Preparação e caracterização de filmes de nanocompósitos de poliestireno-b-poli(2- vinilpiridina) contendo nanopartículas de ouro organizadas para aplicação como substratos e biossensores SERS

Abstract

This study investigates the self-assembly process of gold nanoparticles (AuNPs) using the diblock copolymer poly(styrene-b-2-vinylpyridine) (PS-b-P2VP). PS-b-P2VP with different molecular weights and volume fractions of PS/P2VP, along with pre-synthesized AuNPs, were employed. The PS-b-P2VP films on a glass substrate underwent various reconstruction procedures, including immersion in deionized water or ethanol, exposure to toluene/THF vapor, or thermal treatment. These reconstructed films were immersed in citrate-stabilized AuNP suspensions for varying time intervals. The P2VP microdomains selectively acted as binding sites for negatively charged nanoparticles through electrostatic interactions. The substrates were characterized using UV-VIS spectroscopy and atomic force microscopy. The SERS activity was tested using the Nile Blue (NB) dye as a molecular probe. The results revealed that the treatments and copolymer molecular weight strongly influenced nanoparticle dispersion and, consequently, SERS signal enhancement. Cross-linking using 1,4-diiodobutane (DIB) as a cross-linking agent was performed to prevent possible reconstructions of PS-b-P2VP films by the colloidal solution, thereby preserving the final morphology of AuNPs/PS-b-P2VP films. The results showed that cross-linking the AuNPs/PS-b-P2VP films directly influenced the organization of AuNPs. These films were tested as reusable SERS substrates. Nile Blue and Rhodamine-6G dyes were used as molecular probes. After obtaining SERS spectra of these dyes, the film was exposed to UV radiation, leading to the photocatalytic degradation of the dye. The substrate remained SERS-active even after 4 cycles of use and "cleaning." The AuNPs/PS-b-P2VP films were also used for the direct detection of human immunoglobulin G (IgG) and adenosine triphosphate (ATP). UV-VIS and SERS spectroscopy were used to characterize each step of substrate functionalization and the specific interaction between antiIgG and the target analyte, IgG. UV-VIS results showed a redshift of the LSPR band as the AuNP surface was functionalized, and SERS measurements exhibited consistent changes in spectral features. Principal component analysis (PCA) was used to discriminate between samples before and after affinity tests. Furthermore, the designed biosensor demonstrated sensitivity to different concentrations of IgG and ATP, with a detection limit (LOD) of down to 1 μg/mL. Finally, the construction of a dip-coating equipment using recycled materials was presented. Using this equipment, AuNP/PS-b-P2VP layer-by-layer self-assembled films were produced. The results obtained through UV-VIS and Raman spectroscopy indicated a gradual increase in the concentration of adsorbed AuNPs as the number of bilayers increased. Thus, the constructed dip-coating equipment proved to be efficient in producing thin films for nanoparticle adsorption in polymeric matrices.