Comparative study of the electrochemical behavior and analytical applications of (bio)sensing platforms based on the use of multi-walled carbon nanotubes dispersed in different polymers

Two birds with one stone: integrating exfoliation and immunoaffinity properties in multi-walled carbon nanotubes by non-covalent functionalization with human immunoglobulin G

An innovative strategy is proposed to simultaneously exfoliate multi-walled carbon nanotubes (MWCNTs) and generate MWCNTs with immunoaffinity properties. This strategy was based on the non-covalent functionalization of MWCNTs with human immunoglobulin G (IgG) by sonicating 2.5 mg mL^-1 MWCNTs in 2.0 mg mL^-1 IgG for 15 min with sonicator bath. Impedimetric experiments performed at glassy carbon electrodes (GCE) modified with the resulting MWCNT-IgG nanohybrid in the presence of anti-human immunoglobulin G antibody (Anti-IgG) demonstrated that the immunoglobulin retains their biorecognition properties even after the treatment during the MWCNT functionalization. We proposed, as proof-of-concept, two model electrochemical sensors, a voltammetric one for uric acid quantification by taking advantages of the exfoliated MWCNTs electroactivity (linear range, 5.0 × 10^-7 M - 5.0 × 10^-6 M; detection limit, 165 nM) and an impedimetric immunosensor for the detection of Anti-IgG through the use of the bioaffinity properties of the IgG present in the nanohybrid (linear range, 5-50 µg mL^-1; detection limit, 2 µg mL^-1).

Ultrasensitive multiwall carbon nanotube-mesoporous MCM-41 hybrid-based platform for the electrochemical detection of ascorbic acid

An ultrasensitive multiwall carbon nanotube-MCM-41 hybrid-based ascorbic acid sensor for electro-detection in real samples is proposed. The MWCNT–MCM-41 hybrid preparation via dispersion was optimized through an experimental design based on CCD/RSM.

Sandwich-type electrochemical aptasensor based on hollow mesoporous carbon spheres loaded with porous dendritic Pd@Pt nanoparticles as signal amplifier for ultrasensitive detection of cardiac troponin I

Signal amplification is crucial to improve the sensitivity for the electrochemical detection of cardiac troponin I (cTnI), one of the ideal biomarkers for early acute myocardial infarction (AMI) diagnosis. Herein, we developed a novel signal amplification strategy to construct a sandwich-type electrochemical aptasensor for the detection of cTnI. Core-shell Pd@Pt dendritic bimetallic nanoparticles loaded on melamine modified hollow mesoporous carbon spheres (Pd@Pt DNs/NH₂-HMCS) was prepared as labels to conjugate with thiol-modification DNA aptamers probe for signal amplification. While introducing numerous amino groups, the melamine functionalized hollow mesoporous carbon spheres (NH₂-HMCS) retained the edge-plane-like defective sites for the adhesion and electrocatalytic reduction of H₂O₂. With the unique characteristics of NH₂-HMCS, it not only enhanced the dispersity and loading capacity of core-shell Pd@Pt dendritic bimetallic nanoparticles (Pd@Pt DNs), but also improved the stability of bonding by the affinity interaction between Pd@Pt DNs and amino groups of melamine. Meanwhile, the synergistic catalysis effect between Pd@Pt DNs and NH₂-HMCS significantly enhanced the electrocatalytic reduction of H₂O₂ and further amplified the signal. Under optimal conditions, this recommended aptasensor for cTnI detection displayed a wide dynamic range from 0.1 pg/mL to 100.0 ng/mL and a low detection limit of 15.4 fg/mL (S/N = 3). The sensor also successfully realized the analysis of cTnI-spiked human serum samples, meaning potential applications in AMI diagnosis.

