Droplet based microfluidics lab-on-a-chip

V. Srinivasan, V.K. Pamula, and R.B. Fair Droplet-Based Microfluidic Lab-on-a-Chip for Glucose Detection. Anal. Chim. Acta 507, 145 (2004). 

Srinivasan, V., Pamula, V. K., Fair, R. B. (2004). Droplet-based microfluidic lab-on-a-chip for glucose detection. Analytica ChimicaActa, 507, 145-150. 

Srinivasan V, Pamula VK, Fair RB (2004) Droplet-based microfluidic Lab-on-a-Chip for glucose detection. Anal Chim Acta 507(1) 145-150... 

Shestopalov, J. D. Tice, and R. F. Ismagilov, Multi-step synthesis of nanoparticles performed on millisecond time scale in a microfluidic droplet-based system, Lab on A Chip, vol. 4, no. 4, pp. 316-321, 2004. 

A digital microfluidic lab-on-a-chip based on electrowetting actuation of droplets has been demonstrated for the deteetion of 2,4,6-trinitrotoluene (TNT). We have used DMSO as a solvent instead of aeetone or acetonitrile which is commonly used. We have demonstrated a linear range of deteetion for TNT between 12.5 pg/mL - 50 pg/mL in less than 5 minutes. We have also demonstrated simultaneous deteetion of various eoneentrations of TNT and feasibility of detection of 2,4-dinitrotoluene (DNT). Future work would involve inereasing the detection limits of the system from pg/mL to ng/mL and simultaneous deteetion of other nitroaromaties sueh as DNT and TNB. 

Chen, H., Fang, Q., Ym, X. R, and Fang, Z. L., Microfluidic chip-based liquid-hquid extraction and preconcentration using a subnanoliter-droplet trapping technique. Lab on a Chip, 5, 719-725, 2005. 

M.G. Pollack, A.D. Shenderov, R.B. Fair, Electrowetting-based actuation of droplets for integrated microfluidics. Lab on a Chip, 2002, 2, 96-101. 

Microfluidics is a key functionality in the success of microdevices. It is defined as a branch of physics and biotechnology that studies the behavior of fluids at tire microscale and mesoscale, volumes thousands of times smaller than a common droplet. It also concerns the design of systems in which such small volumes of fluids will be used. For example, the gene chips and labs-on-a-chip are based on the transport of nanoliter or picoliter volumes of fluids through microchannels within a glass or plastic chip. 

A. Bransky, N. Korin, M. Khoury, and S. Levenberg, A microfluidic droplet generator based on a piezoelectric actuator, Lab on a Chip, 9, 516-520,... 

P. Paik, V.K. Pamula and R.B. Fair, Electrowetting-based droplet mixers for microfluidic systems, Lab on a chip 3 (2003) 28-33. 

Droplet-based Lab-on-a-Chip devices represent a class of microfluidic systems that have been developed to miniaturize chemical, biochemical, or cellular analysis. These devices utilize various droplet dispensing and manipulatiOTi mechanisms to isolate and control liquid-phase droplets of samples and/or reagents surrounded by a gas or an immiscible liquid. The droplets may be completely surrounded by the medium or may be placed onto a solid surface whose material properties are chosen to provide droplet confinement, chemical functionalization, or control of droplet motion. The devices also have some type of assay readout method with associated hardware, software, and data display. 

The droplet-based microfluidic platforms for Lab-on-a-Chip applications can be fundamentally divided into two basic setups, the channel-based and the planar surface approach [2]. The channel-based systems are mostly pressure driven with droplet generation and manipulation relying on actuation via liquid flows within closed microchaimels. For the planar surface-based platforms, droplets can be arbitrarily moved in two dimensions representing planar programmable Lab-on-Chips. They are actuated by electrowetting (EWOD) or surface acoustic waves (SAW). 

In droplet-based microfluidics, these reaction vessels are formed by droplets of a dispersed phase, which are embedded into a continuous phase. Both liquid phases are immiscible. A huge amount of such droplet reactors can be generated, transported, controlled, and processed in parallel in a droplet-based lab-on-a-chip device. These devices can be characterized as application specific microfiuidic networks that implement and automate a conventional laboratory workflow in a microfluidic chip device or system. They are built up by appropriately intercoimecting microfluidic operation units, which provide the required laboratory operations at the microscale. Consequently, for each conventional laboratory operation, its microscale counterpart is required. 

Starting after the turn of the millennium with the exploration of droplet-based microfluidic operations and conceptional work on initial application concepts, recent research activities are directed toward an efficient, model-based design and cost-efficient preparation of droplet-based lab-on-a-chip devices. 

This actuation concept can be used for transport and sorting applications in droplet-based microfluidics. The results show the potential use of ferrofluid droplets as both a vehicle and a microreaction platform for droplet-based Lab-on-a-Chip applications. 

P. Paik, V.K. Pamula, M.G. Pollack, R.B. Fair, Electrowetting-based droplet mixers for microfluidic systems. Lab on a Chip, 3, pp. 28 (2003) V. Srinivasan, V. Pamula, M. Pollack, R. Fair, A digital microfluidic biosensor for multianalyte detection. Proceedings of the IEEE 16th Annual International Conference on Micro Electro Mechanical Systems, p. 327 (2003). 

In previous chapters, many emerging microlenses based on various mechanisms covering non-tunable and tunable types were presented. However, these microlenses have their optical axes perpendicular to the substrates, thus requiring optical alignment of the different layers. This causes complicated structures for applications such as labs on chips. In this chapter, we discuss horizontal microlenses integrated in microfluidics. Their optical axes are parallel to the substrates of the microfluidic networks. These horizontal microlenses include those formed by a hot embossing process hydrodynamically tuned cylindrical microlenses and tunable and movable liquid droplets as microlenses. 

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