Multi-band single bio-molecule detection through inverse-designed graphene-folded spherical particle dimers

The present research employs graphene-coated spherical nano-particles as the basis of optical dimers for multi-frequency refractive index sensing applications. Under parallelly polarized incoming waves, dual operating bands are attained owing to the presence of localized surface plasmon resonances (LSPRs) on graphene shells. Thus, enormous local near-field enrichment is detected at the gap middle as a result of plasmonic hybridization and strong coupling. The potential usage of the proposed dimer as a dual-band high-performance refractive index sensor, with the typical sensitivity of S ₁= 2.8143 × 10⁴ nm/RIU and figure of merit of FOM₁= 213.2860 RIU^-1 in the first band, and sensitivity of S ₂= 1.8070 × 10⁴ nm/RIU and figure of merit of FOM₂= 305.1521 RIU^-1 in the second band, is illustrated. Importantly, the enormous near-field enhancement is maintained for particles with different radii, making the element suitable for single bio-molecule recognition of various types by tuning the quality of the graphene layer. The spectral tuning is correspondingly viable after production by imposing a suitable Fermi level on the graphene shells. Finally, machine learning forward and reverse problems based on the random forest (RF), decision tree (DT), and eXtreme Gradient Boosting (XGBoost) algorithms are implemented to propose a method respectively for analysis of the sensor's performance and to design an appropriate sensor for each desired molecule.