Surface functionalization of graphene oxide with tannic acid: Covalent vs non-covalent approaches

Redox-active graphene dispersant and its ability to improve the conductivity and pseudo-capacitance of carbon film

HYPOTHESIS

Strong van der Waals force and π-π interaction make graphene difficult to be uniformly distributed in basic matrix for fabricating graphene-based composites. Employing dispersant is a major solution, however, current existing dispersants such as commercially available surfactants and polymer stabilizers scarcely provide ideal effect. Besides, they are always "useless" in final composites but difficult to remove. Therefore, endowing dispersant with specific property that matching the application of the final composite is essential.

EXPERIMENTS

Herein, a redox-active graphene dispersant (RAGD) is developed based on the grafting of p-phenylenediamine (PDA) with epoxy groups and further reacting with ethylamine. Homogeneous aqueous graphene dispersion is prepared by tip-sonication, and uniform graphene-based films are prepared via vacuum filtration method.

FINDINGS

Graphene can be homogenously dispersed in water with concentration up to 15 mg mL-1 in the presence of RAGD, and it can stably exist at room temperature for over six months. The π-π interaction of RAGD with graphene is tunable due to the PDA conjugated center is redox-active, and RAGD can be partially eliminated from graphene under alkali treatment. The electrical conductivity of the graphene film increases by about 34% after treated by 1 mol L-1 NH3·H2O. Additionally, the graphene-based film including RAGD also shows much higher specific charge capacitance than those made with commonly used surfactants.

Emerging Trends in Silane-Modified Nanomaterial-Polymer Nanocomposites for Energy Harvesting Applications

Nanomaterials (NMs) have gained tremendous attention in various applications in the modern era. The most significant challenge associated with NMs is their strong propensity to aggregate. The chemical surface modification of NMs has garnered notable attention in managing NM dispersion and aggregation. Among the modification approaches, the silane modification of NMs has generated great interest among researchers as a versatile approach to tailoring the surface characteristics of NMs. This review comprehensively examined the recent advancements in silane modification techniques with a focus on triboelectric nanogenerator (TENG) applications. It provides an overview of silane chemistry and its interaction with diverse NMs, elucidating the underlying mechanisms governing the successful surface functionalization process. This review emphasized the silane modification, such as improved mechanical properties of composites, enhanced electrical and thermal conductivity, functional coatings, water treatment, textile industries, catalysis, membrane applications, and biomedical applications, of various NMs. In particular, the role of silane-modified NMs in advancing energy harvesting technologies was highlighted, showcasing their potential to enhance the performance and stability of next-generation devices.

Tannic acid as a multifunctional additive in polysaccharide and protein-based films for enhanced food preservation: A comprehensive review

Fossil-based polymers continue to dominate the market for single-use food packaging, despite increasing concerns about their sustainability. In response, natural and renewable polymers, such as proteins and polysaccharides, are gaining attention as potential alternatives due to their biodegradability and biocompatibility. However, their broader adoption is hindered by the need to improve their mechanical, barrier, and thermal properties. Tannic acid (TA) has emerged as a particularly effective additive for biopolymer-based films, offering strong antioxidant and antimicrobial properties. It also enhances mechanical and barrier characteristics through physical and/or covalent crosslinking. As a result, TA shows great potential as an additive for bioplastics, improving food packaging performance and extending product shelf life, while benefiting both the environment and the food industry. Despite the promising applications of TA, comprehensive reviews that focus on recent developments in its performance and bioactive properties remain limited. This review aims to highlight the effectiveness of TA as both an active ingredient and a crosslinking agent in various biopolymer films, offering valuable insights into its role in sustainable food packaging solutions by critically examining the latest advancements.

Fabrication of MnSnO2 intercalated TA-rGO modified sensor for selective electrochemical detection of chloramphenicol in real samples

