Ok Ja Yoon

Amine-modified single-walled carbon nanotubes protect neurons from injury in a rat stroke model

Stroke results in the disruption of tissue architecture and is the third leading cause of death in the United States. Transplanting scaffolds containing stem cells into the injured areas of the brain has been proposed as a treatment strategy, and carbon nanotubes show promise in this regard, with positive outcomes when used as scaffolds in neural cells and brain tissues. Here, we show that pretreating rats with amine-modified single-walled carbon nanotubes can protect neurons and enhance the recovery of behavioural functions in rats with induced stroke. Treated rats showed less tissue damage than controls and took longer to fall from a rotating rod, suggesting better motor functions after injury. Low levels of apoptotic, angiogenic and inflammation markers indicated that amine-modified single-walled carbon nanotubes protected the brains of treated rats from ischaemic injury.

Reduced graphene oxide field-effect transistor for label-free femtomolar protein detection.

We report reduced graphene oxide field effect transistor (R-GO FET) biosensor for label-free ultrasensitive detection of a prostate cancer biomarker, prostate specific antigen/α1-antichymotrypsin (PSA-ACT) complex. The R-GO channel in the device was formed by reduction of graphene oxide nanosheets networked by a self-assembly process. Immunoreaction of PSA-ACT complexes with PSA monoclonal antibodies on the R-GO channel surface caused a linear response in the shift of the gate voltage, V(g,min), where the minimum conductivity occurs. The R-GO FET can detect protein-protein interactions down to femtomolar level with a dynamic range over 6-orders of magnitude in the V(g,min) shift as a sensitivity parameter. High association constants of 3.2 nM(-1) and 4.2 nM(-1) were obtained for the pH 6.2 and pH 7.4 analyte solutions, respectively. The R-GO FET biosensor showed a high specificity to other cancer biomarker in the phosphate buffered saline solutions as well as in the human serum.

pH sensing characteristics and biosensing application of solution-gated reduced graphene oxide field-effect transistors

Solution-gated reduced graphene oxide field-effect transistors (R-GO FETs) were investigated for pH sensing and biochemical sensing applications. A channel of a networked R-GO film formed by self-assembly was incorporated as a sensing layer into a solution-gated FET structure for pH sensing and the detection of acetylcholine (Ach), which is a neurotransmitter in the nerve system, through enzymatic reactions. The fabricated R-GO FET was sensitive to protons (H(+)) with a pH sensitivity of 29 mV/pH in terms of the shift of the charge neutrality point (CNP), which is attributed to changes in the surface potential caused by the interaction of protons with OH surface functional groups present on the R-GO surface. The R-GO FET immobilized with acetylcholinesterase (AchE) was used to detect Ach in the concentration range of 0.1-10mM by sensing protons generated during the enzymatic reactions. The results indicate that R-GO FETs provide the capability to detect protons, demonstrating their applicability as a biosensing device for enzymatic reactions.

Kynurenic acid attenuates MPP(+)-induced dopaminergic neuronal cell death via a Bax-mediated mitochondrial pathway.

Kynurenic acid (KYNA), a tryptophan metabolite in the kynurenine pathway, is protective against various insults. However, the molecular mechanism of this protective effect has not been identified. In this study, we examined the protective effects of KYNA against 1-methyl-4-phenylpyridinium (MPP(+)), the best-characterized toxin inducing pathological changes resembling Parkinsons disease (PD), using SH-SY5Y and SK-N-SH human neuroblastoma cells. Pre-treatment of KYNA attenuated MPP(+)-induced neuronal cell death in SH-SY5Y and SK-N-SH cells. MPP(+)-induced cell death was preceded by increases in Bax expression and mitochondrial dysfunction, such as collapse of mitochondrial membrane potential (DeltaPsi(m)), release of cytochrome c from mitochondria into the cytoplasm, and increases in caspase-9/-3 activities. KYNA effectively inhibited all of these mitochondrial apoptotic processes. Our results indicate that KYNA plays a protective role by down-regulating Bax expression and maintaining mitochondrial function in MPP(+)-induced neuronal cell death, and suggest that KYNA may have therapeutic potential in PD.

