The Hybrid Nano-Biointerface between Proteins/Peptides and Two-Dimensional Nanomaterials

In typical protein-nanoparticle surface interactions, the biomolecule surface binding and consequent conformational changes are intermingled with each other and are pivotal to the multiple functional properties of the resulting hybrid bioengineered nanomaterial. In this review, we focus on the peculiar properties of the layer formed when biomolecules, especially proteins and peptides, face two-dimensional (2D) nanomaterials, to provide an overview of the state-of-the-art knowledge and the current challenges concerning the biomolecule coronas and, in general, the 2D nano-biointerface established when peptides and proteins interact with the nanosheet surface. Specifically, this review includes both experimental and simulation studies, including some recent machine learning results of a wide range of nanomaterial and peptide/protein systems.

Nanobio Interface Between Proteins and 2D Nanomaterials

Two-dimensional (2D) nanomaterials have significantly contributed to recent advances in material sciences and nanotechnology, owing to their layered structure. Despite their potential as multifunctional theranostic agents, the biomedical translation of these materials is limited due to a lack of knowledge and control over their interaction with complex biological systems. In a biological microenvironment, the high surface energy of nanomaterials leads to diverse interactions with biological moieties such as proteins, which play a crucial role in unique physiological processes. These interactions can alter the size, surface charge, shape, and interfacial composition of the nanomaterial, ultimately affecting its biological activity and identity. This review critically discusses the possible interactions between proteins and 2D nanomaterials, along with a wide spectrum of analytical techniques that can be used to study and characterize such interplay. A better understanding of these interactions would help circumvent potential risks and provide guidance toward the safer design of 2D nanomaterials as a platform technology for various biomedical applications.

Investigation of thymine as a potential cancer biomarker employing tryptophan with nanomaterials as a biosensor

Tryptophan and tryptophan-based nanomaterials sensors in a solution have been developed to directly evaluate thymine. The determination of thymine has been done via quenching of the fluorescence of tryptophan and tryptophan-based nanomaterials such as graphene (Gr), graphene oxide (GO), gold nanoparticles (AuNPs), gold-silver nanocomposite (Au-Ag NC) in a physiological buffer. As the concentration of thymine rises, the fluorescence of tryptophan and tryptophan/nanomaterials becomes less intense. Trp, Trp/Gr, and tryptophan/(Au-Ag) NC systems' quenching mechanisms were dynamic, but tryptophan /GO and tryptophan/AuNPs' quenching mechanisms were static. The linear dynamic range for the determination of thy by tryptophan and tryptophan /nanomaterials is 10 to 200 μM. The detection limits for tryptophan, tryptophan /Gr, tryptophan /GO, tryptophan /AuNPs, and tryptophan/Au-Ag NC were 3.21, 14.20, 6.35, 4.67and 7.79 Μm, respectively. Thermodynamic parameters for the interaction of the Probes with Thy include the enthalpy (H°) and entropy (S°) change values, were assessed, as well as the binding constant (Ka) of Thy with Trp and Trp-based nanomaterials. A recovery study was conducted utilizing a human serum sample after the addition of the required quantity of the investigational thymine.

Bio-inspired sustainable synthesis of novel SnS2/biochar nanocomposite for adsorption coupled photodegradation of amoxicillin and congo red: Effects of reaction parameters, and water matrices

This study aims to fabricate a novel integrated photocatalytic adsorbent (IPA) via a green solvothermal process employing tea (Camellia sinensis var. assamica) leaf extract as a stabilizing and capping agent for the removal of organic pollutants from wastewater. An n-type semiconductor photocatalyst, SnS_2, was chosen as a photocatalyst due to its remarkable photocatalytic activity supported over areca nut (Areca catechu) biochar for the adsorption of pollutants. The adsorption and photocatalytic properties of fabricated IPA were examined by taking amoxicillin (AM) and congo red (CR) as two emerging pollutants found in wastewater. Investigating synergistic adsorption and photocatalytic properties under varying reaction conditions mimicking actual wastewater conditions marks the novelty of the present research. The support of biochar for the SnS₂ thin films induced a reduction in charge recombination rate, which enhanced the photocatalytic activity of the material. The adsorption data were in accordance with the Langmuir nonlinear isotherm model, indicating monolayer chemosorption with the pseudo-second-order rate kinetics. The photodegradation process follows pseudo-first-order kinetics with the highest rate constant of 0.0450 min^-1 for AM and 0.0454 min^-1 for CR. The overall removal efficiency of 93.72 ± 1.19% and 98.43 ± 1.53% could be achieved within 90 min for AM and CR via simultaneous adsorption and photodegradation model. A plausible mechanism of synergistic adsorption and photodegradation of pollutants is also presented. The effect of pH, Humic acid (HA) concentration, inorganic salts and water matrices have also been included.The photodegradation activity of SnS₂ under visible light coupled with the adsorption capability of the biochar results in the excellent removal of the contaminants from the liquid phase.

