Effectively collecting and storing light energy through optical confinement remains a persistent challenge in maximising energy utilisation in plasmonic systems. Optically confined energy significantly enhances processes such as Raman scattering and photoluminescence, and can drive catalytic chemical reactions . Especially, surface-enhanced Raman scattering (SERS) strongly benefits from confined energy, scaling approximately with the fourth power of the local electric field . Although plasmonic nanostructure-based SERS holds great promise for signal amplification and multiplexing, it faces significant challenges. These include the difficulty of synthesising nanoparticles that yield strong yet quantitative SERS signals, reliably analysing complex and dynamically fluctuating signals, accurately quantifying target analytes, ensuring data reproducibility, and developing probes and substrates that operate at very low laser powers for stable, noise-minimised detection and reduced cost .