Doble role of bathocuproine disulfonic acid as multi-walled carbon nanotubes dispersing agent and copper preconcentration ligand: Analytical applications for the development of hydrogen peroxide and glucose electrochemical sensors

We are reporting a new strategy for preparing carbon nanotubes (CNTs)-based hydrogen peroxide and glucose amperometric sensors by taking advantage of the dual role of bathocuproine disulfonic acid (BCS) as dispersing agent of multi-walled carbon nanotubes (MWCNTs) and as ligand for the preconcentration of Cu(II). The platform was obtained by casting glassy carbon electrodes (GCE) with the dispersion of MWCNTs in BCS (MWCNTs-BCS) followed by the preconcentration of Cu(II) by surface complex formation at open circuit potential (GCE/MWCNTs-BCS/Cu). The resulting electrode was used for the sensitive amperometric quantification of hydrogen peroxide at 0.400 V catalyzed by the preconcentrated copper, with a linear range between 5.0 × 10^-7 and 7.4 × 10^-6 M, a sensitivity of 24.3 mA.M^-1, and a detection limit of 0.2 μM. The adsorption of GOx at GCE/MWCNTs-BCS/Cu followed by the immobilization of Nafion (Naf), allowed the construction of a sensitive and selective amperometric glucose biosensor with a linear range between 5.0 × 10^-6 M and 4.9 × 10^-4 M, a sensitivity of (477 ± 3) μA.M^-1 and a detection limit of 2 μM. The proposed (bio)sensors were successfully used for the quantification of hydrogen peroxide in enriched milk samples and glucose in milk and commercial beverages without any pretreatment.

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

Multi-walled carbon nanotubes functionalized with bathocuproinedisulfonic acid: analytical applications for the quantification of Cu(II)

This work reports the successful non-covalent functionalization of multi-walled carbon nanotubes (MWCNTs) with bathocuproinedisulfonic acid (BCS) and the analytical application of the resulting dispersion (MWCNTs-BCS) to develop an electrochemical sensor for Cu(II) quantification. The sensor was obtained by casting glassy carbon electrodes (GCEs) with MWCNTs-BCS. The sensing mechanism was based on the open circuit preconcentration of Cu(II) at the electrode surface by complexation of Cu(II) through the phenanthroline ring nitrogen of the BCS that supports the MWCNTs, the reduction of the preconcentrated Cu(II), and final differential pulse voltammetry-anodic stripping in 0.020 M acetate buffer, pH 5.00. The sensitivity of the sensor was (2.73 ± 0.08) μA μM^-1, with a linear range between 5.0 × 10^-7 M and 6.0 × 10^-6 M, a detection limit of 0.15 μM (9.5 μg L^-1), and reproducibility of 6.2% using the same dispersion and 7.1% using three different MWCNTs-BCS dispersions. The quantification of Cu(II) was highly selective even in the presence of As³⁺, Cr³⁺, Cd²⁺, Ni²⁺, Pb²⁺, Co²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Rh, Ir, and Ru. The proposed sensor was successfully used for quantifying Cu(II) in tap water. Graphical abstract.

Co2TiO4/Reduced Graphene Oxide Nanohybrids for Electrochemical Sensing Applications

For the first time, the synthesis, characterization, and analytical application for hydrogen peroxide quantification of the hybrid materials of Co2TiO4 (CTO) and reduced graphene oxide (RGO) is reported, using in situ (CTO/RGO) and ex situ (CTO+RGO) preparations. This synthesis for obtaining nanostructured CTO is based on a one-step hydrothermal synthesis, with new precursors and low temperatures. The morphology, structure, and composition of the synthesized materials were examined using scanning electron microscopy, X-ray diffraction (XRD), neutron powder diffraction (NPD), and X-ray photoelectron spectroscopy (XPS). Rietveld refinements using neutron diffraction data were conducted to determine the cation distributions in CTO. Hybrid materials were also characterized by Brunauer-Emmett-Teller adsorption isotherms, Scanning Electron microscopy, and scanning electrochemical microscopy. From an analytical point of view, we evaluated the electrochemical reduction of hydrogen peroxide on glassy carbon electrodes modified with hybrid materials. The analytical detection of hydrogen peroxide using CTO/RGO showed 11 and 5 times greater sensitivity in the detection of hydrogen peroxide compared with that of pristine CTO and RGO, respectively, and a two-fold increase compared with that of the RGO+CTO modified electrode. These results demonstrate that there is a synergistic effect between CTO and RGO that is more significant when the hybrid is synthetized through in situ methodology.

