Light-induced magnetization detected by magnetic force microscopy: from basic concept to first applications

我们提出了一种基于光生三重态（TSP，三重态自旋探针）作为自旋探针的高灵敏度磁共振力显微镜（MRFM）电子自旋检测的新概念，即磁力显微镜光感应磁化检测（LIMFM）。这扩展了现有的MRFM检测方案，应用于光产生的，短寿命的三重态作为顺磁探针。为此，最初将抗磁性发色团固定在表面上，并被光激发成三重态（S = 1）。这种新颖的探测方案具有以下优点：(1)通过光激发产生的三重态导致强烈的初始电子自旋极化，因此即使在相对较高的温度下，也能在微秒到毫秒的时间尺度上产生强的有效磁化；（ii）该方案允许重复光激发，从而显著提高信噪比；（iii）光激发和悬臂探测的结合将光散射或背景荧光造成的不必要扰动降至最低；（iv）在微米甚至纳米尺度上获得表面上顺磁性物质分布的空间信息；(5)不需要易受二次化学反应影响的稳定顺磁探针。在第一个资助期内，我们可以成功地实施这种新的检测方案，并在原理验证实验中演示其应用。在下一个资助期内，我们现在想研究以下样品，以显示该方法的广泛潜力：首先，该装置将用于(i)量化适配体与底物的结合常数，（ii）扫描三重标记细胞以进行蛋白质定位。我们的研究结果旨在建立一种新的低浓度目标分子传感器。

We have proposed a new concept for highly sensitive magnetic-resonance force microscopy (MRFM) electron-spin detection which is based on the usage of photo-generated triplet-states (TSP, triplet spin probe) as spin probes, called light induced magnetization detection by magnetic force microscopy (LIMFM). This extends the existing MRFM detection schemes by application to light-generated, short-lived triplet states as paramagnetic probes. For this purpose, initially diamagnetic chromophores are immobilized on a surface and are photo-excited into their triplet state (S = 1). This novel detection scheme potentially has the following advantages: (i) generation of triplet states by photo-excitation leads to strong initial electron-spin polarization, and hence strong effective magnetization, on a microsecond to millisecond time scale even at comparatively high temperatures; (ii) the scheme allows repetitive photo-excitation thus leading to significantly enhanced signal-to-noise ratio; (iii) the combination of light-excitation and cantilever-detection minimizes unwanted perturbations due to light scattering or background fluorescence; (iv) spatial information on the distribution of paramagnetic species on surfaces is obtained on a micrometer or even nm scale; and (v) there is no need for stable paramagnetic probes that are susceptible to secondary chemistry. Within the first funding period we could successfully implement this novel detection scheme and demonstrate its application in proof-of-principle experiments. Within the next funding period, we now want to investigate the following samples in order to show the broad potential of this method: First, the setup will be used (i) to quantify aptamer-to-substrate binding constants and (ii) to scan triplet-labeled cells for protein localization purposes. Our results aim towards the establishment of a new sensor for target molecules at low concentration.