Hemicyanine-Based Wash-Free Near-Infrared Fluorescent Probe for Imaging Amyloid-β Aggregates in Alzheimer’s Disease

As a key biomarker of Alzheimer’s disease (AD), amyloid-β (Aβ) is frequently employed for the diagnosis of AD. Near-infrared fluorescence (NIRF) imaging is a non-invasive, low-cost route for visualizing Aβ in vivo. However, most existing Aβ NIRF probes require tedious washing steps, show modest fluorescence turn-on (<50-fold), and stain normal tissue non-specifically. In this work, by fine-tuning the amphiphilicity of a hemicyanine scaffold to place its log P within the appropriate range, we identified P3 as a wash-free NIRF probe for Aβ aggregates. P3 bound Aβ aggregates with high affinity. In vivo, P3 distinguished AD mice from wild-type mice with a 4.8-fold signal ratio, together with adequate brain uptake (1.5 ± 0.1 ID/g at 20 min) and rapid clearance. Unlike Thioflavin T, which indiscriminately labels Aβ aggregates and normal neurons, P3 specifically labeled Aβ aggregates with negligible background, which enabled wash-free imaging with a signal-to-noise ratio of 80 ± 4. This work provides a wash-free, high-affinity NIRF probe for Aβ imaging.