Ultrasensitive flexible FET-type aptasensor for CA 125 cancer marker detection based on carboxylated multiwalled carbon nanotubes immobilized onto reduced graphene oxide film

The development of a novel flexible and ultrasensitive aptasensor based on carboxylated multiwalled carbon nanotubes (MWCNTs)/ reduced graphene oxide-based field effect transistor (FET) has been reported for label-free detection of the ovarian cancer antigen (CA125). The fabricated sensor has a straightforward design based on the noncovalent attachment of MWCNTs/aptamer conjugated onto few layers reduced graphene oxide nanosheets and its integration with poly-methyl methacrylate (PMMA) as a suitable platform for designing flexible field-effect transistors. The surface properties of the aptasensor were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Under optimal conditions, the proposed aptasensor exhibited a wide linear dynamic range for CA125 (1.0 × 10^-9-1.0 U/mL) with a low detection limit of 5.0 × 10^-10 U/mL. The proposed aptasensor was also successfully applied to detect CA125 in real human serum samples. Furthermore, sensor flexibility is also a challenging area in chemical and biological sensors, especially for portable, wearable, or even implantable sensors, so, the reduced graphene oxide-based FET-type aptasensor showed bendable flexibility on the PMMA substrate. In addition, the aptasensor exhibited high sensitivity, selectivity, stability and reproducibility which offers great promise as a high performance and flexible FET-type aptasensor to detect CA125 and other cancer biomarkers in clinical samples and biological fluids.

Linear poly(ethylene imine)s: true molar masses, solution properties and conformation

In-depth characterization of pharmaceutically relevant polymers plays a pivotal role in many areas, including nanoscience, gene therapy, analytical and polymer chemistry etc.

Bio-Inspired Supramolecular Chemistry Provides Highly Concentrated Dispersions of Carbon Nanotubes in Polythiophene

In this paper we report the first observation, through X-ray diffraction, of noncovalent uracil-uracil (U-U) dimeric π-stacking interactions in carbon nanotube (CNT)-based supramolecular assemblies. The directionally oriented morphology determined using atomic force microscopy revealed highly organized behavior through π-stacking of U moieties in a U-functionalized CNT derivative (CNT-U). We developed a dispersion system to investigate the bio-inspired interactions between an adenine (A)-terminated poly(3-adeninehexyl thiophene) (PAT) and CNT-U. These hybrid CNT-U/PAT materials interacted through π-stacking and multiple hydrogen bonding between the U moieties of CNT-U and the A moieties of PAT. Most importantly, the U···A multiple hydrogen bonding interactions between CNT-U and PAT enhanced the dispersion of CNT-U in a high-polarity solvent (DMSO). The morphology of these hybrids, determined using transmission electron microscopy, featured grape-like PAT bundles wrapped around the CNT-U surface; this tight connection was responsible for the enhanced dispersion of CNT-U in DMSO.

Electrochemical sensing of guanine, adenine and 8-hydroxy-2′-deoxyguanosine at glassy carbon modified with single-walled carbon nanotubes covalently functionalized with lysine

Synthesis and characterization of l-lysine covalently functionalized SWCNT and analytical application for the highly sensitive quantification of guanine, adenine and 8-hydroxy-2′-deoxyguanosine.

Macroscopic Carbon Nanotube-based 3D Monoliths

Carbon nanotubes (CNTs) are one of the most promising carbon allotropes with incredible diverse physicochemical properties, thereby enjoying continuous worldwide attention since their discovery about two decades ago. From the point of view of practical applications, assembling individual CNTs into macroscopic functional and high-performance materials is of paramount importance. For example, multiscaled CNT-based assemblies including 1D fibers, 2D films, and 3D monoliths have been developed. Among all of these, monolithic 3D CNT architectures with porous structures have attracted increasing interest in the last few years. In this form, theoretically all individual CNTs are well connected and fully expose their surfaces. These 3D architectures have huge specific surface areas, hierarchical pores, and interconnected conductive networks, resulting in enhanced mass/electron transport and countless accessible active sites for diverse applications (e.g. catalysis, capacitors, and sorption). More importantly, the monolithic form of 3D CNT assemblies can impart additional application potentials to materials, such as free-standing electrodes, sensors, and recyclable sorbents. However, scaling the properties of individual CNTs to 3D assemblies, improving use of the diverse, structure-dependent properties of CNTs, and increasing the performance-to-cost ratio are great unsolved challenges for their real commercialization. This review aims to provide a comprehensive introduction of this young and energetic field, i.e., CNT-based 3D monoliths, with a focus on the preparation principles, current synthetic methods, and typical applications. Opportunities and challenges in this field are also presented.