Chloramphenicol (CAP), a potent antibiotic capable of inhibiting protein synthesis, presents significant challenges related to long-term dosing and its persistent leaching into the environment, raising concerns about environmental contamination and resistance development. To address this issue, we developed a reliable, low-cost, and biocompatible nanocomposite material comprising tannic acid (TA)-reduced graphene oxide (rGO) intercalated into manganese-doped tin oxide nanoparticles (MnSnO₂ NPs). The structural formation and catalytic activity of the MnSnO₂ NPs/TA-rGO nanocomposite were characterized using field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. This material exhibits robust interfacial interactions and synergistic effects, resulting in an admirable electrocatalytic reduction response for CAP sensing. The presence of co-interference molecules improved the selectivity performance of the MnSnO2 NPs/TA-rGO-modified glassy carbon electrode. The fabricated exhibited a two linear determination range (0.011-103.43 μmol L-1 and 103.43-1924.16 μmol L-1), with a detection limit (LOD) is 6.7 nmol L-1 and limit of quantification (LOQ) is 12.3 nmol L-1. Furthermore, this sensor demonstrated good sensitivity, admirable reproducibility, repeatability, and storage stability. Finally, the practicability of the fabricated MnSnO2 NPs/TA-rGO glassy carbon electrode sensor was evaluated by analyzing the CAP content in milk, honey, eye drops, biofluids (human serum and urine), and river water, and satisfactory recovery rates of 95.4 %-100.3 % were noted.

Graphene oxide-based fluorescent biosensors for pathogenic bacteria detection: A review

BACKGROUND

Pathogenic bacteria are widespread in nature and can cause infections and various complications, thereby posing a severe risk to public health. Therefore, simple, rapid, sensitive, and cost-effective methods must be developed to detect pathogenic bacteria. Biosensors are prominent platforms for detecting pathogenic bacteria owing to their high sensitivity, specificity, repeatability, and stability. With the development of nanotechnology, graphene oxide (GO) has been increasingly introduced into the construction of fluorescent biosensors to enhance their performance owing to its unique physicochemical properties.

RESULTS

This review systematically summarizes the development of GO-based fluorescent biosensors for the detection of pathogenic bacteria. First, we introduce the functionalization and modification of GO. The design and signal amplification strategies for GO-based fluorescent biosensors are also discussed. Finally, we explore the challenges and new perspectives associated with this field, with the aim of facilitating the development of GO-based fluorescent sensing technologies to prevent the spread of multidrug-resistant bacteria.

SIGNIFICANCE

This review will aid in the development of high-performance biosensors for pathogenic bacterial assays.

Interaction of graphene oxide with tannic acid: computational modeling and toxicity mitigation in C. elegans

Graphene oxide (GO) undergoes multiple transformations when introduced to biological and environmental media. GO surface favors the adsorption of biomolecules through different types of interaction mechanisms, modulating the biological effects of the material. In this study, we investigated the interaction of GO with tannic acid (TA) and its consequences for GO toxicity. We focused on understanding how TA interacts with GO, its impact on the material surface chemistry, colloidal stability, as well as, toxicity and biodistribution using the Caenorhabditis elegans model. Employing computational modeling, including reactive classical molecular dynamics and ab initio calculations, we reveal that TA preferentially binds to the most reactive sites on GO surfaces via the oxygen-containing groups or the carbon matrix; van der Waals interaction forces dominate the binding energy. TA exhibits a dose-dependent mitigating effect on the toxicity of GO, which can be attributed not only to the surface interactions between the molecule and the material but also to the inherent biological properties of TA in C. elegans. Our findings contribute to a deeper understanding of GO's environmental behavior and toxicity and highlight the potential of tannic acid for the synthesis and surface functionalization of graphene-based nanomaterials, offering insights into safer nanotechnology development.

Graphene-Oxide Peptide-Containing Materials for Biomedical Applications

This review explores the application of graphene-based materials (GBMs) in biomedicine, focusing on graphene oxide (GO) and its interactions with peptides and proteins. GO, a versatile nanomaterial with oxygen-containing functional groups, holds significant potential for biomedical applications but faces challenges related to toxicity and environmental impact. Peptides and proteins can be functionalized on GO surfaces through various methods, including non-covalent interactions such as π-π stacking, electrostatic forces, hydrophobic interactions, hydrogen bonding, and van der Waals forces, as well as covalent bonding through reactions involving amide bond formation, esterification, thiol chemistry, and click chemistry. These approaches enhance GO's functionality in several key areas: biosensing for sensitive biomarker detection, theranostic imaging that integrates diagnostics and therapy for real-time treatment monitoring, and targeted cancer therapy where GO can deliver drugs directly to tumor sites while being tracked by imaging techniques like MRI and photoacoustic imaging. Additionally, GO-based scaffolds are advancing tissue engineering and aiding tissues' bone, muscle, and nerve tissue regeneration, while their antimicrobial properties are improving infection-resistant medical devices. Despite its potential, addressing challenges related to stability and scalability is essential to fully harness the benefits of GBMs in healthcare.

