Applications of surface plasmon resonance (SPR) for the characterization of nanoparticles developed for biomedical purposes

Abstract

Great interest is currently being devoted to the development of nanoparticles (NPs) for biomedical purposes, designed to improve the pharmacokinetic profile of their cargos (either imaging probes or drugs) and to enhance the specific targeting at the disease site. Recent works suggest that Surface Plasmon Resonance (SPR), widely used for the analysis of biomolecular interactions, represents a technique of choice for rapid and quantitative analyses of the interaction between NPs--functionalized with specific ligands--and their putative biological targets. Moreover, SPR can provide important details on the formation and the role of the protein "corona", i.e., the protein layer which coats NPs once they come into contact with biological fluids. These novel applications of SPR sensors may be very useful to characterize, screen and develop nanodevices for biomedical purposes.

Figure 1.

SPR approaches to study interactions between functionalized NPs and their putative biological targets. (a) Flowing of the target onto ligand-functionalized NPs immobilized on the sensor surface. (b) Flowing of ligand-functionalized NPs onto immobilized target (note the possibility that multivalent interactions underlie the binding of a single NP).

Figure 2.

Capture of nanoliposomes on SPR chip surface. Sphingomyelin:cholesterol liposomes, including or not 20% of dimyristoylphosphatidic acid (PA, b), cardiolipin (CL, c), or monosialoganglioside GM1 (GM1, d) were flowed for 5 min (association phase) over a chip surface protruding lipophilic undecyl chain anchors. Panels show the raw sensorgrams, i.e., the SPR signal in Resonance Units, RU, versus time, each normalized to a baseline value of 0. The results obtained in six parallel surfaces are shown in each panel. No decrease of SPR signal was observed during the dissociation phase, indicating a stable capture of liposomes.

Figure 3.

Flowing of functionalized NPs onto biological targets immobilized on SPR chip surface. Amyloid-β (Aβ) species and BSA (reference protein) were immobilized in parallel-flow channels of a sensor chip. Plain liposomes (sphingomyelin:cholesterol 1:1) or liposomes carrying 20% of cardiolipin (CL) or phosphatidylcholine (PC) were flowed for 3 min (bar), followed by 11 min dissociation phase. Panels show the raw sensorgrams, i.e., the SPR signal in Resonance Units, RU, versus time. The presence of cardiolipin (CL-liposomes, blue lines) confers the ability to bind to immobilized Aβ, in particular Aβ fibrils (a), whereas no binding was observed on BSA (c). No or negligible binding was detected with plain liposomes (black lines) or with liposomes bearing phosphatidylcholine (PC-liposomes, light blue lines). Data from [18] with modifications.

Figure 4.

SPR study of protein corona. (a–c): PMMA NPs were preincubated in human plasma for 1 hour, precipitated by centrifugation, resuspended in buffer and injected for 3 min onto chip surfaces immobilizing LRP-1 (a), anti-ApoE Ab (b) or anti-HSA Ab (c). Purple lines show the corresponding sensorgrams. As internal controls we injected NPs samples preincubated in buffer (blue sensorgrams) or sample obtained, with the same procedure (centrifugation and resuspension) from plasma alone (red sensorgrams). Black sensorgrams were obtained as difference between the purple and the red sensorgrams, to highlight the signal specifically due to proteins adsorbed to NPs during the incubation in plasma. (d–f): Black sensorgrams were obtained as described above. Resuspended NPs samples underwent further centrifugation and supernatants were injected (gray sensorgrams). See text for details.