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The fabrication of electrochemical biosensors to directly, rapidly and ultrasensitively detect disease markers in urine or blood samples has become a new and competitive challenge in the field of sensor research. In this paper, a novel electrochemical immunosensor with high selectivity and sensitivity for the detection of the depression marker human apolipoprotein A4 (Apo-A4) was successfully constructed using zeolite imidazole ester metal organic skeleton-nitrogen doped graphene composites (ZIF-8@N-Gr). To this end, because of the higher surface area and biocompatibility, ZIF-8 with abundant biomolecular binding sites provided a good microenvironment for effectively immobilizing antigens. ZIF-8@N-Gr presented a flake structure, as the electrode displayed excellent electrical conductivity, which enhanced the electron transfer and significantly amplified the current signal of the immunosensor. More importantly, these immunosensors are capable of assaying human apolipoprotein A4 (Apo-A4) in 100% serum without suffering from any significant biological interference. Under optimized experimental conditions, the sensor was used for the analysis of whole serum samples and presented a wide linear range from 1.47 × 10 -10 g/mL to 3.00 × 10 -7 g/mL with a low detection limit of 8.33 × 10 -11 g/mL (3σ, n = 15). The satisfactory results of human serum sample analysis indicated that the proposed immunosensor had promising potential in the clinical diagnosis of depression., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020. Published by Elsevier B.V.)

As a new type of conductive material, polyaniline functionalized graphene quantum dots (PAGD), which were prepared by in-situ polymerization had been used to construct a novel electrochemical immunosensor for early screening of depression markers-heat shock protein 70 (HSP70). Profiting from the huge specific surface area, good bioactivity and excellent structure of PAGD, a variety of heat shock protein 70 (HSP70) was firmly loaded on the surface of PAGD for successful construction of basic electrode (HSP70/PAGD/GCE), which was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Due to the HSP70 fixed on the surface of basic electrode and the HSP70 in the samples can competitively combine with the horseradish peroxidase labeled human HSP70 antibody (HRP-Strept-Biotin-Ab). As a result, there is negative correlation between the concentration of HSP70 in samples and the detection signal of the proposed electrochemical immunosensor (HRP-Strept-Biotin-Ab-HSP70/PAGD/GCE) in the test liquid. Under conditions optimized for determining HSP70, wide linearity was obtained in the range of 0.0976-100 ng/mL, with a low detection limit of 0.05 ng/mL at 3σ. Moreover, the proposed electrochemical immunosensors was successfully applied to detect HSP70 in plasma samples, and exhibited good precision, acceptable stability and reproducibility. Therefore, this study provides a novel and convenient method for early clinical screening of depression markers, and also provides a reliable and objective analysis method for the diagnosis of depression at the molecular level., (Copyright © 2020 Elsevier B.V. All rights reserved.)

In this study, a novel electrochemical immunosensor for early screening of depression markers-heat shock protein 70 (HSP70) was successfully developed based on the porous graphene (PG) with huge specific surface area and excellent structure. Benefiting from the strong adsorption and good bioactivity of PG which was initially prepared via a simple pyrolysis process, a variety of heat shock protein70 (HSP70) can be firmly loaded on the PG to construct the basic electrode (HSP70/PG/GCE)，which was characterized by the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), respectively. Due to the HSP70 fixed on the surface of basic electrode and the HSP70 in the samples can competitively combine with the horseradish peroxidase labeled human HSP 70 antibody (HRP-Strept-Biotin-Ab). As a result, it presented a negative correlation between the concentration of HSP70 in samples and the detection signal of the proposed electrochemical immunosensor (HRP-Strept-Biotin-Ab-HSP70/PG/GCE) in the test liquid. The application of PG with excellent electrical conductivity in construction of immunosensor remarkably improved the sensitivity of the immunosensor for detection of HSP70. The proposed immunosensor demonstrated a wide linear range of 0.0448 ~ 100 ng/mL with a low detection limit of 0.02 ng/mL at 3σ. Moreover, the proposed immunosensor could be applied for the sensitive and efficient detection of HSP70 in real samples with good precision, acceptable stability, reproducibility and satisfactory results. Therefore, the HSP70 immunosensor provides a novel and convenient method for early clinical screening of depression markers-heat shock protein 70., (Copyright © 2018 Elsevier B.V. All rights reserved.)

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 1000ng/mL with a detection limit of 0.05ng/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., (Copyright © 2016 Elsevier B.V. All rights reserved.)

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)3(3+). 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., (Copyright © 2016 Elsevier B.V. All rights reserved.)

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, 1.24s(-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%., (Copyright © 2014 Elsevier B.V. All rights reserved.)

CPP1b is a pectic polysaccharide isolated from Codonopsis pilosula, and it possesses potent antitumor activity. In this study, a HNO3-Na2SeO3 method was performed to synthesize selenium-CPP1b (sCPP1b). The effects of BaCl2 usage amount and HNO3 concentration on the yield and selenium content of sCPP1b were investigated by single-factor experiments. Reaction time, reaction temperature and the ratio of polysaccharide to Na2SeO3 were optimized by orthogonal experimental design at three levels of each of the three factors (L9(3)(4)) based on antitumor activity, selenium content and yield of sCPP1b. Our results showed that 5h of reaction time, 60°C of reaction temperature, and 2:2 ratio of polysaccharide to Na2SeO3 were the optimal selenylation modification conditions. The validation experiments completed under the optimal conditions gave the mean selenium content and yield of sCPP1b were 478.17μg/g (RSD=5.7%) and 595mg/g (RSD=1.6%), respectively. Selenylation modification can significantly increase the antitumor activity of CPP1b in vitro. The structural characterization of sCPP1b was further characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, and high-performance gel permeation chromatography coupled with multi-angle laser light scattering. These structure analysis results indicated that sCPP1b has been successfully selenylation modified with similar structure to polysaccharide of CPP1b., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A pectic polysaccharide (CPP1b) was at first isolated from Codonopsis pilosula. Sugar analysis revealed that CPP1b is composed of rhamnose (Rha), arabinose (Ara), galactose (Gal) and galacturonic acid (GalA) with a molar ratio of 0.25:0.12:0.13:2.51. The result of esterification assay showed that about 46.7±0.4% of carboxylic groups in GalA residues existed as methyl ester. Combined with chemical and spectroscopic analyses, a preliminary structure of CPP1b was proposed as follows: 1,4-linked α-D-GalpA and 1,4-linked α-D-GalpA6Me interspersed with rare 1,2-linked β-L-Rhap, 1,2,6-linked α-D-Galp and terminal α-L-Arap. CPP1b had an average molar mass and root-mean square radius (RMS) of 1.45×10(5) Da and 29.7 nm, respectively, and presented a linear random coil conformation in 0.9% NaCl. The ultrastructure of CPP1b was further investigated by transmission electron microscope (TEM) and scanning electron microscope (SEM). CPP1b exhibited obvious cytotoxicity to human lung adenocarcinoma A549 cells in a dose- and time-dependent manner., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

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., (Copyright © 2013 Elsevier B.V. All rights reserved.)