Effect of UV radiation on the structure of graphene oxide in water and its impact on cytotoxicity and As(III) adsorption

Carbon Nanomaterial Fluorescent Probes and Their Biological Applications

Fluorescent carbon nanomaterials have broadly useful chemical and photophysical attributes that are conducive to applications in biology. In this review, we focus on materials whose photophysics allow for the use of these materials in biomedical and environmental applications, with emphasis on imaging, biosensing, and cargo delivery. The review focuses primarily on graphitic carbon nanomaterials including graphene and its derivatives, carbon nanotubes, as well as carbon dots and carbon nanohoops. Recent advances in and future prospects of these fields are discussed at depth, and where appropriate, references to reviews pertaining to older literature are provided.

Hydroxyapatite-Gold Modified Screen-Printed Carbon Electrode for Selective SARS-CoV-2 Antibody Immunosensor

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), or coronavirus disease 2019 (COVID-19), is still spreading worldwide; therefore, the need for rapid and accurate detection methods remains relevant to maintain the spread of this infectious disease. Electrochemical immunosensors are an alternative method for the rapid detection of the SARS-CoV-2 virus. Herein, we report the development of a screen-printed carbon electrode immunosensor using a hydroxyapatite-gold nanocomposite (SPCE/HA-Au) directly spray-coated with the immobilization receptor binding domain (RBD) Spike to increase the conductivity and surface electrode area. The HA-Au composite synthesis was optimized using the Box-Behnken method, and the resulting composite was characterized by UV-vis spectrophotometry, TEM-EDX, and XRD analysis. The specific interaction of RBD Spike with immunoglobulin G (IgG) antibodies was evaluated by differential pulse voltammetry and electrochemical impedance spectroscopy methods in a [Fe(CN)6]4-/3- solution redox system. The IgG was detected with a detection limit of 0.0561 pg mL-1, and the immunosensor had selectivity and stability of 103-122% and was stable until week 7 with the influence of storage conditions. Also, the immunosensor was tested using real samples from human serum, where the results were confirmed using the chemiluminescent microparticle immunoassay (CMIA) method and showed satisfactory results. Therefore, the developed electrochemical immunosensor can rapidly and accurately detect SARS-CoV-2 antibodies.

Promotion effect of ultraviolet light on graphene oxide aggregation in the presence of different climatic zone's humic and fulvic acid

Aggregation of graphene oxide (GO) is significantly affected by dissolved organic matter (DOM) in natural waters, while DOM's climate zone and light irradiation is seldom considered. This study investigated the effect of humic/fulvic acid (HA/FA) from various climate zones of China on aggregation of small (200 nm) and large (500 nm) GO under 120-h UV irradiation. GO aggregation was promoted by HA/FA because UV irradiation decreased hydrophilicity of GO and steric forces among particles. GO generated electron and hole pair under UV irradiation, which reduce GO with more hydrophilic oxygen-containing functional group (C-O) to rGO with high hydrophobicity and oxidize DOM into organic matter with smaller molecular weight. Most severe GO aggregation was observed with Makou HA from Subtropical Monsoon climate zone and Maqin FA from Plateau and Mountain climate zone, which was primarily because HA/FA's high molecular weight and aromaticity dispersed GO initially that facilitated UV penetration. GO aggregation ratio was positively correlated with graphitic fraction content (R2 = 0.82-0.99) and negatively correlated with C-O group content (R2 = 0.61-0.98) in the presence of DOM under UV irradiation. This work highlights different dispersity of GO during photochemical reactions in various climate zones, providing new insight into the environmental implications of nanomaterial release.

