# Fluorimetric Detection of Insulin Misfolding by Probes Derived from Functionalized Fluorene Frameworks

## TL;DR

Scientists developed fluorescent probes that detect abnormal insulin structures, which could help in diagnosing and understanding diseases related to protein misfolding.

## Contribution

The study introduces new fluorene-based fluorescent probes that can detect insulin misfolding and amyloid aggregation with high sensitivity.

## Key findings

- Fluorene derivatives exhibit native fluorescence that changes with insulin conformation.
- The compounds act as 'turn-on' sensors for abnormal insulin conformations with dissociation constants in the 5–10 μM range.
- The probes also show antioxidant properties by scavenging reactive oxygen species.

## Abstract

A group of functionalized fluorene derivatives that are structurally similar to the cellular prion protein ligand N,N′-(methylenedi-4,1-phenylene)bis [2-(1-pyrrolidinyl)acetamide] (GN8) have been synthesized. These compounds show remarkable native fluorescence due to the fluorene ring. The substituents introduced at positions 2 and 7 of the fluorene moiety are sufficiently flexible to accommodate the beta-conformational folding that develops in amyloidogenic proteins. Changes in the native fluorescence of these fluorene derivatives provide evidence of transformations in the amyloidogenic aggregation processes of insulin. The increase observed in the fluorescence intensity of the sensors in the presence of native insulin or amyloid aggregates suggest their potential use as fluorescence probes for detecting abnormal conformations; therefore, the compounds can be proposed for use as “turn-on” fluorescence sensors. Protein–sensor dissociation constants are in the 5–10 μM range and an intermolecular charge transfer process between the protein and the sensors can be successfully exploited for the sensitive detection of abnormal insulin conformations. The values obtained for the Stern–Volmer quenching constant for compound 4 as a consequence of the sensor–protein interaction are comparable to those obtained for the reference compound GN8. Fluorene derivatives showed good performance in scavenging reactive oxygen species (ROS), and they show antioxidant capacity according to the FRAP and DPPH assays.