A Novel Fluorescent Probe Triphenylamine Rhodamine-3-Acetic Acid (mRA) for the Detection of Amyloid-β Aggregates in Alzheimer's Disease

Raja Chinnappan^1*Mateen A. Khan^1*Taj Mohammad²Sarah Mohammed Allwaibh¹Shanmugam Easwaramoorthi³Ahmed Yaqinuddin¹Sandhanasamy Devansan⁴Ahmad Mir⁵Imtaiyaz Hassan²

• ¹Alfaisal University, Riyadh, Saudi Arabia
• ²Jamia Millia Islamia Centre for Interdisciplinary Research in Basic Sciences, New Delhi, India
• ³CSIR - Central Leather Research Institute, Chennai, India
• ⁴King Saud University, Riyadh, Saudi Arabia
• ⁵King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia

Amyloid-β (Aβ) is implicated in the pathophysiology of Alzheimer's disease (AD) and plays a significant role in neuronal degeneration. Aβ in solution is essential during the initial stages of developing lead compounds that influence Aβ fibrillation. The tendency of the Aβ peptide to misfold in solution is correlated with the aetiology of AD. Therefore, the early detection of Aβ serves as a critical foundation for diagnostic testing and routine clinical assessment of Alzheimer's disease (AD). Herein, an aggregation-induced fluorescence probe, triphenylamine rhodamine-3acetic acid (mRA), was exploited to detect Aβ aggregates. The fluorescence results showed a strong interaction between the fluorescence probe mRA and Aβ aggregates. mRA specifically binds with high affinity to Aβ aggregatesand the limit of detection (LOD) of Aβ aggregates was 0.12µg/mL. Molecular docking studies showed that the mRA has significant binding affinity towards the Aβ peptide at the N/C-terminal region, with a binding energy of -6.5 kcal/mol. Furthermore, CD studies confirmed that the mRA binds to Aβ aggregates, and its binding induces significant structural alteration of the Aβ aggregates. To further understand the interaction between mRA and Aβ aggregates at the molecular level, thermodynamic properties revealed that Aβ aggregates binding to mRA is a spontaneous process, driven by enthalpy and favoured by entropy.The negative ΔH suggests that hydrogen bonding is a dominant force for the mRA interaction with Aβ aggregates. This study provides a rationale for using mRA as a biosensor for the detection of Aβ aggregates in biological fluids, offering a potential tool for the early diagnosis and monitoring of amyloid progression in Alzheimer's disease (AD)