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Analytical Chemistry

Multicolored Crystals Synthesized For Bar Codes

Microrods could have applications for counterfeiting prevention, biological sensing

by Jyllian Kemsley
March 31, 2014 | A version of this story appeared in Volume 92, Issue 13

Credit: J. Am. Chem. Soc.
A letter stamped with transparent microrod-based ink can be illuminated with infrared light.
Micrograph shows a stamped “S” made with microrod ink and a magnified image showing individual green microrods with red tips.
Credit: J. Am. Chem. Soc.
A letter stamped with transparent microrod-based ink can be illuminated with infrared light.

Luminescent materials find wide use in areas such as anticounterfeiting and biological sensors, especially when patterned as bar codes. Such materials, however, can be difficult to make or require expensive instrumentation to detect. New microrods can be easily synthesized to emit multiple colors by doping with various lanthanides, reports a group led by Xiaogang Liu of the National University of Singapore (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja5013646). The rods are composed of NaYF4 and doped with ytterbium, thulium, or erbium in varying proportions to emit blue, green, or red light in response to infrared radiation. The researchers grew single-color rods in solution to dimensions of 1.7 µm long and 0.14 µm in diameter. They then added tips of another color by incubating the rods with nanoparticles containing a different dopant. The rods and their tips can be distinguished by using a standard optical microscope. Dispersing the microrods in dimethyl sulfoxide yielded an ink that remains transparent under ambient light. The researchers used the ink to stamp letters on paper and illuminated them with IR light. In cell culture experiments, the rods penetrated the outer membranes of cancer cells, showing promise for biological applications.

Micrograph shows fluorescent microrods, one red with blue tips and one blue with green tips.
Credit: J. Am. Chem. Soc.
Selective doping leads to 2-µm-long rods of various colors.


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