ACS Nano http://doi.org/6cg (2015)

ACS Nano http://doi.org/6ch (2015)

Paper is light, flexible, inexpensive, biodegradable, and is made from abundantly available materials such as plants and non-pathogenic bacteria found on fruits. As a result, it is a useful substrate for many applications in diagnostics and electronics. Two independent research groups have now shown that paper can be given optical properties for biosensing applications, and can be turned into invisible electronics for anti-theft applications in art and packaging materials.

Arben Merkoçi and colleagues from institutes in Spain, Iran, and the Czech Republic created paper that exhibits plasmonic and photoluminescent properties by depositing either gold, silver or upconversion nanoparticles on bacterial cellulose paper. When thiourea is added to the gold-containing paper, it causes the gold nanoparticles to aggregate and the paper changes from red to dark red. Similarly, the drug methimazole could be optically detected when added to the silver-containing paper. By decorating the paper with antibodies, quantum dots, and graphene oxide, the paper is used to detect the presence of bacteria.

Alternatively, Jun Zhou and colleagues at Huazhong University of Science and Technology and the University of Maryland created a transparent-paper-based generator that is powered by applying pressure with a finger. The generator is made by adhering one sheet of carbon-nanotube-containing transparent paper to another similar sheet that has an additional polyethylene film. Polyethylene is an electret — a polarized piece of dielectric material. When pressure is applied to the generator, the air gap between the two papers decreases. This causes a differential charge distribution in the papers and induces current flow, which is used to power a liquid-crystal display. When implemented on artwork or packaging material, the generator can reveal critical information, such as a logo or date, by simply pressing and releasing the generator.