(Press-News.org) An evanescent wave arises at the interface of two media when light propagates from a more to a less-dense medium under total internal reflection. The wave is distributed over a superficial area because its amplitude decays exponentially with distance from the interface. The evanescent wave intensity at the interface can be larger than that of the incident beam. Evanescent waves have widespread current use in the imaging of chemical, bio-chemical and biological phenomenon. For example, an evanescent wave is responsible for fluorophore excitation in total internal reflection fluorescence microscopy, which is used to visualize single-molecules on the surface of living cells, and can detect cell membranes in micro-domains. An interesting scientific question is the possibility of directly using evanescent waves to image a monolayer, and how to improve the image contrast. The authors have observed an adsorbed protein layer using evanescent wave imaging and used both experimental and theoretical techniques in their investigation.
The authors first considered the possibility of visualizing a protein monolayer at a glass-liquid interface. A plane light wave and classic theoretical simulation were used to investigate the evanescent wave behavior. The resulting image of the protein monolayer demonstrated the difficulty in such visualization, due to low image contrast (about 10-5) between the protein layer and glass substrate.
Evanescent waves arise from the oblique incidence angle, which would change the polarization state of the reflected light wave. Thus, a polarized beam was applied. The optimized polarization setting resulted in a 100 times improvement in image contrast. However, this was still insufficient to adequately visualize the protein monolayer.
A surface-enhanced medium (e.g. a gold layer) was used at the glass interface, to provide a surface-enhanced effect for evanescent wave imaging. The gold layer thickness was selected and using an optimized incident angle, the image contrast increased by about 107 of that without the gold layer. The adsorbed protein monolayer on the gold surface was satisfactorily visualized.
Finally, the polarization state was optimized and the maximum image contrast increased slightly. However, this improvement was more apparent at image regions which neighbored those of maximum contrast.
In this study, the effect on image contrast of incident angle, gold layer and polarization were also theoretically simulated. The authors observed that the angle of incidence could be optimized to achieve a maximum imaging contrast and a 100 times increase could be obtained when an optimized polarization was applied as well. When the gold layer surface enhancement effect was incorporated, a dramatic contrast increase of 107 was observed. Interestingly, the image contrasts of the gold-induced imaging with and without polarization optimization were almost identical. This was vastly different when imaging was performed without the gold layer. The gold layer appeared to produce a surface enhanced effect on image contrast, while at the same time having a depolarization effect. Thus, polarization optimization seems no longer to be necessary in imaging applications using a gold layer.
Image contrast is very sensitive to the thickness of the gold layer and also very sensitive to the gold layer refractive index, which was not simulated in this study. In practice, the gold layer thickness and refractive index is much harder to control than in simulation, so experimental measurements were generally carried out in non-optimized conditions. The real setting in experiments becomes the neighboring region of optimization, where polarization played an important role in improving image contrast.
"This paper emphasizes the visualization of a protein monolayer by evanescent wave imaging and its optimization of conditions. The theoretical simulation and experiment results are of academic and practical significance." said one journal reviewer. A series of papers about biosensor applications with evanescent wave imaging have been published by the authors in various scientific journals, which offer us new prospects for developing evanescent wave imaging and associated applications.
INFORMATION:
The authors are affiliated with the Biophotonics group at the National Microgravity Laboratory (NML) of the Institute of Mechanics at the Chinese Academy of Sciences (IMech, CAS). This group is conducting research predominantly on protein microarray biosensors and applications, spatially-resolved and time-resolved ellipsometric techniques, and the characterization of biomaterials with ellipsometry and SNOM.
Funding from the National Basic Research Program of China (Grant No. 2009CB320300) and the National High Technology Research Development Program of China (Grant No 2008AA02Z419), supported this research.
See the article: Liu L., Niu Y., Chen S., et al.. Optimization of evanescent wave imaging for visualization of protein adsorption layer. SCI CHINA Physics, Mechanics & Astronomy, No.10 issue 2010
http://www.springerlink.com
doi: 10.1007/s11434-010-9977-9
Evanescent wave imaging of adsorbed protein layers
2010-12-04
[Attachments] See images for this press release:
ELSE PRESS RELEASES FROM THIS DATE:
Proposal for the establishment of a new branch within the discipline of aerothermodynamics
2010-12-04
Researchers from the College of Physical Sciences, GUCAS, have proposed to establish a new branch, unsteady aerothermodynamics, within the discipline of aerothermodynamics. The principal objectives of this new branch, to treat by theoretical means the study of physical phenomena relating to attached boundary layer flows, have been outlined in a preliminary investigation. A report based on a feasibility study has appeared in Vol. 54 No. 8 of Science China Physics, Mechanics & Astronomy.
Aerothermodynamics, a cross-discipline based mainly on aerodynamics and thermodynamics, ...
