For years, paper has been used in relatively simple medical diagnostics, like pregnancy tests, while more complex analyses have required expensive lab-on-a-chip technologies, with channels created in glass or plastic and tiny pumps and valves directing the flow of fluids for testing.
Now researches have developed “microfluidic” devices from ordinary wax paper:
A laser is used to burn off the hydrophobic coatings in lines, dots and patterns, exposing the underlying water-absorbing paper only where the patterns are formed.
“Since the hydrophobic agent is already present throughout the thickness of the paper, our method creates islands of hydrophilic patterns,” Ziaie said. “This modified surface has a highly porous structure, which helps to trap and localize chemical and biological aqueous reagents for analysis. Furthermore, we’ve selectively deposited silica microparticles on patterned areas to allow diffusion from one end of a channel to the other.”
Those microparticles help to wick liquid to a location 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.”