Surface Engineering of Superparamagnetic Graphene Oxide Nanosheet as a Chemically Tunable Platform for Facial Biofuel Production by Lipase

In this research, we utilized an efficient approach to synthesize superparamagnetic graphene oxide (SPGO) rapidly in a one-pot method using microwave irradiation of graphene oxide (GO), urea, and Fe(III) ion. Tannic acid (TA) was introduced to the surface of SPGO through a straightforward and eco-friendly process. Methods were devised to furnish GO nanosheets and modify their surfaces with TA in an environmentally friendly manner. Two series of nanosheets, namely, SPGO/TA-COOH and SPGO/TA-IM, were engineered on the surface and used for immobilizing lipase enzyme. Through various analytical tools, the unique biocatalysts SPGO/TA-COOH/L and SPGO/TA-IM/L were confirmed. These biocatalysts exhibited enhanced stability at high temperatures and pH levels compared with free lipase. They also demonstrated prolonged storage stability and reusability over four months and seven cycles, respectively. Furthermore, the catalytic activity of immobilized lipase showed minimal impairment based on kinetic behavior analysis. The kinetic constants of SPGO/TA-IM/L were determined as Vmax = 0.24 mM min-1, Km = 0.224 mM, and kcat = 0.8 s-1. Additionally, the efficiency of biocatalysts for biodiesel production from palmitic acid was studied, focusing on various reaction parameters, such as temperature, alcohol to palmitic acid molar ratio, water content, and lipase quantity. The esterification reaction of palmitic acid with methanol, ethanol, and isopropanol was tested in the presence of SPGO/TA-COOH/L and SPGO/TA-IM/L, and the corresponding esters were obtained with a yield of 30.6-91.6%.

Surface Functionalization of Bamboo via Photo-Grafting Tannic Acid for Enhanced Silver Ion Loading Properties

Photo-grafting is a gentle, simple, and precise approach to incorporating specific functional molecules for the surface functionalization of substrates. In this work, ultraviolet (UV)-induced tannic acid (TA) grafting onto the surface of bamboo was proposed as a viable strategy for functionalizing bamboo. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) clearly indicated that TA was successfully introduced to the bamboo's surface. The optimal conditions for the grafting reaction were determined to be 15 mM Methyl-2-benzoylbenzoate (BB), 30 mM TA, 20 min, and a pH = 8. Under these conditions, the amount of TA grafted onto the bamboo's surface was measured to be 19.98 μg/cm2. Results from Inductively Coupled Plasma (ICP) and Energy Dispersive Spectrometer (EDS) analyses showed that the silver ion loading capacity of tannic acid-grafted bamboo was significantly improved compared to that of raw bamboo and tannic acid-impregnated bamboo. Furthermore, the presence of TA grafted on the bamboo's surface exhibited a positive correlation with the loading of silver ions, indicating that grafted TA plays an important role in the surface functionalization of bamboo. We believe that photo-grafted TA may help generate multifunctional bamboo with diverse properties.

Unveiling the power of MXenes: Solid lubrication perspectives and future directions

The interaction between two surfaces leads to the generation of friction and wear of material. Friction and wear are some of the major challenges that may readily be overcome by the third part of tribology called lubrication. Utilizing solid lubricants including polymers, carbon-based materials, soft metals, transition metal dichalcogenides, along with their potential benefits and drawbacks in dry environments can reduce friction. Recently, an emerging class of two-dimensional (2D) transition metal nitrides, carbides or carbonitrides commonly known as MXenes have emerged as an attractive alternative for solid lubrication because of their ability to establish wear-resistant tribo layers and well as low friction and shear strength. Furthermore, the inherent hydrophilic nature of these substances has led to limited dispersion stability and phase compatibility when combined with pure base oils. As a result, their potential use as solid lubricants and lubricant additives has been impeded. To address this issue and enhance the applicability of MXenes as solid lubricants, their surface modification can be an attractive tool. Therefore, this review provides a succinct summary of the current state-of-the-art in surface functionalization of MXenes, a subject that has not yet been thoroughly addressed. Further, the mechanical behavior of MXenes and composites has been discussed, followed by the potential of MXenes as a solid lubricant at micro- and macro-scale. Finally, the existing opportunities and challenges of the research area have been discussed with possible future research directions. We believe, this article will be a valuable resource for MXenes and opens the door to improve the chemical, physical and mechanical properties of MXenes in various applications, such as solid lubrication.

Rational Design of Stimuli-Responsive Inorganic 2D Materials via Molecular Engineering: Toward Molecule-Programmable Nanoelectronics

The ability of electronic devices to act as switches makes digital information processing possible. Succeeding graphene, emerging inorganic 2D materials (i2DMs) have been identified as alternative 2D materials to harbor a variety of active molecular components to move the current silicon-based semiconductor technology forward to a post-Moore era focused on molecule-based information processing components. In this regard, i2DMs benefits are not only for their prominent physiochemical properties (e.g., the existence of bandgap), but also for their high surface-to-volume ratio rich in reactive sites. Nonetheless, since this field is still in an early stage, having knowledge of both i) the different strategies for molecularly functionalizing the current library of i2DMs, and ii) the different types of active molecular components is a sine qua non condition for a rational design of stimuli-responsive i2DMs capable of performing logical operations at the molecular level. Consequently, this Review provides a comprehensive tutorial for covalently anchoring ad hoc molecular components-as active units triggered by different external inputs-onto pivotal i2DMs to assess their role in the expanding field of molecule-programmable nanoelectronics for electrically monitoring bistable molecular switches. Limitations, challenges, and future perspectives of this emerging field which crosses materials chemistry with computation are critically discussed.

A Review on Graphene Analytical Sensors for Biomarker-based Detection of Cancer

The engineering of nanoscale materials has broadened the scope of nanotechnology in a restricted functional system. Today, significant priority is given to immediate health diagnosis and monitoring tools for point-of-care testing and patient care. Graphene, as a one-atom carbon compound, has the potential to detect cancer biomarkers and its derivatives. The atom-wide graphene layer specialises in physicochemical characteristics, such as improved electrical and thermal conductivity, optical transparency, and increased chemical and mechanical strength, thus making it the best material for cancer biomarker detection. The outstanding mechanical, electrical, electrochemical, and optical properties of two-dimensional graphene can fulfil the scientific goal of any biosensor development, which is to develop a more compact and portable point-of-care device for quick and early cancer diagnosis. The bio-functionalisation of recognised biomarkers can be improved by oxygenated graphene layers and their composites. The significance of graphene that gleans its missing data for its high expertise to be evaluated, including the variety in surface modification and analytical reports. This review provides critical insights into graphene to inspire research that would address the current and remaining hurdles in cancer diagnosis.

Nanomaterial surface modification toolkit: Principles, components, recipes, and applications

Surface-functionalized nanostructures are at the forefront of biotechnology, providing new opportunities for biosensors, drug delivery, therapy, and bioimaging applications. The modification of nanostructures significantly impacts the performance and success of various applications by enabling selective and precise targeting. This review elucidates widely practiced surface modification strategies, including click chemistry, cross-coupling, silanization, aldehyde linkers, active ester chemistry, maleimide chemistry, epoxy linkers, and other protein and DNA-based methodologies. We also delve into the application-focused landscape of the nano-bio interface, emphasizing four key domains: therapeutics, biosensing, environmental monitoring, and point-of-care technologies, by highlighting prominent studies. The insights presented herein pave the way for further innovations at the intersection of nanotechnology and biotechnology, providing a useful handbook for beginners and professionals. The review draws on various sources, including the latest research articles (2018-2023), to provide a comprehensive overview of the field.

Graphene-based biosensors for detecting coronavirus: a brief review

The coronavirus (SARS-CoV-2) disease has affected the globe with 770 437 327 confirmed cases, including about 6 956 900 deaths, according to the World Health Organization (WHO) as of September 2023. Hence, it is imperative to develop diagnostic technologies, such as a rapid cost-effective SARS-CoV-2 detection method. A typical biosensor enables biomolecule detection with an appropriate transducer by generating a measurable signal from the sample. Graphene can be employed as a component for ultrasensitive and selective biosensors based on its physical, optical, and electrochemical properties. Herein, we briefly review graphene-based electrochemical, field-effect transistor (FET), and surface plasmon biosensors for detecting the SARS-CoV-2 target. In addition, details on the surface modification, immobilization, sensitivity and limit of detection (LOD) of all three sensors with regard to SARS-CoV-2 were reported. Finally, the point-of-care (POC) detection of SARS-CoV-2 using a portable smartphone and a wearable watch is a current topic of interest.

Assembling phenyl-modified colloidal silica on graphene oxide towards ethanol redispersible graphene oxide powder

Recently, ethanol has shown promising potential in the large-scale reduction of graphene oxide (GO) into graphene. However, dispersion of GO powder in ethanol is a challenge due to its poor affinity, which hinders permeation and intercalation of ethanol between GO molecule layers. In this paper, phenyl-modified colloidal silica nanospheres (PSNS) were synthesized by phenyl-tri-ethoxy-silane (PTES) and tetra-ethyl ortho-silicate (TEOS) using a sol-gel method. PSNS was then assembled onto a GO surface to form a PSNS@GO structure by possible non-covalent π-π stacking interactions between the phenyl groups and GO molecules. The surface morphology, chemical composition, and dispersion stability were analyzed by scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, Raman spectroscopy, X-ray diffractometry, nuclear magnetic resonance, and particle sedimentation test. The results showed that the as-assembled PSNS@GO suspension had excellent dispersion stability with an optimal PSNS concentration of 5 vol% PTES. With the optimized PSNS@GO, ethanol can permeate between the GO layers and intercalate along with PSNS particles via formation of hydrogen bonds between assembled PSNS on GO and ethanol, achieving a stable dispersion of GO in ethanol. The optimized PSNS@GO powder remained redispersible after drying and milling according to this interaction mechanism which is favorable for large scale reduction processes. Higher PTES concentration may result in agglomeration of PSNS and formation of wrapping structures of PSNS@GO after drying and worsen its dispersion capability.

Graphene in nanomedicine: A review on nano-bio factors and antibacterial activity

Graphene-based nanomaterials possess potent antibacterial activity and have engrossed immense interest among researchers as an active armour against pathogenic microbes. A comprehensive perception of the antibacterial activity of these nanomaterials is critical to the fabrication of highly effective antimicrobial nanomaterials, which results in highly efficient and enhanced activity. These materials owing to their antimicrobial activity are utilized as nanomedicine against various pathogenic microbes. The present article reviews the antimicrobial activity of graphene and its analogs such as graphene oxide, reduced graphene oxide as well as metal, metal oxide and polymeric composites. The review draws emphasis on the effect of various nano-bio factors on the antibacterial capability. It also provides an insight into the antibacterial properties of these materials along with a brief discussion on the discrepancies in their activities as evidenced by the scientific communities. In this way, the review is expected to shed light on future research and development in graphene-based nanomedicine.

Toxic Ag+ detection based on Au@Ag core shell nanostructure formation using Tannic acid assisted synthesis of Pullulan stabilized gold nanoparticles

Herein, a sensitive colorimetric detection strategy is proposed for Ag⁺ detection based on the use of environmentally friendly synthesis of gold nanoparticles (AuNPs), at room temperature, using (tannic acid, TA), as the reductant and pullulan (PUL) as stabilizing agent. The colloidal solution (TA/PUL-AuNPs), at the optimal synthesis conditions, showed maximum absorbance at 529 nm with a berry red color. TEM and FESEM validated that the particles are spherical and monodispersed, while other characterization results elucidated the role of pullulan in the nano-synthesis. Ag⁺ addition to the probe (TA/PUL-AuNPs), pH 11, resulted in naked-eye color changes, owing to Au@Ag core shell nanostructure formation. Further, the added Ag⁺ is reduced to AgNPs, on the surface of the TA/PUL-AuNPs probe. A hypsochromic shift in the absorption maximum, from 529 to 409 nm was observed, while (A_Ag+-A_bl)@409 nm exhibited linearity with Ag⁺ concentrations, from 0.100 to 150 µM. The estimated limit of detection was 30.8 nM, which is far lower than the acceptable limit of 0.930 µM from the regulatory agency. The TA/PUL-AuNPs probe was further tested for Ag⁺ detection in lake water samples, and it displayed satisfactory detection performances for real sample applications.

Surface Engineering of Nanomaterials with Polymers, Biomolecules, and Small Ligands for Nanomedicine

Nanomedicine is a speedily growing area of medical research that is focused on developing nanomaterials for the prevention, diagnosis, and treatment of diseases. Nanomaterials with unique physicochemical properties have recently attracted a lot of attention since they offer a lot of potential in biomedical research. Novel generations of engineered nanostructures, also known as designed and functionalized nanomaterials, have opened up new possibilities in the applications of biomedical approaches such as biological imaging, biomolecular sensing, medical devices, drug delivery, and therapy. Polymers, natural biomolecules, or synthetic ligands can interact physically or chemically with nanomaterials to functionalize them for targeted uses. This paper reviews current research in nanotechnology, with a focus on nanomaterial functionalization for medical applications. Firstly, a brief overview of the different types of nanomaterials and the strategies for their surface functionalization is offered. Secondly, different types of functionalized nanomaterials are reviewed. Then, their potential cytotoxicity and cost-effectiveness are discussed. Finally, their use in diverse fields is examined in detail, including cancer treatment, tissue engineering, drug/gene delivery, and medical implants.