Fluidics

Byoung-Hwa Kwon, Kyoung G. Lee, Tae Jung Park, Hyunki Kim, Tae Jae Lee, Seok Jae Lee, Duk Young Jeon

ZnSe/ZnS core/shell quantum dots (QDs) with efficient blue emission are in situ synthesized using a novel microfluidic reaction system. This advances research on both simple one-step synthesis of core/shell QDs and their production using thermoplastic-based microfluidic reaction systems. Furthermore, QD light-emitting diodes (LEDs) are demonstrated using ZnSe/ZnS QDs as wavelength converters.

Smal

lVolume 8, Issue 21, pages 3257–3262, November 5, 2012

DOI: 10.1002/smll.201200773

Eunpyo Choi ,  Hyung-kwan Chang ,  Chae Young Lim ,  Taesung Kim and Jungyul Park

We present a robust microfluidic platform for the stable generation of multiple chemical gradients simultaneously using in situ self-assembly of particles in microchannels. This proposed device enables us to generate stable and reproducible diffusion-based gradients rapidly without convection flow: gradients are stabilized within 5 min and are maintained steady for several hours. Using this device, we demonstrate the dynamic position control of bacteria by introducing the sequential directional change of chemical gradients. Green Fluorescent Protein (GFP)-expressing bacterial cells, allowing quantitative monitoring, show not only tracking motion according to the directional control of chemical gradients, but also the gradual loss of sensitivity when exposed to the sequential attractants because of receptor saturation. In addition, the proposed system can be used to study the preferential chemotaxis assay of bacteria toward multiple chemical sources, since it is possible to produce multiple chemical gradients in the main chamber; aspartate induces the most preferential chemotaxis over galactose and ribose. The microfluidic device can be easily fabricated with a simple and cost effective process based on capillary pressure and evaporation for particle assembly. The assembled particles create uniform porous membranes in microchannels and its porosity can be easily controlled with different size particles. Moreover, the membrane is biocompatible and more robust than hydrogel-based porous membranes. The proposed system is expected to be a useful tool for the characterization of bacterial responses to various chemical sources, screening of bacterial cells, synthetic biology and understanding many cellular activities.

Lab Chip, 2012,12, 3968-3975
DOI: 10.1039/C2LC40450H 

Zhi Zhu, Wenhua Zhang, Xuefei Leng, Mingxia Zhang, Zhichao Guan, Jiangquan Lu and Chaoyong James Yang

Genetic alternations can serve as highly specific biomarkers to distinguish fatal bacteria or cancer cells from their normal counterparts. However, these mutations normally exist in very rare amount in the presence of a large excess of non-mutated analogs. Taking the notorious pathogen E. coli O157:H7 as the target analyte, we have developed an agarose droplet-based microfluidic ePCR method for highly sensitive, specific and quantitative detection of rare pathogens in the high background of normal bacteria. Massively parallel singleplex and multiplex PCR at the single-cell level in agarose droplets have been successfully established. Moreover, we challenged the system with rare pathogen detection and realized the sensitive and quantitative analysis of a single E. coli O157:H7 cell in the high background of 100 000 excess normal K12 cells. For the first time, we demonstrated rare pathogen detection through agarose droplet microfluidic ePCR. Such a multiplex single-cell agarose droplet amplification method enables ultra-high throughput and multi-parameter genetic analysis of large population of cells at the single-cell level to uncover the stochastic variations in biological systems.

Lab Chip, 2012,12, 3907-3913
DOI: 10.1039/C2LC40461C 

Gerardo Perozziello, Rosanna La Rocca, Gheorghe Cojoc, Carlo Liberale, Natalia Malara, Giuseppina Simone, Patrizio Candeloro, Andrea Anichini, Luca Tirinato, Francesco Gentile, Maria Laura Coluccio, Ennio Carbone, Enzo Di Fabrizio

This study aims to adoptively reduce the major histocompatibility complex class I (MHC-I) molecule surface expression of cancer cells by exposure to microfluid shear stress and a monoclonal antibody. A microfluidic system is developed and tumor cells are injected at different flow rates. The bottom surface of the microfluidic system is biofunctionalized with antibodies (W6/32) specific for the MHC-I molecules with a simple method based on microfluidic protocols. The antibodies promote binding between the bottom surface and the MHC-I molecules on the tumor cell membrane. The cells are injected at an optimized flow rate, then roll on the bottom surface and are subjected to shear stress. The stress is localized and enhanced on the part of the membrane where MHC-I proteins are expressed, since they stick to the antibodies of the system. The localized stress allows a stripping effect and consequent reduction of the MHC-I expression. It is shown that it is possible to specifically treat and recover eukaryotic cells without damaging the biological samples. MHC-I molecule expression on treated and control cell surfaces is measured on tumor and healthy cells. After the cell rolling treatment a clear reduction of MHC-I levels on the tumor cell membrane is observed, whereas no changes are observed on healthy cells (monocytes). The MHC-I reduction is investigated and the possibility that the developed system could induce a loss of these molecules from the tumor cell surface is addressed. The percentage of living tumor cells (viability) that remain after the treatment is measured. The changes induced by the microfluidic system are analyzed by fluorescence-activated cell sorting and confocal microscopy. Cytotoxicity tests show a relevant increased susceptibility of natural killer (NK) cells on microchip-treated tumor cells.

