Polyethylenimine-interlayered silver-shell magnetic-core microspheres as multifunctional SERS substrates

Abstract

The fabrication of an ideal noble metal modified magnetic microsphere as high performance SERS substrate that possesses good dispersibility, strong magnetic responsiveness, and high sensitivity is still a challenge. Herein, we reported a novel route to fabricating Ag-coated magnetic core-shell microspheres (Fe 3 O 4 @PEI@Ag) with most of the desired advantages by using polyethyleneimine (PEI) as an interlayer. The size and coverage level of the Ag-NPs shell on Fe 3 O 4 @PEI@Ag microspheres were easily controlled by varying the amount of AgNO 3 .Meanwhile, the magnetic core endowed the Fe 3 O 4 @PEI@Ag microspheres with superior magnetic nature, which enabled convenient separation and further enhanced Raman signals due to enrichment of targeted analytes and abundant interparticle hotspots created by magnetism-induced aggregation. Considering these features, the Fe 3 O 4 @PEI@Ag is expected to be a versatile SERS substrate, which was verified by the detection of adsorbed PATP molecules and human IgG with a detection limit as low as 10 -11 M and 10 -14 g/mL, respectively. Therefore, the novel Fe 3 O 4 @PEI@Ag microsphere has an enormous potential for practical SERS detection applications, especially in the target protein quantitative detection field.Surface-enhanced Raman scattering (SERS) is a powerful fingerprint vibrational spectroscopy with high sensitivity, and it is widely used in biochemical detection, analytical chemistry, environment monitoring and biological sensing. 1-3 All these applications are based on proper utilization of "free-electron-like" metal materials, such as Au, Ag, and Cu, and only these noble metal structures with rough surface can provide obvious SERS effect. 4 Therefore, the key of its prominent application lies in fabricating high performance SERS substrates. So far, researchers have fabricated many SERS substrates, among which metal film over periodic nanostructure and Au/Ag colloids in suspension are extensively utilized. 5 The periodic nanostructure can achieve well sensitivity and high reproducibility, but has disadvantages of high cost and difficult to be further chemically modified. Au/Ag colloidal nanoparticles are more efficient with flexible control over individual geometry, easy to mass fabricate, and have good biocompatibility. 6 However, the drawbacks of Au/Ag colloid substrates are their limited enhancement ability and poor stability. 7 Therefore, a reliable and practical SERS substrate with high sensitivity is still a challenge. It should be noted that, up to now, the main problem of SERS detection is that it is difficult to conduct quantitative analysis and hard to apply in the complex system only depend on the noble metal SERS substrate itself.Magnetic microspheres have been extensively investigated for various applications. 8 Due to their excellent magnetic responsiveness, magnetic microspheres can assist in convenient recycling of novel metals, magnetic enrichment of analytes and rapid separation from reaction system. 9, 10 Recently, noble metal modified magnetic micro...

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

“…For example, Fe3O4@Au NPs are assembled into arrayed microstructures on a wafer scale with enhancement factors >10 6 [151]. Ag-coated magnetic core-shell microspheres (Fe3O4@PEI@Ag) has been developed using polyethyleneimine (PEI) as an interlayer to construct a versatile SERS substrate, which is verified by the detection of adsorbed p-aminothiophenol molecules and human IgG with a detection limit as low as 10 −11 M and 10 −14 g mL −1 , respectively ( Figure 8) [152]. AgFe3O4 nanocomposites are assembled into an orderly arrayed SERS substrate holding clean and reproducible properties with an applied external magnetic field for detection of 4-mercaptobenzoic acid.…”

Polyethylenimine-interlayered core–shell–satellite 3D magnetic microspheres as versatile SERS substrates

“…Curve a-is the typical UV-visible spectra of bare Fe 3 O 4 microspheres, as the same as reference. 41 In that study, we mainly studied and introduced a novel route to fabricating the 300 nm-scale Fe 3 O 4 @Ag microspheres by using PEI as an interlayer, and discussed the SERS effect with the Ag shell geometry. 2b)， which was probably because the dense Au seeds were distributed on the surface of the PEI-coated Fe 3 O 4 very uniformly, and the 3 nm Au seeds were too small to impact the microspheres' structure to induce plasmonic coupling.…”

Vancomycin-modified Fe₃O₄@SiO₂@Ag microflowers as effective antimicrobial agents

“…Curve a in Figure 1G shows the XRD spectra of the Fe 3 O 4 @SiO 2 microspheres, which fitted well to the Fe 3 O 4 bulk phases (JCPDS card no 75-1609). 43,44 As the SiO 2 shell was amorphous, no diffraction peaks corresponding to SiO 2 were observed. With the deposition of Ag seeds, four additional diffraction peaks were observed at 2θ values of 38.2°, 44.3°, 64.5°, and 77.5°, which correspond to the reflections of the (111), (200), (220), and (311) crystal planes of Ag, respectively (curve b of Figure 1G).…”