A DNAzyme-gold nanostar probe for SERS-fluorescence dual-mode detection and imaging of calcium ions in living cells

As a universal second messenger, Ca2+ plays an important role in many cellular processes. In this work, we have developed a novel dual-mode nanoprobe, including "turn on" fluorescence and "turn off" SERS, which can be used for sensitive and selective Ca2+ determination. The proposed nanoprobe combines gold nanostars (AuNSs) and DNAzyme (recognition element), among which AuNSs are used to quench fluorescence and enhance Raman signals. When the substrate chain modified with Cy5 hybridizes with the enzyme chain on the surface of AuNSs, a Ca2+-specific DNAzyme is formed. At this time, the fluorescence is quenched and the SERS signal is strong. With the help of Ca2+, Cy5-labeled substrate chain is cleaved and released from the surface of AuNSs, which leads to the reduction of the SERS signal and the recovery of fluorescence signal. The proposed strategy is also successfully used to monitor Ca2+ in the process of T-2 toxin-induced apoptosis. This is the first report of the simultaneous fluorescence-SERS imaging technique using DNAzyme to detect Ca2+ in cells. The proposed nanoprobe combines the advantages of SERS and fluorescence and has good versatility in various cell lines, which is helpful to better understand the role of Ca2+ in cellular pathways.