Recently, surface-enhanced spectroscopy techniques have attracted a strong interest due to the large variety of applications. Most of them exploit the strong field enhancement in proximity of metal nanostructures that sustain traveling or localized surface plasmon polaritons (SPPs). Surface- and tip-enhanced Raman scattering (SERS and TERS), surface plasmon resonance (SPR), and surface-enhanced infrared absorption (SEIRA) are among the most widely spread techniques of this family, with the potential to become a fundamental asset in biophotonics, drug discovery, and for biomedical research in general by assessing the concentration, orientation, conformation, or configuration of organic biomolecules.

However, to take full advantage of the vectorial nature of the electromagnetic field and make use of it to characterize the three-dimensional structure of biomolecules in their natural aqueous environment, the use of differently polarised surface electromagnetic modes is a key feature. This is one of the reasons why recently the propagation of surface electromagnetic modes at the interface between a dielectric photonic crystal and a dielectric homogeneous medium, including water and biological buffers, has attracted a renewed interest. In fact, besides featuring negligible material absorption losses, they can be both TM (transverse magnetic) and TE (transverse electric) polarized, with the exciting opportunity of a full control over the polarization state resulting from their superposition.

SPIRAL aims at experimentally demonstrating the strength of such a concept for a specific case of study, the analysis of chiral biomolecules. Chiral biomolecules are ubiquitous in living organisms and the vast majority of new drugs developed by the pharmaceutical industry are chiral. Proteins are also chiral and changes in their folded conformation are linked with many degenerative diseases. Chiroptical techniques employ polarized light for the molecular structure characterization and are flexible, low-cost, and time-effective. However, they suffer from a limited sensitivity, preventing their integration for on-chip chiral analysis. We will establish the novel paradigm of superchiral surface waves at the surface of dielectric multilayers, with a signal enhancement of two orders of magnitude in the analysis of chiral molecules. This will allow for the integration of chiroptical techniques with microfluidic networks, enriching the widespread lab-on-chip technology with new functionalities not available so far. As a test case, we will apply these concepts to the enzyme-catalysed synthesis of chiral molecules. Here, the enhanced sensitivity paves the way towards studying molecular interactions on enzymatic surfaces for the on-chip biocatalysed synthesis in microreactors, a trend shared by many modern approaches aiming at safer and cost-effective processes, characterized by a low carbon footprint.