Multifunctional fluorescent SPIONs display exceptional optical/magnetic contrast and enhanced photoconductivity in interdigitated electrode based photoresponsive devices

Abstract

SPION based multifunctional nanostructures have gained significant attention in multiscale imaging and therapeutic applications. Multistep synthesis and post-synthesis modifications/doping have been extensively used to synthesize such nanostructures; however, single step synthesis and in situ surface coating/doping are still challenging and require the development of a robust method. Using a direct synthesis approach, we address this research dilemma by synthesizing nitrogen doped carbon coated core–shell SPIONs along with nitrogen doped carbon dots as a biproduct. This method allows for the creation of two products from a single synthesis as well as in situ doping in both products. The synthesized core–shell SPIONs demonstrated unique two-photon absorption, multicolor emission behavior and optical nonlinearity, which are essential for optical and fluorescence imaging applications. Moreover, by customizing the core shape and shell surface coating, core–shell SPIONs demonstrated high saturation magnetization, increased magnetic contrast, and high T2 relaxivity (R = 156 mM⁻¹ s⁻¹). Additionally, in order to assess the efficacy of photoinduced conduction, we constructed an interdigitated electrode device utilizing these SPIONs. The generation of photocurrent was evaluated across various illumination conditions. The device demonstrated exceptional photoconductivity, as evidenced by the observed photo-to-dark current ratio (ION-IDark/IDark) of 7.53 and 6.64 under green and red laser illumination, respectively. The photocurrent study measured the rise and fall times of device response to be 93/281 milliseconds under green laser illumination determining the strong applicability of SPIONs in device applications. The enhanced photoelectronic capabilities may be attributed to the utilization of carbon shells as active light harvesting sites and nitrogen doping as charge donors within the core–shell architecture. The current study elucidates a synthesis technique for the production of multifunctional fluorescent SPIONs and reveals their immense potential for applications in photoresponsive devices and multiscale imaging.