Er3+/Yb3+ co-doped nanocrystals modified with 6-aminocaproic acid for temperature sensing in biomedicine

Abstract

We report β-PbF₂:Er³⁺/Yb³⁺ nanocrystals (NCs) modified with 6-aminocaproic acid (6AA) via wet chemical etching of glass ceramics (GCs). NCs body-doped with trivalent rare-earth (RE³⁺) ions were released from the GCs by etching of the glass matrix and modified with bifunctional 6AA ligands to enhance their water solubility. They have good stability in water with an average diameter of 56 nm and display efficient green (521, 550 nm) and red (660 nm) emission under the excitation of a 940 nm laser. High absolute sensitivity (S_A) and relative sensitivity (S_R) (0.0027 K⁻¹ and 1.18% K⁻¹, respectively) and high resolution (0.25 K) were achieved for temperature sensing in the biological temperature range, using the fluorescence intensity ratio (FIR) technique. All of the experimental results indicate that the Er³⁺/Yb³⁺ co-doped NCs modified with 6AA may potentially be useful as fluorescent biological temperature sensors.