What if diagnosing a bacterial infection took minutes instead of hours? Vanderbilt scientists are working to make that a reality.
Every year, 23 million Americans visit hospitals and clinics to be treated for infections. Most patients will be swabbed or poked to collect one of many forms of bodily fluid containing the bacteria that is making them sick. But before the culprit bacteria can be identified in a lab, it must be grown and multiplied over the course of several hours until enough bacteria is present to be tested.
This process, called culturing, is time-consuming and not always effective. Meanwhile, patients must wait for a diagnosis and for antibiotic treatment.
A team of scientists at Vanderbilt is developing a new, one-step method of testing for bacterial infections that removes those steps and identifies bacteria directly by measuring light scatter when lab technicians shine a laser on a sample of saliva.
Bacteria reflect light in wavelengths corresponding to the chemical bonds within their cell structure. Scientists can collect the wavelengths of light reflected by a saliva sample and read them like a list of bonds, which can be used to identify the bacteria in the sample. Sophia Juarez, an undergraduate in the Locke Biosensing Lab which is leading this research, refers to this as the bacteria’s “fingerprint.”
In practice, lab technicians place a droplet of saliva on a two-millimeter-wide square of paper mounted on a thumb-sized glass plate, stick the plate in a laser machine, and read the reflected wavelengths of the sample to identify the bacteria.
Currently, Juarez is testing the concentration of bacteria needed to reflect an accurate fingerprint, which depends on the enhancement of reflected light using gold nanoparticles. These beads, which Juarez has nestled into microscopic perforations of the paper, are one-thousandth the diameter of a bacterium. Scattered like a bed of nails across the paper, the nanoparticles create an electromagnetic field around the bacteria that amplifies the light they reflect back, turning up the volume on the signal in the reading.
“This method has a lot of potential, but it’s not well understood and characterized right now because the only confirmed methods of it working are with a liquid sample in a liquid solution,” Juarez said.
Juarez affixed the nanoparticles to paper to minimize inconsistencies produced by mobile, randomly scattered nanoparticles in solution and is currently testing its efficacy. The switch to paper also makes the nanoparticles more shelf-stable, allowing them to be transported. This durability, combined with a handheld version of the laser system used in the Locke Biosensing Lab, could make this method of bacterial diagnosis accessible in remote settings.
“A lot of the methods of detecting pathogens are expensive, time consuming, and require trained personnel to do, so people in low-resource settings have no access to them,” Juarez said. “This test can be performed with a portable system, and you don’t have to prepare your sample before you run it. You just kind of drop it on there. So the process itself is really efficient and user friendly.”
Additionally, because the nanoparticles amplify reflected light, the laser is weak and runs on low power — half a milliwatt.
Juarez’s research is one step in the process of bringing this faster, more accurate, and less resource-intensive method of testing to hospitals and clinics of the future.
“My work is really a balance between what I’m actually doing in the lab in a vacuum and thinking about if it’s ever going to make it out of here,” Juarez said. “I think that’s a good thing. It keeps me looking at the big picture.”
References
“Bacteria Culture Test: What It Is, Types, Procedure & Results.” Cleveland Clinic, https://my.clevelandclinic.org/health/diagnostics/22155-bacteria-culture-test. Accessed 28 Mar. 2025.
Han, Xiao Xia, et al. “Surface-Enhanced Raman Spectroscopy.” Nature Reviews Methods Primers, vol. 1, no. 1, Jan. 2022, pp. 1–17. www.nature.com, https://doi.org/10.1038/s43586-021-00083-6.
“Infectious Diseases.” National Institutes of Health (NIH), 29 Jan. 2020, https://www.nih.gov/about-nih/what-we-do/nih-turning-discovery-into-health/our-biggest-health-challenges/infectious-diseases.
Juarez, Sophia, et al. “Design of a Paper-Based Surface-Enhanced Raman Spectroscopy Substrate for Bacteria Detection in Biofluid.” Biomedical Imaging and Instrumentation, 2024, https://2024bmesannual.eventscribe.net/searchGlobal.asp?mode=Presentations&SearchQuery=Sophia+juarez.McAden, E., et al. “Availability and Access of Bacterial Infection Diagnostics in the United States.” Prepared by Eastern Research Group, Inc. for the Office of the Assistant Secretary for Planning and Evaluation (ASPE), U.S. Department of Health and Human Services (HHS), Dec. 2024. https://aspe.hhs.gov/sites/default/files/documents/69ebc7133ec33e573a7786915f7918b6/bacterial-diagnostics-erg-research-synopsis.pdf.