Small
Volume 8, Issue 18, pages 2886–2894, September 24, 2012
DOI: 10.1002/smll.201200160

Deying Xia, Juchao Yan, Shifeng Hou

With the development of nanotechnology, great progress has been made in the fabrication of nanochannels. Nanofluidic biochips based on nanochannel structures allow biomolecule transport, bioseparation, and biodetection. The domain applications of nanofluidic biochips with nanochannels are DNA stretching and separation. In this Review, the general fabrication methods for nanochannel structures and their applications in DNA analysis are discussed. These representative fabrication approaches include conventional photolithography, interference lithography, electron-beam lithography, nanoimprint lithography and polymer nanochannels. Other nanofabrication methods used to fabricate unique nanochannels, including sub-10-nm nanochannels, single nanochannels, and vertical nanochannels, are also mentioned. These nanofabrication methods provide an effective way to form nanoscale channel structures for nanofluidics and biosensor devices for DNA separation, detection, and sensing. The broad applications of nanochannels and future perspectives are also discussed.

Small

Volume 8, Issue 18, pages 2787–2801, September 24, 2012

DOI: 10.1002/smll.201200240

Jason C. Harper, Thayne L. Edwards, Travis Savage, Svetlana Harbaugh, Nancy Kelley-Loughnane, Morley O. Stone, C. Jeffrey Brinker, Susan M. Brozik

This is the first report of a living cell-based environmental sensing device capable of generating orthogonal fluorescent, electrochemical, and colorimetric signals in response to a single target analyte in complex media. Orthogonality is enabled by use of cellular communities that are engineered to provide distinct signals in response to the model analyte. Coupling these three signal transduction methods provides additional and/or complementary data regarding the sample which may reduce the impact of interferants and increase confidence in the sensor's output. Long-term stability of the cells was addressed via 3D entrapment within a nanostructured matrix derived from glycerated silicate, which allows the device to be sealed and stored under dry, ambient conditions for months with significant retention in cellular activity and viability (40% viability after 60 days). Furthermore, the first co-entrapment of eukaryotic and bacterial cells in a silica matrix is reported, demonstrating multianalyte biodetection by mixing disparate cell lines at intimate proximities which remain viable and responsive. These advances in cell-based biosensing open intriguing opportunities for integrating living cells with nanomaterials and macroscale systems.

Small

Volume 8, Issue 17, pages 2743–2751, September 10, 2012

DOI: 10.1002/smll.201200343

Soojeong Cho ,  Tae Soup Shim and Seung-Man Yang

We describe high-throughput optofluidic platforms for mosaic-patterned microfibers by generating stratified laminar flows. An inert carrier liquid flow near PDMS channel walls conveyed a photopolymerizable liquid which permitted stable production of microfibers with particular morphologies and compositional patterns. Finally, mosaicked microfibers were prepared with desired configurations toward multiplex biomolecular analysis.

Lab Chip, 2012,12, 3676-3679
DOI: 10.1039/C2LC40439G

Luciano De Sio ,  Marilisa Romito ,  Michele Giocondo ,  Andreas E. Vasdekis ,  Antonio De Luca and Cesare Umeton

We report on the fabrication and characterization of a new generation of electro-switchable optofluidic devices based on flexible substrates, combined with the extraordinary properties of reconfigurable soft-materials. A conductive polydimethylsiloxane microstructure has been first sputtered with an Indium Tin Oxide (ITO) layer and then functionalized with an amorphous film of SiOx. Then, the “layer” by “layer” microstructure has been infiltrated with an anisotropic and reconfigurable fluid (Nematic Liquid Crystal, NLC). The sample has been characterized in terms of morphological, optical and electro-optical properties: the soft-conductive microstructure exhibits a uniform and regular morphology, even after testing with mechanical stretching and deformations. Combination of the conductive ITO with the functionalization film (which has been employed for inducing in-plane alignment of NLC molecules) enables us to carry out a series of optical and electro-optical experiments; these confirm excellent properties in terms of a reconfigurable device and a diffractive element as well.

Lab Chip, 2012,12, 3760-3765
DOI: 10.1039/C2LC40668C