Potential Of Graphene Oxide Research Articles

Graphene Oxide Triggers Toll‐Like Receptors/Autophagy Responses In Vitro and Inhibits Tumor Growth In Vivo

Graphene oxide (GO) is a nanomaterial with burgeoning bioapplications, while autophagy is implicated in cancer therapy. Although induction of autophagy by nanomaterials is reported, the underlying signaling mechanism in cancer cells and how this implicates the potential of GO in cancer therapy remain obscure. Here, it is shown that GO itself can induce the toll-like receptors (TLRs) responses and autophagy in cancer cells and confer antitumor effects in mice. GO can be phagocytosed by CT26 colon cancer cells, simultaneously triggering autophagy as well as TLR-4 and TLR-9 signaling cascades. By dissecting the crosstalk between the TLRs and autophagy pathways, it is uncovered that the GO-activated autophagy is regulated through the myeloid differentiation primary response gene 88 (MyD88)- and TNF receptor-associated factor 6 (TRAF6)-associated TLR-4/9 signaling pathways. Injection of GO alone into immunocompetent mice bearing the CT26 colon tumors not only suppresses the tumor progression but also enhances cell death, autophagy, and immune responses within the tumor bed. These data altogether implicate the potential of GO as an effective nanomaterial for autophagy induction and cancer therapy.

Hydration Patterns of Graphene-Based Nanomaterials (GBNMs) Play a Major Role in the Stability of a Helical Protein: A Molecular Dynamics Simulation Study

Graphene-based nanomaterials (GBNMs) [graphene oxide (GO), reduced graphene oxide (rGO), and graphene] have been recognized as potential candidates for various biomedical applications ranging from biosensing platform to cellular delivery of proteins and peptides. However, GBNMs induced conformational changes in proteins are the major concerns in realizing their full potential in aforementioned applications. Despite several studies, the effect of GBNMs on the conformation of proteins is still not well understood. Therefore, an attempt was made to investigate the effect of GBNMs on the adsorption and conformation of positively charged cytoplasmic protein using molecular dynamics (MD) simulations. Our study showed that the adsorption of protein on GO was highly selective and mediated through electrostatic interactions (hydrogen bond/salt bridge interactions), whereas the van der Waals and π-π stacking interactions were the major driving forces for the adsorption of protein on rGO and graphene. The secondary structure analysis showed the conformational stability of the protein on GO may be attributed to the extensive hydration of GO surface and the absence of tyrosine residues in π-π stacking with π regions of GO. The GO surface acts as a hydrogen bond acceptor similar to the protein's natural receptor present in a physiological environment. This computational study has also explored the artificial protein receptor like potential of GO.

Effects of surface curvature and surface characteristics of carbon-based nanomaterials on the adsorption and activity of acetylcholinesterase

Carbon-based nanomaterials (NM) are promising candidates for a myriad of applications ranging from drug delivery to biosensing platforms. In the physiological environment, proteins can be adsorbed onto the surface of NM that can alter their structure and function. Little is known of the effect of NM on larger proteins and enzymes and an attempt has been made in this study to investigate the effect of carbon-based NM such as carbon black (CB), graphene oxide (GO) and fullerene (C60) on the adsorption and activity of acetylcholinesterase (AChE), a key enzyme present in brain, blood and nervous system and a suitable neurotoxicity biomarker. Experimental and computational results showed that all the carbon-based NM tested adsorb AChE but they have different effects on the catalytic activity of the enzyme. The most efficient AChE inhibitor is CB. In contrast, AChE adsorbed on the GO surface retains its native conformation and most of its activity. As compared to GO and CB, C60 was found to be an inefficient adsorbent of AChE. The distinctive adsorption pattern of NM and their inhibitory potential could be related to the surface characteristics of NM. Our studies also demonstrate the potential of GO as a substrate for immobilization of AChE.

