Biochips beads

Based on IgG-bearing beads, a chemiluminescent immuno-biochip has been also realized for the model detection of human IgG. Biotin-labeled antihuman IgG were used in a competitive assay, in conjunction with peroxidase labelled streptavidin59. In that case, the planar glassy carbon electrode served only as a support for the sensing layer since the light signal came from the biocatalytic activity of horseradish peroxidase. Free antigen could then be detected with a detection limit of 25 pg (108 molecules) and up to 15 ng. 

In a similar way, the use of oligonucleotide-immobilized beads enabled the realization of DNA sensitive biochips that could be used to detect biotin labelled sequence as 5.108 molecules59. 

Composite sensing layers, consisting of bioactive molecule-charged beads entrapped in a polymeric structure, have been successfully used to realize multi-purpose biochips for DNA, proteins or enzymes. For all these different biochips, the chemiluminescence and electro-chemiluminescence measurements required only a CCD camera and neither light sources nor optical filters are needed. 

Homogeneous Phase Bead Biochips Suspension Array Technology. 121... 

Three different systems could be distinguished according to the organization of the beads bead arrays, composed of highly organized beads bead biochips, using beads as immobilization support without precise positioning of each bead and the beads in microfluidic networks, characterized by a possible displacement of the beads. 

Bead biochips are characterized by a non-ordered relative position of each bead. The microspheres are in this case used to increase the specific surface of the support and to facilitate either the immobilization chemistry or the handling of the DNA probes. 

Two main categories of bead biochips could be distinguished associated to the use of the beads in an immobilized state or in an homogeneous phase. 

The electron microscopy images presented in Fig. 3A and C illustrate two possibilities of arraying populations of identical beads at the surface of a biochip [12-14]. 

Immobilized bead biochips are furthermore an interesting alternative to the dramatically complex bead arrays. Indeed, different populations of DNA... 

Beads in microfluidic systems are an interesting evolution of the homogeneous phase bead biochips. Indeed, examples of microfluidic platforms in which biospecific molecules are immobilized on an internal channel surface are still rare [26]. 

The different approaches presented in this review have already proved the overall potential of beads based chips, either in bead arrays, bead biochips or flow cytometry systems. Taking advantage of this diversity, beads based chips could become highly flexible analytical tools in the near future. 

The world of beads appears to have an important part to play in future DNA biochip developments. 

Many biochips use dyes that fluoresce when illuminated. Different color dyes can be used to determine, not only whether a reaction has taken place, but specific details of sample reactants. Other biochips may work with small magnetic beads. 

Zyomyx (Hayward, GA) has developed the Zyomyx human cytokine biochip that uses microfluidics to measure 30 different human cytokines simultaneously. Biosite (San Diego, GA) markets commercial microfluidic chip-based immunoassay for clinical applications. Multiplexed assays using fluorescent microspheres/beads in Lab-on-Ghip format manufactured by Becton-Dickinson (Franklin, NJ), Diasorin (Stillwater, MN), and Luminex Gorp. (Austin, TX) are also available for use in clinics. 

A review of biochips and microarrays [4] considers requirements for biochemical and medical diagnostic applications, focusing on sihcon manufacturing technology coupled with magnetic beads, nucleic acid recognition, and enzyme catalysis. This review includes optical as well as electrochemical measurement methods. 

For system automation and integration we have made an actuation/control unit (fig. 4). To operate it the user will insert a biochip in the reader, place sample (with lysis buffer and magnetic beads) in the sample reservoir, and start the LabView program SMART-BioControF which... 

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