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In the present study, the effect of nanosized graphene oxide layer on thermal stability and biocompatibility of gold nanorods has been examined. The graphene oxide-wrapped gold nanorods were prepared by electrostatic interaction between negatively charged graphene oxide and positively charged nanorods. The resulting nanohybrids were then heated at different time intervals to 95 °C in a water bath to assess the effect of heat on the rods morphology. The structural changes in gold nanorods were monitored via UV-Vis spectroscopy measurements and transmission electron microscopy images. In similar experiments, the graphene oxide used to wrap gold nanorods was reduced by ascorbic acid in a 95 °C water bath. Our results indicate that while bare gold nanorods are highly vulnerable to elevated temperatures, graphene oxide and reduced graphene oxide-coated gold nanorods remain thermally stable with no structural changes. We also confirmed that the enhanced thermal stability is highly dependent on the concentration of deposited graphene oxide available on the surface of the gold nanorods. In addition, we performed an MTT (3-[4,5-dimethylthiazol-2yl]-2,5-diphenyltetrazoliumbromide) assay to make a comparison between the cytotoxicity of the nanohybrids and their primary building blocks on human dermal fibroblast cells as a normal cell line. We found evidence that graphene oxide can enhance the biocompatibility of the rods through covering toxic chemicals on the surface of them.ᅟ [ABSTRACT FROM AUTHOR]

Herein, a novel electrochemical bi-aptasensor using green synthesized reduced graphene-poly(amidoamine)/gold nanocomposite (rGO-PAMAM/Au nano ) as supporting matrix for covalent immobilization of flavin adenine dinucleotide (FAD) and thionine (Th) on the first (W 1 ) and second (W 2 ) surfaces of dual working electrode screen printed electrode has proposed. FAD and Th probes were immobilized by glutaraldehyde linker based on a reaction between primary amines (–NH 2 ) of FAD and Th with –NH 2 of rGO-PAMAM/Au nano modified dual working electrode for simultaneous determination of cytochrome c (CYC) and vascular endothelial growth factor (VEGF 165 ) tumor markers. The principle response of proposed bi-aptasensor was based on the selective interaction of CYC with W 1 /rGO-PAMAM-FAD/Au nano /Anti-ptamer CYC and VEGF 165 with W 2 /rGO-PAMAM-Th/Au nano /Anti-ptamer VEGF165 , respectively. This selective interaction, leads to decrease of response currents of immobilized electrochemical probes of FAD and Th that have different formal potential (E 0 ′). Electrochemical behavior of bi-aptasensor was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The liner calibration curve for tumor markers determination was 2.5–320.0 pM. The limit of detections (LOD) for CYC was 1.0 pM and for VEGF 165 was 0.7 pM (3σ/S). The biomarker-aptamer dissociation constant (k d ) was calculated based on the change in current to be 63.9 pM for CYC/Anti-aptamer CYC and 38.4 pM for VEGF 165 /Anti-aptamer VEGF165 , respectively. This bi-aptasensor was used for the determination of VEGF 165 and CYC in the human serum sample. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Use of graphene oxide and reduced graphene oxide as visual labels for lateral flow assay. • Reduced graphene oxide shows higher visual signal than graphene oxide. • It has been applied for one step detection of E. coli O157:H7 in food samples. Abstract In this study, graphene oxide (GO) and reduced graphene oxide (rGO) were used as visual labels in a lateral flow assay for detection of E. coli O157:H7. The color intensity was employed for the quantitative measurements of the target bacteria. Quantitative results showed that in comparison to GO, rGO can provide higher color intensity owing to enhanced light absorption following chemical reduction. Our results confirm that the visual limit of detection of the target bacteria by rGO is ∼105 colony forming unit per milliliter (CFU/ml), which closely compares with current alternative techniques using gold nanoparticles. The performance and practicability of the rGO-based test strips for detection of the target bacteria in milk and drinking water were validated with conventional plating and colony counting techniques. Results suggest that the proposed lateral flow assay is sensitive, specific, and affordable. It has also the potential to become a widely used detection technique for E. coli O157:H7 and a wide variety of other analytes. [ABSTRACT FROM AUTHOR]