# Special Issue on Recent Advances and Future Trends in Nanophotonics II
###### Abstract  
The proposed approach to the development of a novel  
it is noteworthy that these studies did not consider the back-reflection effect, which is crucial for transmitter functionality [15]. In contribution 3, [PERSON] and coauthors investigate fluorophores that find widespread biomedical utility as tracers and markers, such as when linked to DNA strands in devices for virus detection in blood samples. The application of such techniques in lab-on-a-chip setups holds promise [16], especially during pandemics, offering rapid virus detection in airports or other public areas. Additionally, they can serve as markers for verifying the authenticity of certain manufactured goods, thwarting counterfeiting attempts, as proposed here. Fluorimetry boasts rapid response times, sensitivity of excited states to local environments, and the ability to incorporate fluorophores into chips/devices, enabling simultaneous measurement of multiple samples in a short duration [17]. While fluorophores are commonly used for tracing and marking [17; 18], operating them in the strong-coupling regime is unusual. Recent advancements have explored strong coupling for potential quantum chip applications, employing fluorophores tethered to oligonucleotide strands and integrated into cavities [19]. These DNA or RNA oligonucleotide strands offer the flexibility to position the probe within the cavity or link it with a plasmonic nanoobject (e.g., a gold nanosphere), akin to an external cavity [20; 21]. However, this advantage is counterbalanced by the relatively high design and purification costs associated with oligonucleotides, compounded by aging issues (stability of oligonucleotide probes within the cavity). Contribution 3 introduces a novel fluorescence technique leveraging the intense light-matter interaction of an embedded nanoprobe within a plasmonic cavity. The strong light-matter interactions between nanoprobes and cavity modes typically manifest as changes in the excitation spectrum (electronic or vibrational) of the coupled system [22]. The article by [PERSON] et al. (contribution 4) introduces an innovative design for a surface-enhanced Raman spectroscopy (SERS) substrate, aiming to achieve exceptional sensitivity and rapid, intimate contact between the target structure and the optical hotspots. The proposed substrate offers an enhancement factor of \(10^{8}\) or greater, potentially enabling the detection of immunomagnetically densified bacteria. Indeed, rapid detection of bacterial infections is a pressing concern in infectious disease diagnostics and treatment, with sepsis alone claiming over 25 percent of its victims [23]. However, the current clinical standards for sepsis diagnosis can take up to five days to culture and identify bacteria [24]. SERS emerges as a label-free optical biosensing technique, leveraging a modified form of Surface Plasmon Resonance (SPR). In Raman spectroscopy, when laser light interacts with a sample, it undergoes inelastic scattering, resulting in a change in wavelength according to the vibrational modes of the molecules [25]. This shift provides detailed vibrational information about the chemical bonds, offering high spatial resolution [26]. SERS enhances Raman signals using metallic nanomaterials, typically in the form of SERS tags, which consist of modified metallic nanoparticles equipped with specific capturing probes or Raman reporter molecules [27]. This study introduces a new SERS substrate design aimed at achieving high sensitivity and rapid, close contact between the target structure and optical hotspots for immunomagnetic bacteria concentration. The substrate utilizes inverted nanocone structures made of transparent PDMS, guiding light to plasmonic gold nanorods positioned at the top of the cones. With a highly reflective and low-loss outer layer, photons undergo multiple reflections, significantly increasing photon density at hotspots, potentially enabling the detection of immunomagnetically densified bacteria. Finally, contribution 5 is an interesting review by [PERSON] et al.