Derivatization of SWCNTs with cobalt phthalocyanine residues and applications in screen printed electrodes for electrochemical detection of thiocholine

Single-walled carbon nanotubes (SWCNTs) derivatized with cobalt phthalocyanine (CoPh) were applied onto screen-printed graphite electrodes (SPEs) to be used for the low-potential electrochemical oxidation of thiocholine (TCh). Covalent attachment of CoPh to SWCNTs via stable sulfonamide bonds was confirmed by Raman/FT-IR spectroscopy and thermogravimetric analysis (TGA) coupled with FT-IR detection. The resulting modified SPE surfaces (CoPh-SWCNT-SPEs) were characterized by cyclic voltammetry and electrochemical impedance spectroscopy (EIS) with the redox probe [F₃(CN)₆]^3−/4−. Detection of TCh was accomplished using cyclic voltammetry and amperometry; a lower overpotential (100 mV vs. Ag/AgCl pseudoreference electrode) was obtained using CoPh-SWCNT-SPEs as compared to unmodified SPEs and SPEs modified with non-functionalized SWCNTs (SWCNT-SPEs). The linear range for TCh detection was 0.077–0.45 mM, with a sensitivity of 5.11 × 10⁻¹ μA mM⁻¹ and a limit of detection of 0.038 mM according to the 3 s/m definition.     

Triple functionalisation of single-walled carbon nanotubes with doxorubicin, a monoclonal antibody, and a fluorescent marker for targeted cancer therapy

Single-walled carbon nanotubes (SWCNTs) have been identified as a transporter for anti-cancer drugs, as they are capable of penetrating mammalian cell membranes and allow for a high drug loading due to their nanoscale dimensions and high aspect ratio. In addition, they can assist the targeting of therapeutic agents to the desired site of action by conjugation to antibodies or ligands of cancer cell surface receptors, which increases the effectiveness of the treatment and reduces side effects. In this work, we present a method for the triple functionalisation of oxidised SWCNTs with the anti-cancer drug doxorubicin, a monoclonal antibody, and a fluorescent marker at non-competing binding sites. The proposed methodology allows for the targeted delivery of the anti-cancer drug to cancer cells and the visualisation of the cellular uptake of SWCNTs by confocal microscopy. We show that the complex is efficiently taken up by cancer cells with subsequent intracellular release of doxorubicin, which then translocates to the nucleus while the nanotubes remain in the cytoplasm.     

基于3D打印技术构建石墨烯电化学生物传感器及其应用研究

超高灵敏度和特异性的电化学生物传感器在环境风险物质监测以及生物医学检测领域具有重要意义,而构建生物亲和性高、制备工艺简单、成本低廉的检查电极是电化学生物传感器走向应用的关键。本文采用3D打印技术制备出重复性良好的三维石墨烯复合电极,然后通过电化学氧化的方法调控表面石墨烯的形貌和氧化基团。所制备的电化学生物传感器在环境污染物微囊藻毒素(MC-LR)的检测中展现出超高的灵敏度,其线性检测区在4×10^-6~1 μg/L,检测限为1.5×10^-7 μg/L。同时,通过改变适配体检测探针后,该电化学生物传感器对于多巴胺、重金属Hg²⁺、四环素等均具有极高的检测灵敏度。本研究为电化学适配体生物传感器走向应用化提供了一种新的思路,为开发超高灵敏度环境监测和生物医学检测传感器提供一定的基础数据。     

A comparative study of electrochemical and biointerfacial properties of acid- and plasma-treated single-walled carbon-nanotube-film electrode systems for use in biosensors

The electrocatalytic and biointerfacial properties of acid- and O₂-plasma-treated single-walled carbon nanotube (SWCNT) electrodes were investigated. The SWCNT-modified electrodes were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. The electrochemical performance of these electrodes was analyzed by cyclic voltammetry and chronoamperometry. Glucose oxidase was covalently immobilized on the surface of the treated SWCNTs, and the analytical characteristics of the integrated glucose sensor were investigated using glucose as a target analyte. The plasma-activated SWCNT electrode exhibited a much higher sensitivity to the glucose and a lower detection limit than the acid-treated electrode, indicating that a larger amount of enzyme was immobilized on the plasma-treated SWCNT electrode than on the acid-treated electrode. This is due to the fact that the oxygenated functional groups are mainly located at the ends of the tubes in the acid-treated SWCNTs, while the plasma-treated SWCNTs have an even larger surface area available for enzyme immobilization owing to the functional groups covering the entire surface of the SWCNTs.     

