Researchers discuss findings, applications of discovered gold properties.
With applications ranging from plant pathology and medicine to food and water quality, nanoporous gold (NPG) offers a faster, more cost-effective method in early pathogen detection.
After three years of research on NPG specific to pathogen detection, the UC Davis Seker Lab recently published two papers demonstrating usage of the sensor coating material in sensing viral and bacterial DNA.
“Nanoporous gold is a material you can picture as metal sponge, like a gold sponge,” said Erkin Seker, senior author of the study and assistant professor of electrical and computer engineering at UC Davis. “The pores are the size of a thousandth of a hair. We can use this as a coating for a biosensor for DNA molecules in pathogens like viruses or bacteria. If DNA molecules come in contact with the sensor, it sends a signal so can we can tell if we’ve contacted a pathogen or not.”
The spongy nature of NPG’s surface results in an increased surface area, which increases the degree of detection in less-than-optimal environments.
“Since [NPG] has a very high surface area, it can pack more molecules into the electrode which enables us to go to very low detection limits of infected DNA,” said Pallavi Daggumati, main researcher and graduate student in the Department of Electrical and Computer Engineering. “If the infected DNA is present in low amounts, normal techniques in labs cannot pick up on such low quantities of DNA, but this material can.”
Detection methods used today differ from NPG in time and portability. Sometimes, pathogens are located in complex environments. For example, blood also contains other cells and proteins which need to be cleared out to isolate the target DNA molecules. While other methods take a significant amount of time in sample purification and pathogen identification, NPG results are read in just a couple of hours.
“In one method, they get the blood sample and let it culture for a while to let the bacteria grow,” Seker said. “When they grow, you can detect it by a color change, which takes about a week. And then you do the identification about what kind of pathogen it is, so it’s lengthy. There are some technologies that take 10 to 12 hours or a day, but these have shortcomings with the sample clean-up.”
In contrast, NPG’s porous surface allows it to act as a sieve in complex environments, eliminating the necessity of an extra purification step. Researchers predict this will greatly decrease the time spent on sample preparation.
“Blood has lots of different things [involved in it],” Daggumati said. “DNA, protein and other big molecules that can interfere with the molecule of interest. Generally, labs use materials to block these, but these materials are not very reliable and it’s hard to get the coating off the sensor material. With this spongy gold, DNA can easily go through.”
DNA molecules on the surface of the sensor enable it to be specific to certain types of viruses or bacteria. Researchers can also control how porous the material is to aid in sensing target DNA.
“We can manipulate or tune the morphology of the nanoporous gold material, so we can make it more porous or less porous” said Zimple Matharu, the main researcher of the study and post-doctorate in the Department of Electrical and Computer Engineering. “It’s very controllable. We saw that we have different morphologies that show completely different target concentration ranges.”
Currently, the identification process occurs in what is known as a “bench-top system,” a system used on a laboratory workbench. However, the Seker Lab is looking to develop handheld devices, enabling researchers to take devices into the field.
Applications of this device could impact agriculture, health and medicine. NPG can be used to detect infection in plants before symptoms are visible. In humans, early detection could save money, decrease unnecessary treatments and allow a faster response in treating the infection. The material can also be used to detect contaminants in food and water.
“This can also go into the food and agricultural industry,” Daggumati said. “We can tailor the sensor to work in such environments as well; it’s just changing the recognition material on the sensors. As of now, we’ve just demonstrated all the concepts. The next phase is clinical trials.”
Because use of the device is in vitro (outside the body), no FDA approval is required, making it easier for the Seker Lab to begin clinical trials.
“We’ve started a collaboration with the medical school to look at real blood samples of patients to verify diseases in patients,” Seker said. “We’re also looking into detecting fruit pathogens or plant pathogens.”
Seker is also interested in studying applications of NPG in neurological disorders, especially epilepsy.
“Devices can be inserted into brain to detect activity,” Seker said. “One goal is to detect electrical activity that may signal an epileptic seizure is occurring. Once we detect that, the sponge can be activated to release drug molecules.”
Christopher Chapman, researcher and fourth-year graduate student in biomedical engineering, works in Seker’s lab group, which is studying this application.
“If we can create a device that has the ability to record long term from an epileptic trigger point, you basically would know where the epileptic seizure is starting and be able to plant a device with nanoporous gold sensing on that trigger point,” Chapman said. “So we’d be able to chronically record that signal and also release drugs from the electrode. We’d be able to sense upcoming seizures and apply drugs directly to the trigger point.”
Seker’s work with pathogen detection is funded by UC Davis Research Investments in the Sciences and Engineering and an award from the National Science Foundation. The research surrounding NPG involved a collaboration with various departments, including biomedical engineering, microbiology and plant pathology.
“I think it’s a very exciting area,” Matharu said. “This is something new we are working on and I think it will be very, very beneficial for the biomedical industry.”