Ternary self-assembled monolayers (SAM) composed of 2-aminoethanethiol (AET), 2-mercaptoethanesulfonic acid (MES), and 1-dodecanethiol (DDeT) form two types of domains as if it were a two-component SAM: DDeT-rich hydrophobic domains and electrostatically stabilized hydrophilic domains composed of MES and AET on Au(111). MES and AET behave virtually as a single surface-active species. Two distinct reductive desorption peaks in cyclic voltammograms (CV) and binarized images of scanning tunneling microscopy clearly show nanometer scale, yet macroscopically distinguishable, phase separation over a wide range of the mixing ratio of DDeT and MES-AET in the bathing solution. X-ray photoelectron spectroscopy measurements indicate that the ratio of MES to AET in the hydrophilic domains is unity and that both terminal groups are in the charged states, that is, the sulfonate group and the ammonium group. With decreasing the total concentration of the thiols, the mole fraction of DDeT in the bathing solution at which the surface coverage of MES-AET domains is equal to that of DDeT domains dramatically decreases. This suggests that the adsorption kinetics plays a crucial role in the formation of the domains structure.

In the present work, we reported the fabrication of a novel electrochemical sensing platform to detect 2,4-dichlorophenol (2,4-DCP) by using a copper benzene-1,3,5-tricarboxylate–graphene oxide (Cu–BTC/GO) composite.

No abstract

A carbon fiber cloth (CFC)‐supported Au nanodendrite (AuND@CFC) sensor was used to simultaneously measure the concentrations of Pb(II), Cu(II) and Hg(II) in real water samples. The sensor had a large electrochemically active surface area due to the hierarchical nanodendrite structure and the formation of the nanodendrite structure on the CFC was accomplished in just 5 minutes by single‐step electrodeposition. After the optimization of important experimental conditions, such as pH and pre‐concentration time, the achieved limit of detections (LODs) in the measurements of Pb(II), Cu(II) and Hg(II) were 0.15, 0.07, and 0.13 ppb, respectively, which were superior and comparable to those reported in previous studies. The electrochemical responses of each analyte (concentration: 2.0 ppb) were not influenced when the concentrations of interferants (Cr(IV), Ni(II), Mn(II), Zn(II), Al(III), Ca(II) and Mg(II)) were even 500‐fold greater (1.0 ppm); while only the signal of Cu(II) decreased when the Ni(II) concentration were 4.0 ppm (2000‐fold larger). When eight separately prepared AuND@CFC sensors were used to measure the samples, the relative standard deviations (RSDs) of the peak intensities of these metals were lower than 5.0 %, thereby indicating the superior sensor‐to‐sensor reproducibility. When real river and lake water samples were analyzed, the determined concentrations were similar to those measured with ICP‐MS and the recoveries ranged from 93.2 %–118.7 %. Overall, the proposed sensor is versatile enough to be incorporated into a portable analytical system for on‐site detection of Pb(II), Cu(II) and Hg(II) in real field samples.

Viscosity is an important property of liquids. A viscosity change of aqueous substances that deviates from their normal levels usually implies a compromise in quality due to degradation or microorganism proliferation. Monitoring of macro-scale viscosity can be simply realized by various conventional tools, such as rotational viscometers, capillary tubes, falling bodies, and so forth. Nevertheless, today, micro-volume viscosity measurement remains a challenging endeavor, resulting in rare, expensive, or difficult-to-obtain samples not very well studied. For this reason, a novel technique for micro-viscosity based on rotational Brownian motion is presented in this paper. Janus microbeads were made by coating fluorescent polystyrene beads with gold film. Taking advantage of the bead configuration of half gold/half fluorescence, the rotational Brownian signal was expressed in terms of blinking fluorescent intensity. The characteristic correlation time was derived from the blinking intensity of trace amounts of a selected medium over a certain time period, and results were correlated with viscosity. Given a volume of only 2 μL for each measurement, calibration of a series of glycerol–water mixtures (100%–1% (v/v) water content) yielded good agreement with the expected viscosity predictions over the range of 0.8–574.8 cP. Five common oil products, including lubricant oil, baby oil, food oil, olive oil, and motor oil, were further investigated to demonstrate the feasibility and practicability of the proposed technique. Data measured by the rotational Brownian motion-based diffusometer were comparable with those measured by a commercial rotational viscometer. The method also explicitly showed viscosity degradation after the oils were heated at a high temperature of over 100 °C for 10 min. Evaluation proved the proposed Janus microbead-enabled rotational diffusometric technique to be a promising approach for rapid and micro-scale viscosity measurement.