Scientists at Singapore’s Institute of Microelectronics (IME)
have developed a rapid and sensitive integrated system to test
simultaneously for specific cardiac biomarkers in finger prick
amount of blood.
The silicon-based integrated system’s features could help
physicians quickly arrive at the right diagnosis for timely medical
intervention in patients suspected of having heart attacks —
particularly individuals who do not show obvious signs of chest
pains or shortness of breath, according to researchers at IME, one
of the research institutes sponsored by Singapore’s A*STAR (Agency
for Science, Technology and Research).
The IME-developed cardiac biomarker testing system significantly
cuts the time needed for sample preparation and analysis to just 45
minutes from the six hours typically required for the conventional
testing platform known as ELISA (Enzyme-linked Immunosorbent
Assay).
Because of its multiplexing capability – measuring several
cardiac biomarkers simultaneously — the new system contributes to
the detail and certainty of diagnosis.
“The key to saving lives in heart attack scenarios is time and
the quicker and more accurate the diagnosis can be made, the faster
proper care and treatment can be instituted,” said Philip Wong,
M.D., Senior Consultant at the Singapore National Heart Centre,
which worked with IME in developing the new system.
“The test kits can be rapidly deployed, and tests to confirm
clinical diagnosis can be completed within short time frames,” said
Dr. Wong. “As the kits are deployed on-site as opposed to a central
laboratory, confirmation of condition is rapid without the need to
transport patients’ specimens.”
The IME-developed system is a label-free technology that uses
semiconducting silicon nanowires (SiNWs) as biosensors. The working
principle behind the nanowire biosensors is the field-effect
transistor, which is responsible for generating a measurable
electrical response when specific antibody-antigen interactions
occur on the nanowire surface.
Specific antibodies that are immobilized onto the nanowire
surface will elicit antibody-antigen interactions when allowed to
come into contact with the variety of charged cardiac biomarkers.
Released into the blood when the heart is injured, cardiac protein
biomarkers such as troponin-T and creatinine kinases, are the basis
of medical tests of patients in which a heart attack is
suspected.
The IME-developed system is a label-free technology – thus
eliminating the tagging step, thereby saving time and reagent
consumption costs. In classical biochemical methods, the tagging of
a fluorescent dye to the targeted analyte is used to detect and
quantify the targeted analyte.
The IME-developed system’s parallel detection of several
biomarkers is made possible by the integration of the following
elements into one single microsystem:
- In-built filtration to extract almost instantaneously the test
serum from the whole blood sample - An array of SiNW chips coated with different antibodies for
simultaneous detection of several biomarkers - A recording microchip for concurrent and immediate
signal-readout from multiple SiNW sensors
The first demonstration of the full system capability revealed
impressive sensitivity and speed because it can attain in just
under 45 minutes a low detection limit of 1 pg/ml for cardiac
biomarkers, troponin-T and creatinine kinases, from 2 μl
blood.
Commercially available test kits require more than 1 ng/ml of
cardiac biomarkers in order for them to be detected, which is 1000
times less sensitive than the IME-developed system.
The technology and processes used for fabricating this
integrated device have yielded two patents to date.
“IME’s proprietary nanotechnology behind the new silicon-based
integrated system can be extended to other protein-based
diagnostics from blood and saliva samples to provide fast,
sensitive, accurate and portable solutions for protein-based
disease screening,” said Kwong Dim-Lee, Ph.D., IME’s Executive
Director.
Cardiac biomarkers, such as troponin-T and creatinine kinases
are proteins used for heart attack diagnosis. Troponin and
creatinine are constituents of the cardiac muscle cells that are
released into the blood when the cells and tissues are injured
after a heart attack. Hence elevated levels of troponin-T or
creatinine kinases in the blood alert the doctors that a heart
attack has taken place.
Troponin-T is established as a sensitive marker of myocardial
injury in the general population. The troponin-T level in the blood
increases within 4 to 6 hours after the onset of a heart attack and
peaks at about 24 hours. This increase lasts for 10 to 14 days.
Today, the first test performed on a patient who is suspected of
having a heart attack would be an electrocardiogram, commonly known
as the ECG. However, normal results from an ECG do not rule out the
occurrence of a heart attack, because the test is not sensitive
enough to detect minute anomalies in the reading, particularly when
the anomaly needs to be captured within a narrow time window of 2
– 30 minutes following the onset of a heart attack. When an
abnormal ECG reading cannot be established, the patient has to
undergo further blood tests to detect the relevant cardiac
biomarkers.
ELISA, which is the current method for detecting cardiac
biomarkers, uses fluorescent labeling technology. This biochemical
technique is laborious and time-consuming; the entire set-up
requires specialized personnel and instruments to implement,
thereby contributing to the per analysis cost. Hence, ELISA does
not favor prompt diagnosis for critical split-second medical
decisions.
