Lab-in-a-fiber biosensors

In recent years, lab-in-a-fiber has emerged as a new technology that benefits from the development of microstructured optical fibers and optofluidics. Similar to state-of-the-art lab-on-a-chip technology, the lab-in-a-fiber technology is a miniaturized one-dimensional device that integrates multiple functionalities into a single fiber device, including bringing solutions, sample treatment, and analytes assay, which are typically performed in a large laboratory. Unlike the traditional optical fiber biosensors, which perform the biological analysis function on the outer surface of the optical fiber and requires additional sample containers, the lab-in-a-fiber biosensor employs the microstructured optical fibers, which provide both light-guiding fiber cores and microchannels, and performs the whole process inside the designed microfluidic channels that runs within the optical fiber. Such highly integrated fiber devices only need a minimal volume of samples (microliter) to perform immediate analysis with high sensitivity. Therefore, the lab-in-a-fiber biosensor has become a promising candidate for point-of-care testing in the fields of clinical diagnosis, healthcare, food safety, and life science. In this review, we first introduce the types of optical fibers commonly found in the optical fiber laboratory with an emphasis on their signal transmission mechanism and fabrication methods. Then, we review the current state and progress of the well-developed lab-in-a-fiber biosensor devices. These devices can be classified as in-fiber surface-enhanced Raman scattering sensors, in-fiber absorption sensors, in-fiber fluorescent sensors, in-fiber interferometric biosensors, and in-fiber bioparticle analyzing devices. Finally, we summarize the advantages of lab-in-a-fiber technology and present the new development trends and challenges moving into the future.