Final Report Summary - NANOSTRBIOSENS (NANOSTRUCTURED ALUMINA WAVEGUIDES FOR DUAL-OUTPUT BIOSENSING: STRESS INDUCED FABRICATION AND CHARACTERIZATION)
Better sensitivity for an optical biosensor can be defined with longer shifts on spectral and angular locations of narrow reflection dips when there is smaller amount of refractive index change due to molecular interactions on the sensor’s surface. The response of the sensor can be enhanced by adjusting the structure, thickness, and material types of optical transducer layers or by modifying the layers and surface structures. Nanostructuring has the potential to improve the sensitivity of optical sensors based on waveguide and surface plasmon principles. In order to achieve better sensitivity (lower limit of detection), both the dimensions and the aspect ratio of two major dimensions of the structures (i.e. periodic gratings, pillars) need to be optimized depending on wavelength, optical properties and thicknesses of the sensor layers as well as optical properties of the top sensing layer and the cover medium. Tuning dimensions of the optical transducer structure requires flexible, simple and economic fabrication method.
This proposal calls for modelling, fabrication and validation of nanostructured waveguide sensors that consist of metallic and dielectric layers including a thin layer of nanostructured alumina (Al2O3). Multilayered and nanostructured alumina waveguides would convert the waveguide mode to additional modes, excite more of them, enhance and control sensitivity of sensors in the cover medium with a thin sensing layer. It is created by gas or biological molecules especially around the surface nanostructures. Outputs of the sensor can be total internal reflection, elastic and Raman scattering signals to provide better information about both the binding and organization of molecules via polarization controlled scattering. In this project both hydrothermal process and anodization are chosen as methods to fabricate nanostructures since they are economic and straightforward. Atomic layer deposited thin and smooth alumina layers are modified with hydrothermal process at low temperatures. Anodization is the second type of fabrication methods for nanostructuring aluminum films to fabricate porous anodic alumina waveguides.
The main objective of this proposal is to design, fabricate and test nanostructured alumina waveguides for molecular biosensing applications in gas and liquid environments. In order for this research program to achieve this main goal, we proposed four tasks:
WP1: Development of an experimental system to test waveguides and to take measurements based on reflection and the scattering approach.
WP2: Fabrication of waveguides, including the fabrication of waveguide grating couplers, deposition of alumina waveguides and fabrication of nanostructures on the waveguide surface.
WP3: Testing waveguides to understand their optical responses at a given refractive index range.
WP4: Bio-sampling, surface preparation, and evaluation of the sensor structures with bio-samples.
Work packages proposed for the project have been successfully achieved. Experimental system development in WP1 and fabrication of the waveguides in WP2 has been done during first period of the project. Three different optical platforms consist of detectors, light sources, opto-mechanic components, sample holders, and flow cells have been developed in order to take necessary waveguide testing and measurements. Fabrication, structural and optical characterizations of waveguides that consist of metallic and dielectric layers and a nanostructured alumina layer were accomplished. In addition to that, modeling and optimization for layers of waveguides has been completed during the first period as well.
The waveguides fabricated are capable to excite multi surface plasmon wave guide modes of electromagnetic waves. Types of waveguides fabricated so far are nanostructured alumina waveguides, waveguides with gold coated over nanostructured alumina layers, plasmonic waveguides with gold-silver-flat/nanostructured alumina layers, Au and Ag coated daisy-like surface nanostructures, and porous anodic alumina-aluminum plasmonic waveguides. Two nanofabrication processes: hydrothermal process and anodization were explored for the nanofabrication.
During the final period of the project WP3 and WP4 have been completed successfully. Alumina waveguides that have high sensitivities in gas and liquid environments have been fabricated and tested during this period as well. Most of testing the waveguides has been performed in the last period. Final results indicate that it is feasible to use them in a commercial biosensor system as a chip. As continuation of this work, writing new research and small business proposals has been initiated.
This proposal calls for modelling, fabrication and validation of nanostructured waveguide sensors that consist of metallic and dielectric layers including a thin layer of nanostructured alumina (Al2O3). Multilayered and nanostructured alumina waveguides would convert the waveguide mode to additional modes, excite more of them, enhance and control sensitivity of sensors in the cover medium with a thin sensing layer. It is created by gas or biological molecules especially around the surface nanostructures. Outputs of the sensor can be total internal reflection, elastic and Raman scattering signals to provide better information about both the binding and organization of molecules via polarization controlled scattering. In this project both hydrothermal process and anodization are chosen as methods to fabricate nanostructures since they are economic and straightforward. Atomic layer deposited thin and smooth alumina layers are modified with hydrothermal process at low temperatures. Anodization is the second type of fabrication methods for nanostructuring aluminum films to fabricate porous anodic alumina waveguides.
The main objective of this proposal is to design, fabricate and test nanostructured alumina waveguides for molecular biosensing applications in gas and liquid environments. In order for this research program to achieve this main goal, we proposed four tasks:
WP1: Development of an experimental system to test waveguides and to take measurements based on reflection and the scattering approach.
WP2: Fabrication of waveguides, including the fabrication of waveguide grating couplers, deposition of alumina waveguides and fabrication of nanostructures on the waveguide surface.
WP3: Testing waveguides to understand their optical responses at a given refractive index range.
WP4: Bio-sampling, surface preparation, and evaluation of the sensor structures with bio-samples.
Work packages proposed for the project have been successfully achieved. Experimental system development in WP1 and fabrication of the waveguides in WP2 has been done during first period of the project. Three different optical platforms consist of detectors, light sources, opto-mechanic components, sample holders, and flow cells have been developed in order to take necessary waveguide testing and measurements. Fabrication, structural and optical characterizations of waveguides that consist of metallic and dielectric layers and a nanostructured alumina layer were accomplished. In addition to that, modeling and optimization for layers of waveguides has been completed during the first period as well.
The waveguides fabricated are capable to excite multi surface plasmon wave guide modes of electromagnetic waves. Types of waveguides fabricated so far are nanostructured alumina waveguides, waveguides with gold coated over nanostructured alumina layers, plasmonic waveguides with gold-silver-flat/nanostructured alumina layers, Au and Ag coated daisy-like surface nanostructures, and porous anodic alumina-aluminum plasmonic waveguides. Two nanofabrication processes: hydrothermal process and anodization were explored for the nanofabrication.
During the final period of the project WP3 and WP4 have been completed successfully. Alumina waveguides that have high sensitivities in gas and liquid environments have been fabricated and tested during this period as well. Most of testing the waveguides has been performed in the last period. Final results indicate that it is feasible to use them in a commercial biosensor system as a chip. As continuation of this work, writing new research and small business proposals has been initiated.