Core-Shell Nanocables Decorated with Carbon Spherical Shells and Silver Nanoparticles for Sensing Ethinylestradiol Hormone in Water Sources and Pills.

The selective, rapid detection of low levels of hormones in drinking water and foodstuffs requires materials suitable for inexpensive sensing platforms. We report on core-shell Ag@C nanocables (NCs) decorated with carbon spherical shells (CSSs) and silver nanoparticles (AgNPs) by using a hydrothermal green approach. Sensors were fabricated with homogeneous, porous films on screen-printed electrodes, which comprised a 115 nm silver core covered by a 122 nm thick carbon layer and CSSs with 168 nm in diameter. NCs and CSSs were also decorated with 10-25 nm AgNPs. The NC/CSS/AgNP sensor was used to detect ethinylestradiol using square wave voltammetry in 0.1 M phosphate buffer (pH 7.0) over the 1.0-10.0 µM linear range with a detection limit of 0.76 µM. The sensor was then applied to detect ethinylestradiol in tap water samples and a contraceptive pill with recovery percentages between 93 and 101%. The high performance in terms of sensitivity and selectivity for hormones is attributed to the synergy between the carbon nanomaterials and AgNPs, which not only increased the sensor surface area and provided sites for electron exchange but also imparted an increased surface area.

Microbial nanocellulose adherent to human skin used in electrochemical sensors to detect metal ions and biomarkers in sweat.

The pursuit of biocompatible, breathable and skin-conformable wearable sensors has predominantly focused on synthetic stretchable hydrophobic polymers. Microbial nanocellulose (MNC) is an exceptional skin-substitute natural polymer routinely used for wound dressing and offers unprecedented potential as substrate for wearable sensors. A versatile strategy for engineering wearable sensing platforms is reported, with sensing units made of screen-printed carbon electrodes (SPCEs) on MNC. As-prepared SPCEs were used to detect the toxic metals cadmium (Cd2+) and lead (Pb2+) with limits of detection of 1.01 and 0.43 µM, respectively, which are sufficient to detect these metal ions in human sweat and urine. SPCEs functionalized through anodic pre-treatments were used for detecting uric acid and 17ß-estradiol in artificial sweat, with detection limits of 1.8 µM and 0.58 µM, respectively. The electrochemical treatment created oxygen groups on the carbon surfaces, thus improving wettability and hydrophilicity. MNC was herein exploited as an adhesive-free, yet highly skin-adherent platform for wearable sensing devices that also benefit from the semi-permeable, non-allergenic, and renewable features that make MNC unique within the pool of materials that have been used for such a purpose. Our findings have clear implications for the developments on greener and more biocompatible but still efficient substrates and may pave the route for combining immunosensing devices with drug delivery therapies.

Electrochemical biosensor made with tyrosinase immobilized in a matrix of nanodiamonds and potato starch for detecting phenolic compounds.

The envisaged ubiquitous sensing and biosensing for varied applications has motivated materials development toward low cost, biocompatible platforms. In this paper, we demonstrate that carbon nanodiamonds (NDs) can be combined with potato starch (PS) and be deposited on a glassy carbon electrode (GCE) in the form of a homogeneous, rough film, with electroanalytical performance tuned by varying the relative ND-PS concentration. As a proof of concept, the ND/PS film served as matrix to immobilize tyrosinase (Tyr) and the resulting Tyr-ND-PS/GCE biosensor was suitable to detect catechol using differential pulse voltammetry with detection limit of 3.9 × 10-7 mol L-1 in the range between 5.0 × 10-6 and 7.4 × 10-4 mol L-1. Catechol could also be detected in river and tap water samples. This high sensitivity, competitive with biosensors made with more sophisticated procedures and materials in the literature, is attributed to the large surface area and conductivity imparted by the small NDs (<5 nm). In addition, the ND-PS matrix may have its use extended to immobilize other enzymes and biomolecules, thus representing a potential biocompatible platform for ubiquitous biosensing.

Sensitive detection of estriol hormone in creek water using a sensor platform based on carbon black and silver nanoparticles.

