Low-cost rapid pathogen test with enhanced analyte entrapment by ferromagnetic particles and cascaded microring resonator detector

Silicon-on-insulator microring resonators have attracted significant research in recent decades for their capability as highly sensitive biosensors. However, adoption in point-of-care medical devices remains limited due to challenges including complex sample preparation, reliance on bulky and expensive tunable lasers or optical spectrum analyzers, high limits of detection, and slow microfluidics that depend on particle diffusion to the sensor’s active area. We propose and model a platform which achieves binding of over 99% of target analytes to manipulable magnetic nanoparticles/nanobeads within 15 minutes, rapid transport of these labeled analytes to the functionalized microring surface, and detection with enhanced sensitivity via direct intensity interrogation rather than conventional resonant wavelength shift detection. The last advancement enables use of a broadband light source (e.g., SLED) and a simple photodiode, eliminating the need for a tunable laser and spectrum analyzer. Ultimately, we demonstrate through multiple numerical modeling methods that as few as five magnetic nanoparticles can induce a 5 dB transmission attenuation in a cascaded microring resonator configuration. This corresponds to a detection threshold on the order of five particles per milliliter, enabled by high binding effiency and specificity. Preliminary numerical studies suggest that further improvements may be achieved using magnetic nanoparticles modified or coated with materials that have a high imaginary refractive index (e.g., gold) or a high real refractive index (e.g., germanium).