Lab-on-chip systems are a class of miniaturized analytical devices that integrate fluidics, electronics and various sensorics. They are capable of analysing biochemical liquid samples, like solutions of metabolites, macromolecules, proteins, nucleic acids, or cells and viruses. Supplementary to their measuring capabilities, the lab-on-chip devices facilitate fluidic transportation, sorting, mixing, or separation of liquid samples. A type of lab-on-chip devices, named biochip, is devoted specifically to genomic, proteomic and pharmaceutical tests. The significance of such miniaturized devices lies in their potentiality of automating laboratory procedures, which highly reduces the time of biomedical tests and laboratory work. This review summarizes numerous fabrication methods and procedures for producing lab-on-chip devices and also envisages future evolution.

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Measurements and analysis are presented of the incremental magnetic susceptibilities, χ∥(H0) and χ⊥(H0), of magnetic fluids subjected to an external polarizing field, H0. The technique of placing a fluid sample in a cylindrical coil positioned between the poles of a magnet and determining the susceptibility, at a fixed frequency, when the long axis of the sample is (1) parallel (χ∥(H0)) and (2) perpendicular (χ⊥(H0)), to H0, provides a convenient method for the determination of the magnetic moment, and hence the effective particle size, of nano-particles in magnetic fluids. Two magnetic fluids samples consisting of magnetite and cobalt-zinc ferrite particles, respectively, are investigated and the results obtained are found to be in good agreement with those of the manufacturer. As the samples are cylindrical in shape, the demagnetizing field, HD, for both the perpendicular and parallel orientations of the samples, is accounted for in calculating χ∥(H0) and χ⊥(H0).