# A Biocompatible and High-Sensitivity Lanthanide Coordination Complex for Luminescent Temperature Sensor Constructed from Non-Steroidal Anti-Inflammatory Drug Ketoprofen

## TL;DR

This paper introduces a new luminescent temperature sensor made from a lanthanide complex with ketoprofen, showing high sensitivity and biocompatibility.

## Contribution

A novel lanthanide coordination complex using ketoprofen is developed as a highly sensitive and biocompatible luminescent thermometer.

## Key findings

- The complex shows a maximum relative thermal sensitivity of 4.72% K–1 at 343 K.
- The emission color shifts from yellow to red with increasing temperature, indicating temperature-dependent luminescence.
- The compound has favorable cell viability and a temperature uncertainty of 0.07 K.

## Abstract

Temperature is a
crucial thermodynamic parameter for sustaining
life, driving industrial development, and regulating environmental
processes. In this context, luminescence thermometry has emerged as
an effective, rapid, and noninvasive method for temperature measurement.
In this work, we synthesized a new complex containing Eu3+ and Tb3+ ions coordinated by 2,2′-bipyridyl (bpy)
and the nonsteroidal anti-inflammatory drug ketoprofen (keto), with
the empirical formula [Eu0.4Tb1.6(keto)6(bpy)2]. The ligand’s T1 energy
of 23364.48 cm–1 makes it effective for sensitizing
lanthanide ions. The complex was fully characterized by infrared spectroscopy,
elemental (CHN) analysis, powder X-ray diffraction, and thermal analysis.
Photophysical studies revealed temperature-dependent emission, with
the emission color shifting from yellow at cryogenic temperatures
to red at 393 K. This behavior is consistent with a temperature-activated
Tb3+ → Eu3+ energy-transfer contribution,
as supported by the decrease in τ­(5D4)
from 1.278 to 0.789 ms between 283 and 343 K. The compound was evaluated
as a luminescent thermometer using the intensity ratio between the 5D4 → 7F5 (Tb3+) and 5D0 → 7F2 (Eu3+) transitions as the thermometric parameter. The
complex exhibited a maximum relative thermal sensitivity of 4.72%
K–1 at 343 K, a minimum temperature uncertainty
of 0.07 K, and reproducibility of 91.7% over the range 283–343
K. Its high sensitivity, together with favorable cell-viability results,
indicates that [Eu0.4Tb1.6(keto)6(bpy)2] is a promising candidate for use as an efficient
luminescent thermometer, including potential applications as a temperature
sensor in biological systems.