As a novel “turn on” fluorescent probe, 4-((1Z,3Z)-1,4-bis(4-(methoxycarbonyl)phenyl)-4-(pyridin-4-yl)buta-1,3-dien-1-yl)-1-methylpyridin-1-ium hexafluorophosphate (TABD-Py-PF₆) with an aggregation-induced emission characteristic was synthesized for in-situ quantitation of γ-globulins in the blood serum. It was shown that the TABD-Py-PF₆ probe was highly specific for γ-globulins and that other components in the blood serum, including serum albumins, fibrinogen, glucose, urea, and cholesterol, barely interfered with the molecular interactions between TABD-Py-PF₆ and γ-globulins. The high specificity of this probe enabled in-situ quantitative detection of γ-globulins without isolation of γ-globulins from the blood serum. The fluorescence intensity of TABD-Py-PF₆ was linearly correlated with the concentration of γ-globulins in the ranges of 7.89−300 μg/mL. The detection limit of γ-globulins was determined to be 7.89 μg/mL. The fluorescence response time of TABD-Py-PF₆ for detecting γ-globulins was very short (below 5 s), allowing for real-time detection. The mechanism of the fluorescent turn-on behavior of the TABD-Py-PF₆ probe was investigated and electrostatic interactions between TABD-Py-PF₆ and γ-globulins were identified.