Materials exhibiting strong absorption in the NIR-II region are appealing for photothermal conversion-based imaging, diagnosis, and therapy, due to better thermal effect and decreased absorption of water in such a region. 3,3′,5,5′-Tetramethylbenzidine (TMB), the typical substrate in ELISA, has been explored in photothermal immunoassay, since its oxidation product (oxTMB) is photothermally active in the NIR region. However, its absorption at 1064 nm (the most often used laser wavelength in photothermal studies) is not appreciable, thus limiting the assay sensitivity. Here, we proposed a derivative of TMB (3,3′-dimethoxy-5,5′-dimethylbenzidine, 2-OCH₃) bearing higher NIR-II absorption for 1064 nm-excited photothermal immunoassay. Since electron-donating groups can help decrease the energy gap of molecules (here −CH3 → −OCH₃), the oxidation product of 2-OCH₃ exhibited substantially red-shifted absorption as compared with oxTMB, leading to a more than twofold higher absorption coefficient at 1064 nm. As a result, 2-OCH₃ showed enhanced sensitivity over TMB in a photothermal immunoassay (PTIA), yielding a limit of detection (LOD) of 0.1 ng/mL for prostate-specific antigen (PSA). The feasibility of 2-OCH₃-based PTIA for diagnosis was further validated by analyzing PSA in 61 serum samples. Considering its superior photothermal performance, 2-OCH₃ can be explored for a broad range of photothermal applications.

中文翻译：

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用于 1064 nm 激发光热免疫测定的 NIR-II 吸收 TMB 衍生物

在 NIR-II 区域表现出强吸收的材料对于基于光热转换的成像、诊断和治疗很有吸引力，因为该区域具有更好的热效应和减少的水吸收。 3,3',5,5'-四甲基联苯胺 (TMB) 是 ELISA 中的典型底物，由于其氧化产物 (oxTMB) 在近红外区域具有光热活性，因此已在光热免疫分析中得到探索。然而，它在 1064 nm（光热研究中最常用的激光波长）处的吸收并不明显，因此限制了测定灵敏度。在这里，我们提出了一种 TMB（3,3'-二甲氧基-5,5'-二甲基联苯胺，2-OCH ₃）衍生物，具有更高的 NIR-II 吸收，适用于 1064 nm 激发光热免疫分析。由于给电子基团有助于减小分子的能隙（此处为−CH3→−OCH _{3 ），因此与oxTMB相比，2-OCH 3}的氧化产物表现出明显的红移吸收，导致吸收高出两倍以上1064 nm 处的系数。结果，2-OCH ₃在光热免疫测定 (PTIA) 中表现出比 TMB 更高的灵敏度，前列腺特异性抗原 (PSA) 的检测限 (LOD) 为 0.1 ng/mL。通过分析61份血清样本中的PSA，进一步验证了基于2-OCH ₃的PTIA诊断的可行性。考虑到其优越的光热性能，2-OCH ₃可用于广泛的光热应用。