A bio lab on a chip

The semiconductor technology company STMicroelectronics has pro-duced a silicon chip with micro arrays that support on-chip DNA analysis at the genetic level. When DNA from diseased and healthy sources is added to the silicon, it becomes a platform for genetic research into the cause of diseases. The mono-lithic (one-chip) array includes the sensing and supporting electronics.

A media group taken to Cata-nia, Sicily in South Italy was shown a machine placing dro-plets containing DNA onto silicon; through a scanner, com-puter and software. We then saw the array of color dots representing healthy gene pairs and those that were likely candidates for specific diseases.

The array of tiny dots on a silicon surface allow genetic researchers to accurately place a single polynucleotide strand of the twin-strand, double-helix DNA from individuals with spe-cific diseases (the target DNA) along with a strand of healthy DNA as reference (the probe). The objective is to find out the precise difference between the two DNA strands, thus identify-ing the genes that could be res-ponsible for the disease.

Like a lock and key, the two strands will come together completely if the specific deox-yribose and phosphate groups are complementary, forming strong covalent (chemical) bonds. If there is a difference, that pair will not form the bond, showing a different color characteristic. One end of the DNA strand itself forms a covalent bond with the silicon, anchoring it firmly in place.

The chromatically marked DNA fluoresces when excited by electrons, and this can be detected by photo-sensors.

 Different colors indicate whe-ther the gene pairs have paired correctly or not, and therefore whether they are identical or different.

Such a micro-array silicon platform for DNA allows the monitoring of expressions of 10,000 or more genes at a time. And the single piece of silicon contains the active electronics, and even the micro-channels carrying the DNA fluid, all inte-grated into one piece of silicon, increasing the speed of analysis and reducing its cost. The solution with the DNA can even be transported by capillary forces in the micro-channels.

The silicon chip integrates even the photo-sensors. This is an achievement, as silicon’s optical properties are not suited to either photoreceptor or light source use, which is why devices like LEDs tend to use gallium arsenide and other ‘III-V’ compounds, so called because they belong to groups III and V of the periodic table of elements. But this would mean that adding an LED or photo-receptor to a silicon device would involve multiple stages and devices. To integrate the whole device out of a single piece of silicon, STMicroele-ctronics engineers ‘doped’ the silicon with specific ‘impurities’ to change its optical proper-ties, in this case to create a photoreceptor element on a silicon chip, which can detect the fluorescence and color of the DNA just above it.

Thus, adding optical func-tions to silicon helps allow act-ive DNA analysis within a silicon chip, and the integrated electr-onics in the same silicon senses and communicates the color changes in the DNA pairs in the array. Using silicon for the base substrate for the DNA analysis also has other advantages–mainly, a great benefit in signal to noise ratio. Glass itself would fluoresce, so such background noise from glass would have to be ‘subtracted’ from the results of such an experiment.

Parallel with the silicon bio-sensor array development is ongoing research into DNA str-ands to explore genetic pairs as alternative memories, includ-ing research on organisms that change state or color after abs-orbing a photon, making them candidates for future ‘optical storage’.

While yet at the research and testing stage, STMicro officials say they expect to manufacture the ‘gene platform’ bio-sensors in a year for ‘simple stuff’ and in three years for ‘more com-plex stuff’.

The $ 6.3 billion STMicro-electronics is the fourth largest semiconductor company in the world. Headquartered in Gen-eva, Switzerland, ST has three regional headquarters in Dallas, Texas (USA), Singapore (Asia-Pacific) and Tokyo (Japan). It has 17 manufacturing sites across the world including Catania in Italy, the USA, and elsewhere. It is particularly strong in ‘system-on-chip’ technology and supplies chips to inter al, Alcatel, Nokia, Philips, Siemens and Sony, inkjet print-heads to HP, and automotive electronics systems to DaimlerChrysler and Ford. 

Prasanto K Roy

(CNS)