Functionalized single-walled carbon nanohorns for electrochemical biosensing

Hierarchical Composite Nanoarchitectonics with a Graphitic Core, Dendrimer and Fluorocarbon Domains, and a Poly(ethylene glycol) Shell as O2 Reservoirs for Reactive Oxygen Species Production

Graphene oxide (GO), single-walled carbon nanohorn (CNHox), and nitrogen-doped CNH (N-CNH) were functionalized with fluorinated poly(ethylene glycol) (F-PEG) and/or with a fluorinated dendrimer (F-DEN) to prepare a series of assembled nanocomposites (GO/F-PEG, CNHox/F-PEG, N-CNH/F-PEG, N-CNH/F-DEN, and N-CNH/F-DEN/F-PEG) that provide effective multisite O₂ reservoirs. In all cases, the O₂ uptake increased with time and saturated after 10-20 min. When graphitic carbons (GO and CNHox) were coated with F-PEG, the O₂ uptake doubled. The O₂ loading was slightly higher in N-CNH compared to CNHox. Notably, coating N-CNH with F-DEN or F-PEG, or with both F-DEN and F-PEG, was more effective. The best performance was obtained with the N-CNH/F-DEN/F-PEG nanocomposite. The O₂ uptake kinetics and mechanisms were analyzed in terms of the Langmuir adsorption equation based on a multibinding site assumption. This allowed the precise determination of multiple oxygen binding sites, including on the graphitic structure and in the dendrimer, F-DEN, and F-PEG. After an initial rapid, relatively limited release, the amount of O₂ trapped in the nanomaterials remained high (>95%). This amount was marginally lower for the functionalized composites, but the oxygen stored was reserved for longer times. Finally, it is shown that these systems can generate singlet oxygen after irradiation by a light-emitting diode, and this production correlates with the amount of O₂ loaded. Thus, it was anticipated that the present nanocomposites hierarchically assembled from components with different characters and complementary affinities for oxygen can be useful as O₂ reservoirs for singlet oxygen generation to kill bacteria and viruses and to perform photodynamic therapy.

Tailoring the performance of electrochemical biosensors based on carbon nanomaterials via aryldiazonium electrografting

Carbon nanomaterials (CNs) offer some of the most valuable properties for electrochemical biosensing applications, such as good electrical conductivity, wide electrochemical stability, high specific surface area, and biocompatibility. Regardless the envisioned sensing application, endowing CNs with specific functions through controlled chemical functionalization is fundamental for promoting the specific binding of the analyte. As a versatile and straightforward method of surface functionalization, aryldiazonium chemistry have been successfully used to accommodate in a stable and reproducible way different functionalities, while the electrochemical route has become the favourite choice since the deposition conditions can be readily controlled and adapted to the substrate. In particular, the modification of CNs by electrochemical reduction of aryl diazonium salts is established as a powerful tool which allows tailoring the chemical and electronic properties of the sensing platform. By outlining the stimulating results disclosed in the last years, this article provides not only a comprehensively review, but also a rational assessment on contribution of aryldiazonium electrografting in developing CNs-based electrochemical biosensors. Furthermore, some of the emerging challenges to be surpassed to effectively implement this methodology for in vivo and point of care analysis are also highlighted.

Structure, synthesis, and sensing applications of single-walled carbon nanohorns

Single-walled carbon nanohorns (SWCNHs), a type of tapered carbon nanomaterials, are generally prepared by laser ablation method, arc method, and Joule heating method without the addition of metal catalysts, which makes them pure and environmentally friendly. The obtained aggregates of SWCNHs mainly have three different types of structure, dahlia-like, bud-like, and seed-like. Over the past few decades, they have been widely used in the fields of energy, medicine, chemistry, and sensing. The SWCNHs-based sensors have shown high sensitivity, rapid response, and excellent stability, which are mainly attributed to the excellent electrical conductivity, large electrochemical window, large specific surface area, and mechanical strength of SWCNHs. In this review, we systematically summarizes the structures, synthesis methods, and sensing applications of SWCNHs, including electrochemical sensors, photoelectrochemical sensors, electrochemiluminescence sensors, fluorescent sensors, and resistive sensors. Moreover, the development prospects of SWCNHs in this field are also discussed.

