Researchers have found that enhancements in signal strength during surface-enhanced fluorescence and Raman spectroscopy can penetrate a nanoscale protective barrier. This breakthrough could significantly boost the sensitivity of biosensors and pave the way for innovative point-of-care diagnostic tools.
While we often imagine a biologist as someone studying a single bacterium under a microscope, contemporary scientists have access to advanced equipment that allows them to examine the inner workings of living cells at much finer scales. Fluorescence and Raman spectroscopy have emerged as essential techniques for observing biological activities without intrusive methods. Both approaches utilize a light source, typically a laser, to excite electronic transitions in fluorescence and molecular vibrations in Raman spectroscopy.
Nonetheless, the application of fluorescent tags can interfere with the natural behavior of cells, and Raman spectroscopy frequently produces weak signals. Utilizing a more intense laser or extending exposure times risks damaging sensitive biological molecules. Earlier versions of these techniques enhanced signal strength through metallic substrates or nanostructures, yet some adaptations could lead to cellular damage.
Now, a study published in Light: Science & Applications by researchers from Osaka University has introduced a novel technique for enhancing fluorescence and Raman signals over extended distances using a dense random array of silver (Ag) nanoislands. The analyte molecules are shielded from metallic structures by a 100-nanometer thick column-structured silica layer. This thickness is sufficient to safeguard the molecules being analyzed while still allowing the collective electromagnetic oscillations in the metal, known as plasmons, to amplify the spectroscopic signal. “We showed that plasmons in metals can influence areas greater than 100 nanometers, well beyond traditional theoretical predictions,” said lead author Takeo Minamikawa.
The research team demonstrated that employing these biocompatible sensor substrates can boost the signal by an astonishing ten million times. Moreover, since the metal nanostructures do not directly contact the molecules under examination, they are particularly well-suited for biological environments that might be affected by traditional methods. “Our substrates’ chemical stability and mechanical strength make them ideal for various applications, including detecting environmental pollutants or conducting medical diagnoses,” noted senior author Mitsuo Kawasaki. Additionally, these sensor substrates can be quickly and extensively produced using a thin-film fabrication technique known as sputtering, making new biosensing devices more cost-effective for industrial and healthcare settings.
