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

我们提出了一个新的概念，高灵敏度的磁共振力显微镜（MRFM）的电子自旋检测的基础上使用的光生三重态（TSP，三重自旋探针）作为自旋探针，称为光诱导磁化检测磁力显微镜（LIMFM）。这扩展了现有的MRFM检测方案的应用程序，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，并光激发成它们的三重态（S = 1）。这种新的探测方案潜在地具有以下优点：（i）通过光激发产生三重态导致强的初始电子自旋极化，并且因此即使在相对高的温度下也在微秒到毫秒的时间尺度上导致强的有效磁化;（ii）该方案允许重复光激发，因此导致显著增强的信噪比;（iii）光激发和荧光检测的组合使由于光散射或背景荧光引起的不希望的扰动最小化;（iv）在微米或甚至nm尺度上获得关于表面上顺磁性物质分布的空间信息;和（v）不需要对次级化学反应敏感的稳定顺磁性探针。在第一个资助期内，我们可以成功实施这种新的检测方案，并在原理验证实验中展示其应用。在下一个资助期内，我们现在希望研究以下样品，以显示该方法的广泛潜力：首先，该装置将用于（i）定量适体与底物的结合常数和（ii）扫描三联体标记的细胞用于蛋白质定位目的。我们的研究结果旨在建立一个新的传感器的目标分子在低浓度。

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.