Diazonium functionalized exfoliated graphitic carbon as a binderless and covalently modified electrochemical interface for mercury sensing

A sensitive and selective electrochemical sensing platform for mercury quantification at picomolar level has been described. The interface was constructed using exfoliated graphitic carbon covalently functionalized with mercaptobenzothiozole (MBT) as a selective indicator species in mercury determination. It was characterized using Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) techniques and subsequently used in the fabrication of surface renewable binderless bulk modified robust pellet electrode. The fabricated electrode was used in the measurement of mercury in alkaline medium using differential pulse anodic stripping voltammetry (DPASV). The developed interface showed linearity in the concentration range 1-20 pM with a detection limit of 1 pM. The analytical utility of the proposed interface has been validated by determining the mercury levels from various water and industrial effluent samples with least interference from commonly encountered cations and anions that are generally present in industrial effluents. The storage stability of the proposed interface has been studied over a period of 6 months and the results were found to be highly reproducible with a relative standard deviation of ±6. © 2013 Elsevier B.V

Covalent modification of glassy carbon spheres through ball milling under solvent free conditions: A novel electrochemical interface for mercury(II) quantification

A simple and green chemistry protocol has been proposed based on the covalent anchoring of benzamide molecule on glassy carbon spheres through ball milling under solvent free condition. The modification proceeds through the formation of an amide bond between carboxylic group of glassy carbon spheres and the amino group of modifier molecule. The formation of covalent bond was ascertained using X-ray photoelectron spectroscopy. Scanning electron microscopy was used to study the surface morphology of milled glassy carbon spheres. The aqueous colloidal solution of modified glassy carbon spheres was used in the preparation of thin film electrodes and subsequently used as a novel electrochemical interface in the quantification of mercury at trace level using a differential pulse anodic stripping voltammetric technique. The modified electrode showed good sensitivity and selectivity towards mercury with a detection limit of 1 nM with least interference from most of the ions. The analytical utility of the proposed electrode has been validated by determining the mercury levels in number of sample matrices. © 2014 Elsevier B.V

A binderless, covalently bulk modified electrochemical sensor: Application to simultaneous determination of lead and cadmium at trace level

A new type of covalent binderless bulk modified electrode has been fabricated and used in the simultaneous determination of lead and cadmium ions at nanomolar level. The modification of graphitic carbon with 4-amino salicylic acid was carried out under microwave irradiation through the amide bond formation. The electrochemical behavior of the fabricated electrode has been carried out to decipher the interacting ability of the functional moieties present on the modifier molecules toward the simultaneous determination of Pb 2+ and Cd 2+ ions using cyclic and differential pulse anodic stripping voltammetry. The possible mode of interaction of functional groups with metal ions is proposed based on the pKa values of the modifier functionalities present on the surface of graphitic carbon particles. The analytical utility of the proposed sensor has been validated by measuring the lead and cadmium content from pretreated waste water samples of lead acid batteries. © 2012 Elsevier B.V

AKR1C3-mediated adipose androgen generation drives lipotoxicity in women with polycystic ovary syndrome

Context: Polycystic ovary syndrome (PCOS) is a prevalent metabolic disorder, occurring in up to 10% of women of reproductive age. PCOS is associated with insulin resistance and cardiovascular risk. Androgen excess is a defining feature of PCOS and has been suggested as causally associated with insulin resistance; however, mechanistic evidence linking both is lacking. We hypothesized that adipose tissue is an important site linking androgen activation and metabolic dysfunction in PCOS. Methods We performed a human deep metabolic in vivo phenotyping study, examining the systemic and intra-adipose effects of acute and chronic androgen exposure in ten PCOS women, in comparison to ten body mass index-matched healthy controls, complemented by in vitro experiments. Results: PCOS women had increased intra-adipose concentrations of testosterone (p=0.0006) and dihydrotestosterone (p=0.01), with increased expression of the androgen-activating enzyme aldoketoreductase type 1 C3 (AKR1C3, p=0.04) in subcutaneous adipose tissue. Adipose glycerol levels in subcutaneous adipose tissue microdialysate supported in vivo suppression of lipolysis after acute androgen exposure in PCOS (p=0.04). Mirroring this, non-targeted serum metabolomics revealed pro-lipogenic effects of androgens in PCOS women only. In vitro studies showed that insulin increased adipose AKR1C3 expression and activity while androgen exposure increased adipocyte de novo lipid synthesis. Pharmacological AKR1C3 inhibition in vitro decreased de novo lipogenesis. Conclusions: These findings define a novel intra-adipose mechanism of androgen activation that contributes to adipose remodelling and a systemic lipotoxic metabolome, with intra-adipose androgens driving lipid accumulation and insulin resistance in PCOS. AKR1C3 represents a promising novel therapeutic target in PCOS.This work was funded by the Wellcome Trust (Clinical Research Training Fellowship 099909, to MOR, and Project Grant 092283, to WA), the BBSRC (BB/L006340/1, to DH) and the National Institute of Health Research (NIHR) UK

Graphene–platinum nanocomposite as a sensitive and selective voltammetric sensor for trace level arsenic quantification

A simple protocol for the chemical modification of graphene with platinum nanoparticles and its subsequent electroanalytical application toward sensitive and selective determination of arsenic has been described. Chemical modification was carried out by the simultaneous and sequential chemical reduction of graphene oxide and hexachloroplatinic acid in the presence of ethylene glycol as a mild reducing agent. The synthesized graphene–platinum nanocomposite (Gr–nPt) has been characterized through infrared spectroscopy, x-ray diffraction study, field emission scanning electron microscopy and cyclic voltammetry (CV) techniques. CV and square-wave anodic stripping voltammetry have been used to quantify arsenic. The proposed nanostructure showed linearity in the concentration range 10–100 nM with a detection limit of 1.1 nM. The proposed sensor has been successfully applied to measure trace levels of arsenic present in natural sample matrices like borewell water, polluted lake water, agricultural soil, tomato and spinach leaves