Researchers find mathematical patterns to forecast earthquakes
2010-12-04
Researchers from the Universidad Pablo de Olavide (UPO) and the Universidad de Sevilla (US) have found patterns of behaviour that occur before an earthquake on the Iberian peninsula. The team used clustering techniques to forecast medium-large seismic movements when certain circumstances coincide.
"Using mathematical techniques, we have found patterns when medium-large earthquakes happen, that is, earthquakes greater than 4.4 on the Richter scale," Francisco Martínez Álvarez, co-author of the study and a senior lecturer at the UPO revealed to SINC.
The research, which ...
Forget your previous conceptions about memory
2010-12-04
Memory difficulties such as those seen in dementia may arise because the brain forms incomplete memories that are more easily confused, new research from the University of Cambridge has found. The findings are published today in the journal Science.
Currently, memory problems are typically perceived to be the result of forgetting previously encountered items or events. The new research (using an animal model of amnesia), however, found that the ability of the brain to maintain complete, detailed memories is disrupted. The remaining, less detailed memories are relatively ...
The initial and final state of SNe Ia from the single degenerate model
2010-12-04
Type Ia supernovae (SNe Ia) play an important role as cosmological distance indicators and have been used successfully to determine cosmological parameters, which resulted in the discovery of the accelerating expansion of the Universe. However, the exact nature of SN Ia progenitors is still not well understood. There is a popular theory that SNe Ia originate from runaway thermonuclear events in carbon–oxygen white dwarves (CO WD) in binary systems. The CO WD accretes material from its companion. When the CO WD increases its mass above the maximum stable mass, it will explode.
Based ...
The race against age
2010-12-04
Impairments to health and physical performance are not primarily a result of aging but of unfavorable lifestyle habits and lack of exercise. This is the position taken by Dieter Leyk and his coauthors in the new issue of Deutsches Ärzteblatt International (Dtsch Arztebl Int 2010; 107[46]: 809).
Sporty elderly people have a life expectancy that is almost 4 years higher and are often faster than younger athletes.
In their study, the sports scientists analyzed the stamina of more than 600 000 marathon and half marathon runners and asked participants about their ...
Soya beans could hold clue to treating fatal childhood disease
2010-12-04
Scientists from The University of Manchester say a naturally occurring chemical found in soy could prove to be an effective new treatment for a fatal genetic disease that affects children.
Dr Brian Bigger, from the University's MPS Stem Cell Research Laboratory, found that genistein – derived from soya beans and licensed in the US as an osteoporosis drug – had a dramatic effect on mice suffering from the human childhood disease Sanfilippo.
"Sanfilippo is an untreatable mucopolysaccharide (MPS) disease affecting one in 89,000 children in the United Kingdom," said Dr ...
Smoking may thin the brain
2010-12-04
Philadelphia, PA, 2 December 2010 - Many brain imaging studies have reported that tobacco smoking is associated with large-scale and wide-spread structural brain abnormalities.
The cerebral cortex is a specific area of the brain responsible for many important higher-order functions, including language, information processing, and memory. Reduced cortical thickness has been associated with normal aging, reduced intelligence, and impaired cognition.
However, prior research had not described the impact of smoking upon cortical thickness.
A new study, published in ...
Low-status leaders are ignored
2010-12-04
People who are deemed social misfits or "losers" aren't effective leaders, even if they are crusading for a cause that would benefit a larger group, according to new research from Rice University, the University of Texas and Universitat de Valencia.
The study's authors observed the contributions of 80 participants in a repeated public-goods game and found that players were more likely to mimic the actions of a leader they perceived as a high-status individual; they ignored leaders perceived as low-status and, when they had a chance, punished them for trying to lead. ...
Do our bodies' bacteria play matchmaker?
2010-12-04
Tel Aviv ― Could the bacteria that we carry in our bodies decide who we marry? According to a new study from Tel Aviv University, the answer lies in the gut of a small fruit fly.
Prof. Eugene Rosenberg, Prof. Daniel Segel and doctoral student Gil Sharon of Tel Aviv University's Department of Molecular Microbiology and Biotechnology recently demonstrated that the symbiotic bacteria inside a fruit fly greatly influence its choice of mates.
The research was done in cooperation with Prof. John Ringo of the University of Maine, and was recently published in the Proceedings ...
Widely used arthritis pill protects against skin cancer
2010-12-04
A widely-used arthritis drug reduces the incidence of non-melanoma skin cancers – the most common cancers in humans – according to a study published this week in the Journal of the National Cancer Institute. The COX-2 inhibitor celecoxib (brand name Celebrex), which is currently approved for the treatment of osteoarthritis, rheumatoid arthritis and acute pain in adults led to a 62 percent reduction in non-melanoma skin cancers, which includes basal cell carcinomas and squamous cell carcinomas.
Celecoxib, a prescription-strength nonsteroidal anti-inflammatory drug (NSAID), ...