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Those microparticles help to wick liquid to a loca- tion where it would combine with another chemical, called a reactant, causing it to change colors and indicating a positive or negative test result.
Having a patterned hydrophilic surface is needed for many detection methods in biochemistry, such as enzyme-linked immunosorbent assay, or ELISA, used in immunology to detect the presence of an antibody or an antigen in a sample, Ziaie said.
To demonstrate the new concept, the researchers created paper strips containing arrays of dots dipped in luminol, a chemical that turns fluorescent blue when exposed to blood.
“Then we sprayed blood on the strips, showing the presence of hemoglobin,” said Ziaie, whose research is based at the Birck Nanotechnology Center in the university‘s Discovery Park. “This is just a proof of concept.”
Laser modification is known to alter the “wettability” of materials by causing structural and chemical changes to surfaces. However, this treatment has never before been done on paper, he said.
The researchers performed high-resolution imaging and spectroscopic analysis to study the mechanism behind the hydrophobic-hydrophilic conversion of laser-treated parchment paper. The new approach is within a research area called paper microfluidics.
“Other techniques in paper microfluidics are more complicated,” Ziaie said.
11-05 :: May/June 2011
For example, other researchers have developed a method that lays down lines of wax or other hydro- phobic material on top of untreated, hydrophilic paper.
“Our process is much easier because we just use a laser to create patterns on paper you can purchase commercially and it is already impregnated with hydrophobic material,” Ziaie said. “It‘s a one-step process that could be used to manufacture an in- expensive diagnostic tool for the developing world where people can‘t afford more expensive analytical technologies.”
The strips might be treated with chemicals that cause color changes when exposed to a liquid sample, with different portions of the pattern revealing specific details about the content of the sample. One strip could be used to conduct dozens of tests, he said.
The strips might be inserted into an electronic rea- der, similar to technology used in conventional glu- cose testers. Color changes would indicate the pre- sence or absence of specific chemical compounds.
Girish Chitnis, Zhenwen Ding, Chun-Li Chang, Cagri A. Sa- vran and Babak Ziaie: Laser-treated Hydrophobic Paper: An Inexpensive Microfluidic Platform, In: Lab on a Chip, Vol. 11(2011), Issue 6, Pages 1161-1165, DOI:10.1039/ C0LC00512F: