electrode, exhibiting a well-defined anodic peak of guanine at +0.830 V at 50 mV s⁻¹. The electrochemical response could be used to describe cell growth and evaluate the effectiveness of antitumor drug methotrexate on tumor cells. The proposed method offered potential advantages for drug sensitivity test with little usage of cells. It could be developed as a convenient means for the study of the tumor cells growth and the cytotoxicity of antitumor drugs.     

Fabrication and Application of a Novel Modified Electrode Based on Multiwalled Nanotubes/Cerium(III) 12‐Tungstophosphoric Acid Nanocomposite

A novel multiwalled nanotubes (MWNTs)/Cerium(III) 12 ‐ tungstophosphoric acid (CePW) nanocomposite film glassy carbon electrode was prepared in this paper. Electrochemical behaviors of the CePW/MWNTs modified electrode were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This modified electrode brought new capabilities for electrochemical devices by combining the advantages of carbon nanotubes, rare‐earth, and heteropoly‐acids. The results demonstrated that the CePW/MWNTs modified electrode exhibited enhanced electrocatalytic behavior and good stability for the detection of guanine and adenine in 0.1 M PBS (pH 7.0). The experimental parameters were optimized and a direct electrochemical method for the simultaneous determination of guanine and adenine was proposed. The detection limit (S/N=3) for guanine and adenine was 2.0×10^?8 M and 3.0×10^?8 M, respectively. Further, the acid‐denatured calf thymus DNA was also detected and the result was satisfied.     

Hydrophobic adsorption of surfactants on water-soluble carbon nanotubes: A simple approach to improve sensitivity and antifouling capacity of carbon nanotubes-based electrochemical sensors

Water-soluble multi-walled carbon nanotubes (MWNTs) were prepared by the strong adsorption of Congo red (CR) on MWNTs. The CR-functionalized MWNTs (MWNTs–CR) had a high solubility, a high purity and a special property of strong rebundling when dried, capable of forming uniform and compact MWNTs films with a 3D network structure of nanosizes on a glassy carbon electrode (GCE). Compared with GCE, the electrochemical response of estradiol at a MWNTs–CR modified glassy carbon electrode (MWNTs–CR/GCE) was greatly enhanced, which was further amplified by the addition of trace cetyltrimethylammonium bromide (CTAB) in solution, along with the accomplishment of antifouling capacity of the modified electrode. The weak hydrophobic adsorption of surfactants on the hydrophobic and smooth surface of MWNTs was found to be the key for simultaneously improving the sensitivity and antifouling capacity of carbon nanotube-based electrochemical sensors by surfactants.     

Electrochemical Reduction of Oxygen on Multi-walled Carbon Nanotubes Electrode in Alkaline Solution

The multi-walled carbon nanotubes (MWNTs) electrode was constructed using polytetrafluoroethylene as binder, and the electrochemical reductive behavior of oxygen in alkaline solution was first examined on this electrode. Compared with other carbon materials, MWNTs show higher electrocatalytic activity, and the reversibility of O2 reduction reaction is greatly improved. The experiments reveal that the electrochemical reduction of O2 to HO2 is controlled by adsorption. The preliminary results illustrate the potential application of MWNTs in fuel cells.     

Some Properties of Sodium Dodecyl Sulfate Functionalized Multiwalled Carbon Nanotubes Electrode and Its Application on Detection of Dopamine in the Presence of Ascorbic Acid

A sodium dodecyl sulfate (SDS) functionalized multiwalled carbon nanotubes (MWNTs) electrode (SDS/MWNTs) was successfully constructed in this study. The electrochemical property of the SDS/MWNTs electrode has been characterized by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Nyquist plots suggest that the immersion time of SDS affects the resistances of the MWNTs electrodes. The thickness of adsorbed SDS on MWNTs surface is estimated to be 1.23 nm, which is close to the value of SDS monolayer. CV results demonstrate a 5‐fold enhanced response for dopamine (DA) at the SDS/MWNTs electrode compared to the bare MWNTs one. DPV results illustrate that DA can be selectively determined in the presence of high concentration ascorbic acid (AA) with a linear range from 20 μM to 0.20 mM and a sensitivity of 0.024 μA μM^?1 at the SDS/MWNTs electrode.     

