Host–Guest Nanoparticles Incorporating a Fluorophore-Conjugated Pt(II) Complex: A Ratiometric Dual Emitter Performing as a Self-Referenced Oxygen Reporter

Ratiometric optical sensors, which provide real-time measurements by comparing the intensities of two spectrally separated emission bands, are highly effective for monitoring oxygen levels. By combining oxygen-independent and oxygen-sensitive emission characteristics, they offer accurate quantification, distinguishing them from other sensor types. In this work, we designed a ratiometric optical sensor concept based on a bis-cyclometalated platinum(II) complex coupled with an organic naphthalonitrile-based fluorophore and incorporated it into mesoporous silica nanoparticles. This encapsulation strategy significantly improved the stability and water-dispersibility of the otherwise hydrophobic coordination compound while preventing aggregation and enhancing its photophysical properties. Both the free molecule and its nanoparticle-encapsulated form were characterized, revealing high sensitivity to oxygen variations with the unique feature of self-referenced ratiometric readout. The sensor’s response was effectively measured at the single-particle level using photoluminescence microscopy, providing temporally and spatially resolved oxygen readouts. The versatility of the system was demonstrated across different experimental setups, including suspensions, solids, and agarose-embedded forms, highlighting its adaptability to a wide range of applications. This system holds significant promise for advanced oxygen monitoring, offering a reliable tool for high-resolution detection in complex environments with multiple orthogonal readouts.