Molecular Reporter-Immobilized Ag-Au Shell-Satellite Nanoassemblies for a SERS-Based Galactose Sensor

Galactosemia is a genetic metabolic disorder caused by a deficiency of galactose-degrading enzymes, leading to the accumulation of galactose and its metabolites in the body. The early diagnosis of galactosemia is crucial, as it can lead to death if left untreated. In this study, we present a surface-enhanced Raman spectroscopy (SERS) sensor based on a capillary tube for the convenient and sensitive detection of galactose. To enhance the SERS signal, we introduced gold nanoparticles (Au NPs) onto the surface of silver nanoshells (Ag NSs) to create an Ag-Au shell-satellite nanoassemblies on the inner wall of a capillary. We then fabricated a Ag-Au shell-satellite structured SERS sensor using 4-mercaptophenylboronic acid (4-MPBA) as a Raman reporter molecule. The galactose detection method relied on the conversion of 4-MPBA to 4-mercaptophenol (4-MPhOH) due to the production of hydrogen peroxide (H₂O₂) resulting from the oxidation of galactose by enzyme (galactose oxidase, GOx). A new SERS band was observed, which can be attributed to the H₂O₂produced during the reaction between galactose and GOx. Additionally, we observed an increase in the band intensity ratio between 418 cm^-1and 390 cm^-1 (I₃₉₀/I₄₁₈) as a function of galactose concentration. This strategy for galactose SERS detection based on a capillary tube-based SERS biosensor demonstrates its potential as an early galactosemia diagnosis platform.