Topographically Flat Nanoplasmonic Sensor Chips for Biosensing and Materials Science

Abstract

Nanoplasmonic sensors typically comprise arrangements of noble metal nanoparticles on a dielectric support. Thus, they are intrinsically characterized by surface topography with corrugations at the 10-100 nm length scale. While irrelevant in some bio- and chemosensing applications, it is also to be expected that the surface topography significantly influences the interaction between solids, fluids, nanoparticles and (bio)molecules, and the nanoplasmonic sensor surface. To address this issue, we present a wafer-scale nanolithography-based fabrication approach for high-temperature compatible, chemically inert, topographically flat, and laterally homogeneous nanoplasmonic sensor chips. We demonstrate their sensing performance on three different examples, for which we also carry out a direct comparison with a traditional nanoplasmonic sensor with representative surface corrugation. Specifically, we (i) quantify the film-thickness dependence of the glass transition temperature in poly(methyl metacrylate) thin films, (ii) characterize the adsorption and specific binding kinetics of the avidin-biotinylated bovine serum albumin protein system, and (iii) analyze supported lipid bilayer formation on SiO surfaces.

Probing the Interaction of Dielectric Nanoparticles with Supported Lipid Membrane Coatings on Nanoplasmonic Arrays

“…More recently, the concept of “indirect nanoplasmonic sensing” has become popular whereby the entire sensor surface is coated with a thin, conformal dielectric layer, oftentimes silica or titanium oxide [ 45 ]. This approach has broadly enabled the fabrication of fluidic, two-dimensional supported lipid bilayers (SLBs) on nanodisk [ 14 , 46 , 47 , 48 , 49 ] and nanohole [ 50 , 51 , 52 ] architectures, opening the door to a wide range of studies involving protein binding [ 11 , 47 , 53 , 54 , 55 ] as well as vesicle adsorption and deformation [ 56 , 57 , 58 , 59 , 60 , 61 ]. As these fabrication approaches gain traction, there has been renewed emphasis on varying the membrane composition to modulate SLB–substrate interactions (e.g., via membrane surface charge) as well as employing the nanostructured sensing platforms to study membrane interactions pertaining to various classes of molecules and nanomaterials such as amphipathic peptides [ 49 ], graphene oxide sheets [ 62 ], and ionic liquids [ 63 ].…”

Indirect Nanoplasmonic Sensing Platform for Monitoring Temperature-Dependent Protein Adsorption

“…Protein adsorption onto metal nanoparticles can be directly measured, or a thin layer of a dielectric material can be deposited on top of the sensor surface in order to study protein adsorption onto dielectric coatings, in which case the underlying nanoparticles serve as indirect nanoplasmonic transducers. − In such sensors, the substrate surface is corrugated on a length scale that is comparable to the nanoparticle size. In a few cases, topographically flat nanoplasmonic substrates based on embedding the nanoparticle transducers in a dielectric matrix have also been reported. , In order to monitor Δλ max shifts, the optical extinction spectrum is typically acquired by ultraviolet–visible spectroscopic measurements in transmission mode, and the measurement readout is ensemble-averaged across a large number of nanoparticles within the spot of incident light. Compared to conventional optical sensor techniques (e.g., SPR, ellipsometry, reflectometry), LSPR-based nanoplasmonic sensors are technically simple to operate and have smaller probing volumes that confer lower sensitivity to bulk refractive index changes such as minor temperature variations .…”

“…In a few cases, topographically flat nanoplasmonic substrates based on embedding the nanoparticle transducers in a dielectric matrix have also been reported. 25,26 In order to monitor Δλ max shifts, the optical extinction spectrum is typically acquired by ultraviolet−visible spectroscopic measurements in transmission mode, and the measurement readout is ensemble-averaged across a large number of nanoparticles within the spot of incident light. Compared to conventional optical sensor techniques (e.g., SPR, ellipsometry, reflectometry), LSPR-based nanoplasmonic sensors are technically simple to operate and have smaller probing volumes that confer lower sensitivity to bulk refractive index changes such as minor temperature variations.…”

Biologically interfaced nanoplasmonic sensors

“…Recent progress in INPS have witnessed the construction of topographically at nanoplasmonic sensors whereby the Au nanodisk transducers are embedded within the support substrate and coated with a at layer of oxide material 36,37 (Fig. 4A).…”

“…The three-dimensional sketch shows the three "layers" of the device, i.e., the wells in the fused silica substrate, the Au nanodisks grown inside the wells, and the topographically flat SiO 2 capping layer. Reproduced with permission from ref 36…”