Date: Nov 03, 2013 Author: Charles Q. Choi Source: Scientific American (
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Smartphone companies often boast how much better their devices' cameras are than those of their rivals, but scientists may have them all beat—they can spot single viruses with a new lightweight, portable imaging system that attaches to smartphones. The power to see single molecules with the system might arrive soon, experts added.
The entire system, housed in a casing made with a 3-D printer, weighs roughly as much as a cup of uncooked white rice. In experiments, the system could spot particles as small as roughly 100 nanometers. (One nanometer is one billionth of a meter.) The researchers found it could also detect single viruses such as human cytomegalovirus, which can endanger the lives of patients with weakened immune systems and measures about 150 to 300 nanometers in size. HIV, rabies and influenza are similarly large viruses. "It is the first time that single nanoparticles and viruses have been detected using a cellphone-based field-portable imaging system," says Aydogan Ozcan, an electrical engineer and bioengineer at the University of California, Los Angeles. Ozcan and his colleagues described their setup in the October 22 issue of ACS Nano.
Molecules called fluorophores help pinpoint the tiny objects under examination. The fluorophores latch onto specific targets (say, a particular virus) and fluoresce under certain wavelengths of light to reveal the location of their quarry. The imaging system shines a blue laser on the fluorophores to excite them, then directs the resulting light through a lens and into the phone's camera. "These results show that you do not necessarily need a sophisticated and expensive microscope to see small objects down to several hundred nanometers in diameter," says physicist Saumyakanti Khatua at Leiden University in the Netherlands, who did not take part in the research. "One very important application could be in detecting viruses in rural areas where laboratory facilities are very limited."
So far, the device can only detect objects tagged with hundreds of fluorophores—it cannot image single fluorophores. But that limitation may be short-lived, researchers say. "We believe detection of single molecules can be achieved through some minor modification of the existing device," says Khatua, who published a commentary about the research with his colleague Michel Orrit in ACS Nano. For instance, the imaging system could readily be equipped with lenses that collect more light and antennas that can make the fluorophores shine brighter. "These proposed changes do not require extensive alteration in the design, so [they] can be implemented soon," Khatua says.
Other researchers have already developed sensors that can detect the presence of single molecules. One advantage of the new microscopy system over such single-molecule sensors is that it not only detects the presence of targets, but can also display where they are located, which can be key in analyzing biological and other complex systems, Khatua says.
In addition to detecting viruses before the first symptoms of illness might appear, potential applications for the smartphone microscope include detecting bacteria or other impurities in food and water. The potential to detect and identify single molecules could open up an even wider range of applications, such as forensic analysis, pollution monitoring and authentication of goods. "Think, for example, of a geologist identifying minerals within their rocky matrix or of a repair workshop immediately able to choose the proper glue for an unknown polymer part," Khatua and Orrit wrote in their commentary. "The ever-growing popularity of smartphones, with already more than a billion in use, coupled with great technological advances in making faster processors and more sensitive cell phone cameras will certainly extend the reach of such devices in the future."
As for Ozcan, his system may soon make the leap from laboratory demonstration to the real world. He has founded a start-up called Holomic to commercialize the device and others like it.
