Pedestal High-Contrast Gratings for Biosensing

Abstract

High-contrast gratings (HCG) are an excellent candidate for label-free detection of various kinds of biomarkers because they exhibit sharp and sensitive optical resonances. In this work, we experimentally show the performance of pedestal HCG (PHCG), which is significantly enhanced in comparison with that of conventional HCG. PCHGs were found to provide a 11.2% improvement in bulk refractive index sensitivity, from 482 nm/RIU for the conventional design to 536 nm/RIU. The observed resonance was narrower, resulting in a higher Q-factor and figure of merit. By depositing Al2O3, HfO2, and TiO2 of different thicknesses as model analyte layers, surface sensitivity values were estimated to be 10.5% better for PHCG. To evaluate the operation of the sensor in solution, avidin was employed as a model analyte. For avidin detection, the surface of the HCG was first silanized and subsequently functionalized with biotin, which is well known for its ability to bind selectively to avidin. A consistent red shift was observed with the addition of each of the functional layers, and the analysis of the spectral shift for various concentrations of avidin made it possible to calculate the limit of detection (LoD) and limit of quantification (LoQ) for the structures. PHCG showed a LoD of 2.1 ng/mL and LoQ of 85 ng/mL, significantly better than the values 3.2 ng/mL and 213 ng/mL respectively, obtained with the conventional HCG. These results demonstrate that the proposed PHCG have great potential for biosensing applications, particularly for detecting and quantifying low analyte concentrations.

Optical Biosensors Based on Nanostructured Silicon High-Contrast Gratings for Myoglobin Detection

“…The fabrication of the conventional and pedestal gratings is described in more detail in our previous work. 8 Here we focus on the added fabrication steps to obtain half-buried HCG from the conventional one. To produce the half-buried HCG, it is necessary to fill the air gaps between the grating bars with an appropriate material (with a refractive index close to SiO 2 ).…”

“…At the same time, the half-buried version is buried partially in the substrate to provide access of the biological targets to the hot points in the fields. In the work, we fabricated and characterized pedestal HCG and demonstrated their improved performance compared to conventional HCGs in terms of volume and surface sensitivity toward model analytes. Here, we compare the biosensing performance of the pedestal and half-buried HCGs.…”

“…22 GMR structures are promising for sensing because the propagation constant of the quasi-guided mode changes in the presence of target analytes, causing a wavelength shift in the resonant reflected light. For example, GMR in HCG structures have been used for the detection of bulk refractive index changes, 23−25 different gases, 26 viruses, 27 and proteins, like avidin 8 and cardiac troponin I. 21 In our recent theoretical work 7 we presented two new highcontrast grating in nanopatterned configurations with improved sensing performance.…”

“…Optical sensor devices are in high demand for biological and chemical detection. There are many optical techniques to detect analytes. − One of the most common methods involves sensing the change in refractive index (RI) caused by the presence of the analyte. − High sensitivity in RI sensing is achieved by having strong optical fields in the proximity of the target analyte. The most widely used and commercialized label-free refractometric sensors are plasmonic devices .…”

“…The main one is losses at optical frequencies, which can lead to the heating of the structure and a change in the RI . One approach to overcome this limitation is to use metal oxides or polymers for the generation of lossy mode resonance (LMR) in optical fiber geometry − or dielectric structures. − Silicon, for example, is transparent in the near-infrared region, so using it at such wavelengths prevents undesirable sample heating. Additionally, low losses and high RI of silicon enable narrow resonances with high-quality factors ( Q factors).…”