Development of Nanoscale Graphene Oxide Models for the Adsorption of Biological Molecules

Graphene oxide (GO), a nanomaterial with promising applications that range from water purification to enzyme immobilization, is actively present in scientific research since its discovery. GO studies with computational methodologies such as molecular dynamics are frequently reported in the literature; however, the models used often rely on approximations, such as randomly placing functional groups and the use of generalized force fields. Therefore, it is important to develop new MD models that provide a more accurate description of GO structures and their interaction with an aqueous solvent and other adsorbate molecules. In this paper, we derived new force field non-bonded parameters from linear-scaling density functional theory calculations of nanoscale GO sheets with more than 10,000 atoms through an atoms-in-molecules (AIM) partitioning scheme. The resulting GAFF2-AIM force field, derived from the bonded terms of GAFF2 parameterization, reproduces the solvent structure reported in ab initio MD simulations better than the force field nowadays widely used in the literature. Additionally, we analyzed the effect of the ionic strength of the medium and of the C/O ratio on the distribution of charges surrounding the GO sheets. Finally, we simulated the adsorption of natural amino acid molecules to a GO sheet and estimated their free energy of binding, which compared very favorably to their respective experimental values, validating the force field presented in this work.

Advancements and Utilizations of Scaffolds in Tissue Engineering and Drug Delivery

The drug development process requires a thorough understanding of the scaffold and its three-dimensional structure. Scaffolding is a technique for tissue engineering and the formation of contemporary functioning tissues. Tissue engineering is sometimes referred to as regenerative medicine. They also ensure that drugs are delivered with precision. Information regarding scaffolding techniques, scaffolding kinds, and other relevant facts, such as 3D nanostructuring, are discussed in depth in this literature. They are specific and demonstrate localized action for a specific reason. Scaffold's acquisition nature and flexibility make it a new drug delivery technology with good availability and structural parameter management.

Histidine-Triggered GO Hybrid Hydrogels for Microfluidic 3D Printing

Graphene oxide (GO) hydrogels have provided tremendous opportunities in designing and fabricating complex constructs for diverse applications, while their 3D printing without photocuring is still a challenging task due to their low viscosity, uncontrollable gelation, and low interfacial tension. Here, we report a histidine-assisted printing strategy to prepare GO hybrid hydrogels through the microfluidic 3D printing technique. We found that the GO additive could significantly hamper the Knoevenagel condensation (KC) reaction between benzaldehyde and cyanoacetate group-functionalized polymers to form a hydrogel, while these GO mixed solutions were rapidly solidified into a hydrogel when histidine was added. This fascinating phenomenon enabled us to prepare low-viscosity GO mixed polymer solutions as printable inks and generate hydrogel microfibers in histidine solutions. The hydrogel fibers could support cell survival and be further constructed into complex 3D structures through microfluidic 3D printing techniques. Moreover, due to the addition of GO, the microfibers exhibited excellent electrical conductivity and could sense the motion changes and convert these stimuli as electrical resistance signals. This strategy adds an option for the design and application of 3D printable aqueous GO inks in many fields.

Simultaneous Visualization of MiRNA-221 and Caspase-3 in Cancer Cells for Investigating the Feasibility of MiRNA-Targeted Therapy with a Dual-Color Fluorescent Nanosensor

MiRNA-targeted therapy holds great promise for precision cancer therapy. It is important to investigate the effect of changes in miRNA expression on apoptosis in order to evaluate miRNA-targeted therapy and achieve personalized therapy. In this study, we designed a dual-color fluorescent nanosensor consisting of grapheme oxide modified with a molecular beacon and peptide. The nanosensor can simultaneously detect and image miRNA-221 and apoptotic protein caspase-3 in living cells. Intracellular experiments showed that the nanosensor could be successfully applied for in situ monitoring of the effect of miRNA-221 expression changes on apoptosis by dual-color imaging. The current strategy could provide new avenues for investigating the feasibility of miRNA-targeted therapy, screening new anti-cancer drugs targeting miRNA and developing personalized treatment plans.

Graphene and Graphene Oxide as a Support for Biomolecules in the Development of Biosensors

Graphene and graphene oxide have become the base of many advanced biosensors due to their exceptional characteristics. However, lack of some properties, such as inertness of graphene in organic solutions and non-electrical conductivity of graphene oxide, are their drawbacks in sensing applications. To compensate for these shortcomings, various methods of modifications have been developed to provide the appropriate properties required for biosensing. Efficient modification of graphene and graphene oxide facilitates the interaction of biomolecules with their surface, and the ultimate bioconjugate can be employed as the main sensing part of the biosensors. Graphene nanomaterials as transducers increase the signal response in various sensing applications. Their large surface area and perfect biocompatibility with lots of biomolecules provide the prerequisite of a stable biosensor, which is the immobilization of bioreceptor on transducer. Biosensor development has paramount importance in the field of environmental monitoring, security, defense, food safety standards, clinical sector, marine sector, biomedicine, and drug discovery. Biosensor applications are also prevalent in the plant biology sector to find the missing links required in the metabolic process. In this review, the importance of oxygen functional groups in functionalizing the graphene and graphene oxide and different types of functionalization will be explained. Moreover, immobilization of biomolecules (such as protein, peptide, DNA, aptamer) on graphene and graphene oxide and at the end, the application of these biomaterials in biosensors with different transducing mechanisms will be discussed.

