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In this Letter, we demonstrate for the first time the experimental capability for the biochemical sensing of resonant nanopillars (RNPs) arrays. These arrays are fabricated over a glass substrate and are optically integrated from the backside of this substrate. The reflectivity profiles of the RNPs arrays are measured by infiltrating different ethanol fractions in water in order to evaluate the optical response for the different refractive indexes, which range from 1.330 to 1.342. A linear fit of the resonant modes shift is observed as a function of the bulk refractive index of the liquid infiltrated. For the type of transducer analyzed, a relative sensitivity of 10017  cm(-1)/Refractive Index Unit (RIU) is achieved, allowing us to reach a competitive Limit of Detection (LoD) in the order of 1×10(-5)  RIU.

In our previous work we demonstrated for the first time, to the best of our knowledge, the experimental capability of resonant nanopillars (R-NP) arrays as biochemical transducers. In this Letter, we provide evidence of the capability and suitability of R-NP arrays on a chip to function as label-free optical multiplexed biosensors. R-NP are based on Si₃N₄/SiO₂ Bragg reflectors with a cavity of SiO₂. In order to demonstrate the biosensing performance, R-NP were biofunctionalized by the immobilization of IgG antibodies acting as a bioreceptor. This immobilization was carried out through the silanization of the pillars sensing surface with APTMS (3-aminopropyltrimethoxysilane). R-NP were integrated in eight different sensing arrays on a quartz surface chip. An optical fiber bundle monitored each sensing array vertically and independently after each biofunctionalization step, and subsequently after every recognition event of increasing concentrations of anti-IgGs. The results report a novel multiplexed optical biosensor made of eight sensing arrays on a chip with promising performance and yield.

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In this work we demonstrate the advantage of performing the biosensing process of a refractive index optical biosensor under dry conditions, in comparison with the biosensing structure immersed in fluid. We developed a biosensing experiment over a specific transducer based on resonant nanopillars (R-NPs) arrays. The optical interrogation to monitor the recognition events was firstly performed with the R-NPs in dry, only in contact with the air, and secondly with the R-NPs immersed in water. We observed a significant enhance in the sensitivity of the biosensing curve response for the R-NPs in dry conditions, leading an improvement of the Limit of Detection (LoD) in more than one order of magnitude. These results are also in good correlation with 3D-Finite difference time domain simulations carried out for both fluid conditions. According to this result, any interferometric optical bio-transducer for in-situ diagnosis will improve the sensitivity in case it can operate in dry conditions. Moreover, measuring in simple drops of biological samples, in dry conditions, will be a relevant issue for Point of Care Devices.

In this work, the authors present a novel fabrication process to create periodic nanostructures with aspect ratio as high as 9.6. These nanostructures reduce spectral reflectance of silicon to less than 4% over the broad wavelength region from 200 to 2000 nm. At the visible range of the spectrum, from 200 to 650 nm, reflectivity is reduced to less than 0.1%. The aspect ratio and reflectance performance that the authors achieved have never been reported before for ordered tapered nanostructures, to our knowledge.