Single Polylactic Acid Nanowire for Highly Sensitive and Multifunctional Optical Biosensing.

Nanowire-based optical biosensors with high sensitivity are highly desired for the detection of biological microenvironments and analysis of cellular processes. However, the current nanowire biosensors are mostly fabricated with metal and semiconductor materials, which are not suitable for long-term use in biological environments due to their incompatible and nondegradable properties. Biosensors based on biofriendly materials (e.g., spider silk) often do not have high enough sensitivity due to high losses or micron sizes. Here, polylactic acid (PLA), a polymer with high optical transparency, good biocompatibility, biodegradability, and flexibility, is used to fabricate nanowires using a directly drawing method for the first time. Because of the strong evanescent wave and abundant carboxyl groups on the surface of nanowires, an ultralow concentration sensing of cytochrome c is achieved with a limit of detection of 1.38 × 10 ^-17 M, which is much lower than other detection results using semiconductor/metal-based nanosensors (10 ^-6 to 10 ^-12 M). On this basis, a label-free and real-time monitoring of cell apoptosis is realized. In addition, by doping quantum dots, the functionalized PLA nanowires can also sense a change in pH. These results are suggestive of the potential for PLA nanowires applied in multifunctional biosensing and biodetection, pushing forward the photomedicine field.