Detection with NO Modification: (N═O)-Au Interactions for Instantaneous Label-Free Detection of N-Nitrosodiphenylamine.

Increasing concerns have been raised about dangerous, yet nearly undetectable levels of nitrosamines in foods, medications, and drinking water. Their ubiquitous presence and carcinogenicity necessitates a method of sensitive and selective detection of these potent toxins. While the detection of two major nitrosamines─N-nitrosodimethylamine and N-nitrosodiethylamine─has seen success, low detection limits are scarcer for the other members of this class. One member, N-nitrosodiphenylamine (NDPhA), has had little progress not only in its detection in low quantities but also in its detection at all. NDPhA has unique difficulty in its identification due to its aromaticity, making it far more problematic to distinguish in the common GC-MS or LC-MS/MS methods used for nitrosamine sensing. Despite this detection barrier, it has been listed among the top 6 carcinogenic nitrosamines by the Food and Drug Administration as of 2023. Due to its evasive nature, a unique methodology must be applied to facilitate its sensitive identification. Herein, we describe the use of surface-enhanced Raman spectroscopy for the first account of liquid-phase detection of NDPhA using cysteamine-functionalized gold nanostars and a portable Raman spectrometer. Our methodology requires no chemical modification to the nitrosated structure as well as the usage of two well-understood biocompatible materials: cysteamine and gold nanoparticles.

Synthesis and Characterization of Magnetoplasmonic Air-Stable Au@FeCo.

The synthesis of FeCo alloys as highly magnetic nanoparticles has been valuable, as far as applications for magnetic nanoparticles are concerned. However, recently, a field of magnetoplasmonics in which magnetic nanoparticles such as the FeCo alloys doped with plasmonic materials such as Au and Ag to create a hybrid nanostructure with both properties has emerged. These magnetoplasmonic metamaterials have greatly enhanced the limit of detection of analytes in spectroscopic methods, as well as providing a more widely applicable nanoparticle to broaden the use of FeCo alloys even further. Herein, we discuss the synthesis of high-yield and fairly monodisperse spherical FeCo and Au-doped FeCo (Au@FeCo) with varying compositions of Au synthesized via the thermal decomposition of iron pentacarbonyl (Fe(CO)5) and dicobalt octacarbonyl (Co2(CO)8), followed by the addition of Au atoms using triphenylphosphine gold(I) chloride ((Ph3P)AuCl) via both coprecipitation and by delayed addition methods. The products were separated using a hand-held magnet, and then characterized via ultraviolet-visible light (UV-vis), scanning electron microscopy coupled with energy-dispersive X-ray analysis (SEM-EDX), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), flame atomic absorption spectrometry (F-AAS), and magnetization measurements. Optical studies revealed a plasmonic peak at 550 nm in the Au@FeCo nanoparticles that had a gold content (%Au) of >2% (by weight), determined using F-AAS. Colocation of the Fe, Co, and Au were demonstrated through EDX analysis. Location of the Au atoms in the core were seen through high-resolution bright-field imaging. To understand the use of these nanoparticles for potential application in therapeutics and/or electronics, resistance measurements were performed to assess power loss as a function of frequency. We also achieved magnetization values as high as 150 emu/g and as low as 50 emu/g for gold-loaded samples based on %Au by weight. This paves the way to continue to develop magneto-plasmonic structures chemically using these synthesis strategies.