Sensitive detection of choline in infant formulas by SERS marker transformation occurring on a filter-based flexible substrate

In this study, we developed a simple and sensitive surface-enhanced Raman scattering (SERS) technique for the detection of choline in infant formulas based on a filter-based flexible substrate. The flexible substrate with excellent SERS activity and reproducibility was fabricated using a syringe filter and Ag triangular nanoplates. The Raman marker, 3-mercaptophenylboronic acid, was oxidised to 3-hydroxythiophenol in the presence of H 2 O 2 , which caused a decrease in the SERS peak intensity ratio (I 1021 cm −1 : I 996 cm −1 ). Utilising the enhanced flexible substrate, a quantitative detection method for H 2 O 2 was developed. Additionally, choline could be hydrolysed by choline oxidase to generate betaine and H 2 O 2 . Thus, the SERS method was successfully applied to detect choline in the concentration range of 10 -3 –10 -7 M with a beneficial limit of detection as low as 8.36 nM. Importantly, the recovery of choline from infant formula milk powder was approximately 99 %. The excellent performance of the flexible substrate-based SERS method demonstrated its potential for application in H 2 O 2 -generated oxidase-based biosensing.