Researchers are developing a new way to identify bacteria in liquids

(a) Schematic of acoustic printing platform and confocal Raman setup. Droplets containing bacteria (purple) and nanorods (gold) suspended in EDTA solution are acoustically printed on a 200 nm gold-coated glass slide (see also Supplementary Figs 2–4). (b) Stroboscopic images of the time evolution of upward droplet ejection at ∼3.5 m/s from an open pool at an acoustic frequency of 44.75 MHz and a droplet ejection repetition rate of 1 kHz. Images were captured with an exposure time of 40 ms, and thus each frame consists of 40 droplet ejections, highlighting the ejection stability. Scale bar is 100 µm (see also Supplementary Figure 2). (c) Plot of droplet diameter versus resonant frequency of the ultrasonic transducer. Droplets were printed at 4.8, 17, 44.75, and 147 MHz and had droplet diameters of 300, 84, 44, and 15 μm, respectively, highlighting the tunability of acoustic droplet ejection. (see also Supplementary Figure 1). (d) Raman spectra of dried cell samples, incl S. epi, E. coliand red blood cells (RBCs) on a gold-coated slide. Credit: Nanograms (2023). DOI: 10.1021/acs.nanolett.2c03015

Shine a laser on a drop of blood, mucus or liquid waste and the light reflected back can be used to positively identify bacteria in the sample.

“We can learn not only that bacteria are present, but specifically which bacteria are present in the sample—E. coli, staphylococcus, streptococcus, salmonella, anthrax and more,” said Jennifer Dionne, associate professor of materials science and engineering and , thanks to radiology at Stanford University. “Each microbe has its own unique optical fingerprint. It’s like genetic and proteomic code written in light.”

Dionne is lead author of a new study in the journal Nanograms detailing an innovative method her team has developed that could lead to faster (near-instant), cheaper, and more accurate microbial testing of almost any liquid one might want to test for microbes.

Traditional cultivation methods still used today can take hours, if not days, to complete. A TB culture lasts 40 days, Dionne said. The new test can be done in minutes and promises better and faster infection diagnoses, improved antibiotic use, safer food, enhanced environmental monitoring and faster drug development, the team says.

Old dogs, new tricks

The breakthrough is not that the bacteria display these spectral fingerprints, a fact that has been known for decades, but in how the team was able to reveal these spectra within the dazzling array of light reflected from each sample.

“Not only does each type of bacteria exhibit unique light patterns, but almost every other molecule or cell in a given sample does as well,” said first author Fareeha Safir, Ph.D. student in Dionne’s lab. “Red blood cells, white blood cells and other components of the sample send back their own signals, making it difficult, if not impossible, to distinguish microbial patterns from the noise of other cells.”

A milliliter of blood—about the size of a raindrop—can contain billions of cells, only a few of which may be microbes. The team had to find a way to separate and amplify the light reflected only by the bacteria. To do this, they ventured off on several surprising scientific tangents, combining a four-decade-old technology borrowed from computers—the inkjet printer—and two cutting-edge technologies of our time—nanoparticles and artificial intelligence.

“The key to separating bacterial spectra from other signals is isolating the cells in extremely small samples. We use the principles of inkjet printing to print thousands of tiny blood dots instead of interrogating a single large sample,” explained co-author Butrus “Pierre” Khuri-Yakub, professor emeritus of electrical engineering at Stanford who helped develop the original inkjet printer in the 1980s.

“But you can’t just buy an inkjet printer off the shelf and add blood or sewage,” Safir pointed out. To circumvent the challenges in handling biological samples, the researchers modified the printer to place samples on paper using acoustic pulses. Each dot of printed blood is then just two trillionths of a liter in volume—more than a billion times smaller than a raindrop. At this scale, the droplets are so small that they may only fit a few dozen cells.

In addition, the researchers injected the samples with gold nanorods that attach to bacteria, if present, and act like antennas, drawing the laser light toward the bacteria and amplifying the signal to about 1,500 times its unamplified power. Properly isolated and amplified, bacterial spectra stick out like scientific sore thumbs.

The final piece of the puzzle is to use machine learning to compare the many spectra reflected from each printed dot of liquid to identify telltale signatures of any bacteria in the sample.

“This is an innovative solution with the potential to save lives. We are now excited about commercialization opportunities that can help redefine the standard of bacterial detection and single-cell characterization,” said senior co-author Amr Saleh, a former postdoctoral fellow at Dionne’s lab and now professor at Cairo University.

While this technique was created and perfected using blood samples, Dionne is equally confident that it can be applied to other kinds of fluids and target cells besides bacteria, such as testing drinking water for purity or perhaps detecting viruses faster, more accurately and lower. cost from current methods.

More information:
Fareeha Safir et al, Combining acoustic bioprinting with AI-assisted Raman spectroscopy for high-throughput identification of bacteria in blood, Nanograms (2023). DOI: 10.1021/acs.nanolett.2c03015

Provided by Stanford University

Reference: Researchers develop new way to identify bacteria in fluids (2023, March 2) Retrieved March 2, 2023, from

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