Surface modification of poly(dimethylsiloxane) microchips using a double-chained cationic surfactant for efficiently resolving fluorescent dye adsorption

This paper described a double-chained cationic surfactant, didodecyldimethylammonium bromide (DDAB). for dynamic surface modification of poly(dimethylsiloxane) (PDMS) microchips to reduce the fluorescent dyes adsorption onto the microchannel. When DDAB with a high concentration was present as the dynamic modification reagent in the running and sample buffer, it not only reversed the direction of electroosmotic flow, but also efficiently suppressed fluorescent dyes pyronine Y (PY) or rhodamine 8 (RB) adsorption onto the chip surface. In addition, vesicles formed by DDAB in the buffer with higher surface charge density and electrophoretic mobility could provide wider migration window and potential for the separation of compounds with similar hydrophobicity. Factors affecting modification, such as pH and concentrations of the buffer, DDAB concentration in the buffer were investigated. Compared with commonly used single-chained cetyltrimethylammonium bromide, DDAB provided a better modification performance.

Counterion exchange at the surface of polyelectrolyte multilayer film for wettability modulation

Counterions present at the surface of polyelectrolyte multilayers (PEMs) were utilized for modulation of surface wettability via ion exchange. The PEM film was dipped in aqueous solutions of different anions, respectively, and the water contact angle of the surface varied from about 10 degrees to 120 degrees, depending on the hydration characteristics of the anion. The ion exchange mechanism was verified by X-ray photoelectron spectroscopy. The process was rapid and reversible. Ionic strength of the polyelectrolyte solution used for preparing the PEMs was found to be crucial to the surface wetting properties and the reversibility and kinetics of the process, and the effects were correlated to the surface density of the excess charge and counterion. This work provides a general, facile and rapid approach of surface property modulation.

The adsorption of dopamine on gold and its interactions with iron(III) ions studied by microcantilevers

The adsorption of dopamine (DA) molecules on gold and their interactions with Fe3+ were studied by a microcantilever in a flow cell. The microcantilever bent toward the Au side with the adsorption of DA due to the change Of Surface stress induced by the intermolecular hydrogen bonds of DA or the charge transfer effect between adsorbates and the Substrate. The interaction process between DA adsorbates and Fe3+ was revealed by the deflection curves of microcantilever. As indicated by the appearance of a variation during the decline of curves, two steps were observed in the curve at relative high concentrations of Fe3+. In this case, Fe3+ reacted with DA molecules only in the outer layers and the complexes removed with solution. Then Fe3+ reacted further with DA molecules forming the surface complex in the first layer next to the gold. At this stage, the stability Of Surface complexes was time dependent, i.e., unstable initially and stable finally. This may be due to the surface complexes change from mono-dentate to bi-dentate complexes. In another case, i.e., at relative low concentration of Fe3+, only the first step was observed as indicated by the absence of a variation.

Chitosan(Chitin)/Cellulose Composite Biosorbents Prepared Using Ionic Liquid for Heavy Metal Ions Adsorption

Chitosan(chitin)/cellulose composites as biodegradable biosorbents were prepared under an environment-friendly preparation processes using ionic liquids. Infrared and X-ray photoelectron spectra indicated the stronger intermolecular hydrogen bond between chitosan and cellulose, and the hydroxyl and amine groups were believed to be the metal ion binding sites. Among the prepared biosorbents, freeze-dried composite had higher adsorption capacity and better stability. The capacity of adsorption was found to be Cu(II) (0.417 mmol/g) > Zn(II) (0.303 mmol/g) > Cr(VI) (0.251 mmol/g) > Ni(II) (0.225 mmol/g) > Ph(II) (0.127 mmol/g) at the same initial concentration 5 mmol L-1. In contrast to some other chitosan-type biosorbents, preparation and component of the biosorbent were obviously more environment friendly. Moreover, adsorption capacity of chitosan in the blending biosorbent could be fully shown.

A DNA nanomachine induced by single-walled carbon nanotubes on gold surface

Single-walled carbon nanotubes (SWNTs) can selectively induce human telomeric i-motif DNA formation at pH 7.0. Based on this property, we design a DNA nanomachine induced by SWNTs on gold surface. The motor DNA is human telomeric G-quadruplex DNA. The reversible hybridization between the motor DNA and its complementary human telomeric i-motif DNA can be modulated by SWNTs without changing solution pH. Up to now, to our knowledge, there is no report to show that a DNA nanomachine is induced by SWNTs or a DNA nanomachine can detect i-motif formation at pH 7.0. Our work may provide a new concept for designing an SWNT-induced DNA nanomachine and for the detection of i-motif DNA structure at pH 7.0. DNA hybridization, conformational transition and i-motif formation have been characterized on surface or in solution by fluorescence confocal microscopy, circular dichroism, DNA melting and gel electrophoresis. The folding and unfolding kinetics of the DNA nanomachine on gold surface were studied by Fourier transform-surface plasmon resonance (FT-SPR). All these results indicate that SWNTs can induce the DNA nanomachine to work efficiently and reversibly.

Kinetics and Statistical Distributions of Single-Molecule Conformational Dynamics

We developed a coarse-grained yet microscopic detailed model to study the statistical fluctuations of single-molecule protein conformational dynamics of adenylate kinase. We explored the underlying conformational energy landscape and found that the system has two basins of attractions, open and closed conformations connected by two separate pathways. The kinetics is found to be nonexponential, consistent with single-molecule conformational dynamics experiments. Furthermore, we found that the statistical distribution of the kinetic times for the conformational transition has a long power law tail, reflecting the exponential density of state of the underlying landscape. We also studied the joint distribution of the two pathways and found memory effects.

Investigations on the adsorption behavior of Neutral Red on mercaptoethane sulfonate protected gold nanoparticles

A detailed investigation on the adsorption behavior of Neutral Red (NR) molecules on mercaptoethane sulfonate-monolayer protected gold clusters (MES-MPCs) has been conducted by the spectroscopic method. It is found that cationic NR molecules are adsorbed on the negatively charged MPCs surfaces via electrostatic attractive forces. The absorption study shows that the optical properties of NR molecules are significantly influenced upon the adsorption. Based on the electrostatic adsorption nature and the excellent stability of MES-MPCs against the electrolytes, this association can be released by the addition of electrolyte salts, which can be monitored by both absorption and fluorescence spectroscopy. In addition, dication Ca2+ is found to be more effective in the release of NR than univalent Na+. Moreover, the MES-MPCs exert energy transfer quenching of NR fluorescence by both static and dynamic quenching. However, static quenching seems to be the dominating quenching mechanism. Furthermore, this energy transfer quenching exhibits strong dependence of Au core size, and 5.0 nm MPCs show stronger ability in quenching the NR fluorescence than that of 2.7 nm MPCs.