Amphiphilic Magneto-Plasmonic Nanostructures for Dual SERS Detection

Abstract Multifunctional gold-decorated β-cyclodextrin magnetic hybrid materials (Fe3O4@SiO2/β-CD/Au) were synthesized via a sequential strategy that integrates magnetically assisted separation, plasmonic activity, and molecular recognition. This work presents a β-cyclodextrin-functionalized magneto-plasmonic substrate designed for the SERS detection towards both hydrophobic and hydrophilic dyes. The β-cyclodextrin was covalently functionalized with the silane coupling agent ICPTES (3-(triethoxysilyl)propyl isocyanate) and co-condensed with silica to form hybrid SiO2/β-CD shells around Fe3O4 cores using a one-pot encapsulation step. Colloidal Au nanospheres were subsequently immobilized by either (i) an in situ route, in which β-CD magnetic nanocomposites were present during Au nanoparticle synthesis, or (ii) an ex situ route, in which Au nanospheres were assembled onto the hybrid surface. The amphiphilic nature of the β-CD based substrates enabled capture and SERS detection of both hydrophobic (Nile red) and hydrophilic (crystal violet) dyes. The ex situ prepared substrates exhibited superior SERS performance, allowing the diagnostic Raman bands of Nile red and crystal violet to remain clearly detectable down to 1 × 10−7 M under the conditions employed. Preliminary limits of detection estimated from the corresponding concentration response plots (2.36 × 10−6 M for Nile red and 1.38 × 10−8 M for crystal violet) are reported as indicative values for comparing the substrates, rather than as validated detection limits. These results demonstrate the potential of the proposed nanocomposites as a proof-of-concept amphiphilic magneto-plasmonic SERS platforms for detecting analytes with contrasting polarity.