The Thermophysical and Physicochemical Properties of the Aqueous Dispersion of Graphene Oxide Dual-Beam Thermal Lens Spectrometry

Modern heat-conducting materials require special attention to analyze their thermophysical properties. Compared to classical methods, thermal lens spectrometry (TLS) has advantages due to its high sensitivity to physical and chemical composition. To avoid a systematic error in the analysis of complex systems, it is necessary to realize the limits of the applicability of the method. This study considers the features of thermal-diffusivity measurements by TLS in the stationary state for dispersed systems with absorbances up to 0.05. The limits of applicability of the method in analyzing heterogeneous systems are shown, and a mathematical apparatus is proposed for indicating a systematic error in finding thermal diffusivity that does not exceed 1%. Graphene oxide (GO), which has attractive physicochemical properties, was used as the object of analysis. GO belongs to 2D objects, the study of which requires highly sensitive methods and special attention when discussing the results. The thermophysical properties of aqueous dispersions of graphene oxide in a wide range of concentrations (up to 2 g/L) and lateral sizes (up to 4 µm) were studied by TLS. It has been found that with increasing nanophase concentration, the thermal diffusivity of graphene oxide dispersions passes through a minimum, which can be used in solving thermal insulation problems. It has been established that prolonged laser irradiation of the dispersion leads to a change in thermal diffusivity, which indicates the photochemical reduction of graphene oxide.

Derivatization of graphene oxide nanosheets with tunable nitric oxide release for antibacterial biomaterials

Graphene oxide (GO) nanosheets are a promising class of carbon-based materials suitable for application in the construction of medical devices. These materials have inherent antimicrobial properties based on sheet size, but these effects must be carefully traded off to maintain biocompatibility. Chemical modification of functional groups to the lattice structure of GO nanosheets enables unique opportunities to introduce new surface properties to bolster biological effects. Herein, we have developed nitric oxide (NO)-releasing GO nanosheets via immobilization of S-nitrosothiol (RSNO) moieties to GO nanosheets (GO-[NH]x -SNO). These novel RSNO-based GO nanosheets were characterized for chemical functionality via Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy, and colorimetric assays for functional group quantification. Stoichiometric control of the available RSNO groups functionalized onto the nanosheets was studied using chemiluminescence-based NO detection methods, showing highly tunable NO release kinetics. Studies of electrical stimulation and subsequent electrochemical reduction of the nanosheets demonstrated further tunability of the NO release based on stimuli. Finally, nanosheets were evaluated for cytotoxicity and antibacterial effects, showing strong cytocompatibility with human fibroblasts in parallel to broad antibacterial and anti-biofilm effects against both Gram-positive and Gram-negative strains. In summary, derivatized GO-(NH)x -SNO nanosheets were shown to have tunable NO release properties, enabling application-specific tailoring for diverse biomedical applications such as antimicrobial coatings and composite fillers for stents, sensors, and other medical devices.

How UV radiation and pH alternation impact graphene oxide mediated environmental toxicant adsorption and resulting safety characteristics - A toxicology study beyond a classic carrier effect

Once released into water, the widely used graphene oxide (GO) is likely to adsorb classical environmental pollutants, exemplified by Microcystin-LR (MCLR) that is a representative double-bond rich liver-toxic endotoxin. While GO-mediated carrier effect is fairly predictable, the involvement of environmental factors like UV and pH may add additional level of sophistication as these factors may impact the adsorption capacity of GO to MCLR. Here, we firstly investigated the changes of GO structure under different UV-radiation durations and pH conditions with a view to establish the correlation in terms of MCLR adsorption onto GO. We demonstrated that GO reduction especially oxygen-containing groups reduction induced by UV- radiation caused the compromised adsorption MCLR capacity on GO. Besides, the higher pH decreased the non-biological MCLR adsorption to GO by reducing GO defect sites and increasing electrostatic repulsion. These abiotic discoveries were further investigated to compare the safety features of GO-MCLR complex. Under dark condition (pH = 7), we revealed the cytotoxicity of GO-MCLR to normal liver cells, which involved the ROS generation and cell ferroptosis caused by Fe²⁺ accumulation. Introduction of UV and pH alternation in environment impacted GO-mediated environmental toxicant adsorption and resulting safety characteristics, which reminded us environmental factors should not be ignored in the GO-mediated carrier effect.