Ferroceneboronic acid for the electrochemical probing of interactions involving sugars

Ferroceneboronic acid (FcBA) was used as a redox-active probe suitable for monitoring of diol–boronate interactions. Voltammetric and amperometric measurements allowed to detect FcBA forms – free and bound in the boronate complex. In this way, the complexation interaction was studied for a set of saccharide molecules as model diols and the corresponding affinity equilibrium constants were determined. A shift of the peak potential on voltammograms accompanying formation of the boronate complex with FcBA was proposed as a probe for electrochemical characterization of surface-confined diol-containing structures. The model experiments were carried out using sorbitol- and 1,6-hexandiol-modified polyepichlorhydrin conjugates deposited on the electrodes; the former compound was able to form the boronate complex while no change of the peak potential for the latter conjugate was observed. This approach seems promising for artificial bioelectronic affinity receptors and technology of reagentless biosensors where the binding interaction directly stimulates a measurable electrochemical event.     

Electrochemical characterization of single-walled carbon nanotubes for electrochemical double layer capacitors using non-aqueous electrolyte

Single-walled carbon nanotubes (SWCNTs) were investigated by cyclic voltammetry and electrochemical impedance spectroscopy in a non-aqueous electrolyte, 1 M Et₄NBF₄ in acetonitrile, suitable for supercapacitors. Further, in situ dilatometry and in situ conductance measurements were performed on single electrodes and the results compared to an activated carbon, YP17. Both materials show capacitive behavior characteristic of high surface area electrodes for supercapacitors, with the maximum full cell gravimetric capacitance being 34 F/g for YP17 and 20 F/g for SWCNTs at 2.5 V with respect to the total active electrode mass. The electronic resistance of SWCNTs and activated carbon decreases significantly during charging, showing similarities of the two materials during electrochemical doping. The SWCNT electrode expands irreversibly during the first electrochemical potential sweep as verified by in situ dilatometry, indicative of at least partial debundling of the SWCNTs. A reversible periodic swelling and shrinking during cycling is observed for both materials, with the magnitude of expansion depending on the type of ions forming the double layer.     

Electrochemical glucose biosensor by electrostatic binding of PQQ-glucose dehydrogenase onto self-assembled monolayers on gold

Efficient binding of enzymes onto the electrode surface has been prerequisite for the construction of sensitive biosensors and biochips. Here, a simple and robust construction of electrochemical glucose biosensor based on pyrroloquinoline quinone-glucose dehydrogenase was demonstrated. The glucose biosensor was fabricated by binding the enzyme onto the anionic self-assembled monolayers on gold electrode via electrostatic interactions. The resulting glucose biosensor gave rise to twofold higher detection sensitivity than that by covalent conjugation under the same condition. Surface plasmon resonance and atomic force microscopy analyses revealed that electrostatic binding of the enzyme leads to much higher surface density of the enzyme. This approach will find wide applications to the development of robust enzyme-based biosensors and biochips.     

Nanoparticle-functionalized nucleic acids: A strategy for amplified electrochemical detection of some single-base mismatches

In this study, nanoparticle-functionalized nucleic acids were employed to improve the sensitivity of electrochemical DNA biosensors that make capable them to detect different types of single-base mismatches (SBMs), including thermodynamically stable ones. The present biosensor was constructed by the immobilization of platinum nanoparticles (Pt-NPs) on the surface of a carbon paste electrode (CPE) via SH-functionalized DNA. A redox probe of 2-mercapto-1-methyl imidazole (MMI), which has different electrochemical behavior on Pt-NP and CPE, was used. This behavior helps to overcome the pinhole effect in DNA hybridization biosensors. Additionally, in the present biosensor, the positioning of the redox probe under the SBM in DNA, which decreases the sensitivity of most DNA biosensors, did not contribute to the observed electrochemical signal.     

