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Posted: Apr 11, 2016
Novel 2D spacer materials for surface plasmon coupled emission sensing
(Nanowerk Spotlight) Inexpensive and rapid handheld sensors for biomarkers can revolutionize healthcare, especially in resource-limited settings widespread in low and middle-income countries. The challenge in fabricating these biosensors is to detect weak emission signals when the biomarkers are at very low concentrations, as in the early stages of the disease.
While graphene and fullerenes perform very well for detecting isolated biomarkers, their ability to amplify emission of biomarkers in a real physiological milieu is limited due to their strong interactions with other biomolecules such as proteins and lipids.
A team of researchers from Clemson University and Sri Sathya Sai Institute of Higher Learning collaboratively developed new sensing platforms that use two-dimensional materials beyond graphene.
Similar to the fullerene-based sensors, these inexpensive biosensors are fabricated by coating thin-films of silver with an overcoat of two-dimensional (2D) spacer layers including MoS2, WS2, and BN.
In these sensors, the isotropic fluorescence from dye-stained biomarkes couples with plasmons from the silver film through the overcoated spacer layers.
Silver thin-films overcoated with MoS2 can enhance the emission from dyes such as Rhodamine by 17 times and thus improve their sensitivity at low concentrations. (Image: Pradyumna Mulpur)
"Metallic thin-films are double-edged swords that both simultaneously enhance and quench the biomarker emission," says Pradyumna Mulpur, a graduate student at Sri Sathya Sai Institute of Higher Learning and first author of this paper. "We previously found that nanocarbons are good spacer layers in addition to protecting the silver film from oxidation."
He notes that, despite their great potential, facile synthesis, and high stability, nanocarbons interact very strongly with a variety of biomolecules through delocalized pi-electron cloud.
The emergence of 2D materials beyond graphene presents new opportunities to overcome challenges posed by nanocarbons by selectively interacting with desired biomarkers.
"Following the realization of graphene, we were able to chemically exfoliate and isolate thin layers of other materials such as MoS2 and WS2," Ramakrishna Podila, an Assistant Professor in the Department of Physics and Astronomy at Clemson University and principal investigator of this study, tells Nanowerk. "Unlike graphene, MoS2 and WS2 do not exhibit strong π-interactions with biomolecules. We used this to our advantage to show that emission of dyes coupled to biomarkers as in the traditional ELISA tests can be enhanced by ∼20 times, even with MoS2 and WS2."
The researchers expect to extend this sensor design to real-time diagnostics in point-of-care settings in the near future. However, some limitations such as realizing continuous and uniform MoS2 and WS2 films without affecting the underlying Ag film still persist. The team hopes to build on the advances in bottom-up synthesis approach methods to resolve these challenges.