Advances in Biologically Applicable Graphene-Based 2D Nanomaterials

Climate change and increasing contamination of the environment, due to anthropogenic activities, are accompanied with a growing negative impact on human life. Nowadays, humanity is threatened by the increasing incidence of difficult-to-treat cancer and various infectious diseases caused by resistant pathogens, but, on the other hand, ensuring sufficient safe food for balanced human nutrition is threatened by a growing infestation of agriculturally important plants, by various pathogens or by the deteriorating condition of agricultural land. One way to deal with all these undesirable facts is to try to develop technologies and sophisticated materials that could help overcome these negative effects/gloomy prospects. One possibility is to try to use nanotechnology and, within this broad field, to focus also on the study of two-dimensional carbon-based nanomaterials, which have excellent prospects to be used in various economic sectors. In this brief up-to-date overview, attention is paid to recent applications of graphene-based nanomaterials, i.e., graphene, graphene quantum dots, graphene oxide, graphene oxide quantum dots, and reduced graphene oxide. These materials and their various modifications and combinations with other compounds are discussed, regarding their biomedical and agro-ecological applications, i.e., as materials investigated for their antineoplastic and anti-invasive effects, for their effects against various plant pathogens, and as carriers of bioactive agents (drugs, pesticides, fertilizers) as well as materials suitable to be used in theranostics. The negative effects of graphene-based nanomaterials on living organisms, including their mode of action, are analyzed as well.

Impact of secondary salts, temperature, and pH on the colloidal stability of graphene oxide in water

The stability of graphene oxide (GO) in water is extremely relevant because of its application as an adsorbent material, as well as for its fate and behavior in the environment. Zeta potential was used to study the effect of secondary salts (carbonate, sulfate, and phosphate), temperature (20 to 60 °C), and pH (5 to 9) on the stability of six different GOs produced from natural, synthetic, and amorphous graphite-with and without the use of attrition milling. Generally, GOs produced with attrition-milled graphites had lower ζ-potentials than their unmilled counterparts because of their smaller particle sizes and higher concentration of oxygen-containing functional groups. It was observed that GO produced from graphite and synthetic graphite had ζ-potential values lower than -30 mV, even at 30 °C. However, it was observed that all the GOs studied were unstable in the presence of carbonate and sulfate salts at concentrations between 170 and 1695 mg L^-1, as they reached a ζ-potential of -4.1 mV. Density-functional theory electronic structure calculations suggested that the instability of GO in the presence of carbonate and sulfate was caused by the abstraction of a proton resulting in interaction energies E _int of 28.3 and 168.9 kJ mol^-1, respectively. Our results suggest that temperatures above 30 °C, as well as carbonate and sulfate salts at concentrations relevant to arid and semi-arid regions, could promote the formation of agglomerates of GO, thus limiting its use and mobility in water.

Experimental Investigations of AlMg3 Components with Polyurethane and Graphene Oxide Nanosheets Composite Coatings, after Accelerated UV-Aging

The use of graphene (Gr) and its derivates graphene oxide (GO) showed that these materials are good candidates to enhance the properties of polyurethane (PU) coatings, especially the anticorrosion ones since graphene absorbs most of the light and provides hydrophobicity for repelling water. An important aspect of these multifunctional materials is that all these improvements can be realized even at very low filler loadings in the polymer matrix. In this work, an ultrasound cavitation technique was used for the proper dispersion of GO nanosheets (GON) in polyurethane (PU) resin to obtain a composite coating to protect the AlMg3 substrate. The addition of GON considerably improved the physical properties of coatings, as demonstrated by electrochemical impedance spectroscopy (EIS) analysis, promising improved anticorrosion performance after accelerated UV-ageing. Computational methods and Differential Scanning Calorimetry (DSC) measurements showed that GON facilitates the formation of additional bonds and stabilizes the PU structures during the ultraviolet (UV) exposure and aggressive attack of corrosive species. Limiting oxygen index (LOI) data reveal a slow burning behaviour of PU-GON coatings during UV exposure, which is better than PU alone.