Target-triggered polymerization for biosensing

Because of the potential applications of biosensors in clini- cal diagnosis, biomedical research, environmental analysis, and food quality control, researchers are very interested in developing sensitive, selective, rapid, reliable, and low-cost versions of these devices. A classic biosensor directly transduces ligand-target binding events into a measurable physical readout. Because of the limited detection sensitivity and selectivity in earlier biosensors, researchers have developed a number of sensing/signal amplification strategies. Through the use of nanostructured or long chain polymeric materials to increase the upload of signal tags for amplification of the signal readout associated with the ligand-target binding events, researchers have achieved high sensitivity and exceptional selectivity. Very recently, target-triggered polymerization-assisted signal amplification strategies have been exploited as a new biosensing mechanism with many attractive features. This strategy couples a small initiator molecule to the DNA/protein detection probe prior to DNA hybridization or DNA/protein and protein/protein binding events. After ligand-target binding, the in-situ polymerization reaction is triggered. As a result, tens to hundreds of small monomer signal reporter molecules assemble into long chain polymers at the location where the initiator molecule was attached. The resulting polymer materials changed the optical and electrochemical properties at this location, which make the signal easily distinguishable from the background. The assay time ranged from minutes to hours and was determined by the degree of amplification needed. In this Account, we summarize a series of electrochemical and optical biosensors that employ target-triggered polymerization. We focus on the use of atom transfer radical polymerization (ATRP), as well as activator generated electron transfer for atom transfer radical polymerization (AGET ATRP) for in-situ formation of polymer materials for optically or electrochemically transducing DNA hybridization and protein-target binding. ATRP and AGET ATRP can tolerate a wide range of functional monomers. They also allow for the preparation of well-controlled polymers with narrow molecular weight distribution, which was predetermined by the concentration ratio of the consumed monomer to the introduced initiator. Because the reaction initiator can be attached to a variety of detection probes through well-established cross-linking reactions, this technique could be expanded as a universal strategy for the sensitive detection of DNA and proteins. We see enormous potential for this new sensing technology in the development of portable DNA/protein sensors for point-of-need applications.     

Improvement single-wall carbon nanotubes (SWCNTs) based on functionalizing with monomers 2-hydroxyethylmethacryate (HEMA) and N-vinylpyrrolidone (NVP) for pharmaceutical applications as cancer therapy

The functionalized carbon nanotubes play significant roles in the fields such as preparation of composite materials and biological technologies. This paper explains the covalent functionalization of single-wall carbon nanotubes (SWCNTs) with biomedical important monomers, 2-hydroxyethylmethacryate (HEMA) and N-vinylpyrrolidone (NVP) by chemical grafting of HEMA and PVP monomers via free radical polymerization. To get carboxylic acid functionalized SWCNTs, first the nanotubes were oxidized with a mixture of nitric acid and sulfuric acid (1:3). Then, the binding of HEMA and NVP onto the surface of SWCNTs was performed by chemical functionalization of HEMA, NVP with acid chloride-bound carbon nanotube by esterification reaction. These results were confirmed by FT-IR and SEM. The cell culture experiments conducted for pharmaceutical applications were used as cancer therapy.     

Competitive MS binding assays for dopamine D2 receptors employing spiperone as a native marker

A competitive MS binding assay employing spiperone as a native marker and a porcine striatal membrane fraction as a source for dopamine D2 receptors in a nonvolatile buffer has been established. Binding of the test compounds to the target was monitored by mass-spectrometric quantification of the nonbound marker, spiperone, in the supernatant of the binding samples obtained by centrifugation. A solid-phase extraction procedure was used for separating spiperone from ESI-MS-incompatible supernatant matrix components. Subsequently, the marker was reliably quantified by LC-ESI-MS-MS by using haloperidol as an internal standard. The affinities of the test compounds, the dopamine receptor antagonists (+)-butaclamol, chlorpromazine and (S)-sulpiride obtained from the competitive MS binding assay were verified by corresponding radioligand binding experiments with [3H]spiperone. The results of this study demonstrate that competitive MS binding assays represent a universally applicable alternative to conventional radioligand binding assays.     

Electrochemical characterization and reactivity of Pt nanoparticles supported on single-walled carbon nanotubes

Carbon nanotubes have been proposed as advanced metal catalyst support for electrocatalysis. In this paper, Pt nanoparticles supported on single-walled carbon nanotubes (SWCNTs)-Pt, were prepared using a solid-state reaction between the SWCNTs and two different Pt precursors, bis(dibenzylideneacetone)platinum [Pt(DBA)₂] or tri(dibenzylideneacetone)platinum [Pt(DBA)₃]. TEM images of the samples show Pt nanoparticles with a particle size around 2.5 nm with a high degree of dispersion on the SWCNTs. A detailed electrochemical characterization of the surface of the samples including irreversibly adsorbed adatoms of Bi and Ge as probe reactions has been carried out. It has been stated that SWCNTs-Pt samples subjected to the classical electrochemical activation induce a serious sintering of the Pt nanoparticles.     

A sensitive electrochemical aptasensor based on water soluble CdSe quantum dots (QDs) for thrombin determination

A novel aptamer biosensor with easy operation and good sensitivity, specificity, stability and reproducibility was developed by immobilizing the aptamer on water soluble CdSe quantum dots (QDs) modified on the top of the glassy carbon electrode (GCE). Methylene blue (MB) was intercalated into the aptamer sequence and used as an electrochemical marker. CdSe QDs improved the electrochemical signal because of their larger surface area and ion centers of CdSe QDs may also had a major role on amplifying the signal. The higher ion concentration caused more combination of aptamer which caused larger signal. The thrombin was detected by differential pulse voltammetry (DPV) quantitatively. Under optimal conditions, the two linear ranges were obtained from 3 to 13 μg mL⁻¹ and from 14 to 31 μg mL⁻¹, respectively. The detection limit was 0.08 μg mL⁻¹ at 3σ. The constructed biosensor had better responses compared with that in the absence of the CdSe QDs immobilizing. The control experiment was also carried out by using BSA, casein and IgG in the absence of thrombin. The results showed that the aptasensor had good specificity, stability and reproducibility to the thrombin. Moreover, the aptasensor could be used for detection of real sample with consistent results in comparison with those obtained by fluorescence method which could provide a promising platform for fabrication of aptamer based biosensors.     

Low micromolar inhibitors of galectin-3 based on 3'-derivatization of N-acetyllactosamine

A strategy for generating potential galectin inhibitors was devised based on derivatization at the C-3' atom in 3'-amino-N-acetyllactosamine by using structural knowledge of the galectin carbohydrate recognition site. A collection of 12 compounds was prepared by N-acylations or N-sulfonylations. Hydrophobic tagging of the O-3 atom in the N-acetylglucosamine residue with a stearic ester allowed rapid and simple product purification. The compounds were screened in a galectin-3 binding assay and three compounds with significantly higher inhibitory activities compared to the parent N-acetyllactosaminide were found. These three best inhibitors all carried an aromatic amide at the C-3' position of the galactose moiety, which indicates that favorable interactions were formed between the aromatic group and galectin-3. The best inhibitor had an IC50 value (4.4 microM) about 50 times better than the parent N-acetyllactosaminide, which implies that it has potential as a valuable tool for studying galectin-3 biological functions and also as a lead compound for the development of galectin-3-blocking pharmaceuticals.     

In vitro detection of superoxide anions released from cancer cells based on potassium-doped carbon nanotubes-ionic liquid composite gels

A newly developed electrochemical biosensor for the determination of superoxide anions (O(2)˙(-)) released from cancer cells using potassium-doped multi-walled carbon nanotubes (KMWNTs)-1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF(6)) ionic liquid composite gels is demonstrated. The KMWNTs-[BMIM]PF(6) can electrocatalyze oxygen reduction to generate a strong current signal in neutral solution. Compared with KMWNTs without [BMIM]PF(6) or MWNTs-[BMIM]PF(6) composites, the KMWNTs-[BMIM]PF(6) can enhance the oxygen reduction peak current by 6.2-fold and 2.8-fold, which greatly increases the detection sensitivity of oxygen. Then, O(2)˙(-) biosensors are fabricated by mixing superoxide dismutase (SOD) in the KMWNTs-[BMIM]PF(6) gels via monitoring oxygen produced by an enzymic reaction between SOD/O(2)˙(-) without the help of electron mediators. The resulting biosensors show a linear range from 0.04 to 38 μM with a high sensitivity of 98.2 μA mM(-1), and a lower detection limit of 0.024 μM. The common interferents such as hydrogen peroxide (H(2)O(2)), ascorbic acid (AA), uric acid (UA), and metabolites of neurotransmitters, do not interfere with the detection of O(2)˙(-). The proposed biosensor is tested to determine O(2)˙(-) in vitro and from liver cancer and leukemia cells and shows good application potential in biological electrochemistry.     

Fabrication of Anti-human Cardiac Troponin I Immunogold Nanorods for Sensing Acute Myocardial Damage

A facile, rapid, solution-phase method of detecting human cardiac troponin I for sensing myocardial damage has been described using gold nanorods-based biosensors. The sensing is demonstrated by the distinct change of the longitudinal surface plasmon resonance wavelength of the gold nanorods to specific antibody–antigen binding events. For a higher sensitivity, the aspect ratio of gold nanorods is increased up to ca 5.5 by simply adding small amount of HCl in seed-mediated growth solution. Experimental results show that the detecting limit of the present method is 10 ng/mL. Contrast tests reveal that these gold nanorods-based plasmonic biosensors hold much higher sensitivity than that of conventionally spherical gold nanoparticles.     

