Relevance: GS-III (Science and Technology; Nanotechnology and applications).

What is new?
A team of researchers has shown a way to “paint” microscopic gold particles with tiny polymer patches using an atomic stencil—much like an artist masks a canvas and applies colour only where needed. At the nanoscale, this masking allows scientists to place different chemicals on different parts of the same particle with near-atomic precision. The result is a patchy nanoparticle that behaves like a smart Lego brick: it knows how and where to stick to other bricks to build complex structures.

Why this matters
Nanoparticles—objects a few to a few hundred nanometres wide—are the building blocks of future catalysts, drug carriers, sensors, electronic inks and energy materials. Until now, making large quantities of particles with different functional patches at precise locations has been difficult. The atomic stencil method promises:

• Precision: patterns can be repeated on many particles, leading to uniform behaviour.
  
• Programmable self-assembly: different patches “recognise” each other, so particles line up into desired shapes (chains, sheets, lattices).
  
• Tunability: by changing the stencil or the polymer “paint,” scientists can switch how particles attract, repel, or react.
  
• Scalability: the chemistry uses solution steps that can, in principle, be scaled up.
  

How it works—simple picture

1. A nanoparticle’s surface is first covered with molecules that can be selectively protected.
   
2. A polymer mask—the stencil—blocks certain zones.
   
3. Exposed zones are “painted” with a different molecule or catalyst site.
   
4. Removing or shifting the mask and repeating the steps creates multi-patch particles, including Janus particles (two different faces) and more intricate patterns.
   

Potential uses

• Green chemistry: catalysts where only the desired reaction site is exposed, improving efficiency for fuel cells or hydrogen production.
  
• Medicine: targeted drug delivery where one patch binds to a tumour marker while another carries a therapeutic.
  
• Electronics and photonics: particles that self-assemble into conductive paths or light-guiding films at low temperatures.
  
• Environmental sensing: surfaces that capture specific toxins selectively.
  

India angle
India’s Nano Mission under the Department of Science and Technology funds nanoscience centres, fabrication facilities and translational projects. Techniques like atomic stencilling align with this mission by enabling high-value materials for energy, health and electronics. Safety guidelines on handling nanomaterials in laboratories will remain important as production scales.

Key terms

• Nanometre: one-billionth of a metre.
  
• Patchy nanoparticle: a particle whose surface has chemically distinct “patches.”
  
• Janus particle: a two-faced particle with different chemistries on opposite sides.
  
• Self-assembly: parts organising themselves into larger structures without external placement.
  
• Catalytic site: a spot on a surface where a reaction happens faster.
  

Exam hook
Use this story to illustrate structure–property links in nanotechnology: controlling where chemistry sits on a particle controls how materials assemble and what they can do.

UPSC Prelims question
Consider the following statements:

1. Patchy nanoparticles can be designed to self-assemble because different surface regions interact selectively.
   
2. The Nano Mission in India is implemented by the Department of Science and Technology.
   Which of the statements given above is/are correct?
   (a) 1 only (b) 2 only (c) Both 1 and 2 (d) Neither 1 nor 2
   Answer: (c)
   

One-line wrap
By masking and “painting” at the atomic scale, scientists are turning nanoparticles into programmable Lego bricks for the next wave of catalysts, medicines and electronics.