Tunable Fano-Resonant Metasurfaces on a Disposable Plastic-Template for Multimodal and Multiplex Biosensing

Abstract

Metasurfaces are engineered nanostructured interfaces that extend the photonic behavior of natural materials, and they spur many breakthroughs in multiple fields, including quantum optics, optoelectronics, and biosensing. Recent advances in metasurface nanofabrication enable precise manipulation of light-matter interactions at subwavelength scales. However, current fabrication methods are costly and time-consuming and have a small active area with low reproducibility due to limitations in lithography, where sensing nanosized rare biotargets requires a wide active surface area for efficient binding and detection. Here, a plastic-templated tunable metasurface with a large active area and periodic metal-dielectric layers to excite plasmonic Fano resonance transitions providing multimodal and multiplex sensing of small biotargets, such as proteins and viruses, is introduced. The tunable Fano resonance feature of the metasurface is enabled via chemical etching steps to manage nanoperiodicity of the plastic template decorated with plasmonic layers and surrounding dielectric medium. This metasurface integrated with microfluidics further enhances the light-matter interactions over a wide sensing area, extending data collection from 3D to 4D by tracking real-time biomolecular binding events. Overall, this work resolves cost- and complexity-related large-scale fabrication challenges and improves multilayer sensitivity of detection in biosensing applications.

Keywords: biosensing; metasurfaces; microfluidics; point-of-care diagnostics; tunable Fano resonances.

Figure 1:

Fano-resonant plastic-templated metasurface and a portable microfluidic sensor. a Optical disc surface consists of dielectric surface-grating used as a metasurface sensor. The surface was coated with Ti (10nm), Ag (30nm), and Au (15nm) multi-layers to fabricate plastic-templated metasurface. b Schematic diagram depicts the microfluidic chip consisting of three layers (plasmonic surface, DSA, and PMMA). c Fabricated metasurface chip is connected with tubing at inlet and outlet ports. d The plastic-templated metasurface based bio-sensing measures the layer-by-layer functionalization of biomolecules and target HIV-1 capture.

Figure 2:

Plastic-templated metasurface fabrication, surface profile and structure-dependent plasmonic Fano resonance modeling. a Plastic-templated metasurface fabrication is based on subsequent steps: (i) removal of top plastic, (ii) removal of PR and metal-coating, (iii) surface cleaning, (iv) chemical etching, (v) plasmonic layer coating, and finally (vi) microfluidic chip assembly. b The fabricated metasurface shows bright rainbow patterns (i); scanning electron microscopy (SEM) image shows uniform surface gratings (ii); and atomic force microscopy (AFM) image depicts 3D profile of coated surface (iii). c WG and SPP modes are present in the plasmonic waveguide (PWG) grating surface. d SPP mode response of the metasurface with dielectric medium (DM) RI varying from 1.33 to 1.42 RIU. We have shown plasmonic field distribution at peak resonance frequency, f_peak =560 nm in water medium. e Plasmonic Fano resonance response of metasurface is tuned by changing the thickness of silver (Ag) layer.

Figure 3:

Bulk RI-sensing on a portable set-up and computational modeling. a Portable set-up measures the plasmonic Fano response of plastic-templated metasurface. b Conceptual block-diagrams of the optical set-up and ray-tracing of the light-transmission and reflection from the metasurface. c Computational and experiment results demonstrating plasmonic Fano resonance tuning from the metasurfaces with medium (air and water) variations. d Plasmonic Fano resonance is tuned using a range of glycerol dilutions in water (2.5–70% v/v). e Plasmonic Fano resonance wavelength shifts as a function of RI variation. Dotted lines indicate the linearity response during simulation and experiment. f Real-time dip and peak plasmonic response to the variation in glycerol concentration.

Figure 4:

Surface sensitivity of plastic-templated metasurface for layer-by-layer modifications. a Summary of surface chemistry steps. b Resonance peak wavelength shifts demonstrated on surfaces etched for 30, 60 and 90 sec. c Layer-by-layer binding response of bio-molecules on the 60 sec etched surface is monitored in real-time. d-f Resonance wavelength shifts as a function various concentrations of protein G, anti-gp120 antibody and rec-gp120 protein are represented via Box-Whisker plots. I-shaped box indicates 25^th and 75^th, red-line median, and whiskers the 95^th and 5^th percentiles. Dots represent data points for each concentration. Non-parametric Kruskal-Wallis analysis followed by Dunn’s multiple comparison test was performed to evaluate the collected data for each concentration at Protein G, anti-gp120 antibody and rec. gp120 protein experiments. The minimum, first quartile, median, third quartile, and maximum of each concentration were presented in Supplementary Table 1. In Protein G experiment, statistical difference was observed between 75 and 1000 μg/mL concentrations (n=3, p<0.05). In anti-gp120 antibody experiments, statistical difference was observed between 30 and 75 μg/mL concentrations (n=3, p<0.05). In rec-gp120 protein experiments, statistical difference was observed between 25 and 200 μg/mL concentrations (n=3, p<0.05).

Figure 5:

Detection and capture of HIV-1 particles. a, b Real-time detection of HIV-1 YU2 molecular clone is demonstrated for the experimental set-2 and 3. c Different experimental sets evaluated the effect of extended incubation time on sensing performance. d Cumulative resonance wavelength shifting is demonstrated usingdifferent HIV-1 concentrationse SEM images of captured HIV-1 particles on both the (i) edge and (ii) top layer of grating surface due to SPP and waveguides modes.