Surface Plasmon Resonance Biosensors: A Review of Molecular Imaging with High Spatial Resolution

Surface plasmon resonance (SPR) is a powerful tool for determining molecular interactions quantitatively. SPR imaging (SPRi) further improves the throughput of SPR technology and provides the spatially resolved capability for observing the molecular interaction dynamics in detail. SPRi is becoming more and more popular in biological and chemical sensing and imaging. However, SPRi suffers from low spatial resolution due to the imperfect optical components and delocalized features of propagating surface plasmonic waves along the surface. Diverse kinds of approaches have been developed to improve the spatial resolution of SPRi, which have enormously impelled the development of the methodology and further extended its possible applications. In this minireview, we introduce the mechanisms for building a high-spatial-resolution SPRi system and present its experimental schemes from prism-coupled SPRi and SPR microscopy (SPRM) to surface plasmonic scattering microscopy (SPSM); summarize its exciting applications, including molecular interaction analysis, molecular imaging and profiling, tracking of single entities, and analysis of single cells; and discuss its challenges in recent decade as well as the promising future.

Towards electrochemical surface plasmon resonance sensor based on the molecularly imprinted polypyrrole for glyphosate sensing

In this research the molecular imprinting technology was applied for the formation of glyphosate-sensitive layer. The glyphosate imprinted conducting polymer polypyrrole (MIPpy) was deposited on a gold chip/electrode and used as an electrochemical surface plasmon resonance (ESPR) sensor. The results described in this study disclose some restrictions and challenges, which arise during the development of glyphosate ESPR sensor based on the molecularly imprinted polymer development stage. It was demonstrated, that glyphosate could significantly affect the electrochemical deposition process of molecularly imprinted polymer on the electrode. The results of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR) have demonstrated that glyphosate molecules tend to interact with bare gold electrode and thus hinder the polypyrrole deposition. As a possible solution, the formation of a self-assembled monolayer (SAM) of 11-(1H-Pyrrol-1-yl)undecane-1-thiol (PUT) before electrochemical deposition of MIPpy and NIPpy was applied. Dissociation constant (KD) and free energy of Gibbs (ΔG0) values of glyphosate on MIPpy and Ppy without glyphosate imprints (NIPpy) were calculated. For the interaction of glyphosate with MIPpy the KD was determined as 38.18 ± 2.33⋅10-5 and ΔG0 as -19.51 ± 0.15 kJ/mol.

Stability of Polydopamine Coatings on Gold Substrates Inspected by Surface Plasmon Resonance Imaging

Polydopamine (PDA)-based surface modification has been used in a variety of fields. However, a vague impression on the stability of PDA still exists due to a lack of systematic studies. To ascertain the issue and make better use of this surface modification method, a technique of surface plasmon resonance imaging (SPRi) was exploited to study the stability of PDA coated on gold surface. The results showed that PDA-coating stability was largely dependent on the pH of aqueous solutions, giving detachment ratios up to 66% and 80% at pH 1.0 and pH 14.0, respectively. However, increasing the ionic strength of aqueous solutions could reduce the detachment of PDA in strong acid and strong alkali conditions. Besides, organic solvents also made a difference on the PDA-coating stability. Among the tested 10 kinds of organic solvents, including n-hexane, toluene, ethyl ether, tetrahydrofuran, ethyl acetate, isopropanol, acetone, acetonitrile, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), DMSO caused the most serious detachment of PDA, up to 56%, followed by DMF with a detachment ratio of 31%. Ultrasonication caused less than 10% detachment of the coated PDA. It should be mentioned that the PDA coatings deposited on gold surface were not detached completely in all the test conditions, even at pH 14.0 (ca. 20% PDA retained). In alkaline conditions, detachment competes with further polymerization, which gave a slight increase of the SPRi signals at pH 9.0-11.0. Based on the obtained information about PDA-coating stability, thickness-controllable and alkali-resistant PDA coatings were prepared. Moreover, the alkali-resistant PDA coatings remained reactive to biomolecules, supporting further functionalization of PDA coatings.

Effects of Interfacial Properties of a Surface Modified Surface Plasmon Resonance Chip on Protein Immobilization Performance

In order to confirm the correlation between interfacial properties of modified surface plasmon resonance (SPR) chips and their SPR responses to immobilized anti-IgG, SPR chips were modified by mercaptoundecanoic acid, poly(ethylene glycol) diacrylate (PEG), PEG-based copolymer and cyclodextrin coupled PEG using self-assembled or radical polymerization methods. The resulting interfacial properties such as film thickness and hydrophilicity were characterized by AFM, elliptic polarization scanners and contact angle meter. Immobilization of human IgG on the modified chips was achieved by EDC/NHS activation through an amide bond. The association between fixed IgG and free anti-IgG was reflected by the variation of SPR responses and the binding ability was evaluated by Langmuir isotherms. As observed, the adsorption between IgG and anti-IgG was affected by the interfacial properties of different modifiers, such that a chip with a thinner and more hydrophilic layer may result in a higher SPR response, producing a larger adsorption equilibrium constant for protein interaction.

Probing the Dynamic Interaction between Damaged DNA and a Cellular Responsive Protein Using a Piezoelectric Mass Biosensor

The binding events between damaged DNA and recognition biomolecules are of great interest for understanding the activity of DNA-damaging drugs and the related DNA repair networks. Herein, a simple and sensitive sensor system was tailored for real-time probing of the dynamic molecular recognition between cisplatin-damaged-DNA (cisPt-DNA) and a cellular responsive protein, high-mobility-group box 1 (HMGB1). By integration of flow injection analysis (FIA) with quartz crystal microbalance (QCM), the interaction time-course of cisPt-DNA and HMGB1 domain A (HMGB1a) was investigated. The highly specific sensing interface was carefully designed and fabricated using cisPt-DNA as recognition element. A hybrid self-assembled monolayer consisting of cysteamine and mercaptohexanol was introduced to resist nonspecific adsorption. The calculated kinetic parameters (k_ass and k_diss) and the dissociation constant (K_D) demonstrated the rapid recognition and tight binding of HMGB1a toward cisPt-DNA. Molecular docking was employed to simulate the complex formed by cisPt-DNA and HMGB1a. The tight binding of such a DNA-damage responsive complex is appealing for the downstream molecular recognition event related to the resistance to DNA repair. This continuous-flow QCM biosensor is an ideal tool for studying specific interactions between drug-damaged-DNAs and their recognition proteins in a physiological-relevant environment, and will provide a potential sensor platform for rapid screening and evaluating metal anticancer drugs.

Investigation of biological cell–small molecule interactions with a gold surface plasmon resonance sensor using a laser scanning confocal imaging-surface plasmon resonance system

In our work, we investigated the interactions between a small molecule, folic acid, and biological cells through the interaction of folic acid and folate receptors using a laser scanning confocal imaging-surface plasmon resonance (LSCI-SPR) system.