• Using a novel approach, researchers at the National Institute for Interdisciplinary Science and Technology (CSIR-NIIST), Thiruvananthapuram have formulated a fast-drying fluorescent ink that retains over 70% photoluminescence intensity even at the end of one month.
  • There was 26% drop in emission intensity within one hour of printing using the ink containing the fluorescent dye and further drop of 2% in two hours.
  • This has become possible with the team encapsulating the fluorescent dye — fluorescein — within double-layered silica nanospheres.
  • Since encasing the dye using a single layer of silica did not completely prevent dye leakage, the researchers used a second layer for encapsulation.
  • The silica nanospheres are 70-80 nanometres in size.
  • As a result of the double-layered encapsulation, fluorescent dye is largely protected from dispersants, solvents and binders present in the ink.
  • So there is less likelihood of reduction in photoluminescence intensity through dye leakage.
  • Encapsulation of the dye in double-layered silica nanoparticles also prevents cluster formation. The dye used without any encapsulation lacks photostability and the fluorescence completely decays within a couple of hours. The results were published in the journal ACS Omega.

The other Angles

  • Fluorescent ink is used for a wide range of applications in domains such as anticounterfeiting, information storage, bioimaging, smart packaging, and nanoelectronics. Retention of photoluminescence for prolonged periods is a major challenge in fluorescent inks.
  • Since the fluorescent dye should not come in contact with the solvent present in the ink as this would cause decay in photoluminescence, we encapsulated it in double-layered silica nanoparticles
  • The fluorescent double-layered silica nanoparticles assemblies were synthesised through a reverse microemulsion technique.
  • When dye encapsulated in double-layered nanoparticles was dispersed in the solvent, it shows strong fluorescence.

Tell us about the Quick drying

  • Another advantage that the team observed is the quick drying of the ink at room temperature.
  • It dried in less than 20 seconds at room temperature.
  • The formulation of the ink was meticulously designed so as to allow quick drying without using any external drying agents
  • The dried ink containing the dye is cream in colour under visible light but turns green when exposed to ultraviolet light.
  • When the UV light is cut, the dye immediately regains its original colour (cream).