Magnetic immobilization and electrochemical detection of leukemia K562 cells

A new protocol was proposed for rapid magnetic isolation, immobilization and electrochemical detection of leukemia K562 cells via their decoration with cationic magnetic nanoparticles (CMNPs). The CMNPs (3-aminopropyltriethoxysilane-treated Fe₃O₄) were synthesized in liquid solution and characterized by transmission electron microscopy. After the incubation of pre-cultured leukemia K562 cells in the coexistence of CMNPs for a period of time, the CMNPs modified living cells could be rapidly isolated from the medium and immobilized firmly on the electrode surface via a magnetic field, as traced by quartz crystal microbalance. The cyclic voltammetric experiments of the cells immobilized at glassy carbon electrode exhibited an irreversible anodic current peak whose height is proportional to cell viability, and the 5-fluorouracil cytotoxicity results obtained from the proposed magnetic-electrochemical method were supported by conventional MTT assays. The proposed method is simple, rapid, inexpensive, and convenient in electrode renewal, which is recommended as a promising experimental platform for wider applications in biosensing and cellular researches.     

Synergistic effects of nano-ZnO/multi-walled carbon nanotubes/chitosan nanocomposite membrane for the sensitive detection of sequence-specific of PAT gene and PCR amplification of NOS gene

The remarkable synergistic effects of the zinc oxide (ZnO) nanoparticles and multi-walled carbon nanotubes (MWNTs) were developed for the ssDNA probe immobilization and fabrication of the electrochemical DNA biosensor. The ZnO/MWNTs/chitosan nanocomposite membrane-modified glassy carbon electrode (ZnO/MWNTs/CHIT/GCE) was fabricated and the ssDNA probes were immobilized on the modified electrode surface. The preparation method is quite simple and inexpensive. The hybridization events were monitored by differential pulse voltammetry (DPV) using methylene blue (MB) as an indicator. As compared with previous MWNTs-based DNA biosensors, this composite matrix combined the attractive biocompatibility of ZnO nanoparticles with the excellent electron-transfer ability of MWNTs and fine membrane-forming ability of CHIT increased the DNA attachment quantity and complementary DNA detection sensitivity. The approach described here can effectively discriminate complementary DNA sequence, noncomplementary sequence, single-base mismatched sequence and double-base mismatched sequence related to phosphinothricin acetyltransferase (PAT) gene in transgenic corn. Under optimal conditions, the dynamic detection range of the sensor to PAT gene complementary target sequence was from 1.0 × 10⁻¹¹ to 1.0 × 10⁻⁶ mol/L with the detection limit of 2.8 × 10⁻¹² mol/L. The polymerase chain reaction (PCR) amplification of nopaline synthase (NOS) gene from the real sample of one kind of transgenic soybeans was also satisfactorily detected with this electrochemical DNA biosensor, suggesting that the ZnO/MWNTs/CHIT nanocomposite hold great promises for sensitive electrochemical biosensor applications.     

Antileishmanial Drug Miltefosine‐dsDNA Interaction in situ Evaluation with a DNA‐Electrochemical Biosensor

Leishmaniasis is one of the most important parasitic neglected disease. The electrochemical evaluation of the antileishmanial drug miltefosine‐dsDNA interaction was investigated in incubated solutions and using dsDNA‐electrochemical biosensors, following the changes in the oxidation peaks of guanosine and adenosine residues, and the occurrence of the free guanine residues, electrochemical signal. The electrochemical behaviour of miltefosine was also investigated, at a glassy carbon electrode, using cyclic, differential pulse and square wave voltammetry and no electrochemical redox processes were observed. The interaction mechanism of miltefosine‐dsDNA occurs in two ways: independent of the dsDNA sequence, and leading to the condensation/aggregation of DNA strands, producing a rigid miltefosine‐dsDNA complex structure, and a preferential interaction between the guanine hydrogen atoms in the C−G base pair and miltefosine, causing the release of guanine residues detected on the electrode surface. Miltefosine did not induce oxidative damage to DNA in the experimental conditions used.     

