Temperature-Controlled Reversible Localized Surface Plasmon Resonance Response of Polymer-Functionalized Gold Nanoprisms in the Solid State

Abstract

Solid-state temperature responsive localized surface plasmon resonance (LSPR)-based nanosensors were constructed by functionalizing the glass substrate-attached gold nanoprisms with the thermoresponsive polymer poly­(allylamine hydrochloride)-<i>co</i>-poly­(<i>N</i>-isopropylacrylamide). The robustness of the sensor was enhanced by chemically attaching polymer to the nanoprism surface through an amide coupling reaction versus simple physisorption of polymer onto nanoprism. The highest sensitivity of this kind of solid sensing platform was obtained by employing chemically synthesized gold nanoprisms for fabrication. The surface ligand chemistry significantly influenced the swelling and shrinking transition of the polymer during the temperature variation, which resulted in the alteration of the local dielectric environment of the nanoprisms, modulation of their LSPR properties, and enhancement of sensing efficiency of the nanosensors. Importantly, we have shown for the first time that the dimension of the nanostructure plays an important role in achieving the highest sensitivity for these types of sensors. For example, the edge length of the nanoprisms plays a critical role in the temperature sensitivity of the nanosensors where nanoprisms with ∼28 and ∼40 nm edge lengths displayed ∼10.9 and ∼18.2 nm LSPR dipole peak red-shift, respectively, as the solution temperature increased from 18 to 56 °C. We believe the higher temperature sensitivity for larger edge-length nanoprisms was achieved due to their larger sensing volume. The nanosensors were found to be very stable and displayed high reversibility, which suggests that our temperature-dependent nanosensors can potentially be used as a reversible thermal switch