In situ fabrication of label-free optical sensing paper strips for the rapid surface-enhanced Raman scattering (SERS) detection of brassinosteroids in plant tissues

A surface-enhanced Raman scattering (SERS)-functionalized, gold nanoparticle (AuNPs)-immobilized paper strip was developed to realize label-free rapid detection of brassinosteroids (BRs) in plant tissues. The AuNPs paper strip was fabricated through utilizing poly(gamma-glutamic acid) (gamma-PGA) as the linker and concentrator for the directly immobilized AuNPs on paper, which can circumvent many drawbacks of the existing SERS substrates. An enhancement factor of 1.13 x10(8), high reproducibility (relative standard deviation of 4.78%), highly sensitive detection limit with a correlation coefficient of 0.99 (1x10(-11) M 4-mercaptophenylboronic acid), and long-term stability for the responses of the SERS-functionalized AuNPs paper strip to Raman intensities were achieved by optimizing reaction conditions including the concentrations of gamma-PGA and HAuCl4/NaBH4. Ultimately, this developed paper strip was applied to the determination of BRs in plant tissues, obtaining precisions with RSD values in a range of 3.0-13.8%. The SERS-functionalized AuNPs paper strip featuring label-free rapid analysis, and high sensitivity could serve as an excellent alternative for on-site rapid detections.