lab-on-a-chip « WordPress.com Tag Feed

Stop-flow lithography to generate cell-laden microgel particles

tanlab — Mon, 21 Jul 2008 14:19:20 +0000

Encapsulating cells within hydrogels is important for generating three-dimensional (3D) tissue constructs for drug delivery and tissue engineering. This paper describes, for the first time, the fabrication of large numbers of cell-laden microgel particles using a continuous microfluidic process called stop-flow lithography (SFL). Prepolymer solution containing cells was flowed through a microfluidic device and arrays of individual particles were repeatedly defined using pulses of UV light through a transparency mask. Unlike photolithography, SFL can be used to synthesize microgel particles continuously while maintaining control over particle size, shape and anisotropy. Therefore, SFL may become a useful tool for generating cell-laden microgels for various biomedical applications.

http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=b804234a&JournalCode=LC

Gold nanoparticles for one step DNA extraction and real-time PCR of pathogens in a single chamber

tanlab — Fri, 11 Jul 2008 20:53:41 +0000

The optothermal properties of nanoparticles are of interest for biosensors and highly sensitive biochip applications. In this respect, the longitudinal resonance of Au nanorods was used to transform near infrared energy into thermal energy in a microfluidic chip. The resulting heat generated effectively caused pathogen lysis. Consequently the DNA was extracted out of the cell body and transferred to a PCR system. This resulted in the successful demonstration of a one step real-time PCR system for pathogen detection without removal or changing of reagents.

http://www.rsc.org/ej/LC/2008/b717382b.pdf

Immobilization of DNAzyme catalytic beacons on PMMA for Pb2+ detection

tanlab — Fri, 11 Jul 2008 20:47:02 +0000

Due to the numerous toxicological effects of lead, its presence in the environment needs to be effectively monitored. Incorporating a biosensing element within a microfluidic platform enables rapid and reliable determinations of lead at trace levels. A microchip-based lead sensor is described here that employs a lead-specific DNAzyme (also called catalytic DNA or deoxyribozyme) as a recognition element that cleaves its complementary substrate DNA strand only in the presence of cationic lead (Pb²⁺). Fluorescent tags on the DNAzyme translate the cleavage events to measurable, optical signals proportional to Pb²⁺ concentration. The DNAzyme responds sensitively and selectively to Pb²⁺, and immobilizing DNAzyme in the sensor permits both sensor regeneration and localization of the detection zone. Here, the DNAzyme has been immobilized on a PMMA surface using the highly specific biotin–streptavidin interaction. The strategy includes using streptavidin physisorbed on a PMMA surface to immobilize DNAzyme both on planar PMMA and on the walls of a PMMA microfluidic device. The immobilized DNAzyme retains its Pb²⁺ detection activity in the microfluidic device and can be regenerated and reused. The DNAzyme shows no response to other common metal cations and the presence of these contaminants does not interfere with the lead-induced fluorescence signal. While prior work has shown lead-specific catalytic DNA can be used in its solubilized form and while attached to gold substrates to quantitate Pb²⁺ in solution, this is the first use of the DNAzyme immobilized within a microfluidic platform for real time Pb²⁺ detection.

http://www.rsc.org/ej/LC/2008/b718624j.pdf

Nano-biopower supplies for biomolecular motors: the use of metabolic pathway-based fuel generating systems in microfluidic devices

tanlab — Fri, 11 Jul 2008 20:42:13 +0000

We report fuel generation systems for molecular motors based on pyruvate kinase, or for the first time, mitochondria, implemented within microfluidic devices. Intact organelles acted as bio-nanopower supplies for molecular motors, using isolated mitochondria to convert chemical energy from succinate to ATP, harnessing nature's enzymatic transformation cascades directly. Motors were activated essentially equally by ATP produced by pyruvate kinase, mitochondria, or direct addition of ATP.

http://www.rsc.org/ej/LC/2008/b801033a.pdf

Electrically controlled microvalves to integrate microchip polymerase chain reaction and capillary electrophoresis

tanlab — Fri, 11 Jul 2008 20:34:55 +0000

Microvalves are key in realizing portable miniaturized diagnostic platforms. We present a scalable microvalve that integrates well with standard lab on a chip (LOC) implementations, yet which requires essentially no external infrastructure for its operation. This electrically controlled, phase-change microvalve is used to integrate genetic amplification and analysis via capillary electrophoresis—the basis of many diagnostics. The microvalve is actuated using a polymer (polyethylene glycol, PEG) that exhibits a large volumetric change between its solid and liquid phases. Both the phase change of the PEG and the genetic amplification via polymerase chain reaction (PCR) are thermally controlled using thin film resistive elements that are patterned using standard microfabrication methods. By contrast with many other valve technologies, these microvalves and their control interface scale down in size readily. The novelty here lies in the use of fully integrated microvalves that require only electrical connections to realize a portable and inexpensive genetic analysis platform.

http://www.rsc.org/delivery/_ArticleLinking/DisplayArticleForFree.cfm?doi=b802853b&JournalCode=LC

Cell research with physically modified microfluidic channels: A review

tanlab — Fri, 11 Jul 2008 20:27:59 +0000

An overview of the use of physically modified microfluidic channels towards cell research is presented. The physical modification can be realized either by combining embedded physical micro/nanostructures or a topographically patterned substrate at the micro- or nanoscale inside a channel. After a brief description of the background and the importance of the physically modified microfluidic system, various fabrication methods are described based on the materials and geometries of physical structures and channels. Of many operational principles for microfluidics (electrical, magnetic, optical, mechanical, and so on), this review primarily focuses on mechanical operation principles aided by structural modification of the channels. The mechanical forces are classified into (i) hydrodynamic, (ii) gravitational, (iii) capillary, (iv) wetting, and (v) adhesion forces. Throughout this review, we will specify examples where necessary and provide trends and future directions in the field.

http://www.rsc.org/ej/LC/2008/b800835c.pdf

Spy watch for insta-DNA testing?

Mark Baard — Tue, 06 May 2008 14:58:20 +0000

Parallelnormal is back on-line after a recent "health scare." Please keep your comments and feedback coming! -- mb

Scientists in authoritarian-ruled Singapore say they've developed a DNA identification assay-on-a-chip that also preps a drop of blood for sampling. This means any one of us might be just a pinprick away from being instantly Identified as a threat. (The watch, below, is one possible form-factor for the DNA tester.)

From the Institute for Bioengineering and Nanotechnology:

...a rapid test for genetic diagnosis that combines the preparation of biological samples with a polymerase chain reaction PCR on one chip. As they report in the journal Angewandte Chemie, the “laboratory device” for all steps in this system is a single drop containing magnetic nanoparticles, which is moved across the chip by a magnetic field.