Sujan Manna, a doctoral student at the Indian Institute of Technology Madras, studies materials chemistry, particularly nanomaterials and their structure-property-function relationships. He examines how gold and silver nanoparticles and nanoclusters—tiny, atomically precise groups of atoms with a fixed molecular formula—interact, aiming to determine which features are best suited for practical applications, such as for use in biosensors, pathogen detection, and point-of-care diagnostics.
Sujan Manna is a spectroscopist, focusing on materials chemistry research, and a data enthusiast.
Sujan Manna
To do this, Manna uses a custom-built instrument that couples single-particle Raman spectroscopy and dark-field imaging. These techniques reveal the chemical species present on or between nanoparticles and determine whether a particle exists as a monomer, dimer, or part of a larger aggregate. When two nanoparticles are extremely close, they can form a “hotspot,” which enhances the Raman signal compared to that of an isolated monomer—a phenomenon known as surface-enhanced Raman spectroscopy (SERS). For instance, sharp-tipped structures such as gold nanotriangles can produce a stronger detected signal.
Under dark-field microscopy, these interactions become vividly apparent. Although the nanoparticles are not inherently gold in color, their light scattering produces bright signals that are a stark contrast to the inky-black background. The process of looking for gold nanoparticles is akin to finding and tracing constellations in the night sky, searching for recognizable patterns in shifting forms.
During one experiment, however, he encountered an unexpected image. “I didn’t see any particular scattering spectrum of gold nanoparticles,” Manna recalled. Puzzled, he scanned the field for his nanotriangles and noticed an unusual form at the edge of his view. At first, it seemed insignificant, but on closer inspection he found himself wondering, “What is this seahorse from the deep blue ocean doing here?”
The dark-field image was devoid of the typical particles, yet it was luminous in its own way—a golden spectacle in the form of a seahorse-shaped structure, as depicted in the above image. The sight made Manna pause. “All that glitters is not [always] gold.”
Sujan Manna uses Raman spectroscopy and dark-field imaging to analyze gold nanoparticles.
Sujan Manna
He remarked that there are many unplanned moments in the life of a scientist, but sometimes these moments are where discoveries lie, much like the accidental discovery of penicillin. “So, sometimes this unexpected result from the experiment can give immense pleasure.” Although the structure was likely formed from organic debris and boundary effects, he described the observation as “complete serendipity,” noting that he had not encountered similar shapes since.
Beyond nanoparticle characterization, Manna expressed his interest in leveraging these methods for biological applications such as SERS-biosensors for bacteria or waterborne contaminants. “Nowadays, surface-enhanced Raman spectroscopy is really having a new frontier opening with biological [research].”
Got an eye-catching, science image that tells a story? Submit it for a feature in our Science Snapshot column!