Bioinspired plasmonic compound eye for on-particle label-free surface-enhanced Raman spectroscopic biosensing of multianalytes

The insect vision systems mainly rely on the apposition compound eyes (CEs) with the omnidirectional light-harvesting and wide-angle sensing abilities for prey recognition and enemy defense. Thus, the insect CEs become a compelling source of inspiration for the development of optoelectronic devices and optical sensors. Herein, inspired by the insect CEs, a biomimetic plasmonic CE biosensor is reported with excellent omnidirectional plasmonic properties for on-particle label-free surface-enhanced Raman spectroscopy (SERS) multiplexed detection of biomarkers. Our biosensor consists of a closely-packed polystyrene microsphere monolayer covered with a dense layer of vertically aligned Au nanowires (v-Au NWs). The omnidirectional distribution of v-Au NWs on the curved surface endows the plasmonic CE biosensor with angle-independent plasmonic responses and uniform SERS signals, verified by our experimental investigations and numerical simulations. Based on the intrinsic SERS fingerprints and dense electromagnetic “hotspots”, the present plasmonic CE biosensor is demonstrated with high sensitivity and excellent selectivity for simultaneous on-particle label-free SERS detection of uric acid, folic acid and adenine oligomer. Moreover, the composition and concentration information of the complex samples integrated in the SERS images is recorded in a smartphone-readable QR code, highlighting its practical potential for label-free SERS multiplexed biosensing.