Langmuir-Blodgett Films of Conjugated Polymer and Silver Nanoparticles: A Possible Substrate for Pesticide SERS-Based Detection.

This study demonstrates the successful fabrication of nanostructured Langmuir-Blodgett (LB) films combining the conjugated copolymer poly(9,9-dioctylfluorene--3,4-ethylenedioxythiophene) (PDOF--PEDOT) with spherical and triangular silver nanoparticles (AgNP). The LB technique allowed precise control over the molecular arrangement and distribution of the nanoparticles at the air-water interface, resulting in compact, reproducible and structurally ordered nanocomposite films. The structural and morphological properties of the interfacial monolayers and LB films were investigated using surface pressure-area isotherms, Brewster angle microscopy, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and quartz crystal microbalance. Monolayers and LB films containing anisotropic nanoparticles exhibited greater restriction in the molecular reorganization of the monolayers and in the degree of transfer and organization of the LB films. Physicochemical characterization confirmed that the organization of the films at the molecular level plays a key role in improving the performance of surface-enhanced Raman scattering (SERS). Films with spherical AgNP showed relatively intense and well-defined Raman signals for the pesticide chlorpyrifos (CLP), even at concentrations less than 6 × 10 mol L, outperforming analogous films prepared by spin coating. In contrast, films with triangular AgNP showed lower spectral reproducibility due to their lower colloidal and structural stability. The results show that the LB technique enables effective nanostructuring and synergistic integration of conducting polymers and plasmonic nanoparticles and offers a promising route to the development of SERS-active platforms. To our knowledge, this is one of the first studies to investigate the use of conjugated polymers as functional matrices and silver nanoparticles organized by the LB technique that can be exploited for SERS-based detection. This work also contributes to the under-explored field of hybrid LB films for chemical detection by highlighting their potential for the construction of highly structured and functionalized interfaces for molecular recognition.