•A HRP-Strept-Biotin-Ab-Cor/AuNPs/MrGO/Nafion@GCE immunosensor was successfully fabricated.•The prepared MrGO was characterized by AFM, XRD, FTIR, VSM, TEM and SEM.•The proposed immunosensor exhibited an broad detection range and low detection limit for cortisol.•The immunosensor can be used for the sensitive, efficient and real-time analysis of cortisol in real samples.A sensitively competitive electrochemical immunosensor for the detection of cortisol was successfully developed based on gold nanoparticles and magnetic functionalized reduced graphene oxide (AuNPs/MrGO). In order to construct the base of the immunosensor, the MrGO was initially fabricated by chemical cross-linking and used to modify the nafion pretreated glassy carbon electrode. Subsequently, the surface of electrode was modified by AuNPs via electrochemical deposition. A variety of cortisol (Cor) can be firmly loaded in the AuNPs/MrGO with large specific surface area and good bioactivity to construct the basic electrode (Cor/AuNPs/MrGO/Nafion@GCE), which was characterized by the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Due to the cortisol on the surface of basic electrode and samples can competitively combine with the cortisol antibody labelled by horseradish peroxidase (HRP-Strept-Biotin-Ab). Finally, the detection signal of electrochemical immunosensor (HRP-Strept-Biotin-Ab-Cor/AuNPs/MrGO/Nafion@GCE) in the test liquid had negative correlations with the concentration of cortisol in samples. The AuNPs/MrGO with excellent electrical conductivity being applied, the electrochemical response of the immunosensor was immensely amplified. The immunosensor displayed excellent analytical performance for the detection of cortisol range from 0.1 to 1000 ng/mL with a detection limit of 0.05 ng/mL at 3σ. Moreover, compared the developed immunoassay with commercially available enzyme linked immunosorbent assay, the proposed method showed good precision, acceptable stability and reproducibility, indicating the immunosensor could be used for the sensitive, efficient and real-time detection of cortisol in real samples. Therefore, the present strategy provides a novel and convenient method for clinical determination of cortisol.

•Hydroxyl radicals were produced by Fenton reagents.•An electrochemical bovine serum albumin (BSA) damage sensor was successfully fabricated.•The proposed biosensor can assess the antioxidant capacity of four flavonoids.•The order of antioxidant activities of flavonoids is as follows: (+)-catechin > kaempferol > apigenin > naringenin.A sensitive electrochemical sensor based on bovine serum albumin (BSA)/poly (diallyldimethylammonium chloride) (PDDA) functionalized graphene nanosheets (PDDA-G) composite film modified glassy carbon electrode (BSA/PDDA-G/GCE) had been developed to investigate the oxidative protein damage and protections of protein from damage by flavonoids. The performance of this sensor was remarkably improved due to excellent electrical conductivity, strong adsorptive ability, and large effective surface area of PDDA-G. The BSA/PDDA-G/GCE displayed the greatest degree of BSA oxidation damage at 40 min incubation time and in the pH 5.0 Fenton reagent system (12.5 mM FeSO4, 50 mM H2O2). The antioxidant activities of four flavonoids had been compared by fabricated sensor based on the relative peak current ratio of SWV, because flavonoids prevented BSA damage caused by Fenton reagent and affected the BSA signal in a solution containing Co(bpy)33 +. The sensor was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). UV–vis spectrophotometry and FTIR were also used to investigate the generation of hydroxyl radical and BSA damage, respectively. On the basis of results from electrochemical methods, the order of the antioxidant activities of flavonoids is as follows: (+)-catechin > kaempferol > apigenin > naringenin. A novel, direct SWV analytical method for detection of BSA damage and assessment of the antioxidant activities of four flavonoids was developed and this electrochemical method provided a simple, inexpensive and rapid detection of BSA damage and evaluation of the antioxidant activities of samples.

•A novel ERGO–based electrochemical sensor of FA was successfully fabricated by using one-step electrodeposition method.•The electrode reaction was an adsorption–diffusion mixed controlled process.•The low detection limit with good selectivity and sensitivity were obtained.•This method was applied for the determination of FA in A. sinensis and biological samples.An electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE) was used as a new voltammetric sensor for the determination of ferulic acid (FA). The morphology and microstructure of the modified electrodes were characterized by scanning electron microscopy (SEM) and Raman spectroscopy analysis, and the electrochemical effective surface areas of the modified electrodes were also calculated by chronocoulometry method. Sensing properties of the electrochemical sensor were investigated by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that ERGO was electrodeposited on the surface of GCE by using potentiostatic method. The proposed electrode exhibited electrocatalytic activity to the redox of FA because of excellent electrochemical properties of ERGO. The transfer electron number (n), electrode reaction rate constant (ks) and electron-transfer coefficient (α) were calculated as 1.12, 1.24 s− 1, and 0.40, respectively. Under the optimized conditions, the oxidation peak current was proportional to FA concentration at 8.49 × 10− 8 mol L− 1 to 3.89 × 10− 5 mol L− 1 with detection limit of 2.06 × 10− 8 mol L− 1. This fabricated sensor also displayed acceptable reproducibility, long-term stability, and high selectivity with negligible interferences from common interfering species. The voltammetric sensor was successfully applied to detect FA in A. sinensis and biological samples with recovery values in the range of 99.91%-101.91%.

