Navigation Links
Seeing previously invisible molecules for the first time

A team of Harvard chemists led by X. Sunney Xie has developed a new microscopic technique for seeing, in color, molecules with undetectable fluorescence. The room-temperature technique allows researchers to identify previously unseen molecules in living organisms and offers broad applications in biomedical imaging and research.

The scientists' results are published in the Oct. 22 issue of Nature. Partial funding for the project was provided by the National Science Foundation (NSF).

Fluorescence is a phenomenon in which an electron in a molecule absorbs energy from light and moves to a higher energy level or excited state. The energy of the light is contained in a unit called a photon.

After a very brief stay at the excited state, the electron returns to its previous energy level, or ground state, by emitting a new photon. The energy of the released photon is discharged in wavelengths of detectable visible light lasting only a few billionths of a second.

Many biologically important colored molecules such as hemoglobin--an oxygen-transport protein in red blood cells--absorb light but do not fluoresce. Instead, the electrons in these molecules release their additional but transient energy by converting it to heat.

"Since these molecules do not fluoresce, they have literally been overlooked by modern optical microscopes," Xie said.

To detect non-fluorescent molecules in biological systems, Xie and his team developed a new type of microscopy based on stimulated emission.

Stimulated emission was first described by Albert Einstein in 1917, and was the basis for today's lasers. In a nutshell, it is a process by which an excited-state electron, perturbed by a photon having the correct energy, drops to its ground state producing an additional photon.

Xie's new microscopic technique generates and records a stimulated emission signal by using two carefully timed input and output pulse trains. In the input pulse train, a modulator switches the intensity of the excitation beam on and off at five megahertz, or MHz. The modulation creates a stimulated emission signal at the same frequency. Each train has an incredibly short pulse duration of approximately 200 femtoseconds. A femtosecond is equal to one billionth of one millionth of a second or 10-15 seconds.

The signal produced by the non-fluorescent molecules provides a highly sensitive image of previously "invisible" molecules.

One of the several possible applications of the scientists' invention is mapping in color the delivery of non-fluorescent drugs to their target cells. Another possible use is imaging tiny structures such as blood vessels including individual red blood cells and single capillaries (see images).

The structure and hemoglobin-dynamics of blood vessels play a major role in many biomedical processes. Two example processes are the transition of tumors from a dormant to malignant state and oxygen delivery in the brain.

Current established imaging technologies like MRIs and CT scans either lack the spatial resolution needed to resolve individual capillaries or require external contrast agents.

Fluorescent labels such as the green fluorescent protein, or GFP, are extensively used for observing the activity of biomolecules and distinguishing target molecules in a cell. The GFP labeling technique provides well-defined images. However, the bulky protein can disturb delicate biological pathways, especially when it is larger than the biomolecules it is illuminating.

Xie's team mapped the delivery of a non-fluorescent drug molecule and imaged blood vessels without fluorescent labels.

Their new technique is also capable of imaging non-fluorescent proteins in cells of live Escherichia coli bacteria.

"While earlier studies made use of similar pump-probe experiments to provide images of fluorescent molecules with spatial resolution comparable to that of confocal fluorescence microscopy and high temporal resolution, this study, for the first time, makes use of stimulated emission microscopy to image non-fluorescent molecules," said Zeev Rosenzweig, a program director in the NSF Division of Chemistry.

Although potential photo-damage, and the complexity and cost of the system still need to be addressed for the technique to gain wide applicability, "there is no doubt that the study provides a unique way to image a wide range of molecules currently inaccessible to today's state-of-the-art optical microscopes," notes Rosenzweig.

"This is just the beginning," added Xie. "Many interesting applications of this new imaging modality are forth coming."


Contact: Jennifer A. Grasswick
National Science Foundation

Related biology news :

1. Seeing the tree from the forest: Predicting the future of plant communities
2. Seeing stem cells helps in fight against peripheral arterial disease
3. Seeing through the skin
4. Crystal (eye) ball: Study says visual system equipped with future seeing powers
5. Seeing Alzheimers amyloids
6. Genome duplication responsible for more plant species than previously thought
7. Oscar Pistorius: Previously confidential study results released on amputee sprinter
8. Lower increases in global temps could lead to greater impacts than previously thought, study finds
9. Evolutionary process more detailed than previously believed, study shows
10. Nations that sow food crops for biofuels may reap less than previously thought
11. Whispering bats are 100 times louder than previously thought
Post Your Comments:
(Date:6/22/2016)... LOS ANGELES , June 22, 2016 ... of identity management and verification solutions, has ... cutting edge software solutions for Visitor Management, ... ® provides products that add functional ... The partnership provides corporations and venues with ...
(Date:6/16/2016)... , June 16, 2016 ... size is expected to reach USD 1.83 billion ... Grand View Research, Inc. Technological proliferation and increasing ... applications are expected to drive the market growth. ... , The development of advanced multimodal ...
(Date:6/7/2016)... , June 7, 2016  Syngrafii Inc. and ... business relationship that includes integrating Syngrafii,s patented LongPen™ ... project. This collaboration will result in greater convenience ... credit union, while maintaining existing document workflow and ... ...
Breaking Biology News(10 mins):
(Date:6/27/2016)... , June 27, 2016 /PRNewswire/ - BIOREM Inc. (TSX-V: BRM) ... advised by its major shareholders, Clean Technology Fund I, ... United States based venture capital funds which ... Biorem (on a fully diluted, as converted basis), that ... of their entire equity holdings in Biorem to TUS ...
(Date:6/27/2016)... ... June 27, 2016 , ... Parallel 6 , the leading ... the Clinical Reach Virtual Patient Encounter CONSULT module which enables both audio ... and clinical trial team. , Using the CONSULT module, patients and physicians can schedule ...
(Date:6/27/2016)... PHILADELPHIA , June 27, 2016  Liquid ... today announced the funding of a Sponsored Research ... study circulating tumor cells (CTCs) from cancer patients.  ... changes in CTC levels correlate with clinical outcomes ... therapies. These data will then be employed to ...
(Date:6/24/2016)... , June 24, 2016 Epic Sciences ... detects cancers susceptible to PARP inhibitors by targeting ... cells (CTCs). The new test has already been ... in multiple cancer types. Over 230 ... damage response pathways, including PARP, ATM, ATR, DNA-PK ...
Breaking Biology Technology: