Tuning Surface Plasmon Resonance Responses through Size and Crosslinking Control of Multivalent Protein Binding-Capable Nanoscale Hydrogels

Abstract

Surface plasmon resonance (SPR) phenomena have been widely studied to detect biomolecules because of their high sensitivity and ability to determine biomolecular interactions with kinetic information. However, highly selective detection in specific concentration ranges relevant to target biomolecules is still a challenging task. Recently, we developed bioresponsive nanoscale hydrogels to selectively intensify SPR signals through multivalent protein binding (MPB) events with target biomolecules, including IL-2, where we were able to demonstrate exceptional selectivity for target biomolecules with minimal responses to nonspecific and monovalent binding events. In this work, we systematically explored the relationship between the physical properties of MPB-capable nanoscale hydrogels and their SPR response induced in the presence of the programmed cell death protein 1 antibody (PD-1Ab) as a model target biomolecule. First, we developed a synthetic protocol by controlling various reaction parameters to construct a library of nanoscale poly­(N-isopropylacrylamide-co-acrylic acid) hydrogels (NHs) with different sizes (from 400 nm to 1 μm) and degrees of crosslinking (from 2 to 8%). Then, by incorporating MPB-capable PD-1 receptors onto the surface of NHs to form PD-1-responsive nanoscale hydrogels (PNHs), the hydrogel size and crosslinking dependency of their SPR responses were investigated. Our results reveal the appropriate hydrogel size regime and degree of crosslinking for effective PD-1Ab detection at specific concentrations range between a few nM and 1 μM. Overall, our study demonstrates that by tuning the physical properties of the nanoscale hydrogel matrix, the sensitivity and detection range of MPB-based SPR sensors can be modulated to potentially benefit clinical applications such as monitoring diverse therapeutic biomolecules.

Method for the Rapid Detection of SARS-CoV-2-Neutralizing Antibodies Using a Nanogel-Based Surface Plasmon Resonance Biosensor

“…We prepared pNIPAm-co-AAc nanogels for the detection of SARS-CoV-2 NAb via a modified aqueous free-radical precipitation polymerization method based on previous studies, 16 , 21 as described in Figure 1 a. NIPAm, AAc, BIS, and APS were used as the main monomer, comonomer, crosslinker, and initiator, respectively. Tween 80 was utilized as a surfactant to yield monodisperse nanogels of suitable size, 18 and the molar ratio of NIPAm/BIS/AAc was set to 88:2:10, which resulted in an appropriate response in the SPR analysis. 18 The hydrodynamic sizes and polydispersity index (PDI) of the nanogels were measured using DLS ( Figure 1 b).…”

“…Tween 80 was utilized as a surfactant to yield monodisperse nanogels of suitable size, 18 and the molar ratio of NIPAm/BIS/AAc was set to 88:2:10, which resulted in an appropriate response in the SPR analysis. 18 The hydrodynamic sizes and polydispersity index (PDI) of the nanogels were measured using DLS ( Figure 1 b). The average diameter and PDI value of the nanogels were 830 nm and 0.02, respectively, indicating monodisperse nanogels.…”

“…NIPAm, AAc, BIS, and APS were used as the main monomer, comonomer, crosslinker, and initiator, respectively. Tween 80 was utilized as a surfactant to yield monodisperse nanogels of suitable size, 18 and the molar ratio of NIPAm/BIS/ AAc was set to 88:2:10, which resulted in an appropriate response in the SPR analysis. 18 The hydrodynamic sizes and polydispersity index (PDI) of the nanogels were measured using DLS (Figure 1b).…”

“… 21 , 22 Briefly, a composition of 88% pNIPAm/10% AAc/2% BIS (poly[ N -isopropylacrylamide- co -acrylic acid]) was used for nanogel synthesis, which was optimized for the biological response in nanogel-modified SPR analysis. 18 The reaction mixture was prepared by dissolving NIPAm and BIS in deionized and filtered water, followed by the addition of Tween 80 as a surfactant. The mixture solution in a reaction vessel was heated to 70 °C and was purged with nitrogen gas.…”

“…Nanogel-incorporated surface plasmon resonance (nSPR) has been shown to be an attractive method to determine protein–protein interactions via multivalent protein binding (MPB) events of target molecules (see Scheme ). − It can also be used as a biosensing platform using a plasmonic sensing mechanism . In particular, cancer biomarkers, such as interleukin (IL)-2 and soluble IL-2 receptor α, in the blood of healthy controls and patients with cancer are quantitatively measurable using the nSPR method mainly due to a high signal-to-noise ratio .…”