Structural and characteristic analysis of carbon nanotubes-ionic liquid gel biosensor

The structure and characteristic of carbon nanotubes-ionic liquid gel biosensor were studied by voltammetry, microscopy and spectroscopy. Various biomolecules were electrochemically detected with this gel biosensor such as glucose oxidase and NADH. The excellent electrochemical behavior of this gel biosensor might be due to the following three main factors: (1) the inherently perfect electrochemical characteristic of multi-wall carbon nanotubes (MWNTs); (2) the better solvent effect and conductivity of ionic liquid as well as the proper interactions between MWNTs and ionic liquid; (3) the proper mixing ratio of MWNTs to ionic liquid. Meanwhile, the interactions between MWNTs and ionic liquid were carefully studied as well. It can be concluded that the non-covalent (π–π) interaction between the imidazole loop of ionic liquid and MWNTs side wall should play an important role. This work gives a further understanding of what results in the high sensitivity and selectivity of such a biosensor to some biomolecules, and provides a simple and easy approach to design new biosensors with various nano-particles and versatile ionic liquid.     

基于BCNTs/GC电极的鸟嘌呤与腺嘌呤电化学行为及其同时检测

利用掺硼碳纳米管（BCNTs）/GC电极研究了鸟嘌呤（G）和腺嘌呤（A）的电化学氧化行为. 与GC和CNTs/GC电极相比,BCNTs/GC电极具有更强的电催化活性,且响应电流明显增加. 两混合样品在BCNTs/GC电极上的氧化峰间隔较大,可实现对A和G的同时检测.     

Impedance DNA Biosensor Using Electropolymerized Polypyrrole/Multiwalled Carbon Nanotubes Modified Electrode

In this paper, we present an electrochemical impedance‐based DNA biosensor by using a composite material of polypyrrole (PPy) and multiwalled carbon nanotubes (MWNTs) to modify glassy carbon electrode (GCE). The polymer film was electropolymerized onto GCE by cyclic voltammetry (CV) in the presence of carboxylic groups ended MWNTs (MWNTs‐COOH). Such electrode modification method is new for DNA hybridization sensor. Amino group ended single‐stranded DNA (NH₂‐ssDNA) probe was linked onto the PPy/MWNTs‐COOH/GCE by using EDAC, a widely used water‐soluble carbodiimide for crosslinking amine and carboxylic acid group. The hybridization reaction of this ssDNA/PPy/MWNTs‐COOH/GCE resulted in a decreased impedance, which was attributed to the lower electronic transfer resistance of double‐stranded DNA than single‐stranded DNA. As the result of the PPy/MWNTs modification, the electrode obtained a good electronic transfer property and a large specific surface area. Consequently, the sensitivity and selectivity of this sensor for biosensing DNA hybridization were improved. Complementary DNA sequence as low as 5.0×10^?12 mol L^?1 can be detected without using hybridization marker or intercalator. Additionally, it was found that the electropolymerization scan rate was an important factor for DNA biosensor fabrication. It has been optimized at 20 mV s^?1.     

Electrochemical biosensor for simultaneous determination of guanine and adenine based on dopamine-melanin colloidal nanospheres–graphene composites

Dopamine-melanin colloidal nanospheres (Dpa-melanin CNDs)–graphene composites-modified glassy carbon electrode (GCE) was prepared by a simple procedure and then successfully used to simultaneously determine guanine and adenine. Scanning electron microscopy (SEM) images and transmission electron microscopy (TEM) were used to characterize the morphology of the Dpa-melanin CNSs–graphene composite. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to characterize the electrode modifying process. Differential pulse voltammetry (DPV) was used to study the electrocatalytic activity toward the electrochemical oxidation of guanine and adenine. The modified electrode exhibited enhanced electrocatalytic behavior and good stability for the simultaneous determination of guanine and adenine compared with bare GCE. The electrochemical biosensor exhibited wide linear range of 0.5 to 150 μM with detection limit of 0.05 and 0.03 μM for guanine and adenine detection (S/N?=?3), respectively. Furthermore, the biosensor showed high sensitivity, good selectivity, good reproducibility, and long-term stability to guanine and adenine detection. At the same time, the fabricated electrode was successfully applied for the determination of guanine and adenine in denatured DNA samples with satisfying results. These results demonstrated that Dpa-melanin CNSs–graphene composite was a promising substrate for the development of high-performance electrochemical biosensor.     

