Nitidine chloride-assisted bio-functionalization of reduced graphene oxide by bovine serum albumin for impedimetric immunosensing

Electrochemical biosensing platform based on AuNWs/rGO-CMC-PEDOT:PSS composite for the detection of superoxide anion released from living cells

Detection of superoxide anion (O2·-) levels holds significant importance for the diagnosis and even clinical treatments of oxidative stress-related diseases. Herein, we prepared a composite electrode material to encapsulate copper-zinc superoxide dismutase (SOD1) for biosensing of O2·-. The sensing material consists of gold nanowires (AuNWs), reduced graphene oxide (rGO), carboxymethyl cellulose (CMC) and PEDOT:PSS. CMC provides abundant -COOH to bind SOD1, with a high adsorption coverage of 1.499 × 10-9 mol cm-2 on the sensor surface. rGO and PEDOT endow the composite with significant conductivity, whereas PSS has antifouling capability. Moreover, AuNWs exhibit excellent electrical conductivity and a high aspect ratio, which promotes electron transfer, and ultimately enhances the catalytic performance of the enzyme. Meanwhile, SOD1(Cu2+) catalyzes the dismutation of O2·- to O2 and H2O2, and H2O2 is then electrochemically oxidized to generate amperometric signals for determination of O2·-. The sensor demonstrates outstanding detection performance for O2·- with a low detection limit of 2.52 nM, and two dynamic ranges (14.30 nM-1.34 μM and 1.34 μM-42.97 μM) with corresponding sensitivity of 0.479 and 0.052 μA μM-1cm-2, respectively. Additionally, the calculated apparent Michaelis constant (Kmapp) of 1.804 μM for SOD1 demonstrates the outstanding catalytic activity and the surface-immobilized enzyme's substrate affinity. Furthermore, the sensor shows the capability to dynamically detect the level of O2·- released from living HepG2 cells. This study provides an inovative design to obtain a biocompatible electrochemical sensing platform with plenty of immobilization sites for biomolecules, large surface area, high conductivity and flexibility.

Enhanced Electrochemical Biosensing of the Sp17 Cancer Biomarker in Serum Samples via Engineered Two-Dimensional MoS2 Nanosheets on the Reduced Graphene Oxide Interface

In the present investigation, we reported a label-free and highly effective immunosensor for the first time employing a nanostructured molybdenum disulfide nanosheets@reduced graphene oxide (nMoS2 NS@rGO) nanohybrid interface for the determination of sperm protein 17 (Sp17), an emerging cancer biomarker. We synthesized the nMoS2 NS@rGO nanohybrid using a one-step hydrothermal technique and then functionalized it with 3-aminopropyltriethoxysilane (APTES). Furthermore, the anti-Sp17 monoclonal antibodies were covalently attached to the APTES/nMoS2 NS@rGO/indium tin oxide (ITO) electrode utilizing 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-N-hydroxy succinimide (EDC-NHS) coupling chemistry. Bovine serum albumin (BSA) was then used to block nonspecific binding regions on the anti-Sp17/APTES/nMoS2 NS@rGO/ITO bioelectrode. The morphological and structural features of the synthesized nanohybrid and the modified electrodes were studied using transmission electron microscopy, scanning electron microscopy with energy dispersive X-ray (EDX) composition studies, atomic force microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The immunoreaction between the Sp17 antigen and anti-Sp17 antibodies on the surface of the BSA/anti-Sp17/APTES/nMoS2 NS@rGO/ITO sensing bioelectrode was applied as the basis for the detection technique, which measured the electrocatalytic current and impedimetric response change. The designed BSA/anti-Sp17/APTES/nMoS2 NS@rGO/ITO bioelectrode showed improved amperometric and impedimetric biosensing performance in the response studies, including remarkable sensitivity (23.2 μA ng-1mL cm-2 and 0.48 kΩ mL ng-1 cm-2), wider linearity (0.05-8 and 1-8 ng mL-1), an excellent lower detection limit (0.13 and 0.23 ng mL-1), and a rapid response time of 20 min. The biosensor exhibited impressive storage durability lasting 7 weeks and showed remarkable precision in identifying Sp17 in serum samples from cancer patients, as confirmed using the enzyme-linked immunosorbent assay method.

