Plasmonic Sensors Based on a Metal–Insulator–Metal Waveguide—What Do We Know So Far?

Metal–insulator–metal (MIM) waveguide-based plasmonic sensors are significantly important in the domain of advanced sensing technologies due to their exceptional ability to guide and confine light at subwavelength scales. These sensors exploit the unique properties of surface plasmon polaritons (SPPs) that propagate along the metal–insulator interface, facilitating strong field confinement and enhanced light–matter interactions. In this review, several critical aspects of MIM waveguide-based plasmonic sensors are thoroughly examined, including sensor designs, material choices, fabrication methods, and diverse applications. Notably, there exists a substantial gap between the numerical data and the experimental verification of these devices, largely due to the insufficient attention given to the hybrid integration of plasmonic components. This disconnect underscores the need for more focused research on seamless integration techniques. Additionally, innovative light-coupling mechanisms are suggested that could pave the way for the practical realization of these highly promising plasmonic sensors.