Electrical Graphene Aptasensor for Ultra‐Sensitive Detection of Anthrax Toxin with Amplified Signal Transduction

Detection of the anthrax toxin, the protective antigen (PA), at the attomolar (aM) level is demonstrated by an electrical aptamer sensor based on a chemically derived graphene field-effect transistor (FET) platform. Higher affinity of the aptamer probes to PA in the aptamer-immobilized FET enables significant improvements in the limit of detection (LOD), dynamic range, and sensitivity compared to the antibody-immobilized FET. Transduction signal enhancement in the aptamer FET due to an increase in captured PA molecules results in a larger 30 mV/decade shift in the charge neutrality point (Vg,min ) as a sensitivity parameter, with the dynamic range of the PA concentration between 12 aM (LOD) and 120 fM. An additional signal enhancement is obtained by the secondary aptamer-conjugated gold nanoparticles (AuNPs-aptamer), which have a sandwich structure of aptamer/PA/aptamer-AuNPs, induce an increase in charge-doping in the graphene channel, resulting in a reduction of the LOD to 1.2 aM with a three-fold increase in the Vg,min shift.

Enhancement of thermomechanical properties of poly( D , L -lactic- co -glycolic acid) and graphene oxide composite films for scaffolds

AbstractThermomechanical and surface chemical properties of composite films of poly(D,L-lactic-co-glycolic acid) (PLGA) were significantly improved by the addition of graphene oxide (GO) nanosheets as nanoscale fillers to the PLGA polymer matrix. Enhanced thermomechanical properties of the PLGA/GO (2 wt%) composite film, including an increase in the crystallization temperature and reduction in the weight loss, were observed. The tensile modulus of a composite film with increased GO fraction was presumably enhanced due to the strong chemical bonding between the GO nanosheets and the PLGA matrix. Enhanced hydrophilicity of the composite film due to the embedded GO nanosheets also improved the biocompatibility of the composite film. Improved thermomechanical properties and biocompatibility of the PLGA composite films embedded with GO nanosheets may be applicable to biomedical applications such as scaffolds.

Toxicity of graphene nanoflakes evaluated by cell-based electrochemical impedance biosensing.

Graphene nanoflake toxicity was analyzed using cell-based electrochemical impedance biosensing with interdigitated indium tin oxide (ITO) electrodes installed in a custom-built mini-incubator positioned on an inverted optical microscope. Sensing with electrochemical measurements from interdigitated ITO electrodes was highly linear (R(2) = 0.93 and 0.96 for anodic peak current (Ipa) and cathodic peak current (Ipc), respectively). Size-dependent analysis of Graphene nanoflake toxicity was carried out in a mini-incubator system with cultured HeLa cells treated with Graphene nanoflakes having an average size of 80 or 30 nm for one day. Biological assays of cell proliferation and viability complemented electrochemical impedance measurements. The increased toxicity of smaller Graphene nanoflakes (30 nm) as measured by electrochemical impedance sensing and optical monitoring of treated cells was consistent with the biological assay results. Cell-based electrochemical impedance biosensing can be used to assess the toxicity of nanomaterials with different biomedical and environmental applications.

Construction of protein-resistant pOEGMA films by helicon plasma-enhanced chemical vapor deposition.

This paper describes the formation of protein-resistant, poly(ethylene glycol) methyl ether methacrylate (pOEGMA) thin films by helicon plasma-enhanced chemical vapor deposition (helicon-PECVD). pOEGMA was successfully grafted onto a silicon substrate, as a model substrate, without any additional surface initiators, by plasma polymerization of OEGMA. The resulting pOEGMA films were characterized by ellipsometry, FT-IR spectroscopy, X-ray photoelectron spectroscopy and contact angle goniometry. To investigate the protein-resistant property of the pOEGMA films, four different proteins, bovine serum albumin, fibrinogen, lysozyme and ribonuclease A, were tested as model proteins for ellipsometric measurements. The ellipsometric thickness change for all the model proteins was less than 3 Å, indicating that the formed pOEGMA films are protein-resistant.

Reduction in oxidative stress during cellular responses to chemically functionalised graphene

The two-dimensional nanocarbon material graphene (Gr) has been extensively studied due to its many potential biomedical applications including regenerative medicine, drug delivery, bioimaging, and biosensing. The effects of nitrogen-functionalisation on chemically driven Gr (CDG) cellular responses were studied by investigating the generation of reactive oxygen species (ROS) and mitochondrial morphology as well as focal adhesion, shape, proliferation and viability of HeLa cells grown on functionalised CDG (f-CDG) films. The drop casting of CDG nanosheets formed thin CDG films and the formation of nitrogen groups on the f-CDG thin films was mediated by N2 plasma treatment without the formation of observable surface defects. N-containing functional groups on the CDG thin films contributed to an increase in hydrophilicity. The proliferation and viability of HeLa cells grown on the f-CDG thin films were enhanced compared to those grown on CDG films alone and control samples. N-functionalisation of CDG thin films effectively reduced the ROS generated from cells on the f-CDG films. These results indicate that N2 plasma treatment of CDG is very useful in improving biocompatibility for the bio-application of graphene materials.