Peptide Conjugate on Multilayer Graphene Oxide Film for the Osteogenic Differentiation of Human Wharton's Jelly-Derived Mesenchymal Stem Cells

Graphene oxide (GO) is extensively studied as a template material for mesenchymal stem cell application due to its two-dimensional nature and unique functionalization chemistries. Herein, a new type of peptide-conjugated multilayer graphene oxide (peptide/m-GO film) was fabricated and used as biomaterial for culturing human Wharton's jelly-derived mesenchymal stem cells (WJ-MSCs). The characterization of the peptide/m-GO films was performed, and the biocompatibility of the WJ-MSCs on the peptide/m-GO films was investigated. The results demonstrated that the peptide conjugate on the m-GO film did not hamper the normal growth of WJ-MSCs but supported the growth of WJ-MSCs after the 6-day culture period. In addition, the osteogenic differentiation of WJ-MSCs on the peptide/m-GO films was enhanced as compared with the parent m-GO film. Therefore, such peptide-conjugated m-GO films could provide a highly biocompatible and multifunctional 2D material to tailor the potential application of WJ-MSCs in bone tissue regeneration.

Fluorescence Determination of Peptidase Activity Based on the Quenching of a Fluorophore-Labelled Peptide by Graphene Oxide

In this study, a fluorescence detection strategy is reported for the peptidase activity assay, which is based on fluorescence resonance energy transfer (FRET) from a fluorophore-labelled peptide to graphene oxide (GO). By the hydrolysis of the peptide, the fluorophore-labelled peptide releases the fluorophore 5-carboxyfluorescein, which can avoid quenching from GO. Thus, the increased intensity of the obtained fluorescence signal in the assay is directly dependent on the peptidase activity. As a model case of the developed strategy, the activity determination of pancreatic elastase (PE) is performed. Under the optimal experimental conditions at an excitation wavelength of 494 nm, the activity of PE can be determined in the range from 0.003 to 0.10 U/mL, with a detection limit of 0.001 U/mL at the emission wavelength of 518 nm. This is ultra-sensitive for the determination of PE. The specificity of the method is demonstrated by the analysis of PE under complex conditions using fetal bovine serum as the substrate. Hence, the developed method might provide an intrinsically convenient, sensitive platform for the PE activity assay and related biochemical studies due to its homogeneous, and fluorescence-based detection strategy.

A moisturizing chitosan-silk fibroin dressing with silver nanoparticles-adsorbed exosomes for repairing infected wounds

Refractory wounds caused by microbial infection impede wound healing, vascular regeneration, nerve system repair and the regeneration of other skin appendages. In addition, large-area infected wounds cause the appearance of multidrug-resistant (MDR) bacterial strains, which pose a major challenge both in clinical and scientific research. Although many stem cell-derived exosomes have been demonstrated to promote skin repair and regeneration, exosomes are seldom applied in the treatment of infective wounds due to the lack of antimicrobial function. In this study, we fabricated an asymmetric wettable dressing with a composite of exosomes and silver nanoparticles (CTS-SF/SA/Ag-Exo dressing) for promoting angiogenesis, nerve repair and infected wound healing. The CTS-SF/SA/Ag-Exo dressing possesses multifunctional properties including broad-spectrum antimicrobial activity, promoting wound healing, retaining moisture and maintaining electrolyte balance. It can effectively inhibit the growth of bacterial and promote the proliferation of human fibroblasts in vitro. Moreover, the in vivo results show that the CTS-SF/SA/Ag-Exo dressing enhanced wound healing by accelerating collagen deposition, angiogenesis and nerve repair in a P. aeruginosa infected mouse skin wound defect model. We hope that this dressing will provide a solution for the repair of infected wounds for treatments in the clinic.

Atomistic Perspective on Biomolecular Adsorption on Functionalized Carbon Nanomaterials under Ambient Conditions

The use of carbon-based nanomaterials is tremendously increasing in various areas of technological, bioengineering, and biomedical applications. The functionality of carbon-based nanomaterials can be further broadened via chemical functionalization of carbon nanomaterial surfaces. On the other hand, concern is rising on possible adverse effects when nanomaterials are taken up by biological organisms. In order to contribute into understanding of interactions of carbon-based nanomaterials with biological matter, we have investigated adsorption of small biomolecules on nanomaterials using enhanced sampling molecular dynamics. The biomolecules included amino acid side chain analogues, fragments of lipids, and sugar monomers. The adsorption behavior on unstructured amorphous carbon, pristine graphene and its derivatives (such as few-layer graphene, graphene oxide, and reduced graphene oxide) as well as pristine carbon nanotubes, and those functionalized with OH-, COOH-, COO-, NH2-, and NH3+ groups was investigated with respect to surface concentration. An adsorption profile, that is, the free energy as a function of distance from the nanomaterial surfaces, was determined for each molecule and surface using the Metadynamics approach. The results were analyzed in terms of chemical specificity, surface charge, and surface concentration. It was shown that although morphology of the nanomaterial has a limited effect on the adsorption properties, functionalization of the surface by various molecular groups can drastically change the adsorption behavior that can be used in the design of nanosurfaces with highly selective adsorption properties and safe for human health and environment.

