Chemistry Reference
In-Depth Information
11
organIc Molecules for optIcal IMagIng
Michael Hon-Wah Lam
Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong SAR, China
Ga-Lai Law
Department of Applied Biology and Chemical Technology, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong SAR, China
Chi-Sing Lee
Laboratory of Chemical Genomics, School of Chemical Biology and Biotechnology, Peking University Shenzhen Graduate School,
Shenzhen University Town, Xili, Shenzhen, China
Ka-Leung Wong
Department of Chemistry, Ho Sin Hang Campus, Hong Kong Baptist University, Kowloon Tong, Kowloon, Hong Kong SAR, China
11.1
IntroductIon
What is the meaning of life? This is not merely a philosophical or religious question, but also one of the ultimate scientific
mysteries that humans, as the conscious species, seek to comprehend. The cell can be regarded as the fundamental func-
tioning unit of living organisms. It is generally believed that by understanding various biochemical processes that sustain a
living cell, we might be able to get a glimpse of the wonder of life itself. In fact, since the establishment of the cell theory in
1839 [1, 2], we have already gained a considerable amount of knowledge about the basic functioning of living cells—enough
for us to realise their complexity. In a sense, a cell resembles a city, where different activities take place at different locations
to maintain its overall operation. There are ports at the border for the selective importation and exportation of materials and
products. There are defence mechanisms to counteract potentially dangerous intruders. There are power plants to generate
energy from burning of fuels. There is a control centre that issues commands to regulate the entire system. All of these activ-
ities are interconnected through the exchange and trafficking of materials, products, signals, and messengers, to and from
different activity units, within and outside the system. Of course, a cell is more complicated than a city. It undergoes cycles
of growth and reproduction. Genetic materials within its nucleus can make exact copies of themselves upon cell division. All
these syntheses and fine manipulations of biomolecules and subcellular structures imply the existence of very delicate
cytokinetic mechanisms, intra- and intercellular communications, and multiple loops of control and regulations. These life
processes are what we would like to understand.
Even after four centuries since its invention, optical microscopy remains one of the major tools for biologists to study
cellular structures, and histo- and cytochemical processes [3, 4]. Visual observations and optical/spectral measurements allow
convenient recording and qualitative and quantitative determination of the spatial and temporal changes of selected subcel-
lular features throughout the cell cycle upon specific treatments and stimulations. Some endogenous biomolecules possess
specific spectroscopic properties that permit their direct detection using a dedicated optical setup. For example, reduced
pyridine nucleotides NADH and NADPH are able to produce two-photon induced (with excitation at ca. 800 nm) fluores-
cence at 400-450 nm [5-9], This enables their fluorescent imaging against the high single-photon autofluorescent cellular
