Harnessing Intramolecular Rotation To Enhance Two‐photon Imaging of Aβ Plaques through Minimizing Background Fluorescence

Abstract

The aggregation of amyloid beta (Aβ) proteins in senile plaques is a critical event during the development of Alzheimer's disease, and the postmortem detection of Aβ‐rich proteinaceous deposits through fluorescent staining remains one of the most robust diagnostic tools. In animal models, fluorescence imaging can be employed to follow the progression of the disease, and among the different imaging methods, two‐photon microscopy (TPM) has emerged as one of the most powerful. To date, several near‐infrared‐emissive two‐photon dyes with a high affinity for Aβ fibrils have been developed, but there has often been a tradeoff between excellent two‐photon cross‐sections and large fluorescence signal‐to‐background ratios. In the current work, we introduced a twisted intramolecular charge state (TICT)‐based de‐excitation pathway, which results in a remarkable fluorescence increase of around 167‐fold in the presence of Aβ fibrils, while maintaining an excellent two‐photon cross section, thereby enabling high‐contrast ex vivo and in vivo TPM imaging. Overall, the results suggest that adopting TICT de‐excitation in two‐photon fluorophores may represent a general method to overcome the tradeoff between probe brightness and signal‐to‐background ratio.

Strategic Design of Amyloid-β Species Fluorescent Probes for Alzheimer’s Disease

“…For example, some novel fluorescence regulation mechanisms, such as photoinduced electron transfer (PeT), aggregation-induced emission (AIE), and resonance energy transfer (RET), combined with ICT mechanisms have been used to develop novel probes for improving the efficacy of ICT-based fluorophores. A twisted intramolecular charge state (TICT) may provide another universal strategy to balance the probe brightness and signal-to-noise ratio . Recently, as Aβ oligomers are regarded as vital toxic forms in Aβ plaques, some fluorescent probes for identifying different pathological states of Aβ have been developed to investigate the role of oligomers in the pathogenesis of AD.…”

The cross-talk modulation of excited state electron transfer to reduce the false negative background for high fidelity imaging in vivo

“…Owing to their reactive specicity, timely reporting and biological affinity, molecular-probe-based uorescence imaging techniques have been rapidly developed for biological monitoring, molecular medicine and even surgical navigation. [1][2][3][4][5][6][7][8][9][10] However, in the actual imaging, there are several problems that are usually neglected: (1) inherent false negative background (FNB): although the background seems to be dark, the real background uorescence will be exposed when the intensity scale of microscopy is compressed (Scheme 1A). Obviously, the real background is covered by the wide intensity scale of microscopy.…”

“…Over time, in the pursuit of accurate and sensitive imaging, researchers have developed many strategies, 9,[15][16][17] including electron transfer, structure rotation, hydrophilicity tuning, uorescence assembly, and so forth. As far as the technique is concerned, whatever the mechanism features, the electron behavior should be the essential factor for controlling the optical properties.…”

Noninvasive Cancer Diagnosis In Vivo Based on a Viscosity-Activated Near-Infrared Fluorescent Probe

“…Fluorescence imaging is a powerful technique for locating and dynamically monitoring biomolecules in living systems with merits of high sensitivity, real-time, and in situ detection. , Especially, two-photon (TP) imaging allows low damage to biosamples, increased tissue penetration, and three-dimensional (3D) optical data storage. Thus, the fluorescence technique can be employed for noninvasive feedback of the subtle concentration changes of biomarkers at the disease sites, greatly facilitating significant advances in cell biology and medical diagnostic imaging.…”