Topic Name: Bioengineers have discovered chemical reactions in a single living cell for the first time
Research persons: Professor Luke Lee, Gang Logan Liu
Location: University of California, Berkeley, United States
Bioengineers at the University of
California, Berkeley, have discovered a technique that for the first time
enables the detection of biomolecules' dynamic reactions in a single living
By taking advantage of the signature frequency by which organic and inorganic
molecules absorb light, the team of researchers, led by Luke Lee, professor of
bioengineering and director of UC Berkeley's Biomolecular Nanotechnology Center,
can determine in real time whether specific enzymes are activated or particular
genes are expressed, all with unprecedented resolution within a single living
The technique, described in the Nov. 18 issue of the journal Nature
Methods, could lead to a new era in molecular imaging with implications for
cell-based drug discovery and biomedical diagnostics.
The researchers point out that other techniques, such as nuclear magnetic
resonance, can at best provide information about a cluster of cells. But to
determine the earliest signs of disease progression or of stem cell
proliferation, it's necessary to drill down deeper to the molecular dynamics
within a single cell.
To study the biochemical processes of a cell, scientists currently cut
through its outer membrane to separate and analyze the cellular components. That
method can never provide a real-time view of how components function together
because the cell is killed in the process of extracting its components.
"Until now, there has been no non-invasive method that exists that can
capture the chemical fingerprints of molecules with nanoscale spatial resolution
within a single living cell," said Lee, who is also a faculty affiliate of
the California Institute for Quantitative Biosciences and the co-director of the
Berkeley Sensor and Actuator Center. "There is great hope that stem cells
can one day be used to treat diseases, but one of the biggest challenges in this
field is understanding exactly how individual cells differentiate. What is
happening inside a stem cell as it develops into a heart muscle instead of a
tooth or a strand of hair? To find out, we need to look at the telltale chemical
signals involved as proteins and genes function together within a cell."
The researchers tackled this challenge by improving upon conventional optical
absorption spectroscopy, a technique by which light is passed through a solution
of molecules to determine which wavelengths are absorbed. Cytochrome c, for
instance, is a protein involved in cell metabolism and cell death that has
several optical absorption peaks of around 550 nanometers.
The absorption spectra of a molecule can change based upon the chemical
changes that occur as it interacts with other molecules, such as oxygen.
"For conventional optical absorption spectroscopy to work, a relatively
high concentration of biomolecules and a large volume of solution is needed in
order to detect these subtle changes in frequencies and absorption peaks,"
said Lee. "That's because optical absorption signals from a single
biomolecule are very weak, so you need to kill hundreds to millions of cells to
fish out enough of the target molecule for detection."
The researchers came up with a novel solution to this problem by coupling
biomolecules, the protein cytochrome c in this study, with tiny particles of
gold measuring 20-30 nanometers long. The electrons on the surface of metal
particles such as gold and silver are known to oscillate at specific frequencies
in response to light, a phenomenon known as plasmon resonance. The resonant
frequencies of the gold nanoparticles are much easier to detect than the weak
optical signals of cytochrome c, giving the researchers an easier target.
Gold nanoparticles were chosen because they have a plasmon resonance
wavelength ranging from 530 to 580 nanometers, corresponding to the absorption
peak of cytochrome c.
"When the absorption peak of the biomolecule overlaps with the plasmon
resonance frequency of the gold particle, you can see whether they are
exchanging energy," said study co-lead author Gang Logan Liu, who conducted
the research as a UC Berkeley Ph.D. student in bioengineering. "This energy
transfer shows up as small dips, something we call 'quenching,' in the
characteristic absorption peak of the gold particle."
A relatively small concentration of the molecule is needed to create these
quenching dips, so instead of a concentration of millions of molecules,
researchers can get by with hundreds or even dozens of molecules. The
sensitivity and selectivity of the quenching dips will improve the molecular
diagnosis of diseases and be instrumental in the development of personalized
medicine, the researchers said.
