No abstract

Real-time measurement of specific biomolecular interactions is critical to many areas of biological research. A number of label-free techniques for directly monitoring biomolecular binding have been developed, but it is still challenging to measure the binding kinetics of very small molecules, to detect low concentrations of analyte molecules, or to detect low affinity interactions. In this study, we report the development of a highly sensitive photonic crystal biosensor for label-free, real-time biomolecular binding analysis. We characterize the performance of this biosensor using a standard streptavidin-biotin binding system. Optimization of the surface functionalization methods for streptavidin immobilization on the silica sensing surface is presented, and the specific binding of biotinylated analyte molecules ranging over 3 orders of magnitude in molecular weight, including very small molecules (<250 Da), DNA oligonucleotides, proteins, and antibodies (>150 000 Da), are detected in real time with a high signal-to-noise ratio. Finally, we document the sensor efficiency for low mass adsorption, as well as multilayered molecular interactions. By all important metrics for sensitivity, we anticipate this photonic crystal biosensor will provide new capabilities for highly sensitive measurements of biomolecular binding.

An optofluidic Fabry–Pérot cavity label-free biosensor with integrated flow-through micro-/nanochannels is proposed and demonstrated, which takes advantages of the large surface-to-volume ratio for analyte concentration and high detection sensitivity and built-in fluidic channels for rapid analyte delivery. The operating principle is first discussed, followed by assembly of a robust sensing system. Real-time measurements are performed to test its sensing feasibility and capability including bulk solvent change and removal/binding of molecules from/onto the internal surface of fluidic channels. The results show that this sensor provides a very promising platform for rapid, sensitive, and high-throughput biological and chemical sensing.

We demonstrate experimentally that in photonic crystal sensors with a side-coupled cavity-waveguide configuration, group velocity of the propagating mode in the coupled waveguide at the frequency of the resonant mode plays an important role in enhancing the sensitivity. In linear L13 photonic crystal microcavities, with nearly same resonance mode quality factors ∼7000 in silicon-on-insulator devices, sensitivity increased from 57 nm/RIU to 66 nm/RIU as group index in the coupled waveguide increased from 10.2 to 13.2. Engineering for highest sensitivity in such planar integrated sensors, thus, requires careful slow light design for optimized sensor sensitivity.

We developed and characterized a rapid, sensitive and integrated optical vapor sensor array for micro-gas chromatography (μGC) applications. The sensor is based on the Fabry-Pérot (FP) interferometer formed by a micrometre-thin vapor-sensitive polymer layer coated on a silicon wafer. The thickness and the refractive index of the polymer vary in response to the vapor analyte, resulting in a change in the reflected intensity of the laser impinged on the sensor. In our study, four different polymers were coated on four wells pre-etched on a silicon wafer to form a spatially separated sensor array. A CMOS imager was employed to simultaneously monitor the polymers' response, thus enabling multiplexed detection of a vapor analyte passing through the GC column. A sub-second detection time was demonstrated. In addition, a sub-picogram detection limit was achieved, representing orders of magnitude improvement over the on-chip vapor sensors previously reported.