Some of the issues for the colloidal nanoparticle approach are avoided in a nanostructure-based approach, and several nanostructured metal surfaces serving as SERS-active substrates in microfluidic platforms have been developed. The existing nanostructure-integrated microfluidic SERS sensors primarily use Ag, including arrays of nanowells,34 nanopillars,35 nanodomes,36 nanograting,37 nanoplates,38 and nanodots.39 Although Ag-based SERS substrates have inherently higher SERS effects compared to Au-based ones, the long-term stability is worse due to the gradual degradation of Ag surfaces. However, after an extensive literature search, we have only identified four papers describing microfluidic SERS sensors bearing immobilized Au-based nanostructures in the past 10 years.31,36,40,41 Gold nanowell arrays,31 fabricated by depositing a thin Au-film on a polystyrene (PS) nanosphere monolayer, were utilized for SERS measurement of urine. Although the LOD for key biomolecules (i.e., urea) was not reported, the paper demonstrated robust detection under various sample PH values, which significantly compromised the colloidal nanoparticle approach. Au-coated nanodome arrays36 were applied to detect 25 mM urea in solutions. Gamby et al.40 reported gold nanowires synthesized in a polycarbonate microchannel by an electrocrystallization technique as an SERS-active device, and isonicotinic acid (10 μM) in perchloric acid (1 mM) was detected. Also, gold nanoparticles41 were deposited in microchannels by laser electrodispersion, and SERS measurement was conducted for 0.1 μM crystal violet (CV) in a continuous flow. We note that Au-coated Ag bimetallic nanoparticles as SERS substrates show higher signal enhancement and biocompatibility than the monometallic Ag nanoparticles,42,43 but there are no reports regarding the integration of bimetallic substrates in microfluidics yet.