A derivative of the Stanford University logo printed from droplets containing a 1:1 mixture of Staphylococcus epidermidis bacteria and mouse red blood cells (RBCs) onto a gold-coated slide. Droplets were printed using 147 MHz acoustic transducer. Credit: Fareeha Safir
Key points:
- Researchers used old inkjet printer technology to create a faster way to identify bacteria in fluid samples.
- The laser-based method relies on detection of spectral fingerprints on a very small scale.
- The technique can also be applied to other fluids and target cells.
A team of scientists from Stanford University have invented a faster and more inexpensive way of identifying bacteria in fluids using laser technology based on the principles of inkjet printing.
The innovation, which can identify bacteria in virtually any fluid in mere minutes, is a much faster approach compared with traditional culturing methods that can take hours or days to complete. It takes advantage of the fact that each type of bacterium demonstrates unique patterns of light. However, every other molecule or cell in a given sample does too, so the researchers first had to figure out how to separate and amplify the light reflecting from the bacteria alone. They discovered the key was to isolate the cells in extremely small samples.
“We use the principles of inkjet printing to print thousands of tiny dots of blood instead of interrogating a single large sample,” explained co-author Butrus “Pierre” Khuri-Yakub, a professor emeritus of electrical engineering at Stanford who helped develop the original inkjet printer in the 1980s.
Khuri-Yakub and colleagues modified the printer to put samples to 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 that scale, the droplets are so small they hold just a few dozen cells.
In addition, the researchers infused the samples with gold nanorods that attach themselves to bacteria, if present, and act like antennas, drawing the laser light toward the bacteria and amplifying the signal 1500 times over. Appropriately isolated and amplified, the bacterial spectra stick out like scientific sore thumbs.
The final piece of the puzzle was the use of machine learning to compare the several spectra reflecting from each printed dot of fluid to spot the telltale signatures of any bacteria in the sample.
“It’s an innovative solution with the potential for life-saving impact. We are now excited for commercialization opportunities that can help redefine the standard of bacterial detection and single-cell characterization,” said senior co-author Amr Saleh, a former postdoctoral scholar in Dionne’s lab and now a professor at Cairo University.
The research team says the technology can be applied to other fluids and target cells beyond bacteria, such as testing drinking water for purity or spotting viruses faster, more accurately, and cheaper than present methods.