Facile Synthesis of Au-Coated Magnetic Nanoparticles and Their Application in Bacteria Detection via a SERS Method

Abstract

This study proposes a facile method for synthesis of Au-coated magnetic nanoparticles (AuMNPs) core/shell nanocomposites with nanoscale rough surfaces. MnFe2O4 nanoparticles (NPs) were first modified with a uniform polyethylenimine layer (2 nm) through self-assembly under sonication. The negatively charged Au seeds were then adsorbed on the surface of the MnFe2O4 NPs through electrostatic interaction for Au shell formation. Our newly developed sonochemically assisted hydroxylamine seeding growth method was used to grow the adsorbed gold seeds into large Au nanoparticles (AuNPs) to form a nanoscale rough Au shell. Au-coated magnetic nanoparticles (AuMNPs) were obtained from the intermediate product (Au seeds decorated magnetic core) under sonication within 5 min. The AuMNPs were highly uniform in size and shape and exhibited satisfactory surface-enhanced Raman scattering (SERS) activity and strong magnetic responsivity. PATP was used as a probe molecule to evaluate the SERS performance of the synthesized AuMNPs with a detection limit of 10(-9) M. The synthesized AuMNPs were conjugated with Staphylococcus aureus (S. aureus) antibody for bacteria capture and separation. The synthesized plasmonic AuNR-DTNB NPs, whose LSPR wavelength was adjusted to the given laser excitation wavelength (785 nm), were conjugated with S. aureus antibody to form a SERS tag for specific recognition and report of the target bacteria. S. aureus was indirectly detected through SERS based on sandwich-structured immunoassay, with a detection limit of 10 cells/mL. Moreover, the SERS intensity at Raman peak of 1331 cm(-1) exhibited a linear relationship to the logarithm of bacteria concentrations ranging from 10(1) cells/mL to 10(5) cells/mL.

Magnetic drug delivery systems

“…Poudyal et al [107] reported a novel method for preparing a FePtAu core-shell structure using solution phase chemistry combined with solvothermal annealing, which showed great promise for various optical, sensing, and biomedical applications. Wang et al [108] designed Au-coated MnFe2O4 nanoparticles, which were first modified with a uniform PEI layer (2 nm). The negatively charged Au seeds were then adsorbed onto the surface of the MnFe2O4 nanoparticles via electrostatic interaction during the formation of the Au shell.…”

Development of nanoparticle-based optical sensors for pathogenic bacterial detection

“…Gold-coated magnetic nanoparticles were synthesized employing hydroxylamine seeding based on a sonochemical method [62]. The nanoparticles had the same size and shape, were stable, and possessed excellent magnetic responsivity and strong surface-enhanced Raman spectroscopy (SERS) activity.…”

SERS Detection of Penicillin G Using Magnetite Decorated with Gold Nanoparticles

“…The upgrade of such sorbents for simultaneous use in water purification and contaminant detection is a challenging task but of great practical interest for sensing applications, thus following current interest in developing multifunctional nanomaterials. In this context, the development of SERS-active magnetic nanomaterials has attracted much attention, because it provides innovative platforms that combine magnetic responsiveness and the ability for Raman monitoring within a single material [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37]. Penicillin G (PG) belongs to the β-lactam antibiotics family whose structure is composed of a five-membered sulfur-containing thiazolidine ring fused to a beta-lactam ring and a phenyl ring attached to the side chain ( Figure S1, Supporting Information).…”