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A novel electrochemical immunosensor was developed for highly sensitive detection of brain-derived neurotrophic factor (BDNF), a well-known depression marker. The immunosensor was fabricated by modifying indium tin oxide-coated polyethylene terephthalate (ITO-PET) with N-doped graphene-polyaniline (NG-PANI) and gold nanoparticles (AuNPs) to enhance the conductivity and protein loading capacity. Subsequently, BDNF was immobilized onto the electrode surface via gold-sulfur bonds, followed by the attachment of biotinylated antibody (Biotin-Ab) and horseradish peroxidase-avidin (HRP-Avidin) to create the final immunosensor (HRP-Avidin-Biotin-Ab-BDNF-AuNPs/NG-PANI/ITO-PET). The proposed immunosensor exhibited a linear range of determination (0.781-400 pg/mL) with a low limit of detection (LOD) of 0.261 pg/mL (S/N = 3) and excellent reproducibility (RSD = 1.4%) and stability (92.7%, RSD = 3.1%). Additionally, the immunosensor demonstrated good anti-interference performance and good recovery (98.1-107%). To evaluate the practical utility of the immunosensor, BDNF levels were quantified in the serum of mice with depression induced by chronic unpredictable mild stress (CUMS). The results indicated that the serum BDNF levels were significantly decreased in the depression model group compared with the control group, highlighting the potential of this immunosensor for clinical detection of BDNF in depression diagnosis and treatment., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

Due to the variety and activity of secondary metabolites of endophytic fungi (SMEF) from medicinal plants, and the operation cumbersome of existing methods for evaluating the activity, there is urgent to establish a simple, efficient and sensitive evaluation and screening technology. In this study, the prepared chitosan functionalized activated carbon (AC@CS) composite as the electrode substrate material was used to modify glassy carbon electrode (GCE), and the gold nanoparticles (AuNPs) was deposited on AC@CS/GCE by cyclic voltammetry (CV). A ds-DNA/AuNPs/AC@CS/GCE electrochemical biosensor for evaluating the antioxidant activity of SMEF from Hypericum perforatum L. (HP L.) was fabricated using the method of layer by layer assembly. The experimental conditions affecting the evaluation results of the biosensor were optimized by square wave voltammetry (SWV) using Ru(NH 3 ) 6 3+ as the probe, and the antioxidant activity of various SMEF from HP L. was evaluated by the proposed biosensor. Meanwhile, the results of the biosensor were also verified by UV-vis. According to the optimized experimental results, the biosensors had a high levels of oxidative DNA damage at pH 6.0 and Fenton solution system with Fe 2+ to OH - ratio of 1:3 for 30 min. Among the crude extracts of SMEF from roots, stems and leaves of HP L., the crude extracts from stems presents a high antioxidant activity, but it was weaker than l-ascorbic acid. This result was consistent with the evaluation results of UV-vis spectrophotometric method, also the fabricated biosensor presents high stability and sensitivity. This study not only provides a novel, convenient and efficient way for rapid evaluating the antioxidant activity of a wide variety of SMEF from HP L., but also provides a novel evaluation strategy for the SMEF from medicinal plants., 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 © 2023 Elsevier B.V. All rights reserved.)

Sleep debt (SD) is one of the important triggers for causing not only physiological and mental illness but also dangerous work. Therefore, achieving an early and objective assessment of SD is of great significance in the precaution against SD-related diseases and unsafe work. Here, an ultrasensitive electrochemical immunosensor was constructed for analysis of SD biomarker amyloid-β (Aβ). The gold nanoparticles/chitosan-coated polyaniline-functionalized activated carbon (AuNPs/AC@PANI@CS) composites were employed as the sensing platforms. Since PANI and AC can form an effective conductive path, it can effectively enhance the penetration of electrolytes on the electrode surface and the rapid transport of charges and ions, significantly enhancing the electrochemical response signal of the immunosensor. Under the optimized experimental conditions, the fabricated immunosensor had a wide linear range of 1.95 pg mL -1 to 1000.00 pg mL -1 , with a low detection limit of 0.014 pg mL -1 . This study not only provides an effective method for the accurate and rapid detection of Aβ, but also offers a novel evaluation strategy for the objective assessment of SD and the study of related pathological mechanisms., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Developing wearable flexible biosensors with excellent electrical conductivity and outstanding flexibility simultaneously for disease diagnosis and health monitoring is a current hot topic in the field of sensor research. In this study, nitrogen-doped graphene (N-Gr) and gold nanoparticles (AuNPs) were successively deposited onto ITO-PET flexible conductive films by chemical deposition, and then a flexible electrochemical immunosensor with high sensitivity and selectivity was constructed for detecting depression markers by exploiting the high affinity between AuNPs and the sulfhydryl groups of depression marker (DM) antibody. Due to the composite of N-Gr, AuNPs and ITO-PET, the prepared flexible sensor can maintain a relatively stable electrical signal response regardless of the deformation such as spiral, rolling, and bending, without shedding or fracture of the N-Gr and AuNPs, and can also significantly amplify the electrochemical response signal of the immunosensor. Under optimized experimental conditions, the fabricated immunosensor showed good linearity over a wide range of 0.023-300.00 ng/mL with a low detection limit of 0.010 ng/mL (3σ, n = 5), when it was used for the determination of depression markers-human Apo-A4 in 100% whole serum samples. The flexibility of the constructed immunosensor and the stability and sensitivity of biomolecular analysis are expected to be further made into implantable depression marker in-situ monitoring probe with the help of micro-machining technology, which will develop a promising method for objective, efficient and accurate clinical diagnosis of depression., (Copyright © 2022 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.)