Due to the high oxidative potential of the hydroxyl radical (•OH), the accumulation of •OH in tissues can cause inflammation, such as that in arthritis. Therefore, the development of •OH detection with high efficiency and sensitivity is important for the treatment of related diseases. In this work, a cypate-modified core-shell NaErF4@NaLuF4 nanoprobe (csEr-Cy) was designed for detecting •OH on the basis of a typical reaction between cypate and •OH. The process resulted in the recovery of 654 nm upconversion luminescence emission of csEr because of a weakened inner filter effect (IFE) and Förster resonance energy transfer (FRET). The short-wavelength infrared (SWIR) emission at 1550 nm was not affected by •OH addition, thus enabling interference-free detection. Density functional theory (DFT) calculations were performed to explain the underlying mechanism. With the SWIR signal used as a reference for •OH detection, the csEr-Cy nanoprobe showed higher sensitivity and penetration than visible reference. This method was successfully used in mice for the diagnosis of arthritis in vivo. Our results provide novel insights into improving the sensitivity of nanoprobes for molecule detection and disease diagnosis.
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