Crystal-amorphous Ni(OH)2 nanocages as SERS substrate with conspicuous defects-induced charge-transfer resonance for ultrasensitive detection of MicroRNA 155

Herein, an innovative Ni(OH)2 nanocages (Ni(OH)2 NCs) with crystal-amorphous structure were fabricated as surface-enhanced Raman scattering (SERS) substrate, which realized excellent SERS enhancement by the significant defects-induced charge transfer resonance and was applied to the construction of SERS biosensor for ultrasensitive microRNA 155 (miRNA 155) detection. The surface oxygen vacancy (Ovs) and defective phases endowed Ni(OH)2 NCs the increased charge carrier density and preponderant energy-level matching with signal molecules methylene blue (MB), thereby inducing the remarkable charge transfer resonance via the augment of electron transition probability for improving the SERS effect of Ni(OH)2 NCs. Impressively, the SERS performance of Ni(OH)2 NCs was stronger than that of amorphous Ni(OH)2 nanocages (a-Ni(OH)2 NCs), ascribing to the abundant Ovs and high degree of charge transfer (ρCT) in Ni(OH)2 NCs. Furthermore, the limited target miRNA 155 was transformed into the plentiful MB molecules by employing the target-related cleavage amplification reaction and hybridization chain reaction (HCR), thus achieving an enhanced SERS intensity for detecting target miRNA 155 based on Ni(OH)2 NCs substrate and obtaining a low detection limit of 30 aM. This strategy developed candidate materials for the practical applications of SERS technology and provided a promising method to disease diagnosis.