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金纳米棒作为生物医学探针因其可调谐等离激元特性备受关注,但其亚细胞尺度精准成像受限于衍射极限与现有超分辨技术的高光损伤、外源标记依赖性等瓶颈。本文提出相干调制振幅投影成像技术,通过飞秒脉冲对的空间相干调制与振幅-相位协同耦合机制,低功率激发就可实现金纳米棒取向分布超分辨探测,同时无需荧光分子标记。该方法将亚衍射极限信息编码至频域,利用傅里叶分析同步解析金纳米棒的空间定位、三维取向及局部微环境响应,规避了荧光分子标记干扰并显著抑制光热效应影响。实验证实相干调制振幅投影成像通过调控脉冲间延时与相位可精确操控金纳米棒光致发光相干态,为研究纳米-生物界面动态过程提供了多维度分析工具。Gold nanorods (AuNRs) are highly promising biomedical probes due to their tunable plasmonic properties, yet real-time, high-resolution imaging of their subcellular behavior—particularly their orientation dynamics, which reflect critical nano-bio interactions—has been hindered by the diffraction limit and drawbacks of existing super-resolution methods, such as reliance on high-intensity lasers and exogenous labeling. To address this, we developed Coherent Modulation Amplitude Projection Imaging (CMAPI), a novel label-free technique that uses spatially and temporally modulated pairs of femtosecond pulses to coherently control the two-photon photoluminescence (TPPL) of AuNRs. By exploiting AuNRs as three-level systems with a measurable intermediate state, CMAPI encodes sub-diffraction-limit spatial and orientational information into the frequency domain through precise manipulation of inter-pulse delay, phase, and polarization. Experimental results confirmed the nonlinear excitation nature of AuNRs, with single-pulse polarization response following a cos²θ dependence. Under two-pulse excitation, the emission exhibited distinct coherence-dependent behavior: at zero delay, the response was governed by quantum superposition; at a delay matching the intermediate state lifetime (0.5 ps), a three-level model accurately described the response; and at longer delays (10 ps), the system reverted to incoherent emission. CMAPI retrieves nanoscale information via Fourier analysis of photon arrival times, producing simultaneous amplitude and phase images that reveal AuNRs’ precise positions (∼60 nm localization precision), in-plane orientations (e.g., quadrant-specific alignment inferred from phase sign), and local environmental coupling, such as plasmon-induced phase jumps, all under ultralow excitation power (<5 μW/μm2) to avoid photodamage. This approach enables visualization of features beyond the diffraction limit, distinguishing multiple AuNRs within a single diffractive spot, as validated by scanning electron microscopy. CMAPI provides a powerful, non-invasive platform for quantifying dynamic biological processes involving anisotropic nanoparticles, including conformational shifts during endocytosis, torque transmission in molecular motors, and real-time tracking of nanoscale interactions, thereby offering profound insights for theranostic probe design and fundamental biophysical research.
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Keywords:
- Two-photon photoluminescence (TPPL) /
- Coherent modulation imaging (CMI) /
- Gold nanorods (AuNRs) /
- Ultrafast spectroscopy
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