Sensitive Detection of Rosmarinic Acid Using Peptide-Modified Graphene Oxide Screen-Printed Carbon Electrode

Peptides have been used as components in biological analysis and fabrication of novel sensors due to several reasons, including well-known synthesis protocols, diverse structures, and acting as highly selective substrates for enzymes. Bio-conjugation strategies can provide a simple and efficient way to convert peptide-analyte interaction information into a measurable signal, which can be further used for the manufacture of new peptide-based biosensors. This paper describes the sensitive properties of a peptide-modified graphene oxide screen-printed carbon electrode for accurate and sensitive detection of a natural polyphenol antioxidant compound, namely rosmarinic acid. Glutaraldehyde was chosen as the cross-linking agent because it is able to bind nonspecifically to the peptide. We demonstrated that the strong interaction between the immobilized peptide on the surface of the sensor and rosmarinic acid favors the addition of rosmarinic acid on the surface of the electrode, leading to an efficient preconcentration that determines a high sensitivity of the sensor for the detection of rosmarinic acid. The experimental conditions were optimized using different pH values and different amounts of peptide to modify the sensor surface, so that its analytical performances were optimal for rosmarinic acid detection. By using cyclic voltammetry (CV) as a detection method, a very low detection limit (0.0966 μM) and a vast linearity domain, ranging from 0.1 µM to 3.20 µM, were obtained. The novelty of this work is the development of a novel peptide-based sensor with improved performance characteristics for the quantification of rosmarinic acid in cosmetic products of complex composition. The FTIR method was used to validate the voltammetric method results.

State of the Art in Carbon Nanomaterials for Photoacoustic Imaging

Photoacoustic imaging using energy conversion from light to ultrasound waves has been developed as a powerful tool to investigate in vivo phenomena due to their complex characteristics. In photoacoustic imaging, endogenous chromophores such as oxygenated hemoglobin, deoxygenated hemoglobin, melanin, and lipid provide useful biomedical information at the molecular level. However, these intrinsic absorbers show strong absorbance only in visible or infrared optical windows and have limited light transmission, making them difficult to apply for clinical translation. Therefore, the development of novel exogenous contrast agents capable of increasing imaging depth while ensuring strong light absorption is required. We report here the application of carbon nanomaterials that exhibit unique physical, mechanical, and electrochemical properties as imaging probes in photoacoustic imaging. Classified into specific structures, carbon nanomaterials are synthesized with different substances according to the imaging purposes to modulate the absorption spectra and highly enhance photoacoustic signals. In addition, functional drugs can be loaded into the carbon nanomaterials composite, and effective in vivo monitoring and photothermal therapy can be performed with cell-specific targeting. Diverse applied cases suggest the high potential of carbon nanomaterial-based photoacoustic imaging in in vivo monitoring for clinical research.

Electrochemical sensor based on the Mn3O4/CeO2 nanocomposite with abundant oxygen vacancies for highly sensitive detection of hydrogen peroxide released from living cells

Based on the strategy of increasing the number of oxygen vacancies to improve the catalytic performance, we have developed a novel electrochemical sensor based on the multivalent metal oxides cerium dioxide and manganous oxide (Mn₃O₄/CeO₂) for reliable determination of extracellular hydrogen peroxide (H₂O₂) released from living cells. The Mn₃O₄/CeO₂ nanocomposite was characterized by high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrochemical performance of the Mn₃O₄/CeO₂ nanocomposite modified glassy carbon electrode (Mn₃O₄/CeO₂/GCE) was investigated. Owing to the abundant oxygen vacancies and strong synergistic effect between the multivalent Ce and Mn, the sensor exhibited excellent catalytic activity and selectivity for the electrochemical detection of H₂O₂ with a low quantitation limit of 2 nM. Moreover, Mn₃O₄/CeO₂/GCE exhibited excellent reproducibility, repeatability, and long-term storage stability. Because of these remarkable analytical advantages, the constructed sensor was able to determine H₂O₂ released from living cells with satisfactory results. The results showed that the Mn₃O₄/CeO₂ sensor is a promising candidate for a nanoenzymatic H₂O₂ sensor with the possibility of applications in physiology and diagnosis.

An electrochemical immunosensor modified with titanium IV oxide/polyacrylonitrile nanofibers for the determination of a carcinoembryonic antigen

A highly sensitive electrochemical carcinoembryonic antigen immunosensor based on TiO₂np/polyacrylonitrile nanofibers electrospun on the surface of the discharged battery coal electrode.

A frogspawn-like Ag@C core–shell structure for an ultrasensitive label-free electrochemical immunosensing of carcinoembryonic antigen in blood plasma

Novel frogspawn-like Ag@C nanoparticles were successfully used to fabricate an ultrasensitive electrochemical immunosensing platform toward CEA in human blood samples.

A Novel Electrochemical Sensor Based on Au-rGO Nanocomposite Decorated with Poly(L-cysteine) for Determination of Paracetamol

Background:

Paracetamol is a common antipyretic and analgesic drug, but its excessive intake can accumulate toxic metabolites and cause kidney and liver damage, so it is critical to determine the content of paracetamol for clinical diagnosis and dose use.

