Interpenetrating porous photonic crystal balls for rapid naked eye detection of uranyl ions

There is an increasing need to develop simple yet effective sensors with high sensitivity, high selectivity, rapid response, and low cost for on-site detection of UO22+ in the environment in planned or emergency situations. Herein, we develop a UO22+ responsive interpenetrating porous photonic crystal ball (IPPCB) sensor by template replication and a two-step activation method. The amidoxime group and carboxyl group in the hydrogel drive the shrinkage of the hydrogel network through the coordination with UO22+, which reduces the lattice spacing, thereby changing the structure color and shifting the reflection peak position. Therefore, we can perform a semi-quantitative analysis of UO22+ with the naked eye or a fiber spectrometer. Benefiting from the sensor's spherical symmetry and periodic interpenetrating porous structure, the sensor can provide angle-independent, fast (12 min), and sensitive (minimum detection concentration of 1 nM) detection of UO22+. Moreover, IPPCBs have high selectivity and excellent regeneration performance, which can be applied to real sample detection.