She worked as a postdoctoral researcher at Bell Laboratories for a year afterward before joining the University of Texas at Austins Chemical Engineering Department. During her time at Bell Labs, Loo, along with Julia Hsu, accidentally uncovered duplicated figures in two papers by Jan Hendrik Schön, the first of many instances of academic fraud from the researcher. In 2004, she was included by MIT Technology Review' on its TR35 list of under-35-year-old innovators for her invention of nanotransfer printing, a technique for printing nanoscale patterns onto plastic surfaces. This technique allows for the creation of organic electronic devices by printing electrical circuit components onto plastic surfaces.
In 2007, Loo joined the faculty of Princetons Chemical and Biological Engineering Department, where, , she is the Theodora D. 78 and William H. Walton III '74 Professor in Engineering. Her research concerns the periodic structures of block polymers, organic semiconductors, and patterning techniques for plastic electronics.
Loo launched the Princeton E-ffiliates Partnership (E-ffiliates) in 2012.
In 2016 she was appointed director of Andlinger Center for Energy and the Environment.
Loos research group studies solution-processable organic semiconductors and conductors. She also researches soft lithography. Using derivatives of Hexabenzocoronene Loos group developed transparent near-UV solar cells for smart windows, which also contain electrochromic polymers that control the window tint.