Carbon nanohorn modified platinum electrodes for improved immobilisation of enzyme in the design of glutamate biosensors

Electrochemical enzymatic biosensors are the subject of research due to their potential for in vivo monitoring of glutamate, which is a key neurotransmitter whose concentration is related to healthy brain function. This study reports the use of biocompatible oxidised carbon nanohorns (o-CNH) with a high surface area, to enhance the immobilization of glutamate oxidase (GluOx) for improved biosensor performance. Two families of biosensors were designed to interact with the anionic GluOx. Family-1 consists of covalently functionalised o-CNH possessing hydrazide (HYZ) and amine (PEG-NH2) terminated surfaces and Family-2 comprised non-covalently functionalised o-CNH with different loadings of polyethyleneimine (PEI) to form a cationic hybrid. Amperometric detection of H2O2 formed by enzymatic oxidation of glutamate revealed a good performance from all designs with the most improved performance by the PEI hybrid systems. The best response was from a o-CNH : PEI ratio of 1 : 10 mg mL-1, which yielded a glutamate calibration plateau, JMAX, of 55 ± 9 μA cm-2 and sensitivity of 111 ± 34 μA mM-1 cm-2. The low KM of 0.31 ± 0.05 mM indicated the retention of the enzyme function, and a limit of detection of 0.02 ± 0.004 μM and a response time of 0.88 ± 0.13 s was determined. The results demonstrate the high sensitivity of these biosensors and their potential for future use for the detection of glutamate in vivo.

A sandwich-type electrochemical aptasensor for Mycobacterium tuberculosis MPT64 antigen detection using C60NPs decorated N-CNTs/GO nanocomposite coupled with conductive PEI-functionalized metal-organic framework

The present work described a novel sandwich-type electrochemical aptasensor for rapid and sensitive determination of Mycobacterium tuberculosis MPT64 antigen. Herein, a novel carbon nanocomposite composed of fullerene nanoparticles, nitrogen-doped carbon nanotubes and graphene oxide (C₆₀NPs-N-CNTs/GO) was facilely synthesized for the first time, which not only possessed a large specific surface area and excellent conductivity, but also exhibited outstanding inherent electroactive property, and therefore served as nanocarrier and redox nanoprobe simultaneously. Gold nanoparticles (AuNPs) was then uniformly anchored onto the surface of such nanocomposite via Au-N bonds to bind with MPT64 antigen aptamer Ⅱ (MAA Ⅱ), forming the tracer label to realize generation and amplification of electrochemical signal. Additionally, conductive polyethyleneimine (PEI)-functionalized Fe-based metal-organic framework (P-MOF) was used as a sensing platform to absorb bimetallic core-shell Au-Pt nanoparticles (Au@Pt), which could accelerate electron transfer and increase the immobilization of MPT64 antigen aptamer Ⅰ (MAA Ⅰ). After the typical sandwich-type protein-aptamer recognition, the inherent electroactivity of the tracer label was provoked by tetraoctylammonium bromide (TOAB), leading to a well-defined current response. Under the optimum condition, the proposed aptasensor showed a wide linear range for MPT64 detection from 1 fg/mL to 1 ng/mL with a limit of detection (LOD) as low as 0.33 fg/mL. More importantly, it was successfully used for MPT64 antigen detection in human serum, exhibiting a promising prospect for TB diagnosis in clinical practice.

An insight into the outer- and inner-sphere electrochemistry of oxygenated single-walled carbon nanohorns (o-SWCNHs)

The electrocatalysis/interference of single-walled carbon nanohorns (o-SWCNHs) in relation to outer-sphere and inner-sphere electron transfer reactions.

Structure, Properties, Functionalization, and Applications of Carbon Nanohorns

Carbon nanohorns (sometimes also known as nanocones) are conical carbon nanostructures constructed from an sp(2) carbon sheet. Nanohorns require no metal catalyst in their synthesis, and can be produced in industrial quantities. They provide a realistic and useful alternative to carbon nanotubes, and possibly graphene, in a wide range of applications. They also have their own unique behavior due to their specific conical morphology. However, their research and development has been slowed by several factors, notably during synthesis, they aggregate into spherical clusters ∼100 nm in diameter, blocking functionalization and treatment of individual nanocones. This limitation has recently been overcome with a new approach to separating these "dahlia-like" clusters into individual nanocones. In this review, we describe the structure, synthesis, and topology of carbon nanohorns, and provide a detailed review of nanohorn chemistry.

