An Indian researcher has found that it is possible to use light as a fuel to move microbots in real-body conditions with intelligent drug delivery that is selectively sensitive to cancer cells

Microswimmers for drug delivery

• Made from the two-dimensional compound poly (heptazine imide) carbon nitride (aka PHI carbon nitride), these microbots are nothing like the miniaturised humans.
• They range from 1-10 micrometre (a micrometre is one-millionth of a metre) in size, and can self-propel when energised by shining light.
• While carbon nitride is an excellent photo-catalyst, the two-dimensional PHI has a sponge-like structure full of pores and voids and charge storage properties.
• The researchers found that the ions in the salty solution passed through the pores of PHI carbon nitride.
• Thus, there was little or no resistance from the salt ions.

How do they swim across the blood?

• The PHI carbon nitride microparticles are photocatalytic.
• Like in a solar cell, the incident light is converted into electrons and holes.
• These charges drive reactions in the surrounding liquid. The charges react with the fluid surrounding them.
• This reaction, combined with the particle’s electric field, makes the microbots (micro-swimmers) swim.
• As long as there is light, electrons and holes are produced on the surface of the swimmers, which in turn react to form ions and an electric field around the swimmer.
• These ions move around the particle and cause fluid to flow around the particle.
• So this fluid flow causes the micro-swimmers to move.

How does the ion movement occur?

• The ions move from the bright surface of the micro-swimmer to the rear end.
• The diffusion of the swimming medium in one direction propels the micro-swimmer in the opposite direction.
• This is like a boat moving in the direction opposite to the oar strokes.
• The particles are nearly spherical, and the incident light illuminates one-half of the sphere, leaving the other dark.
• As photocatalysis is light-driven, it occurs only on the brightened hemisphere.
• As the ions move from the bright side to the dark side, micro-swimmers march in the direction of the light source.

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