Size-controlled synthesis of cyclodextrin-capped gold nanoparticles for molecular recognition using surface-enhanced Raman scattering.

Cyclodextrin (CD)-capped gold nanoparticles (AuNPs) can be applied in sensing, catalysis, and self-assembly processes due to their molecular recognition ability. As the plasmon resonance of AuNPs depends on their size, the size-controlled synthesis of CD-capped AuNPs is essential for the development of these applications. Herein, we successfully synthesized ß-CD-capped AuNPs with diameters of 24-85 nm using a seed-mediated growth method. The AuNPs were prepared using a ß-CD as both the reducing agent and the capping agent. Harsh reagents such as NaBH4 and NaOH were not used. The size-controlled synthesis of ß-CD-capped AuNPs was achieved by changing the amount of seed solution. We fabricated monolayers of ß-CD-capped AuNPs by liquid-liquid interfacial self-assembly for application in surface-enhanced Raman scattering (SERS). The SERS intensity is significantly improved by using larger ß-CD-capped AuNPs. In addition, we found that ß-CDs can detect pyrene with higher sensitivity than α-CDs on the basis of the difference in molecular recognition ability between α-CDs and ß-CDs.