# Exploring Tb3+-Mediated Interactions with Glutathione-Capped Gold Nanoclusters to Develop a Fluorophore-Modified Ratiometric Probe toward Lactoferrin

## TL;DR

This paper describes a new ratiometric fluorescent probe for detecting lactoferrin in clinical samples using gold nanoclusters and terbium ions.

## Contribution

The novel contribution is the development of a Tb3+-mediated ratiometric probe using Au29–43(GSH)27–37 nanoclusters for sensitive lactoferrin detection.

## Key findings

- The probe achieves a wide linear range (0.01–4.0 mg/mL) and a low detection limit (3.4 μg/mL).
- It shows high reproducibility (RSD < 1.2%) and effective performance in diluted human tear samples.
- Mechanistic studies reveal Tb3+ enhances aggregation via reduced electrostatic repulsion and increased van der Waals and bridging interactions.

## Abstract

A ratiometric fluorescent probe for lactoferrin (Lf)
was developed
by conjugating fluorescent BDP-FL molecules onto glutathione (GSH)-capped
gold nanoclusters, Au29–43(GSH)27–37, followed by terbium ion (Tb3+)-induced aggregation-induced
emission enhancement (AIEE) of the clusters. The resultant BDP-FL-conjugated
AIEE dots exhibit characteristic emissions at 517 and 606 nm. Conjugation
of BDP-FL to the Au29–43(GSH)27–37 clusters provides a green-emissive internal reference, enabling
ratiometric signal output. Upon addition of Lf, competitive binding
with Tb3+ disrupts the aggregates, leading to selective
attenuation of the red emission from Au29–43(GSH)27–37 while preserving the green BDP-FL emission. This
ratiometric design affords a wide linear range (0.01–4.0 mg/mL),
a low limit of detection (3.4 μg/mL), and excellent reproducibility
(relative standard deviation < 1.2%). Importantly, the probe remains
effective in 10-fold-diluted human tear samples, achieving recovery
rates of 99.98–101.8% and providing results consistent with
capillary electrophoresis. Mechanistic studies reveal that Tb3+ reduces electrostatic repulsion and enhances van der Waals
and bridging interactions, thereby promoting aggregation of Au29–43(GSH)27–37. Using the Derjaguin–Landau–Verwey–Overbeek
theoretical model, the relative contributions of van der Waals, electrostatic,
and bridging interaction energies were quantified, offering deeper
insight into the aggregation mechanism. This ratiometric AIEE probe
demonstrates practicality, sensitivity, and reliability for Lf determination
in clinical samples and may provide guidance for the rational design
of nanomaterials with tailored optical properties.