Search

A local area temperature monitor is important for precise control of chemical and biological processes in microfluidics. In this work, we developed a facile method to realize micron spatial resolution of temperature mapping in a microfluidic channel quickly and cost effectively. Based on the temperature dependent fluorescence emission of NaYF4:Yb3+, Er3+ upconversion nanoparticles (UCNPs) under near-infrared irradiation, ratio-metric imaging of UCNPs doped polydimethylsiloxane can map detailed temperature distribution in the channel. Unlike some reported strategies that utilize temperature sensitive organic dye (such as Rhodamine) to achieve thermal sensing, our method is highly chemically inert and physically stable without any performance degradation in long term operation. Moreover, this method can be easily scaled up or down, since the spatial and temperature resolution is determined by an optical imaging system. Our method supplied a simple and efficient solution for temperature mapping on a heterogeneous surface where usage of an infrared thermal camera was limited. [ABSTRACT FROM AUTHOR]

Electrodeless dielectrophoresis is the best choice to achieve preconcentration of nanoparticles and biomolecules due to its simple, robust, and easy implementation. We designed a simple chip with microchannels and nano-slits in between and then studied the trapping of DNA in high conductive medium and low conductive medium, corresponding to positive and negative dielectrophoresis (DEP), respectively. It is very important to investigate the trapping in media with different conductivities since one always has to deal with the sample solutions with different conductivities. The trapping process was analyzed by the fluorescent intensity changes. The results showed that DNA could be trapped at the nano-slit in both high and low conductive media in a lower electric field strength (10 V/cm) compared to the existing methods. This is a significant improvement to suppress the Joule heating effect in DEP related experiments. Our work may give insight to researchers for DNA trapping by a simple and low cost device in the Lab-on-a-Chip system. [ABSTRACT FROM AUTHOR]

We report a simple, low-cost and detachable microfluidic chip incorporating easily accessible paper, glass slides or other polymer films as the chip materials along with adhesive wax as the recycling bonding material. We use a laser to cut through the paper or film to form patterns and then sandwich the paper and film between glass sheets or polymer membranes. The hot-melt adhesive wax can realize bridge bonding between various materials, for example, paper, polymethylmethacrylate (PMMA) film, glass sheets, or metal plate. The bonding process is reversible and the wax is reusable through a melting and cooling process. With this process, a three-dimensional (3D) microfluidic chip is achievable by vacuating and venting the chip in a hot-water bath. To study the biocompatibility and applicability of the wax-based microfluidic chip, we tested the PCR compatibility with the chip materials first. Then we applied the wax-paper based microfluidic chip to HeLa cell electroporation (EP). Subsequently, a prototype of a 5-layer 3D chip was fabricated by multilayer wax bonding. To check the sealing ability and the durability of the chip, green fluorescence protein (GFP) recombinant Escherichia coli(E. coli) bacteria were cultured, with which the chemotaxis of E. coliwas studied in order to determine the influence of antibiotic ciprofloxacin concentration on the E. colimigration. [ABSTRACT FROM AUTHOR]

Surface enhanced Raman spectroscopy (SERS) detection in microfluidics is an interesting topic for its high sensitivity, miniaturization and online detection. In this work, a SERS detection in microfluidics with the help of the Ag nanowire aggregating based on dielectrophoresis (DEP) is reported. The Raman intensities of molecule in microfluidics is greatly enhanced in the naturally generated nanogaps of Ag nanowire aggregating modulated by DEP. Firstly, the influence of DEP voltage and time on Ag nanowire aggregating is investigated to figure out the optimal condition for SERS. And then, the SERS intensities of methylene blue and rhodamine6G at various concentration with high reproducibility and uniformity are studied. Furthermore, the experiment data demonstrate this DEP–SERS system could be repeated used for different molecule detections. At last, the SERS of melamine is measured to explore its application on food safety. Our work anticipates this nanowire assisted repeatable DEP–SERS detection in microfluidics with high sensitivity could meet the emerging needs in environmental pollution monitoring, food safety evaluation, and so on. [ABSTRACT FROM AUTHOR]

The effect of the chain length of polyvinyl pyrrolidone (PVP) on the structures of silver nanowires (AgNWs) is explored in this study. It was found in the experiments that PVP, when serving as a capping agent, has a great impact on the morphology and structure of AgNWs. By means of a series of experiments and the inquiry of the growth mechanism, the critical minimum PVP chain length for the successful formation of uniform nanowires was discovered, below which only nanoparticles or short nanorods can be obtained. Surprisingly, a core–shell structure of a nanowire with a polycrystal was observed when PVP with a very long chain length was employed in the processing. [ABSTRACT FROM AUTHOR]