Nucleic acid chip technology

Different electronic transduction means were discussed, including faradaic impedance spectroscopy, chronopotentiometry, chronocoulometry, and micro-gravimetric quartz-crystal-microbalance measuranents. The different methods reveal high sensitivities that allow the detection of 5(X>-2(X)0 copies of DNA in 10-50 jL of samples. These rapid advances in electronic DNA detection open the way to construct electrode chips for the parallel or consecutive analyses of a collection of nucleic acids. The technologies to construct such electrode arrays are available, and robotic methods for the site-specific spotting of such arrays are known. This suggests that the different approaches are sufficiently ripe to be harnessed and optimized for practical targets. 

An array of oligonucleotide which is composed of 20 80-mer oligos, or peptide nucleic acid probes, is synthesized either in situ (i.e., on-chip) or using conventional synthesis followed by on-chip immobilization. The resultant DNA array is then exposed to the labeled sample of DNA, hybridized, and the identity/abundance of complementary sequences determined. This method was developed at Affymetrix, Inc. and called DNA chips. Today, oligonucleotide-based chips are manufactured by many companies using alternative in situ synthesis or depositioning technologies. 

The use of nucleic acids recognition layers represents a new and exciting area in analytical chemistry which requires an extensive study. Besides classical methodologies to detect DNA, novel approaches have been designed, such as the DNA chips [10-12] and lab-on-a-chips based on microfluidic techniques [13]. However, these technologies are still out of the scope of food industry, since it requires simple, cheap and user-friendly analytical devices. 

Micro-arrays can be manufactured in two different ways, by synthesis in situ or by delivery. In the in situ synthesis approach, nucleic acids are synthesized directly on a chip surface. This is made possible by a light-directed chemical synthesis technology developed by scientists at Affymetrix. By using different sets of photolithographic masks, scientitsts can define the chip exposure sites and, thereby, the sequence of the oligonucleotides. In this way, arrays can be synthesized with up to 400,000 different oligonucleotides in an area of 1.6 cm. Every spot contains about... 

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