Study shows nanoshells ideal as chemical nanosensors

'Nanoshells' enhance sensitivity to chemical detection by factor of 10 billion

New research published in the Proceedings of the National Academy of Science finds that tailored nanoparticles known as nanoshells can enhance chemical sensing by as much as 10 billion times. That makes them about 10,000 times more effective at Raman scattering than traditional methods.

When molecules and materials scatter light, a small fraction of the light interacts in such a way that it allows scientists to determine their detailed chemical makeup. This property, known as Raman scattering, is used by medical researchers, drug designers, chemists and other scientists to determine what materials are made of. An enormous limitation in the use of Raman scattering has been its extremely weak sensitivity. While it was discovered almost three decades ago that roughened metallic surfaces could enhance Raman scattering signals by factors of 1 million, this "surface-enhancement" effect has been difficult to control, predict, and reproduce for practical sensing applications. Now, Rice researchers have shown that nanoshells can provide large, clean, reproducible enhancements of this effect, opening the door for new, all-optical sensing applications.

"Not only did we find that nanoshells are extremely effective at magnifying the Raman signature of molecules, we found each individual nanoshell acts as an independent Raman enhancer," said lead researcher Naomi Halas, the Stanley C. Moore Professor of Electrical and Computer Engineering, Professor of Chemistry and Director of Rice's Laboratory of Nanophotonics. "That creates an opportunity to design all-optical nanoscale sensors -- essentially new molecular-level diagnostic instruments -- that could detect as little as a few molecules of a target substance, which could be anything from a drug molecule or a key disease protein to a deadly chemical agent."

About 1/20th the size of a red blood cell, nanoshells are about the size of a virus. They are ball-shaped and consist of a core of non-conducting glass that is covered by a metallic shell, typically either gold or silver. The metal shell "captures" passing light and focuses it, a property that directly leads to the enormous Raman enhancements observed. Furthermore, nanoshells can be "tuned" to interact with specific wavelengths of light by varying the thickness of their shells. This tunability allows for the Raman enhancements to be optimized for specific wavelengths of light.

Discovered by Halas at Rice in the 1990s, nanoshells are already being developed for applications including cancer diagnosis, cancer therapy, diagnosis and testing for proteins associated with Alzheimer's disease, drug delivery and rapid whole-blood immunoassay.

In the current study, Halas and former graduate student Joseph B. Jackson, now with Nanospectra Biosciences, Inc., created thin films of nanoshells deposited atop plates of glass. Films with various densities were studied, as were films containing both silver and gold nanoshells.

Through painstaking analysis, Halas and Jackson showed that the nanoshells' 10 billion-fold increase in Raman effect was due entirely to the interactions of light with individual nanoshells. This is markedly different from the pattern exhibited by pure gold or silver nanoparticle films. In that case, the Raman enhancement is an aggregate effect, due to the presence of localized "junctions" or "hot spots" between metallic regions of the metallic film substrate.

The finding that individual nanoshells can vastly enhance the Raman effect opens the door for biosensor designs that use a single nanoshell, something that could prove useful for engineers who are trying to probe the chemical processes within small structures such as individual cells, or for the detection of very small amounts of a material, like a few molecules of a deadly biological or chemical agent.

Source: Rice University

Related stories:

Rice University researchers create 'nanorice'
Who better to invent "nanorice" than researchers at Rice University? But marketing and whimsy weren't what motivated the team of engineers, physicists and chemists from Rice's Laboratory for Nanophotonics (LANP) to make rice-shaped particles of gold and iron oxide.
Rice scientists unveil 'nanoegg'
Researchers at Rice University's Laboratory for Nanophotonics (LANP) have unveiled the "nanoegg," the latest addition to their family ultrasmall, light-focusing particles. A cousin of the versatile nanoshell, nanoeggs are asymmetric specks of matter whose striking optical properties can be harnessed for molecular imaging, medical diagnostics, chemical sensing and more.
How nanotubes enter cells
Scientists worldwide are teasing apart the precise mechanisms behind how tubes of carbon only nanometers or billionths of a meter wide enter cells, findings that researchers could employ to help these nanotubes deliver medicines or genes into the body, experts told UPI's Nano World.
'Nanoshells' simultaneously detect and destroy cancerous cells
Researchers at Rice University in Texas have developed a new approach to fighting cancer, based on nanoscale particles that can both detect and destroy cancerous cells. The report appears in the April 13 issue of the American Chemical Society's journal Nano Letters. ACS is the world's largest scientific society.
Plasmonics book gives overview of technology that could revolutionise computing
A book which gives an overview of plasmonics, an area of physics that could revolutionise computing and telecommunications over the next two decades, has been published by a researcher at the University of Bath.
Nano World: Acid sensors for cells
Scientists have devised the first sensors only nanometers or billionths of a meter long that can detect how acidic the environment around them is, experts told UPI's Nano World.
Rice scientists make first nanoscale pH meter
Using unique nanoparticles that convert laser light into useful information, Rice University scientists have created the world's first nano-sized pH meter.
Nano World: Gold nano vs. Alzheimer's
Gold particles only nanometers or billionths of a meter wide together with extremely weak microwaves can dissolve the abnormal protein clumps linked with Alzheimer's disease and potentially those linked with other degenerative illnesses as well, experts told UPI's Nano World.

News discussion:

Nanotechnology news