The aqueous solution extracted from raw bile juice is composed primarily of bile salts, with lower levels of bilirubin and its derivatives. Among them, the bilirubin and bilirubin-derived metabolites are the only surface-enhanced Raman scattering (SERS)-active components. An analytical scheme indirectly responsive and able to utilize all bile components, including SERS-inactive bile salts, was explored for SERS-based discrimination of gallbladder (GB) polyp and GB cancer. Initially, the surface of a SERS substrate (Au nanodendrite on Ni foil (AuND@NiF)) was covered with an alkanethiol molecule to generate a SERS signal and attract bile components by mutual interaction. For more effective recognition of bile components, 4 independent substrates covered with 4 different alkanethiols with various functional groups (SH(CH2)2CH3, SH(CH2)2NH2, SH(CH2)2COOH, and SH(CH2)2OH) were prepared. The SERS peaks of each substrate clearly varied on interaction with pure bile components as well as aqueous bile samples, and the SERS peaks in each substrate were individually characteristic. When the principal component (PC) scores of spectra obtained using the SH(CH2)2CH3- and SH(CH2)2OH-covered substrates were combined, the k-Nearest Neighbor-based discrimination accuracy was 100%, superior to those (90.6-96.9%) using individual substrates. The use of complementary bile component-induced spectral information provided by the two substrates was responsible for accurate discrimination. On the other hand, when bare AuND@NiF recognizing only SERS-active bilirubin derivatives was used, discrimination was unsatisfactory (accuracy: 75.0%).
Keywords: Au nanodendrite; Bile juice; Disease discrimination; Gall bladder disease; Surface enhanced Raman scattering.
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