An electrochemical sensor for pesticide assays based on carbon nanotube-enhanced acetycholinesterase activity

There has been urgent demand for rapid, sensitive and cost-effective pesticide assay technologies due to the global attention of environmental and food-safety problems. Acetycholinesterase (AChE)-based electrochemical sensors have attracted significant interest toward this goal. In this contribution, we introduced multiwalled carbon nanotubes (MWNTs) into our sensor design, where they played dual enhancement roles; first is that MWNTs loaded on glassy carbon (GC) electrodes significantly increase surface areas, facilitating the electrochemical polymerization of prussian blue (PB), a redox mediator for the electrochemical oxidation of the enzymatic product, thiocholine (TCh). Second, MWNTs enhance the enzymatic activity of AChE, as manifested by the decreased Michaelis-Menten constant (K(m)). As a result of these two important enhancement factors offered by MWNTs, our electrochemical pesticide sensor exhibited rapid response and high sensitivity toward the detection of a series of pesticides. Moreover, we demonstrated that this sensor was stable, reproducible and selective enough for detection in real samples.     

Amperometric Biosensors for Glucose Based on Layer‐by‐Layer Assembled Functionalized Carbon Nanotube and Poly (Neutral Red) Multilayer Film

Abstract

Multiwalled carbon nanotubes (MWNTs) were treated with a mixture of concentrated sulfuric and nitric acid to introduce carboxylic acid groups to the nanotubes. Conducting polymer film was prepared by electrochemical polymerization of neutral red (NR). By using a layer‐by‐layer method, homogeneous and stable MWNTs and poly (neutral red) (PNR) multilayer films were alternately assembled on glassy carbon (GC) electrodes. With the introduction of PNR, the MWNTs/PNR multilayer film system showed synergy between the MWNTs and PNR, with a significant improvement of redox activity due to the excellent electron‐transfer ability of carbon nanotubes (CNTs) and PNR. The electropolymerization is advantageous, providing both prolonged long‐term stability and improved catalytic activity of the resulting modified electrodes. The MWNTs/PNR multilayer film modified glassy carbon electrode allows low potential detection of hydrogen peroxide with high sensitivity and fast response time. As compared to MWNTs and PNR‐modified GC electrodes, the magnitude of the amperometric response of the MWNTs/PNR composite‐modified GC electrode is more than three‐fold greater than that of the MWNTs modified GC electrode, and nine‐fold greater than that of the PNR‐modified GC electrode. With the immobilization of glucose oxidase onto the electrode surface using glutaric dialdehyde, a biosensor that responds sensitively to glucose has been constructed. In pH 6.98 phosphate buffer, nearly interference‐free determination of glucose has been realized at ?0.2 V vs. SCE with a linear range from 50 µM to 10 mM and response time <10s. The detection limit was 10 µM glucose (S/N=3).     

Detection and distinguishability of leukemia cancer cells based on Au nanoparticles modified electrodes

The Au nanoparticles (Au NPs) modified interface has been fabricated by multi-potential step electrodeposition in this study. Based on the nano-Au interface, we have proposed an electrochemical approach to detect the cancer cell numbers sensitively with a detection limit of about 500 cells. More interestingly, the drug sensitive leukemia K562 cells and drug resistant leukemia K562/adriamycin could be electrochemically distinguished on the interface by the oxidation potential, which did not show any evident differences on the bare electrode. These results indicate the promising application of this nano-interface for constructing the unlabeled potential-discriminative cell biosensors.     

Application of multi-walled carbon nanotubes modified carbon ionic liquid electrode for electrocatalytic oxidation of dopamine

A simple, sensitive, and reliable method based on a multi-walled carbon nanotubes (MWNTs) modified carbon ionic liquid electrode (CILE) has been successfully developed for determination of dopamine (DA) in the presence of ascorbic acid (AA). The acid-treated MWNTs with carboxylic acid functional groups could promote the electron-transfer reaction of DA and inhibit the voltammetric response of AA. Due to the good performance of the ionic liquid, the electrochemical response of DA on the MWNTs/CILE was better than that of other MWNTs modified electrodes. Under the optimum conditions a linear calibration plot was obtained in the range 5.0×10(-8) to 2.0×10(-4) mol L(-1) and the detection limit was 1.0×10(-8) mol L(-1).     

