PDMS flow cells

In a second experiment, Cy5-labelled antiBSA antibodies were immobilised on a silanised glass slide precoated with metallic nanoislands using a polydimethylsiloxane (PDMS) flow-cell. The antibody solution was left for 1 hour to attach and then the cell was flushed with deionised water. The slide was then dried with N2. For this experiment, a portion of the slide was not coated with metallic nanoislands, in order to act as a reference. Figure 20 shows the image recorded using the fluorescence laser scanner mentioned previously. The enhancement in fluorescence emission between those areas with and without nanoislands (B and A, respectively) is again evident. For both chips, an enhancement factor of approximately 8 was recorded. There is considerable interest in the elucidation and exploitation of plasmonic effects for fluorescence-based biosensors and other applications. 

Besides silicon, other materials have also been used in micro fuel cells. Cha et al. [79] made micro-FF channels on SU8 sheets—a photosensitive polymer that is flexible, easy to fabricate, thin, and cheaper than silicon wafers. On top of fhe flow channels, for both the anode and cathode, a paste of carbon black and PTFE is deposited in order to form the actual diffusion layers of the fuel cell. Mifrovski, Elliott, and Nuzzo [80] used a gas-permeable elastomer, such as poly(dimethylsiloxane) (PDMS), as a diffusion layer (with platinum electrodes embedded in it) for liquid-electrolyte-based micro-PEM fuel cells. 

The experimental setup for the PDMS-E microreactor system is shown in Fig. 5. Reactor effluent was analyzed by a Hewlett Packard 1100 HPLC (UV-Vis detector) and an Ocean Optics SD 2000 UV-Vis Spectrometer with fiberoptic flow analysis "Z" cells (FIA Lab). 

A similar PDMS valve control layer was used to achieve rotary liquid pumping for PCR [357]. In another report, a similar valving method was used to deliver cells and to introduce reagents for cell reactions. Solutions were pumped at 5-60 Hz to achieve a linear flow rate of 300-1000 pm/s [368]. 

A single neuron-like PC 12 cell was trapped in an etched glass (30 pm deep) pocket sealed against a PDMS channel layer (20 pm). Quantal release of dopamine (in transient exocytosis) from the cell as stimulated by nicotine was amper-ometrically detected with a carbon fiber electrode. The cells flow into the channels caused by the liquid pressure which was provided by a liquid height at the sample reservoir (e.g., 0.5-2 mm). To facilitate transport of cells in the microchannels, the cell density should not be higher than lOVmL. Serious cell adhesion occurred if the transport speed was low (as provided by liquid height below 0.5 mm),... 

A 2D microwell array was used to trap CHO cells in a chamber containing a weir. Flow control was achieved by pneumatic valving on a PDMS chip. Once the cells were introduced into the chamber, its opening was sealed by valve closure to retain the cells. To show a cell reaction, the cells were lysed by deionized water [843],... 

On the other hand, multiple laminar flow was used to pattern cells and their environments in PDMS chips [858]. For instance, two cell types (chicken erythrocyte and Escherichia coli) have been shown to deposit next to each other on fibronectin-treated surfaces (see Figure 8.17). Moreover, cell detachment occurred only to the cells (BCE) that was passed with a patterned stream containing trypsin/EDTA [858]. 

Chick embryo heart muscle cells were patterned and grown on a fibronectin (FN) surface patterned by PDMS stamping. The PBS solution (containing Ca2+ and K+) was used to stimulate spontaneous muscle contraction [198]. Laminar flows provide a reaction path (buffer plus 1-octanol) and a control patch (buffer only) for study of communication between excitable cells (cardiomyocytes) through gap junctions (see Figure 8.18) [198]. 

Optical traps have also been used to retain cells [176,866-868,1174]. For instance, manipulation of polystyrene beads by optical gradient force (attractive) and scattering force (repulsive) was achieved in a PDMS chip (see Figure 8.26). A polystyrene bead was first retained by an optical trap. Then the bead was moved and released so that it flowed to a desired channel downstream [1174]. 

The flow of leukocytes was studied in square capillaries fabricated on a Si chip, and sealed with a PDMS or Pyrex cover plate. This capillary size (cross section of 4 pm2) is similar to the diameter of a human blood capillary, but is less than both the average diameter of a leukocyte cell (10 pm) and its nucleus (6 pm). Figure 8.32 shows the difference in the flow behavior of two leukocytes (possibly neutrophils) [1175]. Deformation-induced release of ATP from erythrocytes in PDMS channels was studied. The released ATP was detected by chemiluminescence using the luciferin/luciferase system [169]. 

A two-phase air-liquid flow was developed on a PDMS chip (see also Chapter 3, section 3.1.2). It was found that the focused two-phase flow was stable in hydrophobic channels (down to 6 mL/h) see Figure 8.38. Below this flow rate, the sample column no longer maintained its integrity and broke up. This method was used to provide aerodynamic focusing of myoblast cells (C2Ci2) for the flow cytometry study. The cells, which were labeled with Syto 9, was focused and counted in the chip at a rate of 100 cells/s [382]. 

Figure 11. (A) Scheme of the PDMS microfluidic device. Inset channel crossing with the cell trap composed of microstmctured obstacles, (B) Scanning electron micrograph of the cell trap, (C) single cell in a channel navigated by optical tweezers in the microchannel, (D-G) optical micrographs of a single cell at the injection position during SDS lysis. SDS flow is from channel 4 through the cell trap into channel 2.

All details of the pure continents relative molecular mass and rheology, and experimental setup of the ear cell are in reference (5). PIB and PDMS samples behave as Newtonian liquids under the experimental conditions hoe with shear viscosities of 10 Pa-s each (25 °C). The gap width between parallel plates in the Linkam CSS-450 shear cell was consistently set to 36 pm (standard uncertainty 3 pm verified optically by microscope stage translation), with all observations in the vorticity-flow plane. 

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