Label-Free Specific Detection and Collection of C-Reactive Protein Using Zwitterionic Phosphorylcholine-Polymer-Protected Magnetic Nanoparticles

In this study, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)]-protected Fe₃O₄ nanoparticles were prepared and used for the label-free specific detection and collection of an acute inflammation marker, C-reactive protein (CRP), in a simulated body fluid. The Fe₃O₄ nanoparticle surface was modified using poly(MPC) by surface-initiated atom-transfer radical polymerization. The density of poly(MPC) was 0.16 chains/nm², and the colloidal stability of the nanoparticles in aqueous media and human plasma was effectively improved by surface modification. The size of the as-prepared poly(MPC)-protected Fe₃O₄ nanoparticles was ∼200 nm. After coming into contact with CRP, the nanoparticles aggregated as CRP comprises five subunits, and each subunit can bind to a phosphorylcholine group with two free Ca²⁺ ions. The change in the nanoparticle size exhibited a good correlation with the CRP concentration in the range of 0-600 nM. A low limit of detection of 10 nM for CRP was observed. The particles effectively reduced the adsorption of nonspecific proteins, and the change in the nanoparticle size with CRP was not affected by the coexistence of bovine serum albumin at a concentration 1000 times greater than that of CRP. Nanoparticle aggregates formed using CRP were dissociated using ethylenediamine- N, N, N', N'-tetraacetic acid, disodium salt, thereby regenerating poly(MPC)-protected Fe₃O₄ nanoparticles. In addition, CRP was collected from aqueous media using an acidic buffer solution and human plasma. CRP-containing aqueous solutions were treated with poly(MPC)-protected Fe₃O₄. After poly(MPC)-protected Fe₃O₄ nanoparticles were separated using a neodymium magnet and centrifugation, the concentration of CRP in the media dramatically decreased. In stark contrast, the concentration of albumin present in the test solution did not change even after treatment with the nanoparticles. Therefore, nanoparticles specifically recognize CRP from complex biological fluids. Although inhibition tests in the presence of 1,2-dioleoyl- sn-glycero-3-phosphocholine liposomes or free poly(MPC) were also carried out, the binding of poly(MPC)-protected Fe₃O₄ to CRP was not affected by these inhibitors. In conclusion, poly(MPC)-brush-bearing magnetic nanoparticles can serve not only as reliable materials for detecting and controlling the levels of CRP in simulated body fluids but also as diagnostic and therapeutic materials.

Surface-Enhanced Raman Scattering (SERS) With Silver Nano Substrates Synthesized by Microwave for Rapid Detection of Foodborne Pathogens

Rapid and sensitive methods have been developed to detect foodborne pathogens, a development that is important for food safety. The aim of this study is to explore Surface-enhanced Raman scattering (SERS) with silver nano substrates to detect and identify the following three foodborne pathogens: Escherichia coli O157: H7, Staphylococcus aureus and Salmonella. All the cells were resuspended with 10 mL silver colloidal nanoparticles, making a concentration of 107 CFU/mL, and were then exposed to 785 nm laser excitation. In this study, the results showed that all the bacteria can be sensitively and reproducibly detected directly by SERS. The distinctive differences can be observed in the SERS spectral data of the three food-borne pathogens, and the silver colloidal nanoparticles can be used as highly sensitive SERS-active substrates. In addition, the assay time required only a few minutes, which indicated that SERS coupled with the silver colloidal nanoparticles is a promising method for the detection and characterization of food-borne pathogens. At the same time, principle component analysis (PCA) and hierarchical cluster analysis (HCA) made the different bacterial strains clearly differentiated based on the barcode spectral data reduction. Therefore, the SERS methods hold great promise for the detection and identification of food-borne pathogens and even for applications in food safety.

Facing Challenges in Real-Life Application of Surface-Enhanced Raman Scattering: Design and Nanofabrication of Surface-Enhanced Raman Scattering Substrates for Rapid Field Test of Food Contaminants

Surface-enhanced Raman scattering (SERS) is capable of detecting a single molecule with high specificity and has become a promising technique for rapid chemical analysis of agricultural products and foods. With a deeper understanding of the SERS effect and advances in nanofabrication technology, SERS is now on the edge of going out of the laboratory and becoming a sophisticated analytical tool to fulfill various real-world tasks. This review focuses on the challenges that SERS has met in this progress, such as how to obtain a reliable SERS signal, improve the sensitivity and specificity in a complex sample matrix, develop simple and user-friendly practical sensing approach, reduce the running cost, etc. This review highlights the new thoughts on design and nanofabrication of SERS-active substrates for solving these challenges and introduces the recent advances of SERS applications in this area. We hope that our discussion will encourage more researches to address these challenges and eventually help to bring SERS technology out of the laboratory.

Multiplex in vitro detection using SERS

This review focuses on the recent advances in SERS and its potential to detect multiple biomolecules in clinical samples.