Self-Assembly of Ferrocene-Phenylalanine@Graphene Oxide Hybrid Hydrogels for Dopamine Detection

The effect of graphene oxide (GO) is explored on the self-assembly behavior of ferrocene-L-phenylalanine (Fc-F) in solution. The assembly behavior of Fc-F in GO dispersions at different concentrations and pH values was systematically investigated. At pH 8, a stable hybrid material could be formed by facile and elaborate supramolecular assembly. Moreover, the concentration of GO could also be used to adjust the mechanical strength of the hybrid hydrogel. Increasing the concentration of GO in the assembly process, a hydrogel with better mechanical strength could be obtained. The storage modulus could be up to 6.3 kPa by increasing the GO concentration to 1 mg/mL. Finally, the dopamine concentration in the solution could be detected in a high accuracy by loading the hybrid hydrogel onto the electrode surface. The R² of linear fitting equation could reach 0.9915 in the range of 10-200 μmol/L, indicating that it has the potential as biosensing electrode material.

Graphene biosensors for bacterial and viral pathogens

The infection and spread of pathogens (e.g., COVID-19) pose an enormous threat to the safety of human beings and animals all over the world. The rapid and accurate monitoring and determination of pathogens are of great significance to clinical diagnosis, food safety and environmental evaluation. In recent years, with the evolution of nanotechnology, nano-sized graphene and graphene derivatives have been frequently introduced into the construction of biosensors due to their unique physicochemical properties and biocompatibility. The combination of biomolecules with specific recognition capabilities and graphene materials provides a promising strategy to construct more stable and sensitive biosensors for the detection of pathogens. This review tracks the development of graphene biosensors for the detection of bacterial and viral pathogens, mainly including the preparation of graphene biosensors and their working mechanism. The challenges involved in this field have been discussed, and the perspective for further development has been put forward, aiming to promote the development of pathogens sensing and the contribution to epidemic prevention.

Anti-Angiogenic and Anti-Proliferative Graphene Oxide Nanosheets for Tumor Cell Therapy

Graphene oxide (GO) is a bidimensional novel material that exhibits high biocompatibility and angiogenic properties, mostly related to the intracellular formation of reactive oxygen species (ROS). In this work, we set up an experimental methodology for the fabrication of GO@peptide hybrids by the immobilization, via irreversible physical adsorption, of the Ac-(GHHPH)₄-NH₂ peptide sequence, known to mimic the anti-angiogenic domain of the histidine-proline-rich glycoprotein (HPRG). The anti-proliferative capability of the graphene-peptide hybrids were tested in vitro by viability assays on prostate cancer cells (PC-3 line), human neuroblastoma (SH-SY5Y), and human retinal endothelial cells (primary HREC). The anti-angiogenic response of the two cellular models of angiogenesis, namely endothelial and prostate cancer cells, was scrutinized by prostaglandin E2 (PGE₂) release and wound scratch assays, to correlate the activation of inflammatory response upon the cell treatments with the GO@peptide nanocomposites to the cell migration processes. Results showed that the GO@peptide nanoassemblies not only effectively induced toxicity in the prostate cancer cells, but also strongly blocked the cell migration and inhibited the prostaglandin-mediated inflammatory process both in PC-3 and in HRECs. Moreover, the cytotoxic mechanism and the internalization efficiency of the theranostic nanoplatforms, investigated by mitochondrial ROS production analyses and confocal microscopy imaging, unraveled a dose-dependent manifold mechanism of action performed by the hybrid nanoassemblies against the PC-3 cells, with the detection of the GO-characteristic cell wrapping and mitochondrial perturbation. The obtained results pointed out to the very promising potential of the synthetized graphene-based hybrids for cancer therapy.

