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      Voltammetric detection of vitamin D employing Au-MoS 2 hybrid as immunosensing platform

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          Abstract

          A voltammetric immunosensor based on molybdenum sulphide (MoS 2) and gold nanoparticles (Au NPs) for the determination of 25-hydroxy vitamin D 3 (25(OH)D 3) is reported. Anti-vit D (Ab-25(OH)D 3) was immobilized onto the cysteamine-modified MoS 2 and Au NPs which were deposited onto a fluoride tin oxide (FTO) electrode (Ab/Cys/Au/MoS 2/FTO). The MoS 2 sheets were prepared by hydrothermal method followed by an in situ growth of Au film onto the MoS 2/FTO surface. Self-assembled monolayer (SAM) of cysteamine was synthesized onto the Au/MoS 2/FTO which acts as a linker to covalently bind Ab-25(OH)D 3. The Ab-25(OH)D 3-immobilized Cys/Au/MoS 2/FTO was used to detect 25(OH)D 3 using differential pulse voltammetry. The electrochemical system provided an anodic peak current at a potential of +0.21 V vs. Ag/AgCl (satd. KCl) of ferricyanide/ferrocyanide redox couple. The detection principle relies on the inhibition of electron transfer at the electrode surface owing to the hindrance caused by the formation of immune complex between Ab-25(OH)D 3 and 25(OH)D 3. The immunosensor shows linear response from 1 pg mL −1 to 100 ng mL −1 25(OH)D 3 and a sensitivity of 189 μA [log (pg mL −1)] −1 cm −2 along with a low limit of detection (LOD) of 0.38 pg mL −1. The immunosensor is highly selective towards 25(OH)D 3 and presented a long shelf life of 28 days. Also, the immunosensor exhibits satisfactory performance towards spiked human serum samples with recovery between 95.1 and 102% (RSD 1.15–3.22%).

          Supplementary Information

          The online version contains supplementary material available at 10.1007/s00604-021-04862-6.

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          Most cited references 32

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          The role of vitamin D in the prevention of coronavirus disease 2019 infection and mortality

          WHO declared SARS-CoV-2 a global pandemic. The present aim was to propose an hypothesis that there is a potential association between mean levels of vitamin D in various countries with cases and mortality caused by COVID-19. The mean levels of vitamin D for 20 European countries and morbidity and mortality caused by COVID-19 were acquired. Negative correlations between mean levels of vitamin D (average 56 mmol/L, STDEV 10.61) in each country and the number of COVID-19 cases/1 M (mean 295.95, STDEV 298.7, and mortality/1 M (mean 5.96, STDEV 15.13) were observed. Vitamin D levels are severely low in the aging population especially in Spain, Italy and Switzerland. This is also the most vulnerable group of the population in relation to COVID-19. It should be advisable to perform dedicated studies about vitamin D levels in COVID-19 patients with different degrees of disease severity.
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            Controlled, Defect-Guided, Metal-Nanoparticle Incorporation onto MoS2via Chemical and Microwave Routes: Electrical, Thermal, and Structural Properties

            Ultrathin (0.3-3 nm) metal dichalcogenides exhibit confinement of carriers, evolution of band-structure and photophysical properties with thickness, high on/off rectification (in MoS2, WS2, and so forth) and high thermal absorption. Here, we leverage the stable sulfur/nobel-metal binding to incorporate highly capacitive gold nanoparticles (Au NPs) onto MoS2 to raise the effective gate-voltage by an order of magnitude. Functionalization is achieved via both diffusion limited aggregation and instantaneous reaction arresting (using microwaves) with selective deposition on crystallographic edges (with 60° displacement). The electrical, thermal, and Raman studies show a highly capacitive interaction between Au NP and MoS2 flakes (CAu-MoS2 = 2.17 μF/cm(2)), a low Schottky barrier (14.52 meV), a reduced carrier-transport thermal-barrier (253 to 44.18 meV after Au NP functionalization), and increased thermal conductivity (from 15 to 23 W/mK post NP deposition). The process could be employed to attach electrodes to heterostructures of graphene and MoS2, where a gold film could be grown to act as an electron-tunneling gate-electrode connected to MoS2.
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              Is Open Access

              Flower-like PEGylated MoS2 nanoflakes for near-infrared photothermal cancer therapy

              Photothermal cancer therapy has attracted considerable interest for cancer treatment in recent years, but the effective photothermal agents remain to be explored before this strategy can be applied clinically. In this study, we therefore develop flower-like molybdenum disulfide (MoS2) nanoflakes and investigate their potential for photothermal ablation of cancer cells. MoS2 nanoflakes are synthesized via a facile hydrothermal method and then modified with lipoic acid-terminated polyethylene glycol (LA-PEG), endowing the obtained nanoflakes with high colloidal stability and very low cytotoxicity. Upon irradiation with near infrared (NIR) laser at 808 nm, the nanoflakes showed powerful ability of inducing higher temperature, good photothermal stability and high photothermal conversion efficiency. The in vitro photothermal effects of MoS2-PEG nanoflakes with different concentrations were also evaluated under various power densities of NIR 808-nm laser irradiation, and the results indicated that an effective photothermal killing of cancer cells could be achieved by a low concentration of nanoflakes under a low power NIR 808-nm laser irradiation. Furthermore, cancer cell in vivo could be efficiently destroyed via the photothermal effect of MoS2-PEG nanoflakes under the irradiation. These results thus suggest that the MoS2-PEG nanoflakes would be as promising photothermal agents for future photothermal cancer therapy.
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                Author and article information

                Contributors
                nirmalprabhakar@gmail.com , nirmalprabhakar@pu.ac.in
                Journal
                Mikrochim Acta
                Mikrochim Acta
                Mikrochimica Acta
                Springer Vienna (Vienna )
                0026-3672
                1436-5073
                4 June 2021
                2021
                : 188
                : 7
                Affiliations
                [1 ]GRID grid.261674.0, ISNI 0000 0001 2174 5640, Department of Biochemistry, , Panjab University, ; Chandigarh, 160014 India
                [2 ]GRID grid.261674.0, ISNI 0000 0001 2174 5640, Department of Chemistry and Centre for Advanced Studies in Chemistry, , Panjab University, ; Chandigarh, 160014 India
                [3 ]GRID grid.261674.0, ISNI 0000 0001 2174 5640, SAIF/CIL, , Panjab University, ; Chandigarh, 160014 India
                Article
                4862
                10.1007/s00604-021-04862-6
                8176887
                34086134
                © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2021

                This article is made available via the PMC Open Access Subset for unrestricted research re-use and secondary analysis in any form or by any means with acknowledgement of the original source. These permissions are granted for the duration of the World Health Organization (WHO) declaration of COVID-19 as a global pandemic.

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                © Springer-Verlag GmbH Austria, part of Springer Nature 2021

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