Designing Bioconjugated Ti ₃ C ₂ MXene QDs with Excellent Two-Photon Absorption Coefficients for Targeted NIR-II Imaging of Triple-Negative Breast Cancer Cells

Since NIR-II (1000-1700 nm) imaging offers deeper tissue penetration, improved resolution, and higher signal-to-background ratios, development of two-photon excitation NIR-II probes is very important for next-generation bioimaging. Triple-negative breast cancer (TNBC) is inherently aggressive, with poor prognosis and therapeutic resistance, where two-photon diagnostics using the NIR-II probe are very important for effective disease monitoring and management. Herein, we report on the design of strong quantum-confined bioconjugated Ti₃C₂ MXene quantum dots (MXene QDs)-based NIR-II probe with a very large two-photon absorption (TPA) coefficient (β), which can be used for targeted two-photon fluorescence (TPF) imaging of live cancer cells. Our finding reveals that due to the strong quantum confinement effect, anti-AX antibody-conjugated MXene QDs exhibit very high two-photon absorption coefficients (β = -21.9 cm GW^-1), which are several orders of magnitude higher than the β for Ti₃C₂ MXene nanosheets, Nb₂C MXene QDs, black phosphorus QDs, and MoS₂ QDs. Furthermore, we show that photostable and biocompatible antibody-conjugated Ti₃C₂ MXene QDs can be used as NIR-II nanoprobes for the targeted imaging of live MDA-MB-231 and Hs 578T triple-negative breast cancer (TNBC) cells. Moreover, reported data demonstrated that antibody-conjugated QDs have the capability to distinguish TNBC cells with nontargeted HER-2-(+) SK-BR-3 breast cancer cells and (ER) (+) MCF-7 breast cancer cells. Overall, this work provides a facile approach to design antibody-conjugated Ti₃C₂ MXene QDs for NIR-II bioimaging.