Graphene oxide as a solid sorbent for the preconcentration of cobalt, nickel, copper, zinc and lead prior to determination by energy-dispersive X-ray fluorescence spectrometry

A new method for sample preparation using graphene oxide (GO) as a novel sorbent was developed for the preconcentration of trace amounts of Co(II), Ni(II), Cu(II), Zn(II) and Pb(II). The proposed preconcentration procedure is based on dispersive micro-solid phase extraction (DMSPE). It means that GO was dispersed in aqueous samples containing trace elements to be determined. During the stirring of the analyte solution containing the GO suspension, metal ions were sorbed by GO. After the sorption, the solution was filtered under vacuum and GO with the metal ions was collected onto a membrane filter. The obtained samples were analyzed directly by energy-dispersive X-ray fluorescence spectrometry (EDXRF). The parameters affecting the extraction and preconcentration process were optimized. The pH of the analyte solution, the amount of GO, the sample volume, the contact time between analytes and sorbent (stirring time), and the effects of foreign metals are discussed in detail in this paper. The proposed procedure allows us to obtain the detection limits of 0.5, 0.7, 1.5, 1.8 and 1.4 ng mL−1 for Co(II), Ni(II), Cu(II), Zn(II) and Pb(II), respectively. The linearity of the method is in the range of 5–100 ng mL−1. The proposed method was successfully applied in the analysis of water. The accuracy of the method was verified using spiked samples and inductively coupled plasma optical emission spectrometry (ICP-OES) as a comparative technique. The recoveries over the range of 94–106% were obtained. This paper shows the great potential of GO as an excellent sorbent in the preconcentration field of analytical chemistry. The proposed method meets green chemistry rules.

Microwave transmission in graphene oxide

We investigated the radio-frequency transmission properties of reduced graphene oxide (GO) sheets including contact effects with the metal electrodes. GO sheets were prepared by dielectrophoresis and their structural characteristics were analyzed by x-ray photoelectron spectroscopy and Raman spectroscopy. The contact resistance was much higher than the intrinsic resistance over the entire frequency range, thus the contact resistance was considered as a dominant component of impedance in the radio-frequency regime. In the radio-frequency regime, GO sheets showed a drastic decrease in impedance based on a consistent decrease in the intrinsic and contact resistance. These results support the potential of GO as a radio-frequency interconnector with a solution-based fabrication method.

Functionalized Graphene Oxide in Enzyme Engineering: A Selective Modulator for Enzyme Activity and Thermostability

The understanding of interactions between nanomaterials and biomolecules is of fundamental importance to the area of nanobiotechnology. Graphene and its derivative, graphene oxide (GO), are two-dimensional (2-D) nanomaterials with interesting physical and chemical properties and have been widely explored in various directions of biomedicine in recent years. However, how functionalized GO interacts with bioactive proteins such as enzymes and its potential in enzyme engineering have been rarely explored. In this study, we carefully investigated the interactions between serine proteases and GO functionalized with different amine-terminated polyethylene glycol (PEG). Three well-characterized serine proteases (trypsin, chymotrypsin, and proteinase K) with important biomedical and industrial applications were analyzed. It is found that these PEGylated GOs could selectively improve trypsin activity and thermostability (60-70% retained activity at 80 °C), while exhibiting barely any effect on chymotrypsin or proteinase K. Detailed investigation illustrates that the PEGylated GO-induced acceleration is substrate-dependent, affecting only phosphorylated protein substrates, and that at least up to 43-fold increase could be achieved depending on the substrate concentration. This unique phenomenon, interestingly, is found to be attributed to both the terminal amino groups on polymer coatings and the 2-D structure of GO. Moreover, an enzyme-based bioassay system is further demonstrated utilizing our GO-based enzyme modulator in a proof-of-concept experiment. To our best knowledge, this work is the first success of using functionalized GO as an efficient enzyme positive modulator with great selectivity, exhibiting a novel potential of GO, when appropriately functionalized, in enzyme engineering as well as enzyme-based biosensing and detection.