Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Photonic-plasmonic microcavity for ultrasensitive protein detection

20.08.2012
Measuring proteins in real-time down to fM solution concentration levels, corresponding to only a few thousand of protein molecules, has been demonstrated for the first time using a hybrid photonic-plasmonic Whispering Gallery Mode biosensor. Its unprecedented sensitivity is due to optical trapping of proteins at highly sensitive plasmonic hotspots.

Label free optical biosensors enable the monitoring of biomolecules and their interactions in often highly sensitive diagnostic assays. Several methods have been employed for this purpose, including Whispering Gallery Mode (WGM) biosensing, which offers a particularly sensitive approach to quantify the mass loading of biomolecules on the resonator surface with ultimate sensitivity estimated on the single molecule level.



The simplest WGM biosensor is a glass microsphere (typically 50–100 mm in diameter) where the resonant light remains confined by total-internal reflection.

WGM sensors derive their unprecedented sensitivity from the use of high quality-factor (Q-factor) optical resonances to monitor wavelength shift signals upon binding of biomolecules or nanobeads to the resonator surface. Even a single virus could be detected. Yet, if e.g. a single protein molecule shall be detected, the sensitivity has to be boosted.

There have been several approaches, such as the generation of hot spots using a hybrid photonic-plasmonic sensing concept with a gold nanoparticle (NP) layer coupled to a WGM biosensor. However, there are some drawbacks: First, measurements cannot be done directly in solution. Second, real-time analysis is not possible since the proteins have to be pre-adsorbed on the NPs. Third, proteins are adsorbed randomly within the NP layer – outside of plasmonic field enhancements sites – which lowers the detection sensitivity.

A German-American team led by Frank Vollmer and Melik C. Demirel now proposes an alternative concept overcoming these problems: optical trapping of protein molecules at the sites of plasmonic field enhancements in a random gold NP layer. The stable integration of the microsphere WGM biosensor with a wetted gold NP layer is critical for achieving ultra-sensitive detection.

Therefore, the silica microsphere cavity remains fixed on the Au NP layer. The Q-factor of the microsphere drops slightly but is still in the 105 range. After adding bovine serum albumin (BSA) solution at microliter of sample volumes, which enters the NP layer by capillary suction, the researchers observed an unexpectedly large significant wavelength shift.

The achieved sensitivity in the order of femtomole concentration levels was very surprising, and cannot be explained from random binding of the BSA molecules to the NP surface. Instead, the scientists hypothesized that the protein molecules prefer to bind to hotspot locations (i.e. closely spaced random NPs) of plasmon resonances excited in the NP layer due to optical trapping.

To validate this hypothesis, they calculated the electromagnetic field distribution in a model NP layer using generalized Mie theory and simulated the expected wavelength shift due to the binding of proteins. Their calculations showed that, indeed, optical trapping of the proteins at highly sensitive plasmonic hotspot locations is essential for achieving high sensitivity in microcavity biosensing.

The achieved sensitivity in the order of femtomole concentration levels was very surprising, and cannot be explained from random binding of the BSA molecules to the NP surface. Instead, the scientists hypothesized that the protein molecules prefer to bind to hotspot locations (i.e. closely spaced random NPs) of plasmon resonances excited in the NP layer due to optical trapping. To validate this hypothesis, they calculated the electromagnetic field distribution in a model NP layer using generalized Mie theory and simulated the expected wavelength shift due to the binding of proteins. Their calculations showed that, indeed, optical trapping of the proteins at highly sensitive plasmonic hotspot locations is essential for achieving high sensitivity in microcavity biosensing.

The Team, consisting of scientists at the Pennsylvania State University (USA), at BASF SE (Ludwigshafen, Germany), the Massachusetts Institute of Technology (Cambridge, USA), and the Max Planck Institute for the Science of Light (Erlangen, Germany), has established a new promising route towards single molecule resolution in WGM biosensors coupled to engineered or random plasmonic nanoantennas. Using a random NP layer has the advantage of integration to a microfluidic device, and gold NPs can be easily functionalized with recognition elements such as oligonucleotides or proteins. The approach could be of interest for many areas including medical biosensing and drug screening.

(Text contributed by K. Maedefessel-Herrmann)

Santiago-Cordoba, M. A., et al.; J. Biophotonics 5(8-9), 629-638 (2012)

Regina Hagen
Project Editor, Physical Sciences
Scientific, Technical, Medical, and Scholarly
Wiley-VCH Verlag GmbH & Co. KgaA
Rotherstrasse 21
10245 Berlin
Germany
T +49 (0)30 47 031 321
F +49 (0)30 47 031 399
regina.hagen@wiley.com

Regina Hagen | Wiley-VCH
Further information:
http://www.wileyonlinelibrary.com
http://www.wiley.com

More articles from Life Sciences:

nachricht Unique genome architectures after fertilisation in single-cell embryos
30.03.2017 | IMBA - Institut für Molekulare Biotechnologie der Österreichischen Akademie der Wissenschaften GmbH

nachricht Transport of molecular motors into cilia
28.03.2017 | Aarhus University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

'On-off switch' brings researchers a step closer to potential HIV vaccine

30.03.2017 | Health and Medicine

Penn studies find promise for innovations in liquid biopsies

30.03.2017 | Health and Medicine

An LED-based device for imaging radiation induced skin damage

30.03.2017 | Medical Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>