Conjugated Polymer Nanoparticles for Biophotonic Applications: Preparation, Characterization, and Simulation in Biohybrid Interfaces

Biophotonics has gained significant interest in recent years due to its potential in medical theranostic applications, with nano-materials emerging as key enablers for advancing optical and electronic functionalities in biological environments. In this study, conjugated polymer nanoparticles (CP-NPs), namely regio-regular poly(3-hexylthiophene) (P3HT), [6,6]-phenyl C61-butyric acid methyl ester (PCBM), and their blend (P3HT:PCBM), are exploited as nano-materials for biophotonic applications. The CP-NPs, obtained via a nanoprecipitation method, showed an average size of ca. 180 nm. Their optoelectrical properties indicate visible absorbance (350–600 nm) and red/near infra-red (NIR, 650–900 nm) emission, demonstrating their suitability for biophotonic applications, in particular in biohybrid interfaces where effective light absorption and emission in biological environments are crucial. Interestingly, under light stimulation, the photocurrent response of the CP-NPs in electrolyte solution (phosphate-buffered saline, PBS) showed a stable and reproducible signal (current density ranging from 0.18 to 7 nA cm−2) thereby enhancing their potential for bio-sensing/stimulation. Simulations of CP-NPs interactions with biological fluids (i.e., PBS) under light stimulation showed distinct carrier generation and transport behaviors, with P3HT-NPs exhibiting consistent charge generation (up to 3 × 1020 nA cm−3). These findings demonstrate that CP-NPs are promising for biophotonic applications, such as photothermal therapy, due to their efficient charge transport, UV-vis absorption, NIR emission, and controlled interactions with biological environments.