Amyloid-beta (Aβ) deposition has been widely used in early diagnosis of Alzheimer’s disease (AD). Currently, optical imaging techniques have been developed to map the Aβ aggregates by using near-infrared (NIR) fluorescent probe. However, most NIR probes cannot translate into clinical diagnostic tools because of their low specificity to Aβ aggregates. Many efforts have been made to overcome this drawback by designing probes that bind to Aβ aggregates with high-affinity, but the interference of serum albumin, the most abundant protein in body, has not been considered. Here, we introduce a cyanine-derived NIR molecular rotor (Mu1) with ratiometric signal, which shows a significant enhancement in the fluorescence ratio (I₇₁₀/I₅₀₀) in the presence of insulin fibrils. Molecular docking illustrates Mu1 tends to be in a planar state by binding with insulin fibrils, which confirm the enhancement in fluorescence ratio of Mu1 due to the restricted rotation in the excited state. For comparison, the fluorescence ratio of Mu1 remains almost constant due to its twisted conformation in hydrophobic pocket of native BSA and energy transfer from BSA to Mu1. These results suggest that Mu1 may be a promising fibril sensor to overcome the interference of serum albumin for early detection of AD.