HKUST Alumni News 2014
7
The HKUST Edge
D
etection of hidden explosives, tracking of cancer
cells within the body, reading finger prints off any
surface, differentiation between alive and dead bacteria,
monitoring of toxic pollutants in rivers and lakes, a
glucose biosensor for diabetics, analysis of proteins
in the brain in relation to Parkinson’s and Alzheimer’s
diseases… the list of applications for the ground-
breaking research developed at HKUST by Professor
Ben Zhong Tang, Stephen Kam Chuen Cheong Professor of Science
and Chair Professor of Chemistry, and his team is almost endless.
Over a decade of hard work in the laboratories at the Department
of Chemistry, the team has been able to develop a range of advanced
luminescent materials with novel molecular structures and unique
properties, namely high sensitivity, superb specificity and excellent
stability, and thus achieved a major breakthrough in demonstrating for
the first time the phenomenon of aggregation-induced emission (AIE).
Before going on to explain the work he does, Professor Tang
takes time to relate that his fascination with luminescent – that is, light
emitting – materials goes back a long way. “Remember when you
were a kid and you wondered at how you could read the time on your
watch in the dark?” he says. He has taken that early inquisitiveness
and translated it into an academic career focused on functional
molecules, especially fluorescent materials and their high-tech
applications.
Fluorescent molecules are enormously useful because they make
the invisible visible; cellular tracers can monitor biological processes,
pathological pathways and therapeutic effects. However, as Professor
Tang explains, a process called ACQ, or aggregation-caused
quenching, decreases the fluorescence intensity of a given substance.
“Single molecules are highly emissive, but when aggregated they are
quenched,” he says, adding that this is because the substance does
not dissolve in water and is both water repellent and repelled by water.
“They are hydrophobic,” he says. “We observed the phenomena that
if the molecules are in organic solvent, you don’t see the fluorescence
because of the hydrophobia, but the more water you add, we
were surprised to see strong emission. We called this abnormal
photophysical phenomenon aggregation-induced emission, or AIE.”
Because the probes are hydrophobic, as you add more water
they effectively get corralled together to reduce the surface area they
present to water, so they become aggregated. This is called the
“hydrophobic effect”.
With regard to biomedical applications, the team has discovered
a new type of fluorescence “turn-on” probe that is able to trace live
cells over a long period of time. It is non-fluorescent when dissolved
but becomes highly emissive when its molecules are aggregated.
The AIE aggregates are kept inside the cellular compartments and
do not contaminate other cell lines in the system, thus allowing the
differentiation of specific cancerous cells from normal healthy cells, for
example.
This new class of fluorogenic materials developed at HKUST with
AIE characteristics have attracted worldwide attention from hospitals
and biotech companies. “Consider
X-ray, CT scan and MRI machines,”
says Professor Tang. “They are very
big, and often include radioactive
elements; they are fine for big hospitals
in big cities, but what about smaller
hospitals or clinics, especially in rural
or underdeveloped areas? We have
the know-how now to develop smaller, cheaper machines that can
do the same jobs.” Another application he finds not only promising
but exciting, too, relates to environmental pollution. “In Mainland
China, people are worried because the rivers and lakes are often very
polluted,” he notes. “But fluorescent materials can be used as sensors
to detect toxic materials in water.”
Professor Tang says that the scope of applications for his
technology is enormous, and at HKUST they are essentially focusing
on three major areas: optoelectronic devices, such as OLED; chemical
sensors, such as monitoring toxic materials in water; and biological
approaches, mainly long-term tracking of cancer cells. “There is huge
opportunity in this field and how we commercialize these high-value-
added materials is a matter of great urgency and importance. We are
in discussions with potential partners, but the process takes time.”
There is no doubting the enthusiasm Professor Tang shows for
his work, and that infectious atmosphere of pride and energy is also
very apparent in his team, which generally comprises of around 30
people at any one time, mainly post-doctoral researchers and visiting
scholars, postgraduate students and research assistants.
“We are leading the world in this research,” he says. “It took us
a decade to develop this and it has been a very exciting time,” says
Professor Tang. “However, at first, no one took much notice – but
last year AIE received 6,500 citations. We are now attracting a lot
of interest from around the world. Academically it is very valuable,
because it is the opposite of what people believed.”
Professor Tang has been described as having “rock star status”
among scientists in Mainland China, where he is not only the “Most-
cited Scientist” with 500 peer-reviewed papers, cited 15,000 times,
but he has also been named the “Most-invited Speaker”, having been
featured in more than 200 scientific conferences. In March 2014,
he was selected as one of five international laureates of the 27th
Khwarizmi International Award by the Iranian Organization for Science
and Technology in recognition of his outstanding achievements. “I
am delighted with this recognition, and grateful for the support of the
University, my students and research collaborators,” he says. He was
elected to membership of the Chinese Academy of Sciences in 2009,
and the AIE project was incorporated into the National Basic Research
Program (973 Program) in 2012.
“My philosophy is to make things as simple as possible. That
usually makes things cheaper, too. We are constantly developing new
ideas here – now we have hundreds of these materials with different
properties,” he says. And, of course, we all know that the simplest
ideas are usually the best – so let there be light!