We report the electrochemical detection of estriol using carbon black nanoballs (CNB) decorated with silver nanoparticles (AgNP) as electrode material. Homogeneous, porous films on glassy carbon electrodes (GCE) were obtained, with diameters of 20 - 25nm for CNB and 5 - 6nm for AgNP. CNB/AgNP electrodes had increased conductivity and electroactive area in comparison with bare GCE and GCE/CNB, according to cyclic voltammetry and electrochemical impedance spectroscopy. The oxidation potential peak was also down shifted by 93mV, compared to the bare GC electrode. Differential pulse voltammetry data were obtained in 0.1molL-1 PBS (pH 7.0) to detect estriol without the purification step, in the linear range between 0.2 and 3.0µmolL-1 with detection and quantification limits of 0.16 and 0.5µmolL-1 (0.04 and 0.16mgL-1), respectively. The sensor was used to detect estriol in a creek water sample with the same performance as in the official methodology based on high performance liquid chromatography.

Synergy between Printex nano-carbons and silver nanoparticles for sensitive estimation of antioxidant activity.

We report on the synthesis, characterization and applications of a Printex L6 carbon-silver hybrid nanomaterial (PC-Ag), which was obtained using a polyol method. In addition, we also highlight the use of Printex L6 nano-carbon as a much cheaper alternative to the use of carbon nanotubes and graphene. The silver nanoparticles (AgNP) were prepared directly on the surface of the Printex 6L carbon "nanocarbon" material using ethylene glycol as the reducing agent. The hybrid nanomaterial was characterized by High-angle annular dark-field transmission electron microscopy (HAADF-TEM), energy-dispersive X-ray spectroscopy (EDX), selected area electron diffraction (SAED), Raman spectroscopy and cyclic voltammetry. Optimized electrocatalytic activity on glassy carbon electrode was reached for the architecture GC/PC-Ag, the silver nanoparticles with size ranging between 1 and 2 nm were well-distributed throughout the hybrid material. The synergy between PC nano-carbons and AgNPs was verified by detection of gallic acid (GA) at a low applied potential (0.091 V vs. Ag/AgCl). GA detection was performed in a concentration range between 5.0 × 10(-7) and 8.5 × 10(-6) mol L(-1), with a detection limit of 6.63 × 10(-8) mol L(-1) (66.3 nmol L(-1)), which is considerably lower than similar devices. The approach for fabricating the reproducible GC/PC-Ag electrodes is entirely generic and may be explored for other types of (bio)sensors and devices.

Simultaneous determination of epinephrine and dopamine by electrochemical reduction on the hybrid material SiO2/graphene oxide decorated with Ag nanoparticles.

This paper describes the synthesis, characterization and applications of a new hybrid material composed of mesoporous silica (SiO2) modified with graphene oxide (GO), SiO2/GO, obtained by the sol-gel process using HF as the catalyst. The hybrid material, SiO2/GO, was decorated with silver nanoparticles (AgNPs) with a size of less than 20 nanometres, prepared directly on the surface of the material using N,N-dimethylformamide (DMF) as the reducing agent. The resulting material was designated as AgNP/SiO2/GO. The Ag/SiO2/GO material was characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) and high-resolution transmission electron microscopy (HR-TEM). A glassy carbon electrode modified with AgNP/SiO2/GO was used in the development of a sensitive electrochemical sensor for the simultaneous determination of epinephrine and dopamine employing electrocatalytic reduction using squarewave voltammetry. Well-defined and separate reduction peaks were observed in PBS buffer at pH 7. No significant interference was seen for primarily biological interferents such as uric acid and ascorbic acid in the detection of dopamine and epinephrine. Our study demonstrated that the resultant AgNP/SiO2/GO-modified electrode is highly sensitive for the simultaneous determination of dopamine and epinephrine, with the limits of detection being 0.26 and 0.27 µmol L(-1), respectively. The AgNP/SiO2/GO-modified electrode is highly selective and can be used to detect dopamine and epinephrine in a human urine sample.