Combination of microporous hollow carbon spheres and nafion for the individual metal-free stripping detectionof Pb2+ and Cd2+

Here, the combination of Nafion with microporous hollow carbon spheres (MHCS) is first proposed to fabricate a disposable metal-free electrode for heavy metal stripping sensing. The MHCS-Nafion composite film electrode is prepared by drop-casting a mixture of MHCS and Nafion onto the lab-made screen-printed carbon electrode (SPCE*). Results demonstrate that the interfusion of MHCS into Nafion offers enhanced performance for the electro-enrichment and stripping of lead and cadmium over the only Nafion film: 1) abundant MHCS immobilized on the electrode surface serve as effective nucleation sites for metal ion reduction; 2) the mixing of MHCS into Nafion enlarges the active surface of negative-charged Nafion for the electrostatic adsorption of metal cations. The proposed MHCS-Nafion/SPCE* provides linear responses for Pb2+ and Cd2+ in the range of 2 - 200 mu g/L, with a detection limit of 1.37 and 1.63 mu g/L, respectively. Practical applications of the sensor in water sample detection with good accuracy have also been confirmed

Platinum nanoparticles encapsulated in carbon microspheres: toward electro-catalyzing glucose with high activity and stability

Electro-oxidizing glucose effectively is well known as the critical point in developing analytical sensors and carbohydrate-based fuel cells. Here we prepared a new electrode material, platinum nanoparticles encapsulated in carbon microspheres (Pt/GSH), to promote the glucose electrocatalytic oxidation reaction in neutral media. The Pt/GSH composite was synthesized by using a simple hydrothermal method, with reduced glutathione (R-GSH) as the capping agent and reductant simultaneously, followed by a calcination process. It was found that the obtained Pt particles with a mean size of 26.8 nm were well dispersed in the interconnected carbon microspheres, providing a stable and efficient catalytic platform for glucose electro-oxidation. As a result, the synthesized catalyst exhibited higher activity for electro-catalyzing glucose compared to commercial Pt black and Pt/C catalysts, with a mass activity of 15.4 μA μg , approximately 13 times of Pt black and 2.1 times of Pt/C. Besides, due to the decreased dissolution and agglomeration of Pt NPs in the carbon-encapsulated structure, the Pt/GSH catalyst kept quite stable activity upon reuse even in the presence of chloride ions

Enzyme- and metal-free electrochemical sensor for highly sensitive superoxide anion detection based on nitrogen doped hollow mesoporous carbon spheres

In this work, a highly sensitive enzyme- and metal-free electrochemical method for superoxide anion (O[rad]) detection has been developed by employing screen-printed carbon electrodes (SPCE) modified by nitrogen doped hollow mesoporous carbon spheres (N-HMCS). For comparison, solid carbon spheres (SCS) and hollow mesoporous carbon spheres (HMCS) were also synthesized to fabricate the modified SPCE. Compared with SCS/SPCE and HMCS/SPCE, N-HMCS/SPCE displayed a higher electrochemical performance. When applied for electrochemical detection of O[rad], N-HMCS/SPCE exhibited a high sensitivity of 1.49\ua0μA\ua0cm\ua0μM, better than SCS/SPCE and HMCS/SPCE and many of enzyme- or metal-based superoxide anion sensors. N-HMCS is expected to become a new generation of sensing materials for electrochemical analysis of O[rad]

Carbon blacks as EPR sensors for localized measurements of tissue oxygenation.

