Reactive Molecular Dynamics Simulations of Polystyrene Pyrolysis.

Polymers' controlled pyrolysis is an economical and environmentally friendly solution to prepare activated carbon. However, due to the experimental difficulty in measuring the dependence between microstructure and pyrolysis parameters at high temperatures, the unknown pyrolysis mechanism hinders access to the target products with desirable morphologies and performances. In this study, we investigate the pyrolysis process of polystyrene (PS) under different heating rates and temperatures employing reactive molecular dynamics (ReaxFF-MD) simulations. A clear profile of the generation of pyrolysis products determined by the temperature and heating rate is constructed. It is found that the heating rate affects the type and amount of pyrolysis intermediates and their timing, and that low-rate heating helps yield more diverse pyrolysis intermediates. While the temperature affects the pyrolytic structure of the final equilibrium products, either too low or too high a target temperature is detrimental to generating large areas of the graphitized structure. The reduced time plots (RTPs) with simulation results predict a PS pyrolytic activation energy of 159.74 kJ/mol. The established theoretical evolution process matches experiments well, thus, contributing to preparing target activated carbons by referring to the regulatory mechanism of pyrolytic microstructure.

Photoelectrochemical sensor for the detection of Escherichia coli O157:H7 based on TPA-NO2 and dual-functional polythiophene films.

The detection of Escherichia coli (E. coli) is of great significance for the environment and human health. Herein, a photoelectrochemical (PEC) detection strategy based on molecularly imprinted polymers (MIPs) was proposed for the sensitive detection of E. coli. 4,4',4″-Trinitrotriphenylamine (TPA-NO2) was prepared using a simple nitration reaction. Subsequently, MIP films were polymerized on the surface of TPA-NO2 using 1,3-dihydrothieno[3,2-d]pyrimidine-2,4-dione as the functional monomer with the dual functions of specific recognition and sensitization. The linear range was 10-108 CFU/mL and the limit of detection was 10 CFU/mL. It showed favorable recoveries in real sample tests of milk, orange juice and tomato. Additionally, the ability of functional monomers to bind excellently with E. coli was verified using molecular docking techniques. This research provided broader possibilities for constructing MIPs-PEC sensors and analyzing the interaction mechanism between E. coli and functional monomers.

Post separation adjustment of pH to enable the analysis of aminoglycoside antibiotics by microchip electrophoresis with amperometric detection.

Five aminoglycoside antibiotics (AGs), namely spectinomycin, streptomycin, amikacin, paromomycin, and neomycin, were analyzed by microchip electrophoresis with amperometric detection. Although the electrophoretic separation of AGs was carried out under acidic conditions, the amperometric detection was performed under alkaline conditions with an electrode fabricated by electrodeposition of an alloy of Cu-Sn-Cr. To achieve this, an alkaline solution was introduced into the end of the separation channel through two auxiliary channels, allowing the use of different conditions for each analytical operation. Along with the proposed pH adjustment, the use of electrodes modified with Cu-Sn-Cr enabled extending the lifetime of the electrodes. The alloy was co-electrodeposited on a 25-µm diameter platinum wire, which was then integrated in the microchip and used as working electrode. Furthermore, the effects of the pH and composition of buffer, separation potential, injection time, and detention potential were investigated in an effort to optimize both the separation and detection of AGs. Under the optimum conditions, linear relationships between the signal and the concentration were obtained in the 4.9-316.8 µM range, with regression coefficients of at least 0.99 and LODs ranging from 2.1 µM for amikacin to 4.6 µM for spectinomycin. Applicability of the method was demonstrated by analyzing five aminoglycoside antibiotics in spiked milk samples. The results showed that this alternative method is rapid, sensitive, and portable and enables the analysis of aminoglycoside antibiotics in milk sample.

PDMS microchip coated with polydopamine/gold nanoparticles hybrid for efficient electrophoresis separation of amino acids.

In this paper, a novel, simple, economical and environmentally friendly method based on in situ chemically induced synthesis strategy was designed and developed for the modification of a poly(dimethylsiloxane) (PDMS) microchip channel with polydopamine/gold nanoparticles (PDA/Au NPs) to create a hydrophilic and biofouling resistant surface. Dopamine as a reductant and a monomer, and HAuCl(4) as an oxidant to trigger dopamine polymerization and the source of metallic nanoparticles, were filled into the PDMS microchannel to yield in situ a well-distributed and robust PDA/Au NP coating. Au NPs were highly and uniformly dispersed in/on the PDA matrix with a narrow size distribution, as verified by scanning electron microscopy and UV-vis spectra. Compared with the native PDMS microchannel, the modified surfaces exhibited much better wettability, high stability and suppressed electroosmotic mobility, and less nonspecific adsorption towards biomolecules. The water contact angle and EOF of PDA/Au NP-coated PDMS microchip were measured to be 13° and 4.17×10(-4) cm(2)/V s, compared to those of 111° and 5.33×10(-4) cm(2)/V s from the native one, respectively. Fast and efficient separations of five amino acids such as arginine, proline, histidine, valine and threonine suggested greatly improved electrophoretic performance of the PDA/Au NP-functionalized PDMS microchips. This one-step procedure offers an effective approach for a biomimetic surface design on microfluidic chips, which is promising in high-throughput and complex biological analysis.

