Due to the lack of development in the area of sample preparation, few complete lab-on-a-chip systems have appeared in recent years that can deal with raw samples. Cell lysis and nucleic acid extraction systems are sufficiently complex even before adding the complexity of an analysis system. In this review, a variety of microfluidic sample preparation methods are discussed and evaluated. Microsystems for cell lysis are discussed by grouping them into categories based on their lysis mechanisms: mechanical, chemical, thermal or electrical. We classify the nucleic acid purification techniques according to the mechanism that links nucleic acids to substrates: silica-based surface affinity, electrostatic interaction, nanoporous membrane filtration, and functionalized microparticles. The techniques for microfluidic cell lysis and nucleic acid purification are compared based on the ease of microfabrication and integration, and sample flexibility. These assessments can help us determine the appropriate sample preparation technique for generating a true lab-on-a-chip.

An automated microfluidic nucleic extraction system was fabricated with a multilayer polydimethylsiloxane (PDMS) structure that consists of sample wells, microvalves, a micropump and a disposable microfluidic silica cartridge. Both the microvalves and micropump structures were fabricated in a single layer and are operated pneumatically using a 100 μm PDMS membrane. To fabricate the disposable microfluidic silica cartridge, two-cavity structures were made in a PDMS replica to fit the stacked silica membranes. A handheld controller for the microvalves and pumps was developed to enable system automation. With purified ribonucleic acid (RNA), whole blood and E. coli samples, the automated microfluidic nucleic acid extraction system was validated with a guanidine-based solid phase extraction procedure. An extraction efficiency of ∼90% for deoxyribonucleic acid (DNA) and ∼54% for RNA was obtained in 12 min from whole blood and E. coli samples, respectively. In addition, the same quantity and quality of extracted DNA was confirmed by polymerase chain reaction (PCR) amplification. The PCR also presented the appropriate amplification and melting profiles. Automated, programmable fluid control and physical separation of the reusable components and the disposable components significantly decrease the assay time and manufacturing cost and increase the flexibility and compatibility of the system with downstream components.

SUMMARY A commercial kit for the radioisotopic assay of folate in serum, the Bio-Rad 'Quanta Count' folate kit, produced lower results than the Lactobacillus casei microbiological assay method.Its normal range was 2-0-13 0,ug/l and the reproducibility was similar to that of the microbiological assay method. The kit was also satisfactory for whole blood folate assays. The cost requires careful consideration before the kit is used for routine purposes.For many years most laboratories have depended upon a microbiological technique for folate assays. Radioisotope methods using tritium or carbon-14 labels have been available, but their use has been limited by the expense of appropriate counting equipment. Recently, however, several commercial kits using radioiodinated labelled folate compounds, measurable in widely used gamma counters, have appeared, and we here report our experiences with one of them including comparison with a microbiological assay. Material and methods RADIOISOTOPE TECHNIQUE'Quanta Count' folate kits were supplied by Bio-Rad Laboratories Ltd. The radio-ligand method is based on the principle of saturation analysis. Each kit contains iodine-125 (1251) labelled pteroyl glutamic acid (Pte-Glu) derivative, borate buffer pH 9-6, absorbent charcoal tablets, and ,8 lactoglobulin as binding agent. The six standards supplied consist of lyophilised folate-free human serum containing varying amounts of Pte-Glu, range 0-20 ug/l when reconstituted. The kits available are sufficient for testing 44 or 94 unknown samples in duplicate; 0-1 ml of sample is diluted in 1-0 ml of isotope in borate buffer. The diluted samples are heated for 15 minutes in a boiling bath and cooled to room temperature; 1I0 ml of binder is added and the samples are incubated at room temperature for 30 minutes. An absorbent tablet is added to each tube and, after vortex mixing, the tubes are centrifuged.