Microfluidics pumping method

The liquid pumping in the microfluidic chip is mostly achieved by using electro-osmotic flow (EOF) [324]. Other liquid pumping methods have also been employed for microfluidic flow. Flow has been employed for fraction collection and generation of concentration gradient. Laminar flow in the microfluidic channel allows liquid-liquid extraction and microfabrication to occur within the channels. Moreover, valving and mixing are needed in order to achieve a better flow control. All these microfluidic flow operations are further described in subsequent sections. 

Walker, G.M., Beebe, D.J., A passive pumping method for microfluidic devices. Labchip 2002, 2, 131-134. 

A number of microfluidic circuits have been developed their principles of operation depend on the mechanism of fluid flow in the microchip. In this entry, we shall describe only the fluidic circuits used with pressure-driven flow and electrokinetically driven flow, as these are the two main pumping methods for continuous-flow microfluidic devices. Pressure-driven flow can be obtained by connecting the channel to a syringe pump or a compressed gas. Electroki-netic flow of an ionized electrolyte can be obtained by applying an electric field along the flow direction. 

Lim, D., Kamotani, Y., Cho, B., Mazumder, J., Takayama, S., Fabrication of microfluidic mixers and artificial vasculares using a high-brightness diode-pumped Nd YAC laser direct write method, Lab Chip 2003, 3, 318-323. 

With the help of this method, His-tagged L-lactate dehydrogenase was immobilized. By pumping pyruvic acid as substrate with NADH as cofactor, it was demonstrated that the enzyme was still active in the microchannel. In this case, cofactor was used up. Srinivasan et al. [433] incorporated PikC hydroxylase from Streptomyces venezuelae into a PDMS-based microfluidic channel with a similar approach. The enzyme was immobilized to Ni-NTA agarose beads with an in situ attachment, following the addition of the beads to the microchannel. This enabled the rapid hydroxylation of the macrolide YC-17 to methymycin and neomethymycin (Scheme 4.104) in about equal amounts with a conversion of >90% at a flow rate of 70nl/min. 

The fluidity in the neighborhood of probe molecules can be tested by use of probes capable of intramolecular excimer formation. The probe molecules contain the two excimer-forming moieties linked by an alkyl chain. The extent of excimer formation depends on the viscosity of the environment and can be monitored by measuring the excimer/monomer fluorescence intensity ratio. The dependence of this ratio on reciprocal viscosity for the probe molecule dipyrenylpropane is shown in Fig. 18, in which the obtained microfluidities for surfactant systems are indicated. The fluidities decrease in the order SHS microemulsion, SDS, CTAC, Triton X-100 cf. Ref. 167 (for abbreviations see Tables 6 and 7). The same sequence order was found by Kano et al. (68). In systems containing heavy counterions the method leads to data that must be evaluated carefully, since heavy atom interactions may be different with excited monomers and excimers. The intramolecular excimer technique is also useful in biological studies. For instance, Almeida et al. investigated the sarcoplasmic reticulum membrane in which the activity of the Ca -pumping enzyme is modulated by the membrane fluidity (197). 

In the pharmaceutical industry, large sums of money are used for preclinical and cUnical research. The development of a drug costs miUions of dollars. Hundreds of tests have to be conducted. One of the innovative tools in the field of drug discovery is microchip technology. Microchips require less reagent volume, make analytical processes run faster because of their smaller size, and allow more sensitive detection methods to be implemented. In this way, they reduce costs, save time, and improve quality. Microchips come in two main categories chips based on microfluidics, with components such as pumps, mixers, microinjectors, and microarray chips, which have numerous locations of samples, such as DNA samples, on their surface. Most of the interest now seems to be focused on this second category. 

The apparatus used is known as a microfluidizer with a high-pressure positive displacement pump (500-200 PSI). A microfluidizer consists of small channels called microchannels through which product flows on to an impingement area, resulting in very fine particles of submicron range when pressure is applied by the attached pump Similar to the sonication method, this is also useful for small-batch production of nanoemulsions. Shear forces generated by ultrasonic cavitation result in production of vacuum bubbles which disintegrate the particles to nanometer scale... 

Jeon et al. [6] reported a microcharmel network method for generating defined concentration gradients in a microfluidic device. Solutions of different concentrations were introduced into the microfluidic device by syringe pumps at separate inlets and repeatedly mixed and split through the microchannel network, producing multiple diluted streams with predictable concentrations. These streams flowed side by side in a common chaimel and generated a soluble or... 

Some other methods have been reported recently and can be found elsewhere [1, 28], such as surface/bead hybrid method, pump and mixer integrated microfluidic DNA hybridization, hydrogel-based microfluidic DNA hybridization assays, and electrochemical-based DNA hybridization chip. 

Electroosmotic flow has been used as a major pumping mechanism for microfluidic devices. The current monitoring methods, which use electroosmotic flow as a transport mechanism for solution replacement processes, have been used... 

---