The present invention discloses a pencil-like optical fiber sensor probe, including an inner tube, a light screening casing, a clamping device, an optical fiber and an optical probe; a portable immunosensor, including the pencil-like optical fiber sensor probe, an immersion immune response reagent strip, a touch-screen computer, a compact battery-powered sensitive photon counting detector and a case; and a use of the immunosens in detecting inflammatory markers. The design of the pencil-like optical sensor probe greatly simplifies the immune analysis process by combining the immersion immune response reagent strip. Each optical probe allows for up to 10 immunoassays, which reduces the experimental cost and avoids frequent replacement of the probe. The integrated detecting system is powered by battery which is suitable for in-situ analysis and detection. The sensor also has a high stability and sensitivity.