Nanophotonic Biosensors Within Lab on Chip Optical Systems

For ring resonator based sensors, volumetric limits of detection (LoD) of 5×10^-6 RIU and 8.3×10^-6 RIU (refractive index units) for sensitivities of 246nm/RIU and 2169nm/RIU were reported from FP6 SABIO (at 1.31μm) and FP7 InTopSens (at 1.55μm) respectively. These compare well to the state of art of 7.6×10^-7 RIU for a sensitivity of 163 nm/RIU, as does the porous alumina based membrane sensors in FP7 Positive with their LoD of 5×10^-6 RIU. More interestingly for the membrane sensors, the standard deviation of their measured values was below 5% and their flow through design with lateral distances to the sensor surface less than a diffusion length permit fast response times, short assay times and the use of small sample volumes (< 100 μl). For protein binding recognition, within SABIO a surface LoD of 0.9 pg/mm² for anti-BSA on a gluteraldehyde-covered surface was recorded, corresponding to a 125ng/ml anti-BSA solution, whilst in InTopSens 5pg/mm² and 10ng/ml for biotin on a streptavidin coated surface was seen. For an assay of β-lactoglobulin - anti-P-lactoglobulin - anti-rabbit-IgG-streptavidin conjugated CdSe quantum dots the Positive sensors demonstrated a noise floor for individual measurements of 3.7ng/ml (25pM) for total assay times of under one hour.