The toxicity of graphene oxide affected by algal physiological characteristics: A comparative study in cyanobacterial, green algae, diatom

Though the main toxic mechanisms of graphene oxide (GO) to algae have been accepted as the shading effect, oxidative stress and mechanical damage, the effect of algal characteristics on these three mechanisms of GO toxicity have seldom been taken into consideration. In this study, we investigated GO toxicity to green algae (Chlorella vulgaris, Scenedesmus obliquus, Chlamydomonas reinhardtii), cyanobacteria (Microcystis aeruginosa) and diatoms (Cyclotella sp.). The aim was to assess how the physiological characteristics of algae affect the toxicity of GO. Results showed that 10 mg/L of GO significantly inhibited the growth of all tested algal types, while S. obliquus and C. reinhardtii were found to be the most susceptible and tolerant species, respectively. Then, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the physiological characteristics of the assessed algae. The presence of locomotive organelles, along with smaller and more spherical cells, was more likely to alleviate the shading effect. Variations in cell wall composition led to different extents of mechanical damage as shown by Cyclotella sp. silica frustules and S. obliquus autosporine division being prone to damage. Meanwhile, growth inhibition and cell division were significantly correlated with the oxidative stress and membrane permeability, suggesting the latter two indicators can effectively signal GO toxicity to algae. The findings of this study provide novel insights into the toxicity of graphene materials in aquatic environments.

Construction of a combined enzyme system of graphene oxide and manganese peroxidase for efficient oxidation of aromatic compounds

Manganese peroxidase (MnP) from Irpex lacteus F17 has potential use as a biocatalyst in the field of environmental biotechnology because of its unique properties and ability to decompose harmful aromatic compounds. However, its requirement of harsh acidic reaction conditions and its insufficient catalytic activity restrict its practical applications. Here, we combine graphene oxide (GO) and MnP to construct an efficient enzyme system (GO-MnP) with improved catalytic efficiencies and a wide pH range for the oxidation of aromatic substances and dye decolorization. We found that the Michaelis constant (K_m) of GO-MnP for Mn²⁺ was 2.8 times lower and the catalytic efficiency (k_cat/K_m) of GO-MnP was 4.5 times higher than those of MnP, and that the decolorization of various dyes by GO-MnP was significantly improved over the pH range of 4.5-5.5. A comparison of the midpoint redox potentials also reflects the strong oxidation ability of GO-MnP. Furthermore, we demonstrated that, in the GO-MnP system, the MnP activity is mainly determined by the amounts of epoxy and carboxyl groups in GO, based on an analysis of the functional group changes in GO and reduced GO associated with different reduction degrees as shown by X-ray photoelectron spectroscopy.

Separation and preconcentration of arsenite and other heavy metal ions using graphene oxide laminated with protein molecules

The graphene oxide surface was laminated with bovine serum albumin (BSA) followed by the directional flow through a membrane to prepare a free-standing PLGO (protein laminated GO) composite. BSA immobilization increased the interlayer spacing of GO and led to the formation of capillaries. The column packed with PLGO adsorbent permeated water faster as much as ca. 5 fold as compared to only GO packed column. The PLGO composite was used to develop a solid phase extraction method for the selective preconcentration of As(III) in the presence of As(V), prior to their determination. As(III) binding to sulfhydryl groups of BSA in PLGO plays a key role in the speciation. The coexisting heavy metal ions did not hinder the recovery of trace As(III). The method was advantageously employed for the preconcentration of As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) from water and food samples. A 3 mL of 1 M hydrochloric acid would be adequate for the complete desorption (recovery > 99%) of the adsorbed metal ions. The preconcentration limit achieved for As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) were 1.7, 2.0, 2.0, 2.0, 1.8 and 2.0 μg L^-1 respectively, with an optimized sample flow rate of 10 mL min^-1.

A review on peptide functionalized graphene derivatives as nanotools for biosensing

Peptides exhibit unique binding behavior with graphene and its derivatives by forming bonds on its edges and planes. This makes them useful for sensing and imaging applications. This review with (155 refs.) summarizes the advances made in the last decade in the field of peptide-GO bioconjugation, and the use of these conjugates in analytical sciences and imaging. The introduction emphasizes the need for understanding the biotic-abiotic interactions in order to construct controllable peptide-functionalized graphitic material-based nanotools. The next section covers covalent and non-covalent interactions between peptide and oxidized graphene derivatives along with a discussion of the adsorption events during interfacing. We then describe applications of peptide-graphene conjugates in bioassays, with subsections on (a) detection of cancer cells, (b) monitoring protease activity, (c) determination of environmental pollutants and (d) determination of pathogenic microorganisms. The concluding section describes the current status of peptide functionalized graphitic bioconjugates and addresses future perspectives. Graphical abstractSchematic representation depicting biosensing applications of peptide functionalized graphene oxide.

Ultra-long room-temperature phosphorescent carbon dots: pH sensing and dual-channel detection of tetracyclines

Currently, the synthesis and applications of room-temperature phosphorescent (RTP) materials are promising, but challenging. Herein, a kind of ultra-long phosphorescent carbon dots (P-CDs) were rapidly prepared through a facile microwave-directed method. In particular, the yellow-green phosphorescence of the P-CDs was observed for up to 9 s, and their fluorescence and phosphorescence were observed at 418 nm and 525 nm, respectively, using the same excitation at 354 nm. Moreover, the RTP intensity of the P-CDs gradually decreased with the increasing pH because of the protonation-dissociated hydrogen bonds and disturbed phosphorescence sources, whereas their fluorescence exhibited general stability over a wide pH range of 2.1-12.68. Significantly, we found that both the fluorescence and the phosphorescence of the P-CDs were quenched by the introduction of tetracyclines (TCs). Specifically, the P-CDs described herein have abundant -COOH and -OH groups on their surfaces, which facilitate the linkage of CDs with TCs, thus resulting in the occurrence of an inner filter effect process (IFE). Moreover, the P-CDs showed potential as an ideal candidate for building up dual-channel assays towards the targets.

