Enhanced fluorescence at low excitation powers with GaP hybrid nanoantennas

Nanoantennas, known for their capability to enhance light-matter interactions at the nanoscale, have emerged as essential components in single-photon generation and fluorescence detection. Compared to metallic nanoantennas, all-dielectric nanoantennas are less vulnerable to ohmic losses and non-radiative quenching. Gallium phosphide (GaP), a dielectric material with a high refractive index and multiple electromagnetic resonances, stands out as a particularly compelling candidate for this purpose. In this work, we present a hybrid nanoantenna composed of GaP nanodisks and hydrogen silsesquioxane (HSQ) slotted antennas, enabling nanofocusing of electric fields and enhancing the local density of optical states (LDOS). Thanks to the suppression of absorption losses, the fluorescence spectral intensity is boosted 124 times, and the fluorescence decay rate is nearly doubled, reaching an 18-fold fluorescence enhancement at an ultralow excitation power of 0.5 μW. By leveraging HSQ as a dual-role photoresist and spacer, this metal-free architecture not only ensures biocompatibility, but also enables scalable fabrication of energy-efficient devices for non-destructive bioimaging.