In this study, we propose an easy and cost-effective method to improve the refractive index (RI) sensitivity of hierarchical aluminum (Al) nanocap arrays (HAlNAs) that are suitable for RI sensing applications. By adjusting the deposited Al thickness, deposition rate, and period, HAlNAs with tunable plasmonic and sensing properties could be achieved. The optimal sensitivity could reach 631 nm/RIU, and the detection limit of adenine ethanol solution with different concentration was as low as 1 × 10 −6 M. The experimental results confirmed that the RI sensitivity of the proposed sensor was primarily related to the period and deposited Al thickness. Moreover, a higher deposition rate could narrow the full width at half-maximum (FWHM) of the reflection spectra, resulting in a higher figure of merit (FOM). The simulated electric field (EF) distribution revealed that the high RI sensitivity could be attributed to the strong coupling between propagating surface plasmon polaritons (PSPPs) and localized surface plasmon resonance (LSPR). In addition, HAlNAs with larger periods could generate a greater hot spot density, resulting in higher sensing sensitivity. The results of this study provide a method to easily fabricate Al-based RI sensors that exhibit great promise for the development of highly sensitive and selective biosensors.

Herein, we proposed a simple non-lithographic way to fabricate hierarchical Al nanopit arrays performed as deep ultraviolet (DUV, 200-300 nm) refractive index sensing. Only by adjusting the Al deposition thickness on the Al nanopit array, the hierarchical Al nanopit arrays with tunable plasmonic properties in the DUV region were obtained. The prepared hierarchical Al nanopit arrays are of very good time stability and its RI sensitivity and concentration detection limit of adenine ethanol solution reach 311nm/RIU and "5×" 〖"10" 〗^"-6" " M" , respectively, as the Al deposition thickness is 60 nm. Furthermore, the electric field distribution simulation results show that high RI sensing characteristic are mainly attributed to the local surface plasmon resonance (LSPR). This investigation provides a facile way to develop low cost, high efficient and easily fabricated Al-based RI sensor in the DUV region.