Recent development of carbon electrode materials and their bioanalytical and environmental applications

New synthetic approaches, materials, properties, electroanalytical applications and perspectives of carbon materials are presented.

Label-free signal-on ATP aptasensor based on the remarkable quenching of tris(2,2'-bipyridine)ruthenium(II) electrochemiluminescence by single-walled carbon nanohorn

The quenching of electrochemiluminescence by single-walled carbon nanohorn has been demonstrated for the first time. Moreover, a sensitive, label-free, and signal-on electrochemiluminescence ATP aptasensor was developed using single-walled carbon nanohorn as both quencher and scaffold.

Single-Walled Carbon Nanohorns for Energy Applications

With the growth of the global economy and population, the demand for energy is increasing sharply. The development of environmentally a benign and reliable energy supply is very important and urgent. Single-walled carbon nanohorns (SWCNHs), which have a horn-shaped tip at the top of single-walled nanotube, have emerged as exceptionally promising nanomaterials due to their unique physical and chemical properties since 1999. The high purity and thermal stability, combined with microporosity and mesoporosity, high surface area, internal pore accessibility, and multiform functionalization make SWCNHs promising candidates in many applications, such as environment restoration, gas storage, catalyst support or catalyst, electrochemical biosensors, drug carrier systems, magnetic resonance analysis and so on. The aim of this review is to provide a comprehensive overview of SWCNHs in energy applications, including energy conversion and storage. The commonly adopted method to access SWCNHs, their structural modifications, and their basic properties are included, and the emphasis is on their application in different devices such as fuel cells, dye-sensitized solar cells, supercapacitors, Li-ion batteries, Li-S batteries, hydrogen storage, biofuel cells and so forth. Finally, a perspective on SWCNHs’ application in energy is presented.

Integration of photoswitchable proteins, photosynthetic reaction centers and semiconductor/biomolecule hybrids with electrode supports for optobioelectronic applications

Light-triggered biological processes provide the principles for the development of man-made optobioelectronic systems. This Review addresses three recently developed topics in the area of optobioelectronics, while addressing the potential applications of these systems. The topics discussed include: (i) the reversible photoswitching of the bioelectrocatalytic functions of redox proteins by the modification of proteins with photoisomerizable units or by the integration of proteins with photoisomerizable environments; (ii) the integration of natural photosynthetic reaction centers with electrodes and the construction of photobioelectrochemical cells and photobiofuel cells; and (iii) the synthesis of biomolecule/semiconductor quantum dots hybrid systems and their immobilization on electrodes to yield photobioelectrochemical and photobiofuel cell elements. The fundamental challenge in the tailoring of optobioelectronic systems is the development of means to electrically contact photoactive biomolecular assemblies with the electrode supports. Different methods to establish electrical communication between the photoactive biomolecular assemblies and electrodes are discussed. These include the nanoscale engineering of the biomolecular nanostructures on surfaces, the development of photoactive molecular wires and the coupling of photoinduced electron transfer reactions with the redox functions of proteins. The different possible applications of optobioelectronic systems are discussed, including their use as photosensors, the design of biosensors, and the construction of solar energy conversion and storage systems.

Single-walled carbon nanohorns and their applications

Single-walled carbon nanohorns (SWCNHs) are horn-shaped single-walled tubules with a conical tip. They are generally synthesized by laser ablation of pure graphite without using metal catalyst with high production rate and high yield, and typically form radial aggregates. SWCNHs are essentially metal-free and very pure, which avoids cumbersome purification and makes them user-friendly and environmentally benign. Currently, SWCNHs have been widely studied for various applications, such as gas storage, adsorption, catalyst support, drug delivery system, magnetic resonance analysis, electrochemistry, biosensing application, photovoltaics and photoelectrochemical cells, photodynamic therapy, fuel cells, and so on. This review outlines the research progress on SWCNHs, including their properties, functionalization, applications, and outlook.