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Fig. 12. Electric-field intensity distribution and the polarization magnitude | P | inside a single exosome for the CsPbI 3-coated microresonator, when the exosome position is varied in both angular(± 0.003 rad) and radial( 100 nm shifted) directions.
at k res; CsPbI3 886:6 nm. The resulting hybrid mode is largely confined within the perovskite nanocoating while maintaining a strong evanescent tail in water. Despite the intrinsic material loss of the perovskite, this configuration yields the highest Q f( a factor 2.4 above the uncoated case), the smallest V mode( reduced by 45 %), and the strongest surface field enhancement( electric-field intensity increased by factors of 2.11 and 3.68 relative to the PS-coated and uncoated resonators, respectively), while also establishing a more spatially uniform near-surface field distribution at the sensing interface. To the best of our knowledge, this is the first report of an engineered excitonic – photonic mode coupling in a perovskite-coated WGM microresonator specifically tailored for biosensing.
Coupling the exosome ERI model to the hybrid microresonators, we quantified the resonance-wavelength shifts induced by single healthy, borderline, and cancerous exosomes placed at the sensing position. Both PS and CsPbI 3 nanocoatings substantially increase the absolute resonance shifts compared to the uncoated resonator, with the perovskite-coated device providing the largest enhancement. For example, the healthy-exosome shift increases from 0.75 pm( uncoated) to 1.08 pm( PS-coated) and 1.79 pm( CsPbI 3-coated), corresponding to enhancements of 44 % and 139 %. At the same time, the separation between health states is improved: the difference between cancerous and healthy exosomes, Dk C � Dk H, increases from 0.33 pm( uncoated) to 0.50 pm( PS-coated) and 0.59 pm( CsPbI 3- coated). These results show that the proposed architecture does not merely detect the presence of an exosome but also amplifies the contrast between healthy, borderline, and cancerous ERI values. Taken together, this constitutes, to the best of our knowledge, the first demonstration of an optical WGM biosensor that exploits excitonic – photonic hybridization to both detect and characterize the health state of single exosomes. Importantly, the hybrid-modeinduced field redistribution also reduces the dependence of the sensing response on angular exosome positioning, thereby enhancing robustness against non-ideal binding conditions [ 54 ].
The presented study establishes a complete, simulationbased design workflow that links biochemical composition( protein / NA content) to exosome ERI and ultimately to measurable resonance signatures in a realistic, fiber-coupled WGM biosensor. Future work will focus on translating these designs into fabricated devices, including the controlled
deposition and stabilization of CsPbI 3 nanocoatings on silica microdisks, and on the experimental validation of the predicted single-exosome shifts in microfluidic environments. In this context, controlled delivery and isolation of individual exosomes, e. g., via microfluidic-assisted transport combined with ligand-based surface functionalization, will be essential to ensure precise positioning at the sensing interface and to mitigate multi-particle effects, which are beyond the scope of the present study. Beyond cancer diagnostics, the proposed framework can be extended to other EV subtypes and disease markers, and combined with statistical or machine-learning classifiers to enable robust ERI-based phenotyping of heterogeneous exosome populations. More broadly, our results highlight the potential of excitonic materials as functional nanocoatings for next-generation photonic biosensors operating at the single-particle level.
Funding
Funded by the Deutsche Forschungsgemeinschaft( DFG, German Research Foundation) – Project number 4102100053004. We acknowledge support by the Open Access Publication Fund of the University of Duisburg-Essen.
Conflicts of interest The authors declare no conflicts of interest associated to this work.
Data availability statement
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
Author contribution statement
Modeling: M. M. G., B. B., M. J.; Simulation: M. M. G., M. J.; Investigation: M. M. G., M. J.; Conceptualization: M. J.; Funding acquisition: M. J., D. E.; Supervision: D. E., M. J.; Writing and editing: M. M. G., M. J., D. E.; Review: D. E., M. J.
References
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