The plasmonic optical fiber sensors have attracted wide attention for label-free biosensing application because of their high integration, small footprint and point-of-care measurement. However, the integration of plasmonic nanostructures on optical fiber probes always relies on the top-down nanofabrication approaches, which have several inherent shortcomings, including high cost, time-consuming, and low yields. Here, we develop a plasmonic nanohole-patterned multimode optical fiber probe by self-assembly nanosphere lithography technique with low fabrication cost and high yields. The multimode optical fiber possesses large facet area and high numerical aperture, which not only simplifies fabrication process, but also increases coupling efficiency of incident light. Originating from the resonant coupling of plasmonic modes, the plasmonic fiber nanoprobe has a distinct reflection dip in the spectrum and exhibits strong near-field electromagnetic enhancement. We experimentally investigate the sensing performances of plasmonic fiber nanoprobe, and further demonstrate it in real-time monitoring specific binding of protein molecules. The experimental results imply that the nanohole-patterned multimode optical fiber probe is a good candidate for developing miniaturized and portable biosensing systems.