New electron paramagnetic resonance (EPR) oximetry probes were identified in the class of carbon black materials. These compounds exhibit very high oxygen sensitivity and favorable EPR characteristics for biological applications. At low pO(2), the linewidth is particularly sensitive to changes in oxygen tension (sensitivity of 750 mG/mmHg). The application of the probes for oximetry was demonstrated in vivo: the pO(2) was measured in muscle in which the blood flow was temporarily restricted as well as in tumor-bearing mice during a carbogen breathing challenge. The responsiveness to pO(2) was stable in muscle for at least 3 months. No toxicity was observed using these materials in cellular experiments and in histological studies performed 2, 7, and 28 days after implantation. In view of their EPR characteristics (high sensitivity) as well as the well-characterized production procedure that make them available on a large scale, these probes can be considered as very promising tools for future developments in EPR oximetry

Electrochemical Performance of Micropillar Array Electrodes in Microflows

The microchip-based electrochemical detection system (μEDS) has attracted plenty of research attention due to its merits including the capability in high-density integration, high sensitivity, fast analysis time, and reduced reagent consumption. The miniaturized working electrode is usually regarded as the core component of the μEDS, since its characteristic directly determines the performance of the whole system. Compared with the microelectrodes with conventional shapes such as the band, ring and disk, the three-dimensional (3D) micropillar array electrode (μAE) has demonstrated significant potential in improving the current response and decreasing the limits of detection due to its much larger reaction area. In this study, the numerical simulation method was used to investigate the performance of the μEDS, and both the geometrical and hydrodynamic parameters, including the micropillars shape, height, arrangement form and the flow rate of the reactant solution, were taken into consideration. The tail effect in μAEs was also quantitatively analyzed based on a pre-defined parameter of the current density ratio. In addition, a PDMS-based 3D μAE was fabricated and integrated into the microchannel for the electrochemical detection. The experiments of cyclic voltammetry (CV) and chronoamperometry (CA) were conducted, and a good agreement was found between the experimental and simulation results. This study would be instructive for the configuration and parameters design of the μEDS, and the presented method can be adopted to analyze and optimize the performance of nanochip-based electrochemical detection system (nEDS)

Dendritic mesoporous silica nanoparticles with abundant Ti4+ for phosphopeptide enrichment from cancer cells with 96% specificity

Selective enrichment and sensitive detection of phosphopeptides are of great significance in many bio-applications. In this work, dendritic mesoporous silica nanoparticles modified with polydopamine and chelated Ti (denoted DMSNs@PDA-Ti) were developed to improve the enrichment selectivity of phosphopeptides. The unique central-radial pore structures endowed DMSNs@PDA-Ti with a high surface area (362 m g), a large pore volume (1.37 cm g) and a high amount of chelated Ti (75 μg mg). Compared with conventional mesoporous silica-based materials with the same functionalization (denoted mSiO@PDA-Ti) and commercial TiO, DMSNs@PDA-Ti showed better selectivity and a lower detection limit (0.2 fmol/μL). Moreover, 2422 unique phosphopeptides were identified from HeLa cell extracts with a high specificity (> 95%) enabled by DMSNs@PDA-Ti, better than those in previous reports

Sequential enrichment of singly- and multiply-phosphorylated peptides with zwitterionic hydrophilic interaction chromatography material

An interesting and novel method for the selective and sequential enrichment of singly- and multiply-phosphorylated peptides with a zwitterionic material "Click TE-Cys" is presented. Retention mechanisms between phosphopeptides and Click TE-Cys are systematically investigated by checking the influence of acetonitrile content, pH value, and buffer concentration on the retention of phosphopeptides. Both hydrophilic interaction and electrostatic interaction are involved in retention between phosphopeptides and Click TE-Cys. Based on these results, an optimized method is established for selective enrichment of phosphopeptides using Click TE-Cys. This method not only exhibits high selectivity for phosphopeptides, but also fractionates singly- and multiply-phosphorylated peptides into two fractions. This method was evaluated using relatively complex samples, including peptide mixtures of alpha-casein and bovine serum albumin (BSA) at a molar ratio of 1:10 and skim milk. This efficient and optimized protocol has great potential for enriching multiply-phosphorylated peptides and could be a valuable tool for specific enrichment of phosphopeptides in phosphoproteome analysis. (C) 2015 Elsevier B.V. All rights reserved