Context:

• Scientists from S. N. Bose National Centre for Basic Sciences (DST Institute), Kolkata have discovered a new behavior in the aggregation of gold nanoparticles (AuNPs) influenced by amino acids and salts.

Key Points:

• Scientists found that everyday molecules — such as amino acid (L-Tryptophan) and a commonly used laboratory salt (Guanidine Hydrochloride / GdnHCl) — can control the clustering (aggregation) process of gold nanoparticles.
• When GdnHCl alone is added, nanoparticles form dense clusters quickly, changing their optical and color properties — which can be harmful for the stability of biosensors and optical tools.
• When both L-Tryptophan and GdnHCl are added together, instead of dense clusters, open, branch-like structures are formed. Scientists have named this process “frustrated aggregation” — meaning particles attempt to fully stick together, but the amino acid (L-Trp) obstructs the process.

Technical Aspect and Method:

• The team used one of the world’s most sensitive optical techniques — Evanescent Wave Cavity Ringdown Spectroscopy (EW-CRDS) — which revealed that L-Trp slows down the effect of GdnHCl and maintains the clusters as open and stable.
• This method can measure real-time updates in nanoparticle behavior.

Applications:

• Biosensors: Virus detection
• Diagnostics: Imaging
• Drug Delivery: Targeted therapy
• Environment: Pollutant detection

Gold Nanoparticles (AuNPs) :

• These are nanoscale particles made of gold (Au).
• Their size ranges from 1 to 100 nanometers (nm).

Structure:

• Gold atoms combine to form nanoparticles in shapes such as spheres, rods, shells, and stars.
• Their color is not the typical yellow of bulk gold but can appear red, purple, or blue.

Properties:

• Optical Properties (Surface Plasmon Resonance - SPR): Their color changes due to SPR.
• Chemical Stability: Gold is inert, making AuNPs stable.
• Surface Modification: Their surface can be easily functionalized with biomolecules (DNA, proteins) or drugs.
• Biocompatibility: Safe to use inside the human body.

Synthesis Methods:

• Chemical reduction (e.g., citrate reduction method – the most common).
• Biological synthesis (green synthesis using plant extracts, microorganisms).
• Physical methods (laser ablation, UV irradiation, etc.).

Applications:

Medical and Diagnostics:

• Identification and treatment of cancer cells (drug delivery, photothermal therapy).
• Biosensors (e.g., used in COVID-19 test kits).
• Imaging (MRI/CT scan contrast agents).

Industry and Technology:

• Electronics and nano-circuits.
• Chemical catalysis.
• Environmental pollution detection.

Research and Education:

• Used as model particles in nanotechnology research.

Unique Properties of Gold Nanoparticles (AuNPs)

Surface Plasmon Resonance (SPR):

• When light hits AuNPs, surface electrons oscillate collectively.
• This makes their color different from bulk gold (red, purple, blue).
• This property is highly useful in biosensors, imaging, and diagnostics.

High Surface Area to Volume Ratio:

• Due to their small size, the surface area is very large.
• Molecules can easily attach to the surface.
• Important for drug delivery and catalysis.

Chemical Stability:

• Gold is an inert metal, making AuNPs stable even in reactive environments.
• They do not degrade easily inside biological systems.

Biocompatibility:

• AuNPs are comparatively non-toxic in the human body.
• Hence, they are used in drug delivery, cancer therapy, and vaccines safely.

Optical Properties:

• AuNPs have powerful optical absorption and scattering.
• Their size and shape influence their color and absorption.
• Useful in imaging, photothermal therapy, and biosensors.

Electrical & Catalytic Properties:

• AuNPs have useful electrical conductivity.
• Their small size enhances chemical reactions (catalysis).

Shape & Size Dependent Properties:

• Their optical, electrical, and catalytic behavior changes depending on their shape (spheres, rods, shells, stars).
• This versatility makes them highly valuable.

S. N. Bose National Centre for Basic Sciences (SNBNCBS)

• Established: 1986
• Named after: Famous Indian physicist Satyendra Nath Bose
• It is an autonomous research institute.
• Location: Salt Lake, Kolkata, West Bengal
• Administration: Functions under the Department of Science & Technology (DST), Government of India
• Fields of Work: Conducts advanced research in basic sciences, particularly in physics, chemistry, biology, and interdisciplinary areas.