Novel Functionalized Nanopores for Plasmonic Sensing
Doctoral thesis, 2021

Nanoplasmonic sensors offer a label-free platform for real-time monitoring of biomolecular interactions by tracking changes in refractive index through optical spectroscopy. However, other surface sensitive techniques such as conventional surface plasmon resonance offer similar capabilities with equal or even better resolution in terms of surface coverage. Still, plasmonic nanosensors provide unique possibilities when the nanoscale geometry itself is of interest. By taking the advantage of nanofabrication technology, it is possible to engineer nanostructures with controllable dimensions, curvature and optical properties to study nanometer-sized biomolecules, such as proteins.

  This thesis presents different types of nanoplasmonic sensing platforms, each with a unique geometry in which biomolecules can be probed through plasmonic read out. Two of the structures were fabricated by short-range ordered colloidal self-assembly and etching of the solid support underneath a nanohole array. The structures are denoted as ‘nanocaves’ and ‘nanowells’ depending on the degree of anisotropy. By suitable surface functionalization, the geometry of the plasmonic nanocavities was utilized for location-specific detection of proteins. In addition, nanowells were employed to investigate curvature-dependent biomolecular interactions.

  We have also developed subwavelength apertures in optically thin silicon nitride membranes covered with continuous metal films, referred to as solid-state ‘nanopores’. Plasmonic nanopores in suspended metal-insulator-metal films were fabricated in short-range ordered and long-range ordered arrays using short-range ordered colloidal self-assembly and electron beam lithography, respectively. Both methods prevent the metal from ending up on the silicon nitride walls which is of paramount importance for plasmonic properties and selective chemical functionalization. Preparing nanopores with identical structure but different aperture ordering provides the opportunity to understand how aperture ordering influences plasmonic response, particularly with respect to the nature of far field spectral features. Long-range ordered vs. short-range ordered nanopores exhibit similar optical properties with only a few differences in the plasmonic response.

  By appropriate material-specific modification (thiol and trietoxysilane chemistry) plasmonic nanopores were employed for detection of average sized proteins (~ 60 kg/mol) inside the pores. In addition to nanoplasmonic sensing, we could also construct a credible mimic (in terms of geometry) of nuclear pore complexes, when the size of the solid state nanopores approaches ~ 50 nm. The unique geometry and size of nanopores (diameter ~ 50 nm) opens up the possibility to mimic the geometry of biological nanomachines with integrated optical sensing capabilities.

nanocaves

label-free sensing

nanowells

plasmonic nanostructures

colloidal lithography

nanoplasmonic sensor

surface plasmon resonance

nanopores

extinction spectra

proteins

nuclear pore complex

electron beam lithography

Lecture hall KE, Kemivägen 4
Opponent: Duncan S. Sutherland

Author

Bita Malekian

Chalmers, Chemistry and Chemical Engineering, Applied Chemistry, Andreas Dahlin Group

Nanoscale materials exhibit unique properties, not found in their corresponding bulk counterparts. As the dimensions of a material decrease down to nanoscale, entirely new physical or chemical properties emerge, not by magic, but due to the increased surface-to-volume ratio of the material. This size shrinking or miniaturization, also provides the opportunity for visible light to interact with nanostructures under certain conditions, leading to unusual optical phenomena. To envision how small the nanoscale is, one can take a football and shrink it in size 20 million times to almost reach the size of a nanoobject (~ 10 nm). Interestingly, most of the human body functions are governed by nanometer-sized biomolecules, known as proteins. To better understand how our body works at the molecular level which is of paramount importance in medical diagnosis and treatment, suitable platforms are required to sense proteins and study their behavior.        

   This thesis explores the use of nanotechnology (a series of nanofabrication techniques) to engineer solid-state nanopores with different geometries and certain optical properties to probe molecular interactions involving proteins. The architecture of the nanopores allows us to study protein behavior when proper surface modification is performed on the nanostructure. Nanopores can act as nanoscale chambers, where proteins bind solely inside the pores if they are properly modified, thereby creating a location-specific sensor. Moreover, there are biological nanopores in the human body that control proteins transport. The geometry of the engineered nanopores can also be utilized to mimic such biological nanomachines to better understand the protein transport mechanisms in the human cells. The research herein is aimed toward developing robust nanostructured platforms to utilize nanoscale geometry in combination with surface chemistry to detect protein molecules and study their behavior.

Subject Categories

Nano Technology

Other Natural Sciences

Infrastructure

Nanofabrication Laboratory

Areas of Advance

Materials Science

ISBN

978-91-7905-538-7

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5005

Publisher

Chalmers University of Technology

Lecture hall KE, Kemivägen 4

Online

Opponent: Duncan S. Sutherland

More information

Latest update

8/15/2021