Direct covalent attachment of fluorescent molecules on plasma polymerized nanoparticles: a simplified approach for biomedical applications

Polymeric nanoparticles surface functionalised with fluorescent molecules hold significant potential for advancing diagnostics and therapeutic delivery. Despite their promise, challenges persist in achieving robust attachment of fluorescent molecules for real-time tracking. Weak physical adsorption, pH-dependent electrostatic capture, and hydrophobic interactions often fail to achieve stable attachment of fluorescent markers. While covalent attachment offers stability, it often entails laborious multi-step wet-chemistry processes. This work demonstrates that plasma polymerised nanoparticles (PPNs) can directly and covalently attach fluorescent molecules with no need for additional interim treatment processes. For the first time, we provide evidence indicating the formation of covalent bonds between the fluorescent molecules and PPN surfaces. Two model fluorescent molecules, fluorescein isothiocyanate (FITC) and Nile blue (NB), were attached to PPNs in a one-step process. The attached molecules remained on nanoparticle surfaces even after detergent washing, as confirmed by a combination of X-ray photoelectron spectroscopy (XPS), fluorescence spectroscopy, flow cytometry, and time-of-flight secondary ion mass spectrometry (ToF-SIMS) data. The robust attachment of fluorescent molecules on PPNs ensures their stability and functionality, enhancing the potential of these fluorescently labelled nanoparticles for diagnostic, therapeutic, and imaging applications.