水滑石纳米材料特性及其在电化学生物传感器方面的应用

阐述了水滑石纳米材料结构和性能之间的关系及近年来水滑石纳米材料在电化学生物传感器方面应用的最新进展。重点介绍了水滑石纳米材料在吸附生物酶制备电化学传感器、水滑石纳米片固定生物酶制备电化学传感器、水滑石纳米片固定其它活性组分制备电化学传感器、水滑石自构筑电化学传感器等方面的应用。着重对水滑石纳米材料制备电化学传感器的机理和制备方法进行了系统概述。提出了水滑石纳米材料构筑电化学生物传感器应用研究的发展趋势：对水滑石纳米材料进行多层、多组分、微型化和阵列化等多样化设计,指出高选择性和高灵敏度检测是未来新型电化学生物传感器应用研究的主要发展方向。     

Review on carbon-derived,solid-state,micro and nano sensors for electrochemical sensing applications

The aim of this review is to summarize the most relevant contributions in the development of electrochemical sensors based on carbon materials in the recent years. There have been increasing numbers of reports on the first application of carbon derived materials for the preparation of an electrochemical sensor. These include carbon nanotubes, diamond like carbon films and diamond film-based sensors demonstrating that the particular structure of these carbon material and their unique properties make them a very attractive material for the design of electrochemical biosensors and gas sensors.Carbon nanotubes (CNT) have become one of the most extensively studied nanostructures because of their unique properties. CNT can enhance the electrochemical reactivity of important biomolecules and can promote the electron-transfer reactions of proteins (including those where the redox center is embedded deep within the glycoprotein shell). In addition to enhanced electrochemical reactivity, CNT-modified electrodes have been shown useful to be coated with biomolecules (e.g., nucleic acids) and to alleviate surface fouling effects (such as those involved in the NADH oxidation process). The remarkable sensitivity of CNT conductivity with the surface adsorbates permits the use of CNT as highly sensitive nanoscale sensors. These properties make CNT extremely attractive for a wide range of electrochemical sensors ranging from amperometric enzyme electrodes to DNA hybridization biosensors. Recently, a CNT sensor based fast diagnosis method using non-treated blood assay has been developed for specific detection of hepatitis B virus (HBV) (human liver diseases, such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma caused by hepatitis B virus). The linear detection limits for HBV plasma is in the range 0.5–3.0 µL^? 1 and for anti-HBVs 0.035–0.242 mg/mL in a 0.1 M NH₄H₂PO₄ electrolyte solution. These detection limits enables early detection of HBV infection in suspected serum samples. Therefore, non-treated blood serum can be directly applied for real-time sensitive detection in medical diagnosis as well as in direct in vivo monitoring.Synthetic diamond has been recognized as an extremely attractive material for both (bio-) chemical sensing and as an interface to biological systems. Synthetic diamond have outstanding electrochemical properties, superior chemical inertness and biocompatibility. Recent advances in the synthesis of highly conducting nanocrystalline-diamond thin films and nano wires have lead to an entirely new class of electrochemical biosensors and bio-inorganic interfaces. In addition, it also combines with development of new chemical approaches to covalently attach biomolecules on the diamond surface also contributed to the advancement of diamond-based biosensors. The feasibility of a capacitive field-effect EDIS (electrolyte-diamond-insulator-semiconductor) platform for multi-parameter sensing is demonstrated with an O-terminated nanocrystalline-diamond (NCD) film as transducer material for the detection of pH and penicillin concentration. This has also been extended for the label-free electrical monitoring of adsorption and binding of charged macromolecules. One more recent study demonstrated a novel bio-sensing platform, which is introduced by combination of a) geometrically controlled DNA bonding using vertically aligned diamond nano-wires and b) the superior electrochemical sensing properties of diamond as transducer material. Diamond nano-wires can be a new approach towards next generation electrochemical gene sensor platforms.This review highlights the advantages of these carbon materials to promote different electron transfer reactions specially those related to biomolecules. Different strategies have been applied for constructing carbon material-based electrochemical sensors, their analytical performance and future prospects are discussed.