arXiv subjects

Ershad Mohammadi

Publications and source records attributed to Ershad Mohammadi.

2 recordsLinked to original sources

arXiv2026

Boosting fluorescence and polarization with nanophotonics for single-molecule chiral sensing

Detecting chirality is essential in chemistry and biomedicine. Circular dichroism identifies chiral molecules through their differential absorption of circularly polarized light. However, its sensitivity is limited by vanishing absorption at low concentrations. Fluorescence-based methods have already enabled other optical techniques to reach the single-molecule limit and could, in principle, also extend chiral detection to reach this sensitivity regime. They are marred, however, by the combination of weak fluorescence signals and low polarization contrast. To overcome these limitations, we leverage high-index dielectric nanophotonics to simultaneously enhance both fluorescence and polarization for chiral sensing. We propose a reciprocity-based analytical framework for a chiral dipolar emitter coupled to a nanoantenna and reveal the different contributions and trade-offs governing the enhancement of circularly polarized fluorescence. Guided by this insight, we tailor achiral dielectric nanostructures to reach a 1000-fold enhancement of fluorescence intensity together with a 10-fold increase in polarization. Crucially, we show that accounting for extrinsic polarization effects in the angular emission patterns of nanophotonic structures is indispensable for reliable enantiomer discrimination. Our approach opens a realistic path for single-molecule chiral sensing.

physics.optics↗

arXiv2024

Nanophotonic-Enhanced Thermal Circular Dichroism for Chiral Sensing

Circular Dichroism (CD) can distinguish the handedness of chiral molecules. However, it is typically very weak due to vanishing absorption at low molecular concentrations. Here, we suggest Thermal Circular Dichroism (TCD) for chiral detection, leveraging the temperature difference in the chiral sample when subjected to right and left-circularly polarized excitations. The TCD combines the enantiospecificity of circular dichroism with the higher sensitivity of thermal measurements, while introducing new opportunities in the thermal domain that can be synergistically combined with optical approaches. We propose a theoretical framework to understand the TCD of individual and arrays of resonators covered by chiral molecules. To enhance the weak TCD of chiral samples, we first use individual dielectric Mie resonators and identify chirality transfer and self-heating as the underlying mechanisms giving rise to the differential temperature. However, inherent limitations imposed by the materials and geometries of such resonators make it challenging to surpass a certain level in enhancements. To overcome this, we suggest nonlocal thermal and electromagnetic interactions in arrays. We predict that a combination of chirality transfer to Mie resonators, collective thermal effects, and optical lattice resonance could, in principle, offer more than 4 orders of magnitude enhancement in TCD. Our thermonanophotonic-based approach thus establishes key concepts for ultrasensitive chiral detection.

physics.optics↗