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

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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.