Toxicity of Two-Dimensional Layered Materials and Their Heterostructures

Two-dimensional layered materials (2D LMs) are taking the scientific world by storm. Graphene epitomizes 2D LMs with many interesting properties and corresponding applications. Following the footsteps of graphene, many other types of 2D LMs such as transition metal dichalcogenides, black phosphorus, and graphitic-phase C₃N₄ nanosheets are emerging to be equally interesting as graphene and its derivatives. Some of these applications such as nanomedicine do have a high probability of human exposure. This review focuses on the biological and toxicity effects of 2D LMs and their associated mechanisms linking their chemistries to their biological end points. This review aims to help researchers to predict and mitigate any toxic effects. With understanding, redesign of newer and safer 2D LMs becomes possible.

Two-Dimensional Graphene Family Material: Assembly, Biocompatibility and Sensors Applications

Graphene and its chemically exfoliated derivatives—GO and rGO—are the key members of graphene family materials (GFM). The atomically thick crystal structure and the large continuous π conjugate of graphene imparts it with unique electrical, mechanical, optical, thermal, and chemical properties. Although those properties of GO and rGO are compromised, they have better scalability and chemical tunability. All GFMs can be subject to noncovalent modification due to the large basal plane. Besides, they have satisfying biocompatibility. Thus, GFMs are promising materials for biological, chemical and mechanical sensors. The present review summarizes how to incorporate GFMs into different sensing system including fluorescence aptamer-based sensors, field-effect transistors (FET), and electrochemical sensors, as well as, how to covalently and/or non-covalently modify GFMs to achieve various detection purpose. Sensing mechanisms and fabrication strategies that will influence the sensitivity of different sensing system are also reviewed.

Multi-Organs-on-Chips: Towards Long-Term Biomedical Investigations

With advantageous features such as minimizing the cost, time, and sample size requirements, organ-on-a-chip (OOC) systems have garnered enormous interest from researchers for their ability for real-time monitoring of physical parameters by mimicking the in vivo microenvironment and the precise responses of xenobiotics, i.e., drug efficacy and toxicity over conventional two-dimensional (2D) and three-dimensional (3D) cell cultures, as well as animal models. Recent advancements of OOC systems have evidenced the fabrication of 'multi-organ-on-chip' (MOC) models, which connect separated organ chambers together to resemble an ideal pharmacokinetic and pharmacodynamic (PK-PD) model for monitoring the complex interactions between multiple organs and the resultant dynamic responses of multiple organs to pharmaceutical compounds. Numerous varieties of MOC systems have been proposed, mainly focusing on the construction of these multi-organ models, while there are only few studies on how to realize continual, automated, and stable testing, which still remains a significant challenge in the development process of MOCs. Herein, this review emphasizes the recent advancements in realizing long-term testing of MOCs to promote their capability for real-time monitoring of multi-organ interactions and chronic cellular reactions more accurately and steadily over the available chip models. Efforts in this field are still ongoing for better performance in the assessment of preclinical attributes for a new chemical entity. Further, we give a brief overview on the various biomedical applications of long-term testing in MOCs, including several proposed applications and their potential utilization in the future. Finally, we summarize with perspectives.

A fluorescent biosensor for cardiac biomarker myoglobin detection based on carbon dots and deoxyribonuclease I-aided target recycling signal amplification

A sensitive biosensor using carbon dots and deoxyribonuclease I-aided target recycling signal amplification has been developed to detect myoglobin (MB), which is an important cardiac biomarker and plays a major role in the diagnosis of acute myocardial infarction (AMI). Here, in the absence of MB, the MB aptamer (Ap) is absorbed on the surface of carbon dots (CDs) through π-π stacking interactions, resulting in quenching of the fluorescent label by forming CD-aptamer complexes. Upon adding MB, the Ap sequences could be specifically recognized by MB, leading to the recovery of quenched fluorescence. Thus, quantitative evaluation of MB concentration has been achieved in a broad range from 50 pg mL-1 to 100 ng mL-1, and the detection limit is as low as 20 pg mL-1. This strategy is capable of specific and sensitive detection of MB in human serum, urine, and saliva and can be used for the diagnosis of AMI in the future.

