Polymer microring resonators for biochemical sensing applications

Polymer microring resonators were demonstrated for sensing biomolecules without using fluorescent labels. The microring devices, fabricated by a direct imprinting technique, possess high Q factors of /spl sim/20000. This feature provides high sensitivity and a low detection limit for biochemical sensing applications. With these properties, the devices were used to detect and quantify the biomolecules present either in a homogeneous solution that surrounds the microring waveguide (homogeneous sensing) or specifically bound on the waveguide surface (surface sensing). In the former sensing mechanism, the current devices can detect an effective index change of 10/sup -7/ refractive index units (RIU); in the latter, they can reach a detection limit of /spl sim/250 pg/mm/sup 2/ of biomolecular coverage on the microring surface. In addition, the experiments show that the devices can detect both small and large biomolecules.

I. Introduction

Applications of biological and chemical sensors hold long-standing interests due to their close relationship with human life. Examples include bacteria and virus detection, medical diagnostics, screening of chemical compounds in drug discovery, food safety, and environment monitoring. These aspects stimulate the demand and development of ultrasensitive devices to detect biomolecules with very low concentrations. Among the existing biochemical sensors, planar optical sensors are promising because of their robustness, easy patterning of reagents, and simple incorporation of various materials such as polymers, metals, and dielectrics [1]. In addition, they have high integration capability with electronic devices as well as photonic devices, and can be easily fabricated with mature semiconductor processing technologies. Moreover, these sensors can render label-free detection, compatibility with microfluidic handling, and capability of providing high specificity using surface chemical modifications [2]. Some examples of planar optical sensors include channel waveguide sensors [3], surface plasmon resonance (SPR) sensors [4], directional coupler sensors [5], Mach–Zehnder interferometric sensors [6], and grating-coupled waveguide sensors [7]. Most of these are optical-waveguide-based sensors.