New insights into the colloidal stability of graphene oxide in aquatic environment: Interplays of photoaging and proteins

Wide application leads to release of graphene oxide (GO) in aquatic environment, where it is subjected to photoaging and changes in physicochemical properties. As important component of natural organic matters, proteins may greatly affect the aggregation behaviors of photoaged GO. The effects of a typical model protein (bovine serum albumin, BSA) on the colloidal stability of photoaged GO were firstly investigated. Photoaging reduced the lateral size and oxygen-containing groups of GO, while the graphene domains and hydrophobicity increased as a function of irradiation time (0-24 h). Consequently, the photoaged GO became less stable than the pristine one in electrolyte solutions. Adsorption of BSA on the surface of the photoaged GO decreased as well, leading to thinner BSA coating on the photoaged GO. In the solutions with low concentrations of electrolytes, the aggregation rate constants (k) of all the photoaged GO firstly increased to the maximum agglomeration rate constants (k_fast, regime I), maintained at k_fast (regime Ⅱ) and then decreased to zero (regime Ⅲ) as the BSA concentration increased. In both regime I and III, the photoaged GO were less stable at the same BSA concentrations, and the impacts of BSA on the colloidal stability of the photoaged GO were less than the pristine one, which was attributed to the weaker interactions between the photoaged GO and BSA. This study provided new insights into the colloidal stability and fate of GO nanomaterials, which are subjected to extensive light irradiation, in wastewater and protein-rich aquatic environment.

Growth of binary anatase–rutile on phosphorylated graphene through strong P–O–Ti bonding affords a stable visible-light photocatalyst

Phosphorylated graphene sheets covalently bind, grow and stabilize biphasic anatase–rutile clusters through strong P–O–Ti bridges. The resulting nanocomposites stands as efficient visible-light photocatalysts for the degradation of dyes from water.

Controlled Reduction of Graphene Oxide Using Sulfuric Acid

Sulfuric acid under different concentrations and with the addition of SO₃ (fuming sulfuric acid) was studied as a reducing agent for the production of reduced graphene oxide (RGO). Three concentrations of sulfuric acid (1.5, 5, and 12 M), as well as 12 M with 30% SO₃, were used. The reduction of graphene oxide increased with H₂SO₄ concentration as observed by Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy. It was observed that GO lost primarily epoxide functional groups from 40.4 to 9.7% and obtaining 69.8% carbon when using 12 M H₂SO₄, without leaving sulfur doping. Additionally, the appearance of hexagonal domain structures observed in transmission electron microscopy and analyzed by selected area electron diffraction patterns confirmed the improvement in graphitization. Although the addition of SO₃ in H₂SO₄ improved the GO reduction with 74% carbon, as measured by XPS, the use of SO₃ introduced sulfur doping of 1.3%. RGO produced with sulfuric acid was compared with a sample obtained via ultraviolet (UV) irradiation, a very common reduction route, by observing that the RGO produced with sulfuric acid had a higher C/O ratio than the material reduced by UV irradiation. This work showed that sulfuric acid can be used as a single-step reducing agent for RGO without sulfur contamination.

Preparation and Characterization of Graphene Oxide for Pb(II) and Zn(II) Ions Adsorption from Aqueous Solution: Experimental, Thermodynamic and Kinetic Study

A thermodynamic and kinetic study of the adsorption process of Zn (II) and Pb (II) ions from aqueous solution on the surface of graphene oxide (GO) to establish the mechanisms of adsorbate–adsorbent interaction on this surface. The effect of pH on the retention capacity was studied and adsorption isotherms were determined from aqueous solution of the ions; once the experimental data was obtained, the kinetic and thermodynamic study of the sorption process was carried out. The data were fitted to the Langmuir, Freundlich, Dubinin-Raduskevich and Temkin isotherm models. The results showed that Zn(II) and Pb(II) on the GO adsorbing surface fitted the Langmuir model with correlation coefficients (R²) of 0.996. Kinetic models studied showed that a pseudo-second-order model was followed and thermodynamically, the process was spontaneous according to the values of Gibbs free energy (ΔG^o). N₂ adsorption isotherms were determined and modeled with the NLDFT (nonlocal density functional theory) and QSDFT (quenched solid density functional theory) kernels.