Electrochemical behavior of levodopa at multi-wall carbon nanotubes-quantum dots modified glassy carbon electrodes.

A multi-wall carbon nanotubes (MWNTs)-quantum dots (QDs) composite-modified glassy carbon electrode (GCE) was prepared. The complex was characterized by transmission electron microscopy (TEM). The electrochemical behavior of levodopa at MWNTs and QDs-modified GCEs (MWNTs-QDs/GCE) was studied by cyclic voltammetry (CV) and chronocoulometry (CC). It was found that its electrochemical behavior was a two-charge-two-proton process. The modified electrode had high electrocatalytic activity for levodopa with a standard heterogeneous rate constant of 0.595 cm s(-1), which was greatly increased compared with the values for bare GCE and individual MWNTs modified GCE. The better electrocatalytic activity for levodopa at MWNTs-QDs/GCE may due to a synergistic effect between MWNTs and QDs. This result provides a novel way to promote research on biomicromolecules at nano-dimensions.     

pMB/MWNTs/GC电极对水体中苯二酚异构体的同时测定

通过在多壁碳纳米管修饰玻碳电极上电聚合亚甲基蓝,制备了聚亚甲基蓝/碳纳米管/玻碳电极(pMB/MWNTs/GC)。用循环伏安法研究了3种苯二酚异构体在该电极上的电化学行为,结果表明,在pH7.0的磷酸盐缓冲溶液中,该修饰电极对苯二酚异构体的氧化表现出优异的电催化性能和选择性,对苯二酚、邻苯二酚和间苯二酚的氧化峰分别为0.104、0.203、0.609 V(vs.SCE),峰电位差值分别为99、406 mV。基于苯二酚异构体在pMB/MWNTs/GC修饰电极上的伏安行为,建立了苯二酚3种异构体同时分析的新方法。考察了各影响因素对测定的影响,最优实验条件下,在5.0×10-6~1.5×10-4mol.L-1范围内,3种苯二酚异构体的阳极峰电流与其浓度存在线性关系,检出限均为1.0×10-6mol.L-1。将该法用于水体及冲洗废液中苯二酚异构体含量的测定,结果满意。     

Determination of silver in geological samples using high-resolution continuum source electrothermal atomic absorption spectrometry and direct solid sampling

A DNA biosensor was constructed by immobilizing DNA on a glassy carbon (GC) electrode modified with multiwall carbon nanotubes (MWNTs) dispersed in Nafion (DNA/MWNTs/GCE). The DNA-modified electrode exhibited two well-defined oxidation peaks corresponding to the guanine and adenine residues of DNA, respectively. The effects of the adsorption potential, DNA concentration and quantity of MWNTs used for DNA immobilization were investigated, as were the effects of buffer, pH and scan rate on the voltammetric behavior of DNA. Phenol, m-cresol and catechol showed noticeable inhibition towards the response of the electrode due to their interactions with DNA. These findings were used to design biosensors with linear response to these phenolic pollutants.     

Direct electrochemistry of DNA,guanine and adenine at a nanostructured film-modified electrode

A nanostructured film electrode, a multi-wall carbon nanotubes (MWNT)-modified glassy carbon electrode (GCE), is described for the simultaneous determination of guanine and adenine. The properties of the MWNT-modified GCE were investigated by scanning electron microscopy (SEM) and cyclic voltammetry. The oxidation peak currents of guanine and adenine increased significantly at the MWNT-modified GCE in contrast to those at the bare GCE. The experimental parameters were optimized and a direct electrochemical method for the simultaneous determination of guanine and adenine was proposed. Using the MWNT-modified GCE, a sensitive and direct electrochemical technique for the measurement of native DNA was also developed, and the value of (G+C)/(A+T) of HCl-digested DNA was detected.