Electronic transport in a graphene single layer: application in amino acid sensing

We modeled a type of field-effect transistor device based on graphene for the recognition of amino acids with a potential application in the building of a protein sequencer. The theoretical model used was a combination of density functional theory (DFT) with the non-equilibrium Green's function (NEGF) in order to describe the coherent transport in molecular devices. First, we studied the physisorption of each amino acid on a graphene sheet and we reported the adsorption energy, the adsorption distances, the equilibrium configuration and the charge transfer of ten amino acids that can be considered as representative of all of the amino acids: histidine (His), alanine (Ala), aspartic acid (Asp), tyrosine (Tyr), arginine (Arg), glutamic acid (Glu), glycine (Gly), phenylalanine (Phe), proline (Pro) and lysine (Lys). As a result, significant differences were found in the density of states (DOS) after adsorption and there was a change in the semi-metallic character of the graphene due to the lysine and arginine interactions. Furthermore, we noticed changes in the electrical characteristics of the devices, as the amino acids adsorbed onto the surface of the graphene. The curves of current vs. bias voltage (I-Vb) display a distinct response for each amino acid, i.e. the I-Vb curves produce a characteristic footprint for each amino acid. We identified a possible rectification mechanism related to the voltage profile asymmetry, where the amino acids can control the transport characteristics in the device, i.e. Lys and Phe amino acids physisorbed on graphene act as a molecular diode, where electrons can easily flow in one direction and decrease in the other. This may be promising for the prospect of biosensors: graphene could be used as an amino acid detector.

Directly probing the dissociation effects of graphene oxide nanosheets on hIAPP fibrils

The aggregation of human islet amyloid polypeptides (hIAPP) to mature fibrils is considered as the main cause of type II diabetes. Therefore destroying the pre-formed hIAPP fibrils is expected to be a promising strategy for therapeutic treatments. In this work, the dissociation effects of graphene oxide (GO) nanosheets on hIAPP mature fibrils are investigated. The results clearly demonstrate that hIAPP fibrils can be quickly adsorbed on the GO surface and efficiently broken into short fragments. Meanwhile, the β-sheet structures of hIAPP fibrils are greatly destroyed. Particularly, in situ atomic force microscopy was applied to monitor the real-time interaction between hIAPP fibrils and GO nanosheets. It provides distinct evidence that the disruption of hIAPP fibrils by GO nanosheets mainly occurs at the GO edges. Size-dependent experiments further justify the interfere of edge contribution, which suggest small-sized GO nanosheets exhibit better dissociation ability than large-sized ones. Therefore, this study not only provides valuable information that GO nanosheets (especially small-sized ones) can act as efficient nanoblades to break hIAPP fibrils, but also suggests a powerful and widely available methodology for investigating real-time interaction between nanomaterials and biomolecules.

Recent developments in protease activity assays and sensors

Proteases play a pivotal role in regulating important physiological processes from food digestion to blood clotting. They are also important biomarkers for many diseases such as cancers. The importance of proteases has led to extensive efforts in the screening of proteases and their inhibitors as potential drug molecules. For example, human immunodeficiency virus (HIV) patients have been treated with HIV-1 protease inhibitors to prolong the life expectancy of patients. Such a close relationship between diseases and proteases provides a strong motivation for developing sensitive, selective, and robust protease assays and sensors, which can be exploited to discover new proteases and inhibitors. In this aspect, protease assays based on levels of proteolytic activities are more relevant than protease affinity assays such as immunoassays. In this review, recent developments of protease activity assays based on different detection principles are discussed and compared. For homogenous assays, fluorescence-based techniques are the most popular due to their high sensitivity and quantitative results. However, homogeneous assays have limited multiplex sensing capabilities. In contrast, heterogeneous assays can be employed to detect multiple proteases simultaneously, given the microarray technology that is already available. Among them, electrochemical methods, surface spectroscopy techniques, and enzyme-linked peptide protease assays are commonly used. Finally, recent developments in liquid crystal (LC)-based protease assays and their applications for detecting proteases and their inhibitors are discussed.

Graphene oxide-based biosensing platform for rapid and sensitive detection of HIV-1 protease

HIV-1 protease is essential for the life cycle of the human immunodeficiency virus (HIV), and is one of the most important clinical targets for antiretroviral therapies. In this work, we developed a graphene oxide (GO)-based fluorescence biosensing platform for the rapid, sensitive, and accurate detection of HIV-1 protease, in which fluorescent-labeled HIV-1 protease substrate peptide molecules were covalently linked to GO. In the absence of HIV-1 protease, fluorescein was effectively quenched by GO. In contrast, in the presence of HIV-1 protease, it would cleave the substrate peptide into short fragments, thus producing fluorescence. Based on this sensing strategy, HIV-1 protease could be detected at as low as 1.18 ng/mL. More importantly, the sensor could successfully detect HIV-1 protease in human serum. Such GO-based fluorescent sensors may find useful applications in many fields, including diagnosis of protease-related diseases, as well as sensitive and high-throughput screening of drug candidates. Graphical abstract ᅟ.