•A gelatin functionalized graphene nanosheets (gelatin-GNS) as a nanocarrier for drug delivery.•Gelatin-GNS exhibited excellent biocompatibility and physiological stability.•Methotrexate (MTX) loaded on the gelatin-GNS at a high loading capacity via physisorption.•The release behavior of MTX from gelatin-GNS observably relied on pH value.•Gelatin-GNS attaching MTX exhibited good anticancer activity in vitro.A simple and environmentally friendly synthetic route for the preparation of gelatin functionalized graphene nanosheets (gelatin-GNS) was reported by using exfoliated graphene oxide as a precursor, in which gelatin acted as not only a reducing reagent but also a functionalization reagent to guarantee good dispersibility and stability of the GNS in distilled water and various physiological solutions. The obtained biocompatible gelatin-GNS attaching methotrexate (MTX) via strong π-π stacking interaction, exhibited a high drug loading capacity of MTX and excellent ability for controlled drug release. The pH-dependent release behavior of MTX from MTX@gelatin-GNS showed that the release amount under acid conditions is much higher than that under neutral conditions, which experienced a gelatin-mediated sustained release process. From the cytotoxicity assay, we can see that the MTX@gelatin-GNS showed remarkable toxicity while the gelatin-GNS showed nontoxic at appropriate concentration, both of them might be taken up by A549 cells through a nonspecific endocytosis process. The prepared nanohybrids system offers a novel formulation that combines the unique properties of a biodegradable material, gelatin, and graphene for biomedical applications. Therefore, the gelatin-GNS with good stability and biocompatibility can be selected as an ideal drug carrier to be applied in biomedicine studies.

An electrochemical method based on a directly electrochemically reduced graphene oxide (ERGO) film coated on a glassy carbon electrode (GCE) was developed for the rapid and convenient determination of rutin in plasma. ERGO was modified on the surface of GCE by one-step electro-deposition method. Electrochemical behavior of rutin on ERGO/GCE indicated that rutin underwent a surface-controlled quasi-reversible process and the electrochemical parameters such as charge transfer coefficient (α), electron transfer number (n) and electrode reaction standard rate constant (ks) were 0.53, 2 and 3.4 s−1, respectively. The electrochemical sensor for rutin in plasma provided a wide linear response range of 4.70×10−7−1.25×10−5 M with the detection limit (s/n=3) of 1.84×10−8 M. The assay was successfully used to the pharmacokinetic study of rutin. The pharmacokinetic parameters such as elimination rate half-life (t1/2), area under curve (AUC), and plasma clearance (CL) were calculated to be 3.345±0.647 min, 5750±656.0 µg min/mL, and 5.891±0.458 mL/min/kg, respectively. The proposed method utilized a small sample volume of 10 μL and had no complicated sample pretreatment (without deproteinization), which was simple, eco-friendly, and time- and cost-efficient for rutin pharmacokinetic studies.

Graphene (G) was dispersed into 0.5% chitosan (Chit) solution, then the composite films were coated on glassy carbon electrode (GCE), the electrochemical behavior of rutin on a Chit/G modified GCE was investigated and the electrochemical parameters of rutin were calculated. Rutin effectively accumulated on the Chit/G/GCE and caused a pair of redox peaks at around 408 mV and 482 mV (vs. SCE) in 0.1 M phosphate buffer solution (pH 4.0). Under optimized conditions, the anodic peak current was linear to the rutin concentration in the range of 5×10−7–1.04×10−5 M. The regression equation was: y=9.9219x–0.0025, r= 0.9958. The proposed method was successfully used for the determination of rutin content in tablet samples with satisfactory results.

•The MrGO/Nafion@GCE electrochemical sensor was successfully fabricated.•The prepared MrGO was characterized by AFM, XRD, FTIR, VSM, TEM and SEM.•The proposed electrochemical sensor exhibited a broad detection range and low detection limit for lobetyolin.•The electrochemical sensor can be used for the sensitive and efficient analysis of lobetyolin in real samples.A novel lobetyolin electrochemical sensor based on a magnetic functionalized reduced graphene oxide/Nafion nanohybrid film has been introduced in this work. The magnetic functionalized reduced graphene oxide was characterized by fourier transform infrared spectroscopy, atomic force microscope, X-ray diffraction, transmission electron microscopy and thermogravimetric analysis. The scanning electron microscopy characterized the morphology and microstructure of the prepared sensors, and the electrochemical effective surface areas of the prepared sensors were also calculated by chronocoulometry method. The electrochemical behavior of lobetyolin on the magnetic functionalized reduced graphene oxide/Nafion nanohybrid modified glassy carbon electrode was investigated by cyclic voltammetry and differential pulse voltammetry in a phosphate buffer solution of pH 6.0. The electron-transfer coefficient (α), electron transfer number (n), and electrode reaction rate constant (Κs) were calculated as 0.78, 0.73, and 4.63 s− 1, respectively. Under the optimized conditions, the sensor based on magnetic functionalized reduced graphene oxide/Nafion showed a linear voltammetric response to the lobetyolin concentration at 1.0 × 10− 7 to 1.0 × 10− 4 mol/L with detection limit (S/N = 3)of 4.3 × 10− 8 mol/L. The proposed sensor also displayed acceptable reproducibility, long-term stability, and high selectivity, and performs well for analysis of lobetyolin in real samples. The voltammetric sensor was successfully applied to detect lobetyolin in Codonopsis pilosula with recovery values in the range of 96.12% –102.66%.Schematic diagram of the synthesis of MrGO hybrid and the fabrication process of the MrGO/Nafion/GCE for determination of lobetyolin.