Systematic comparison between photonic sensors based on dielectrics and metals

Photonic biosensors have gained much attention recently due to their high sensitivity, low energy consumption and miniaturization capability, conveying noteworthy advances in biomedicine. In the near future, these sensors will form the basis of the so-called Lab on a Chip (LoC): a device that would incorporate all laboratory functions into a single chip, capable of performing accurate clinical analyzes in any location, forming an important asset for countries with few resources for disease detection. There are a variety of configurations for biophotonic sensors, based on dielectric or metallic (plasmonic) media, ranging from fiber-optic based systems, waveguides, resonators, to nanoparticles and photonic crystals, to name a few. In spite of this great diversity, these devices can be classified into two broad categories: those that require previous mode coupling and those that do not. Although devices in the first category tend to display higher sensitivities, the ones in the second category exhibit many operation advantages, like facile integration and real-time label-free detection, constituting a suitable transducer for a LoC device. One type of free-space sensors are the devices based on excitation of quasi-Guided modes (QGM). QGM-based sensors feature as one of the most promising photonic systems for biosensing applications mainly due to their cost-effective fabrication process and capacity to control the wavelength of operation by design. Even though, in literature, several papers discuss characteristics of both plasmonics and dielectric systems, it is usually hard to find a standardized approach which discriminates the main features of these devices, because each group tends to use a different platform, thus hindering a comparative assessment of the devices. Consequently, given their complementary aspects - while metallic systems are typically more sensitive but feature poor spectral responses, dielectric-based sensors display good spectral responses but are less sensitive - and mostly independent research effort, it is still an open question which kind of sensor, dielectric or plasmonic based, has the best overall performance. The present work aims at accomplishing this task by systematically studying and comparing the core differences between both systems in terms of their sensing performance and spectral characteristics. We use the limit of detection as the figure of merit for the overall performance and show that, overall, dielectric sensors obtain a higher performance.