Carbon dots derived from tobacco for visually distinguishing and detecting three kinds of tetracyclines

Although a number of methods to perform assays of tetracyclines using fluorescent probes have been reported, approaches for discriminating and detecting tetracyclines are few. Herein, bright-blue fluorescent carbon dots (CDs) with a quantum yield (QY) of up to ∼27.9% were hydrothermally synthesized using tobacco as the carbon source. Importantly, the as-prepared carbon dots were employed as a fluorescent probe, enabling selective differentiation of three tetracyclines using a test strip and the related quantitative detection. Towards the mechanism, three kinds of tetracyclines showed different interactions with the CDs, leading to variations in their fluorescence emissions. To be specific, the fluorescence of CDs was quenched by tetracycline (TC) without a fluorescence shift (Em = 440 nm), which was caused by an inner filter effect rather than a change in the energy band gap. Moreover, the introduction of chlorotetracycline (CTC) resulted in a blue shift (Em = 415 nm) of the fluorescence of the CD; this phenomenon was induced by the enlarged energy band gap. The CDs also responded to oxytetracycline (OTC), and their corresponding fluorescence experienced a red shift (Em = 500 nm) due to the narrowed band gap. Consequently, a visual detection strategy for three tetracyclines has been proposed based on the quantitative evaluation of TC, OTC, and CTC concentrations in broad range from 6 × 10-6 to 4 × 10-9 M, 2 × 10-6 to 2 × 10-8 M, and 2 × 10-7 to 2 × 10-8 M, respectively. Moreover, we have successfully applied the current CDs for visually distinguishing the three tetracyclines on a test strip on the basis of CDs exhibiting three types of fluorescence (weak-blue, navy-blue, and chartreuse).

A real-time fluorescence assay for protease activity and inhibitor screening based on the aggregation-caused quenching of a perylene probe

We have established a real-time and label-free fluorescence turn-on strategy for protease activity detection and inhibitor screening via peptide-induced aggregation-caused quenching of a perylene probe. Because of electrostatic interactions and high hydrophilicity, poly-l-glutamic acid sodium salt (PGA; a negatively charged peptide) could induce aggregation of a positively charged perylene probe (probe 1) and the monomer fluorescence of probe 1 was effectively quenched. After a protease was added, PGA was enzymatically hydrolyzed into small fragments and probe 1 disaggregated. The fluorescence recovery of probe 1 was found to be proportional to the concentration of protease in the range from 0 to 1 mU/ml. The detection limit was down to 0.1 mU/ml. In the presence of a protease inhibitor, protease activity was inhibited and fluorescence recovery reduced. Moreover, we demonstrated the potential application of our method in a complex mixture sample including 1% human serum. Our method is simple, fast and cost effective.

A New Strategy Involving the Use of Peptides and Graphene Oxide for Fluorescence Turn-on Detection of Proteins

The detection of proteins is of great biological significance as disease biomarkers in early diagnosis, prognosis tracking and therapeutic evaluation. Thus, we developed a simple, sensitive and universal protein-sensing platform based on peptide and graphene oxide (GO). The design consists of a fluorophore (TAMRA, TAM), a peptide containing eight arginines and peptide ligand that could recognize the target protein, and GO used as a quencher. To demonstrate the feasible use of the sensor for target detection, Bcl-xL was evaluated as the model target. The sensor was proved to be sensitive and applied for the detection of the target proteins in buffer, 2% serum and living cells.

Uptake of Tyrosine Amino Acid on Nano-Graphene Oxide

Graphene oxide (GO) is emerging as a promising nanomaterial with potential application in the detection and analysis of amino acids, DNA, enzymes, and proteins in biological fluid samples. So, the reaction of GO with amino acids should be characterized and determined before using it in biosensing methods and devices. In this study, the reaction of tyrosine amino acid (Tyr) with GO was characterized using FT-IR, UV-vis spectrophotometry, and scanning electron microscopy (SEM) before its use. The optimum conditions for GO’s interaction with Tyr amino acid have been studied under variable conditions. The optimum conditions of pH, temperature, shaking time, and GO and tyrosine concentrations for the uptaking of tyrosine amino acid onto the GO’s surface from aqueous solution were determined. The SEM analysis showed that the GO supplied was in a particle size range between 5.4 and 8.1 nm. A pH of 8.4–9.4 at 25 °C and 5 min of shaking time were the optimum conditions for a maximum uptake of 1.4 μg/mL of tyrosine amino acid onto 0.2 mg/mL of GO.

Visible light induced degradation of pollutant dyes using a self-assembled graphene oxide–molybdenum oxo-bis(dithiolene) composite

An easily separable graphene oxide–molybdenum oxo-bis(dithiolene) ([Ph₄P]₂[MoO(S₂C₂(CN)₂)₂]) composite degraded Rhodamine B and Rose Bengal dye upon visible light exposure.

A turn-on fluorescent sensor for Hg2+ detection based on graphene oxide and DNA aptamers

Hg²⁺-Induced conformational change of DNA aptamers can cause the release of AO from GO surface, which leads to fluorescence recovery.