Scientists at the S.N. Bose National Centre for Basic Sciences, Kolkata, have discovered how common molecules like amino acids and salts regulate the aggregation of gold nanoparticles.

About Gold Nano Particles (AuNPs)

• Overview: Gold Nanoparticles are tiny particles of gold, typically in the size range of 1–100 nanometers.
• At this nanoscale, gold exhibits unique physical, chemical, and optical properties that are very different from bulk gold.

Unique Properties of Gold Nano Particles

• Optical Property – Surface Plasmon Resonance (SPR): AuNPs strongly interact with light.
  • Their colour changes depending on particle size and whether they are dispersed or aggregated.
  • Example: Red → dispersed; Blue/Purple → aggregated.
• High Surface Area-to-Volume Ratio: Makes them highly reactive and useful in catalysis and drug delivery.
• Biocompatibility: Gold is generally safe in biological systems, allowing medical applications.
• Easy Functionalization: Can be coated with biomolecules (antibodies, DNA, drugs) for targeted applications.

Applications of Gold Nano Particles

• Medicine & Diagnostics:
• • Biosensors: Colour change helps detect diseases (e.g., pregnancy test strips, rapid diagnostic kits).
  • Drug Delivery: Targeted delivery of drugs to cancer cells.
  • Imaging: Used in medical imaging and photothermal therapy.
• Environmental Applications: Detects heavy metals, pollutants, or toxins in water and soil.
• Electronics & Optics: Used in optical devices, sensors, and nanoelectronics.
• Catalysis: Enhance chemical reactions due to large surface area.

Key Challenges

• Aggregation Problem: Gold nanoparticles tend to clump together, which changes their properties and reduces effectiveness.
• Cost & Scalability: Large-scale production is still expensive.

Research Findings

• Molecules Studied:
• • Guanidine Hydrochloride (GdnHCl): A strong salt used in labs; caused rapid, dense clustering of nanoparticles.
  • L-Tryptophan (L-Trp): An amino acid present in proteins and linked with sleep/relaxation; disrupted the clustering when combined with GdnHCl.
• Phenomenon Identified: “Frustrated aggregation” — nanoparticles attempt to clump but L-Trp interferes, creating looser, branched, stable structures.

Research Methodology

• Technique Used: Evanescent Wave Cavity Ringdown Spectroscopy (EW-CRDS).
• Utility: Allowed real-time monitoring of nanoparticle behaviour with high sensitivity.
• Observation: L-Trp stabilises guanidinium ions, slowing down aggregation and enabling stable, open nanoparticle structures.

About Evanescent Wave Cavity Ringdown Spectroscopy (EW-CRDS)

• Overview: It is an ultra-sensitive optical technique used to study light–matter interactions at surfaces or interfaces.
• Mechanism: Works by measuring the decay time of light inside an optical cavity, where the evanescent wave (an exponentially decaying field near the surface) interacts with molecules or nanoparticles.
• Scope: Provides real-time, high-precision monitoring of nanoscale processes such as adsorption, aggregation, or chemical reactions.

Significance of the Discovery

• Fundamental Insight: Provides a new understanding of nanoparticle interactions with everyday biomolecules.
• Technological Impact:
• • Enables design of more reliable biosensors.
  • Improves diagnostic tools through stable nanoparticle behaviour.
  • Enhances drug delivery systems by ensuring controlled particle aggregation.
• Scientific Contribution: Demonstrates how advanced optical tools can probe delicate nanoscale processes.

DOWNLOAD PDF