The precise and rapid detection of micro-ribonucleic acid (microRNA) in the incipient stages of cancer can effectively elucidate the pathogenesis, migration, and development of tumors. Most of the current microRNA detection methods require large quantities of purified samples, labeling, extended incubation times, and cell lysis, leading to complex procedures that demand labor-intensive preparations and stringent experimental conditions. In this work, we develop a portable and multifunctional biosensor based on an optical microfiber for the detection of microRNA in the early stages of cancer. An innovative graphene oxide-supported bimetallic nanorod (GO-Au NR-Ag NR) interface is engineered on the surface of the optical microfiber to enhance sensor sensitivity for the early detection of ultralow concentrations of microRNA and to integrate cell lysis capabilities. With the enhancement of interface, the sensor is able to detect microRNA-21 at concentrations ranging from 10 zmol/L to 0.1 nmol/L, with a limit of detection (LOD) of 0.25 amol/L. It is also capable of detecting microRNA-21 in body fluids, such as sweat and serum, with LODs of 0.5 amol/L and 0.9 amol/L, respectively. The nano-interface enables the use of photothermal effects by the microfiber to lyse cells and directly detect intracellular microRNA-21, significantly reducing sample extraction time and simplifying the extraction and detection process. This work provides a portable, ultrasensitive, compact, efficient, and non-invasive tool for point-of-care testing.