Polydopamine Nanoparticles for Deep Brain Ablation via Near-Infrared Irradiation.

Local resection or ablation remains an important approach to treat drug-resistant central neurological disease. Conventional surgical approaches are designed to resect the diseased tissues. The emergence of photothermal therapy (PTT) offers a minimally invasive alternative. However, their poor penetration and potential off-target effect limit their clinical application. Here, polydopamine nanoparticles (PDA-NPs) were prepared and characterized. Studies were performed to evaluate whether PDA-NPs combined with near-infrared (NIR) light can be used to ablate deep brain structures in vitro and in vivo. PDA-NPs were prepared with a mean diameter of ∼150 nm. The particles show excellent photothermal conversion efficiency. PDA-NPs did not show remarkable cytotoxicity against neuronal-like SH-SY5Y cell lines. However, it can cause significant cell death when combined with NIR irradiation. Transcranial NIR irradiation after PDA-NPs administration induced enhanced local hyperthermia as compared with NIR alone. Local temperature exceeded 60 °C after 6 min of irradiation plus PDA while it can only reach 48 °C with NIR alone. PTT with PDA (10 mg/mL, 3 µL) and NIR (1.5 W/cm2) can ablate deep brain structures precisely with an ablation volume of ∼6.5 mm3. Histological analysis confirmed necrosis and apoptosis in the targeted area. These results demonstrate the potential of NP-assisted PTT for the treatment against nontumorous central neurological diseases.

Facile preparation of protein stationary phase based on polydopamine/graphene oxide platform for chip-based open tubular capillary electrochromatography enantioseparation.

A novel chip-based enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing bovine serum albumin (BSA) conjugated polydopamine-graphene oxide (PDA/GO) nanocomposites (PDA/GO/BSA) as stationary phase. After the poly(dimethylsiloxane) (PDMS) microfluidic chip was filled with a freshly prepared solution containing dopamine and graphene oxide, PDA/GO nanocomposites were formed and deposited on the inner wall of microchannel as permanent coating via the oxidation of dopamine by the oxygen dissolved in the solution. The PDA/GO-coated PDMS microchips not only have the adhesion of PDA that make them easily immobilized in the microchannel, but also have the larger surface and excellent biocompatibility of graphene which can incorporate much more biomolecules and well maintain their biological activity. In addition, incorporation of GO in PDA film can make surface morphology more rough, which is beneficial for enhancing the loading capacity of proteins in the microchannels and increasing sample capacity of OT-CEC columns. BSA was stably immobilized in the PDMS microchannel to fabricate a protein-stationary phase. Compared with the native PDMS microchannels, the modified surfaces exhibited much better wettability, more stable electroosmotic mobility, and less nonspecific adsorption. The efficient separation of chiral amino acids (tryptophan and threonine) and chiral dipeptide demonstrate that the constructed OT-CEC columns own ideal enantioselectivity. The presented strategy using PDA/GO coating as a versatile platform for facile conjugation of proteins may offer new processing strategies to prepare a functional surface designed on microfluidic chips.

One-step synthesis of mussel-inspired molecularly imprinted magnetic polymer as stationary phase for chip-based open tubular capillary electrochromatography enantioseparation.

A facile approach for preparation of molecularly imprinted polymers was developed and successfully used as chiral stationary phase for rapid enantioseparation by open tubular capillary electrochromatography (OT-CEC). In this work, molecularly imprinted polymers were one-step prepared employing Fe3O4 nanoparticles (NPs) as the supporting substrate and dopamine as the functional monomer. By simply mixing Fe3O4 NPs with template molecules in a weak alkaline solution of dopamine, a thin adherent polydopamine (PDA) film imprinted with template molecules was formed by the self-polymerization of dopamine on the surface of Fe3O4 NPs. After extracting the embedded template molecules, the produced imprinted Fe3O4@PDA NPs are of three dimensional shape of template molecules favoring high binding capacity and magnetism property for easy manipulation. The imprinted Fe3O4@PDA NPs prepared with l-tryptophan, l-tyrosine, Gly-l-Phe or s-ofloxacin as template molecules were packed in the PDMS microchannel via magnetic field as novel stationary phase for the successful enantioseparation of corresponding target analysts. In addition, the imprinted Fe3O4@PDA NPs-based OT-CEC system exhibited excellent reproducibility, stability and repeatability, which provides a powerful protocol for separation enantiomers within a short analytical time and opens up a promising avenue for high-throughput screening of chiral compounds.