Synchronization of Coupled Oscillators on a Two-Dimensional Plane.

The effect of the transfer rate of signal molecules on coupled chemical oscillators arranged on a two-dimensional plane was systematically investigated in this paper. A microreactor equipped with a surface acoustic wave (SAW) mixer was applied to adjust the transfer rate of the signal molecules in the microreactor. The SAW mixer with adjustable input powers provided a simple means to generate different mixing rates in the microreactor. A robust synchronization of the oscillators was found at an input radio frequency power of 20 dBm, with which the chemical waves were initiated at a fixed site of the oscillator system. With increasing input power, the frequency of the chemical waves was increased, which agreed well with the prediction given by the time-delayed phase oscillator model. Results from the finite element simulation agreed well with the experimental results.

Accelerating the "On Water" Reaction: By Organic-Water Interface or By Hydrodynamic Effects?

A series of organic reactions proceed dramatically faster in a heterogeneous mixture of the reactants and water than in a homogeneous mixture. Currently it is unclear whether the rate acceleration is due to the free OH groups at the organic-water interface, or due to the hydrodynamic effects caused by vigorous stirring, vortexing, or ultrasonication. Herein we produced static droplets in microfluidic devices to answer this question. In the work, a series of organic droplets containing diethyl azodicarboxylate (DEAD) and quadricyclane surrounded by water were produced, which were transferred to and confined in glass capillaries to minimize the hydrodynamic effects. The cycloaddition process of DEAD with quadricyclane was recorded by a CCD camera. The results showed the reaction proceeded in three steps, and the organic-water interface alone was catalytically efficient enough to enhance the reaction rate to the same level as in the bulk emulsion reaction, indicating that the hydrodynamic effects were negligible.

A microreactor and imaging platform for studying chemical oscillators.

We present a laser scanning confocal microscopy (LSCM) and continuous flow microreactor (CFMR)-based platform to study the Belousov-Zhabotinsky (BZ) oscillators. We demonstrated that the scanning laser light below a certain power had no detectable influence on the BZ reaction. The CFMR consisted of the poly(methyl methacrylate) (PMMA) microwell and the polydimethylsiloxane (PDMS) microchannel and maintained the oscillation with a continuous supply of the catalyst-free BZ mixture. The synchronization of the two nonidentical oscillators was studied by the platform. The coupling intensity was controlled by changing the distance between the two oscillators. Results showed that the synchronization occurred as the oscillators were closer than a critical distance. The transition from desynchronization to synchronization was observed when the distance between the oscillators was near a critical value. The results of the numerical simulation by COMSOL agreed qualitatively with the experimental observation.

Single-chain polymers achieved from radical polymerization under single-initiator conditions.

Radical polymerization from a single initiator molecule in a microenvironment is a nearly ideal system in which bimolecular termination, solution concentration, and viscosity changes could be neglected. In this study, we provide two facile methods of preparing polymers via atom-transfer radical polymerization (ATRP) under single-initiator conditions: tether initiators on planar substrates at superlow density through mixed self-assembled monolayers (SAMs) and encapsulated single initiators in microfluidic droplets. The molecular weight (MW) of the resultant polymers characterized by atomic force microscope-based single-molecule force spectroscopy (AFM-based SMFS) showed that the single-chain ATRP had an extraordinarily faster chain propagation rate (2 unit/s) on planar substrates and gave polymers with much higher MWs (10(5)-10(6) g/mol) than those obtained from traditional ATRP (10(3)-10(5) g/mol). The former method offered a general platform for single-chain polymer synthesis and investigation, and the latter could be amplified to obtain abundant single-chain polymers with ultrahigh molecular weight (UHMW) for commercial applications.

Patterning Perfluorinated Surface with Graphene Oxide and the Microarray Applications.

A method was developed to pattern the surface of perfluorinated materials with graphene oxide thin film, and various biological applications of the patterned perfluorinated surface were illustrated. Perfluorinated surfaces such as Teflon, Cytop, and other perfluorinated materials are known to be both hydrophobic and oleophobic, with low adhesion for most materials. Modifying the perfluorinated surfaces has been difficult due to the extraordinary chemical inertness, which limits the applications of perfluorinated materials as anti-fouling substrates. Herein we successfully patterned Cytop surfaces with graphene oxide. Patterns of the graphene oxide thin film with feature dimension down to 40 microns were formed and remained stable on the Cytop surface against washing with water, ethanol and acetone. The graphene oxide thin film on the Cytop surface allowed non-specific protein adsorption. To illustrate the applications of the patterned Cytop surface, we used the patterned Cytop surface as the substrate to study the protein-protein interactions, stem cell culture, and stem cell proliferation.

Novel Substrates for Microarrays.

In the microarray platform, the surface substrate is critical to the result quality in terms of signal consistency and detection sensitivity. Traditional substrates such as glass and nitrocellulose often entail complicated preparation processes such as the activation and functionalization of the reaction spots and surface blocking to prevent nonspecific molecule adsorption. In addition, coffee-ring morphology of the spots is a common issue in the traditional substrates. To address these issues, we introduced a novel substrate based on fluorinated ethylene propylene (FEP) membrane for microarrays.