The researchers repeated the experiment matching the protein hemoglobin with
silver nanoparticles and achieved similar results.
"Our technique kills two birds with one stone," Lee said.
"We're reducing the spatial resolution required to detect the molecule at
the same time we're able to obtain chemical information about molecules while
they are in a living cell. In a way, these gold particles are like 'nano-stars'
because they illuminate the inner life of a cellular galaxy."
Other researchers on the UC Berkeley team are Yi-Tao Long, co-lead author and
postdoctoral scholar in bioengineering; Yeonho Choi, a Ph.D. student in
mechanical engineering; and Taewook Kang, a postdoctoral scholar in
of Science and Technology in Korea helped support this research.
Note for Nuclear magnetic resonance
Nuclear magnetic resonance (NMR) is a physical phenomenon based upon the quantum mechanical magnetic properties of an atom's nucleus. NMR also commonly refers to a family of scientific methods that exploit nuclear magnetic resonance to study molecules.
All nuclei that contain odd numbers of protons or neutrons have an intrinsic magnetic moment and angular momentum. The most commonly measured nuclei are hydrogen-1 (the most receptive isotope at natural abundance) and carbon-13, although nuclei from isotopes of many other elements (e.g. 15N, 14N 19F, 31P, 17O, 29Si, 10B, 11B, 23Na, 35Cl, 195Pt) can also be observed.
NMR resonant frequencies for a particular substance are directly proportional to the strength of the applied magnetic field, in accordance with the equation for the Larmor precession frequency.
NMR studies magnetic nuclei by aligning them with an applied constant magnetic field and perturbing this alignment using an alternating electric field, those fields being orthogonal. The resulting response to the perturbing magnetic field is the phenomenon that is exploited in NMR spectroscopy and magnetic resonance imaging, which use very powerful applied magnetic fields in order to achieve high resolution spectra, details of which are described by the chemical shift and the Zeeman effect.
NMR phenomena are also utilised in low field NMR and earth's field NMR spectrometers, and some kinds of magnetometer.
Note for Cytochrome c
Cytochrome c, or cyt c (horse heart: PDB 1HRC) is a small heme protein found loosely associated with the inner membrane of the mitochondrion. It is a soluble protein, unlike other cytochromes, and is an essential component of the electron transfer chain. It is capable of undergoing oxidation and reduction, but does not bind oxygen. It transfers electrons between Complexes III and IV.
Cytochrome c is a highly conserved protein across the spectrum of species, found in plants, animals, and many unicellular organisms. This, along with its small size (molecular weight about 12,000 daltons), makes it useful in studies of evolutionary divergence. Its primary structure consists of a chain of 100 amino acids.
The cytochrome c molecule has been studied for the glimpse it gives into evolutionary biology. Both chickens and turkeys have the identical molecule (amino acid for amino acid) within their mitochondria, whereas ducks possess molecules differing by one amino acid. Similarly, both humans and chimpanzees have the identical molecule, while rhesus monkeys possess cytochromes differing by one amino acid.
In figure, Lights scatter from metallic nanoplasmonic
particles upon excitation of an external light source. UC Berkeley researchers
coupled the metallic nanoparticles with biomolecules to detect chemical signals
within a single living cell at unprecedented resolution.
Prof. Dr. Luke P. Lee
Prof. Dr. Luke P. Lee
Professur für System Nanobiologie
Main phone: +41 61 387 31 50
Since October 2006, Luke P. Lee has been Full Professor of system biology at ETH Zurich.
Lee worked in the technology industry until 1996. His doctorate in Applied Physics and Bio-engineering at Berkeley followed in 2000; five years later he became a full professor at the same institute. In addition Lee has been Co-Director of the “Sensor and Actuator Center” since 1999 and Director of the “Bio-molecular Nanotechnology Center" since 2001. He received the “National Academies Keck Futures Initiative Award" in 2005.
His scientific focus is the technological development of nano-scale and micro-scale tools with which cellular processes can be described quantitatively.
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