Tom Shelley reports on some latest
developments in chip based biosensing and analysis
Laboratories on a chip, predicted in Eureka's September 1996
cover story are now a reality and set to become the basis of a
multi billion dollar industry.
New configuration devices use optical readout of fluorescence
effects, with electrically read devices for future hand held
systems following hard on their heels. Long predicted sensing
devices using immobilised cells are under development.
Primary intended uses are for DNA testing and drug development
although chemical and biological analyses are obvious further
applications. The makers, however, consider their devices
unsuitable for military and security applications and make it
very clear that they have no wish to become involved in such
markets.
The labs on a chip are the brainchild of Infineon Technologies in
Munich, www.infineon.com
the world's sixth largest semiconductor manufacturer by sales,
second in the world in automotive and third in DRAM products. The
breakthrough made by Infineon is to etch their 'Flow-Thru'
silicon chips into an array of vertical flow through passages as
opposed to horizontal passages on top surfaces.
According to Austrian born Infineon researcher, Dr Michaela
Fritz, the chips are 500 microns thick, and patterned into an
array of 10 micron holes, each a tenth of the diameter of a human
hair. There are a million of these per square centimetre, so the
chips are mostly holes in a honeycomb arrangement. Infineon has
teamed up with Gettysburg USA based MetriGenix to seed the arrays
with up to 400 samples of DNA strands. The DNA strands
(nucleotides) attach themselves to the walls of the channels.
Each gene sample is distributed across around 100 holes. Three
reagents are then pumped through in sequence. The first is a
blocker, the second the tissue or blood sample under test and the
third, a fluorescing reagent dye. Some of the genes in the fluid
under study bind to some of the immobilised genes. The others are
washed off. The bindings are detected by means of a marker, such
as a luminescent dye that is split up by an added enzyme, which
causes it to release light, detected by a CCD camera. If the
pattern of light regions matches that of healthy tissue, medical
treatment is judged to be effective. Unhealthy patterns can be
matched against patterns arising from known diseases or known
organisms.
Because molecules are repeatedly pumped through
the chips as opposed to relying on diffusion, and because the
channel structure allows more molecules to react with each other,
total test time is about two hours, as opposed to 16 to 24 hours
with conventional equipment. Seeded chips cost euros 200 to 250
each and total system cost is euros 60,000. Standard products
available at the present time include arrays for the
identification of breast cancer, tissue proliferation and
inflammation, and for the detection of neural changes that are
the causes of diseases such as Alzheimers, Parkinson's or
Multiple Sclerosis. Thirty systems have been sold so far.
Dr Thomas Klaue, Infineon's Vice President for
Business Development described how the technology involved
working with 5nanolitre quantities, a thousandth of the volume of
the average mosquito bite. The company refers to its development
as 4D, because the chip is three dimensional and additionally
aims to compress timescales for the development of new drugs by
one to two years, not to mention faster DNA analysis. It is
expected to be possible to establish which patients have genetic
propensities for certain diseases, and has already been shown
able to detect DNA from cancerous tissue and identify which type
of cancer it is. Making an early and correct diagnosis can be of
immense benefit in initiating the most suitable treatment. Wrong
treatments can in many cases make patients worse.
Dr Klaue also claimed that by using a slightly different process,
it should be possible to use the chip to detect antibiotic
resistant germs, and quickly establish which antibiotics from a
range of possibles will kill them. According to research by
Heinrich Heine University in Dusseldorf, about 10,000 patients
die each year in Germany alone from multi antibiotic resistant
germs picked up in hospitals. "A rather quick test will also
show if food has been genetically modified" he added. In the
longer term, based on blood samples, it is hoped that it will be
possible to identify exactly what an individual patient is
suffering from, pre-test medications, and devise an optimum
treatment optimised for their particular needs.
Dr Klaue then went on to reveal fully electronic Biochips which
are expected to be ready for launch in two to three years.
Initial devices have a 16 x 8 array of sensors areas in a device
die 4.5mm x 6.4mm. Each sensor consists of a series of parallel
gold finger electrodes on a passivated CMOS surface. For DNA
assessment, the nucleotides are attached to the gold electrodes.
Binding causes an electrochemical redox reaction. The electric
currents produced are in the picoamp to nanoamp range, so signal
processing has to be undertaken on chip.
The main intended field of application is in doctor's office or
hospital bedside assessment of what patients might be suffering
from and the rapid development of suitable treatments.
The stage beyond that is the devlopment of the Neuro-Chip, in
which nerve cells are grown on a biocompatible surface on a chip,
and interrogated electrically. Working with the Max-Plank
Institute for Biochemistry in Martinsried, Munich, a device has
been developed with 128 x 128 sensors in a one millimetre square
area. Each sensor collects are least 2,000 electrical signals per
second from the nerve cells, amplifies and forwards them to the
monitoring computer system.
Intended applications are the non invasive long term study of
networks of nerve cells and the development of new drugs.
Eureka asked what turned out to have been an anticipated question
as to whether any of the devices could form the basis of better
sensors for the detection of chemical or biological warfare
agents. Dr Klaue, supported by researchers present at the
briefing, insisted that the only applications of the devices were
medical. The optically and electronic read chips were regarded as
much too slow to be useful in a military or security application.
The Neuro-Chip is fast enough but it was pointed out that it
requires care in keeping the immobilised cells alive, even though
some US firms are claiming that such devices will be suitable for
detecting chemical and biological agents. Cells can be kept alive
for several weeks apparently, but no longer. It would seem that
in this sphere, little improvement has so far been made over
keeping a canary in a cage. The world wide medical market for
biochips, associated equipment and related services for the
medical market on the other hand is predicted to reach $4 billion
by 2009.
Pointers
* Optically read new silicon biochips bring about a dramatic
acceleration in DNA testing and other biological and medical
analysis tasks
* Electronically read versions now in preparation will bring
about an equally dramatic reduction in cost and system size,
reducing table top systems to hand held size
* Long predicted immobilised cell biosensors show signs of coming
to market within the next very few years
For more technical
developments see www.eurekamagazine.co.uk