Manipulation of light at the nanoscale helps advance biosensing

(Press-News.org) Traditional medical tests often require clinical samples to be sent off-site for analysis in a time-intensive and expensive process. Point-of-care diagnostics are instead low cost, easy-to-use, and rapid tests performed at the site of patient care. Recently, researchers at the Carl R. Woese Institute for Genomic Biology reported new and optimized techniques to develop better biosensors for the early detection of disease biomarkers.

People have long been fascinated with iridescence of peacock feathers, appearing to change color as light hits them from different angles. With no pigments present in the feathers, these colors are a result of light interactions with nanoscopic structures, called photonic crystals, patterned across the surface of the feathers. 

Inspired by biology, scientists have harnessed the power of these photonic crystals for biosensing technologies due to their ability to manipulate how light is absorbed and reflected. Because their properties are a result of their nanostructure, photonic crystals can be precisely engineered for different purposes.

The Nanosensors Group at the University of Illinois Urbana-Champaign, led by Professor of Electrical and Computer Engineering Brian Cunningham (CGD leader), previously developed photonic crystal-based biosensors that amplify the fluorescence using gold nanoparticles, which act as tags for sensing various molecular biomarkers. But while this innovative technology enables low-level detection of biomarker molecules, it still has room for further improvement.

“Traditionally, metal nanoparticles, especially gold, offer the potential for fluorescence enhancement, but suffer from a fundamental flaw at close range,” said Seemesh Bhaskar, an IGB fellow in the CGD research theme and lead author of the study. “These nanoparticles can quench— or decrease—the very fluorescence signals they aim to amplify. This creates a dead zone of detection, limiting the sensitivity of biosensors.”

In a paper published in MRS Bulletin, the research team aimed to overcome this limitation by introducing a new class of cryosoret nanoassemblies; these organized structures comprised of gold nanoparticle subunits are formed via rapid cryogenic freezing. 

“Self-assembly is a fundamental principle of nature, whether it's the formation of planetary systems in cosmology or the precise organization of nucleotides in DNA,” Bhaskar said. “What individual nanoparticles cannot accomplish alone becomes possible through their collective organization. At its core, it’s about engineering optical behavior—both structurally and functionally—through deliberate design.”

By integrating these cryosoret nanoassemblies with specially designed photonic crystals, the fluorescence demonstrated a 200-fold signal enhancement compared to the photonic crystal alone. This showed that fluorescence quenching was effectively minimized, making this technology a promising avenue for detecting low concentrations of biomarkers.

Building upon this work, the team next sought to introduce magnetic tunability into the nanoassemblies, with the long-term goal of developing intelligent, responsive biosensors.

Light is a specific frequency range of electromagnetic radiation; other examples include radio waves, microwaves, and X-rays. Electromagnetic radiation travels through space in the form of waves, and as its name suggests, consists of both electrical and magnetic components. While many biosensing systems take advantage of the electrical component of light, the magnetic component is largely overlooked.

In a study reported in the journal APL Materials, Bhaskar and his colleagues designed magneto-plasmonic cryosoret nanoassemblies. They integrated these nanoassemblies onto a photonic crystal interface and found that it successfully harnessed both the electric and magnetic components of light. They tested their platform using a common fluorophore, which resulted in ultra-sensitive detection in the attomolar range, while still minimizing fluorescence quenching. 

Overall, this dual-mode interaction allows for enhanced control over light-matter interactions at the nanoscale, offering a new method to design highly sensitive and tunable biosensing platforms.

“This work represents a hybrid optical platform where photons are not merely emitted—they are orchestrated,” Cunningham said. “This convergence of photonic-plasmonic simulations, advanced nanofabrication, and chemical engineering principles has far-reaching implications, particularly in the realm of medical diagnostics.”

Moving forward, the researchers plan to continue optimizing the cryosoret nanoassemblies to target specific biomarkers, like microRNAs, circulating tumor DNA, and viral particles, for early detection of cancer and infectious disease. They hope that with further improvement, point-of-care technologies can meet the pressing need for sensitive, accessible, and deployable biosensing systems.

The publication in MRS Bulletin “Photonic-crystal-enhanced fluorescence: Template-free gold cryosoret nanoassembly steering, dequenching, and augmenting the quenched emission from radiating dipoles” can be found at https://doi.org/10.1557/s43577-024-00850-2

The publication in APL Materials “Photonic crystal band edge coupled enhanced fluorescence from magneto-plasmonic cryosoret nano-assemblies for ultra-sensitive detection” can be found at https://doi.org/10.1063/5.0251312 

The work was supported by the National Institutes of Health, National Science Foundation, and Cancer Center at Illinois.

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