Surface plasmon resonance sensing with thin films of palladium and platinum - quantitative and real-time analysis

Trends in surface plasmon resonance biosensing: materials, methods, and machine learning

Surface plasmon resonance (SPR) proves to be one of the most effective methods of label-free detection and has been integral for the study of biomolecular interactions and the development of biosensors. This trend delves into the latest SPR research and progress built upon the Kretschmann configuration, a pivotal platform, and highlights three key developments that have enhanced the capabilities of the technique. We will first cover a range of explorations of novel plasmonic materials that have shaped SPR performance. Innovative signal transduction and collection, which leverages traditional materials and emerging alternatives, will then be discussed. Finally, the evolving landscape of data analysis, including the integration of machine learning algorithms to navigate complex SPR datasets, will be reviewed. We will also discuss the implementation of these improvements that have enabled new biosensing functions. These advancements not only pave the way for enhanced biosensing in general but also open new avenues for the technique to play a more significant role in research concerning human health.

Diameter dependence of transport through nuclear pore complex mimics studied using optical nanopores

The nuclear pore complex (NPC) regulates the selective transport of large biomolecules through the nuclear envelope. As a model system for nuclear transport, we construct NPC mimics by functionalizing the pore walls of freestanding palladium zero-mode waveguides with the FG-nucleoporin Nsp1. This approach enables the measurement of single-molecule translocations through individual pores using optical detection. We probe the selectivity of Nsp1-coated pores by quantitatively comparing the translocation rates of the nuclear transport receptor Kap95 to the inert probe BSA over a wide range of pore sizes from 35 nm to 160 nm. Pores below 55 ± 5 nm show significant selectivity that gradually decreases for larger pores. This finding is corroborated by coarse-grained molecular dynamics simulations of the Nsp1 mesh within the pore, which suggest that leakage of BSA occurs by diffusion through transient openings within the dynamic mesh. Furthermore, we experimentally observe a modulation of the BSA permeation when varying the concentration of Kap95. The results demonstrate the potential of single-molecule fluorescence measurements on biomimetic NPCs to elucidate the principles of nuclear transport.

Visible and angular interrogation of Kretschmann-based SPR using hybrid Au-ZnO optical sensor for hyperuricemia detection

Uric acid is a waste product of the human body where high levels of it or hyperuricemia can lead to gout, kidney disease and other health issues. In this paper, Finite Difference Time Doman (FDTD) simulation method was used to develop a plasmonic optical sensor to detect uric acid with molarity ranging from 0 to 3.0 mM. A hybrid layer of gold-zinc oxide (Au-ZnO) was used in this Kretschmann-based Surface Plasmon Resonance (K-SPR) technique with angular interrogation at 670 nm and 785 nm visible optical wavelengths. The purpose of this study is to observe the ability of the hybrid material as a sensing performance enhancer for differentiating between healthy and unhealthy uric acid levels based on the refractive index values from previous study. Upon exposure to 670 nm wavelength, the average sensitivity of this sensor was found to be 0.028°/mM with a linearity of 98.67 % and Q-factor value of 0.0053 mM - 1 . While at 785 nm, the average sensitivity is equal to 0.0193°/mM with slightly lower linearity at 94.46 % and Q-factor value of 0.0076 mM - 1 . The results have proven the ability of hybrid material Au-ZnO as a sensing performance enhancer for detecting uric acid when compared with bare Au and can be further explored in experimental work.

Stable trapping of multiple proteins at physiological conditions using nanoscale chambers with macromolecular gates

The possibility to detect and analyze single or few biological molecules is very important for understanding interactions and reaction mechanisms. Ideally, the molecules should be confined to a nanoscale volume so that the observation time by optical methods can be extended. However, it has proven difficult to develop reliable, non-invasive trapping techniques for biomolecules under physiological conditions. Here we present a platform for long-term tether-free (solution phase) trapping of proteins without exposing them to any field gradient forces. We show that a responsive polymer brush can make solid state nanopores switch between a fully open and a fully closed state with respect to proteins, while always allowing the passage of solvent, ions and small molecules. This makes it possible to trap a very high number of proteins (500-1000) inside nanoscale chambers as small as one attoliter, reaching concentrations up to 60 gL-1. Our method is fully compatible with parallelization by imaging arrays of nanochambers. Additionally, we show that enzymatic cascade reactions can be performed with multiple native enzymes under full nanoscale confinement and steady supply of reactants. This platform will greatly extend the possibilities to optically analyze interactions involving multiple proteins, such as the dynamics of oligomerization events.

Au-Based Thin-Film Metallic Glasses for Propagating Surface Plasmon Resonance-Based Sensor Applications

We deposited Au-Cu-Si, an Au-based thin-film metallic glass (TFMG) of ∼50 nm thickness, as the activation layer for propagating surface plasmon resonance (PSPR)-based sensors on a BK7 glass substrate to substitute the commonly used gold layer. The film composition was tuned to yield the maximum Au content (∼65 at %), while the structure remained amorphous. The results showed that the Au-based TFMG could support surface plasmon resonance and gave rise to the extinction in the angle-resolved reflection spectrum. Using deionized water and ethyl alcohol with the refractive index difference of ∼0.03 as the analytes, the angle shift given by Au-based TFMG was 4° compared to 5° given by the Au film. Hence, Au-based TFMG is feasible to be used as the activation layer in PSPR-based sensors. Compared to the Au film, Au-based TFMG has the advantages of being less expensive, lacking grain boundary scattering, better adhesion to the substrate, and higher resistance to scratch and corrosion because of its amorphous structure with excellent mechanical properties.

Electrically Switchable Polymer Brushes for Protein Capture and Release in Biological Environments

Interfaces functionalized with polymers are known for providing excellent resistance towards biomolecular adsorption and for their ability to bind high amounts of protein while preserving their structure. However, making an interface that switches between these two states has proven challenging and concepts to date rely on changes in the physiochemical environment, which is static in biological systems. Here we present the first interface that can be electrically switched between a high‐capacity (>1 μg cm⁻²) multilayer protein binding state and a completely non‐fouling state (no detectable adsorption). Switching is possible over multiple cycles without any regeneration. Importantly, switching works even when the interface is in direct contact with biological fluids and a buffered environment. The technology offers many applications such as zero fouling on demand, patterning or separation of proteins as well as controlled release of biologics in a physiological environment, showing high potential for future drug delivery in vivo.