【Angew.Chem.】双通道近红外光声探针实现骨与软骨超200倍高选择性同时显像#

Illustration of the targeting mechanisms: Cart-670 preferentially accumulates in cartilage, consistent with electrostatic interactions with negatively charged proteoglycan-rich matrices, while Osteo-750 shows preferential retention in bone, consistent with interactions with calcium-rich hydroxyapatite. These interactions are proposed to contribute to the observed tissue-selective accumulation. The chromophore cores in both probes are derived from commercially available NHS esters whose complete chemical structures are proprietary and not disclosed by the vendor; accordingly, Scheme 1 depicts all non-proprietary structural elements (targeting moieties, linkers, and the point of conjugation).#

Absorbance spectra and photoacoustic behavior of the NIR dyes. (A) Absorption spectra of 1 µM QSY21 and (B) ICG in: PBS (pH 7.4) (red/ green, respectively); 50% plasma (maroon/ teal, respectively); after photoacoustic laser irradiation for 10 min (black). QSY21 absorbs broadly with _λ_max at 660 nm and ICG has a peak at ∼780 nm but still exhibits ∼50% of max absorption at 680 nm. Both dyes show high molar extinction (> 104 M−1cm−1). The spectra remain well-defined (with minor red-shift and broadening) in the protein-rich environment of 50% plasma. Black curves are photostability test results: These data are absorption after 10 min of pulsed laser irradiation (680 nm, 10 Hz; pulse width: 5 ns; fluence: 20 mJ cm−2) showing no significant change, indicative of high photostability. (C) Photoacoustic signal intensity for QSY21 and (D) ICG. Each curve represents a concentration-response profile (0–10 µM) acquired in PBS, PBS within a skin-mimicking (SM) phantom, and 50% plasma. As expected, overall photoacoustic signal intensity decreases in more optically and acoustically attenuating environments due to increased scattering, absorption, and acoustic impedance; however, the signal remains concentration-dependent and readily detectable across conditions. Note: concentrations above ∼10 µM approach detector saturation and were excluded from quantitative comparisons (Figure S14). These properties illustrate that QSY21 is suitable for consistent photoacoustic signal generation under biological conditions.#

In vitro characterization of targeted NIR dyes. (A) Absorption spectra of Cart-670 and (B) Osteo-750 in: PBS (pH 7.4) (blue/ brown, respectively); 50% plasma (purple/orange, respectively); after photoacoustic laser irradiation for 10 min (black). (C) Schematic of the photoacoustic imaging setup and multi-well phantom used for concentration-dependent (0–100 µM) measurements and representative photoacoustic images acquired in PBS, illustrating signal intensity as a function of decreasing dye concentration. (D) Photoacoustic signal amplitude as a function of concentration for Cart-670 and (E) Osteo-750 in PBS, 50% plasma, and skin-mimicking (SM) phantom conditions. Insets show the linear region with corresponding R2 values. Error bars represent mean ± s.d. of two replicates.#

在离体鸡关节模型实验中，这两款探针展现出了极高的组织特异性与出色的光声性能。实验结果表明，Cart-670能精准积聚在关节软骨表面，而Osteo-750在骨骼表面的光声信号强度达到了软骨部位的约200倍，经多次洗涤后依然能保持特异性附着。由于两款探针的吸收峰具有约100纳米的显著光谱差异，团队利用680纳米和750纳米两个波长进行激发，并结合光谱解混算法成功消除通道间的信号串扰，完美实现了骨与软骨界面的双颜色清晰光声图像重建，同时该系统通过数毫米的模拟组织覆盖后仍可检测到有效成像信号。

Ex vivo specificity. (A) Imaging plane and anatomical context. (B) Photoacoustic imaging demonstrating tissue-selective signal localization for cartilage- and (C) bone-associated probes. (Left) Co-registered ultrasound images of the joint. (Right) Photoacoustic images acquired independently for each probe, showing preferential signal localization of Cart-670 to cartilage (B, red) and Osteo-750 to bone (C, blue). Pseudo-color assignments (red: Cart-670 channel; blue: Osteo-750 channel) are arbitrary and do not correspond to the gross visual appearance of the tissue.#

Dual-channel photoacoustic imaging. (A) Schematic of co-administration of Cart-670 and Osteo-750 at varying molar ratios, followed by photoacoustic imaging. (B-E) Representative co-registered ultrasound (grayscale) and spectrally unmixed photoacoustic images acquired with varying ratios (Cart-670 = 0:100 (B), 25:75 (C), 50:50 (D), 75:25 (E)) with total probe concentration held constant. Bone-associated signal (blue) and cartilage-associated signal (red) are shown overlaid after Ex.: 680 nm and 750 nm. Increasing Cart-670 fraction results in progressive enhancement of cartilage-localized signal while maintaining detectable bone signal, demonstrating tunable contrast between cartilage and bone within the same imaging field.#