Multifunctional Fe3O4@TiO2@Ag-Au microspheres (MS) were synthesized by grafting Ag nanoparticles onto 3-Aminopropyltrimethoxysilane (APTMS) modified Fe3O4@TiO2 MS, followed by galvanic replacement approach to fabricate Ag-Au bimetallic nanostructures with variable bimetallic molar ratios. The composite with Au-to-Ag ratio of 1:1 exhibits optimal catalytic activity for reduction of 4-nitrophenol (4-NP). Furthermore, finite-difference time-domain (FDTD) simulation study shows that incorporating Au-Ag bimetallic nanostructures onto Fe3O4@TiO2 MS significantly increases the effect of the 'hot spot', offering stronger electromagnetic field enhancements. Indeed, the Fe3O4@TiO2@Ag-Au was demonstrated to be an excellent substrate material for in-situ surface-enhanced Raman scattering (SERS) monitoring of the reaction process. Combined with its good magnetic and photocatalytic performance allowing facile recovery, Fe3O4@TiO2@Ag-Au MS shows great potential for multifunctional platform for simultaneous catalysis and in-situ reaction monitoring. (C) 2016 Elsevier B.V. All rights reserved.