Methods:

Au-reduced graphene oxide (Au-rGO) nanocomposite decorated with poly(L-cysteine) on carbon paste electrode was fabricated for the determination of paracetamol. Au-rGO was first coelectrodeposited on the carbon paste electrode surface. Afterwards, L-cysteine was electropolymerized to fabricate the Au-rGO/poly(L-cysteine) modified carbon paste electrode. Scanning electron microscope was used to characterize the morphology of Au-rGO and poly(L-cysteine)/Au-rGO. The electrochemical properties of the sensor were studied by cyclic voltammetry and differential pulse voltammetry.

Results:

After exploring the optimal conditions, the sensor showed a wide linear response for paracetamol detection in the range of 1-200 μM with a detection limit of 0.5 μM (S/N = 3).

Conclusion:

The fabricated sensor demonstrated good sensitivity with rapid detection capacity in real samples.

Facile Synthesis of ZnMn2O4@rGO Microspheres for Ultrasensitive Electrochemical Detection of Hydrogen Peroxide from Human Breast Cancer Cells

Mixed transition-metal oxides have witnessed increasing attention in catalysts and electrocatalysts. Herein, reduced graphene oxide-wrapped ZnMn₂O₄ microspheres (ZnMn₂O₄@rGO) were facilely synthesized through the solvothermal technique. The microstructure and morphology of ZnMn₂O₄@rGO microspheres were analyzed under Raman, X-ray photoelectron, X-ray diffraction, and energy-dispersive spectroscopies and scanning electron microscopy. The synthesized ZnMn₂O₄@rGO was employed as an excellent electrocatalyst for the reduction of hydrogen peroxide (H₂O₂). The ZnMn₂O₄@rGO-modified glassy carbon electrode (ZnMn₂O₄@rGO/GCE) exhibited a linear detection to H₂O₂ in a wide concentration range of 0.03-6000 μM with a detection limit of 0.012 μM. The biosensor was evaluated to determine H₂O₂ secreted by human breast cancer cells (MCF-7), indicating its promising applications in physiology and diagnosis.

The influence of bovine serum albumin-modified silica on the physicochemical properties of poly(vinyl alcohol) nanocomposites synthesized by ultrasonication technique

In this study, for the first time polymeric nanocomposite (NC) films of poly(vinyl alcohol)/SiO₂@bovine serum albumin (PVA/SiO₂@BSA) were synthesized by solution casting method under facile and fast method of sonication. In this regard, SiO₂ nanoparticles (NPs) were modified by BSA, at room temperature by using phosphate buffer and ultrasonic-assisted method. Then, PVA/SiO₂@BSA NCs were prepared by insertion of variant amount (3, 6 and 9wt%) of SiO₂@BSA into the PVA matrix, under ultrasonic irradiation. The morphological traits of the NCs were surveyed by Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray diffraction and field emission scanning electron microscopy. It was detected that NPs incorporation didn't remarkably affect the crystallinity and morphology of the NCs. TEM images indicated that the inserted NPs have good diffusions in the PVA matrix, and their embedment in the matrix significantly upgraded its thermal, optical and mechanical behaviors. The tensile strength showed more than 2-fold increase and the thermal stability exhibited about 37% enhancement that was higher, in comparison with those of the similar NCs. This showed that the prepared NCs can have potential application in food packaging.∗∗∗.

Scalable Approach To Construct Free-Standing and Flexible Carbon Networks for Lithium-Sulfur Battery

Reconstructing carbon nanomaterials (e.g., fullerene, carbon nanotubes (CNTs), and graphene) to multidimensional networks with hierarchical structure is a critical step in exploring their applications. Herein, a sacrificial template method by casting strategy is developed to prepare highly flexible and free-standing carbon film consisting of CNTs, graphene, or both. The scalable size, ultralight and binder-free characteristics, as well as the tunable process/property are promising for their large-scale applications, such as utilizing as interlayers in lithium-sulfur battery. The capability of holding polysulfides (i.e., suppressing the sulfur diffusion) for the networks made from CNTs, graphene, or their mixture is pronounced, among which CNTs are the best. The diffusion process of polysulfides can be visualized in a specially designed glass tube battery. X-ray photoelectron spectroscopy analysis of discharged electrodes was performed to characterize the species in electrodes. A detailed analysis of lithium diffusion constant, electrochemical impedance, and elementary distribution of sulfur in electrodes has been performed to further illustrate the differences of different carbon interlayers for Li-S batteries. The proposed simple and enlargeable production of carbon-based networks may facilitate their applications in battery industry even as a flexible cathode directly. The versatile and reconstructive strategy is extendable to prepare other flexible films and/or membranes for wider applications.

A novel sandwich-type immunosensor based on three-dimensional graphene–Au aerogels and quaternary chalcogenide nanocrystals for the detection of carcino embryonic antigen

Cu₂ZnSnS₄ nanocrystals were firstly used as electrocatalysts in H₂O₂ reduction for ultrasensitive detection of carcino embryonic antigen.