Core–Shell Au@Metal–Organic Frameworks for Promoting Raman Detection Sensitivity of Methenamine

Abstract

Abuse of methenamine in foodstuff is harmful to the health of people. Routine methods recommended by the national standard are indirect assays with complicated pretreatment of samples or less sensitivity. In this work, core-shell Au nanoparticles@inositol hexaphosphate@MIL-101(Fe) nanoparticles, designated as Au@MIL-101, are successfully synthesized by layer-by-layer assembly. Metal-organic framework (MOF; MIL-101)-modified AuNPs could narrow the distance between neighboring Au@MIL-101, which increases the amount of "hot spots" and contributes excellent enhancement of Raman scattering. In addition, certain target molecules could access the proximity to the "hot spots" by the strong interaction capability of MOF with -COOH groups. Taking the syngeneic effect of "hot spots" and chemical enhancement via specific binding, Au@MIL-101-based Raman protocol with huge sensitivity is developed to achieve direct detection of methenamine. It has good linearity of dynamic concentration from 3.16 × 10 to 1.0 × 10 M with correlation coefficient ( R) of 0.9908. The limit of detection reaches 5.0 × 10 M. As a practical application, such an Au@MIL-101-based Raman protocol could be used for the direct determination of trace methenamine in vermicelli, which meets the requirements of the national standard.

The Role Played by Graphene Oxide in the Photodeposition and Surface‐Enhanced Raman Scattering Activity of Plasmonic Ag Nanoparticle Substrates

“…In contrast, Cai et al. have observed a much higher EF, about sixfold, for methenamine previously adsorbed onto an LbL assembled core–shell AuNP–iron complex, whereas Sun et al. have achieved a similar EF = 6 for 4‐mercapto‐pyridine adsorbed onto LbL assembled core–shell Fe 3 O 4 –SiO 2 –AuNP nanoparticles.…”

“…Although we have found an enhancement factor (EF) between three and four orders of magnitude for rhodamine B deposited onto the photocatalytic deposited AgNP substrates, Aoki et al have found a similar EF ¼ 4 for methylene blue adsorbed onto LbL films of AgNP and phospholipids, [12] and Liu et al have found a maximum of threefold EF for urea adsorbed onto a 3D Ag nanorod LbL assembly. [13] In contrast, Cai et al have observed a much higher EF, about sixfold, for methenamine previously adsorbed onto an LbL assembled coreshell AuNP-iron complex, [14] whereas Sun et al have achieved a similar EF ¼ 6 for 4-mercapto-pyridine adsorbed onto LbL assembled core-shell Fe 3 O 4 -SiO 2 -AuNP nanoparticles. It is worth mentioning that our method is capable of synthesizing and immobilizing AgNP in a single step, using UV light instead of chemical reducing agents.…”

“…In this way, the LbL film assembly is per excellence a powerful method for the construction of layered functional systems with controlled nanoarchitectonics. [11] These attractive features have been explored in the development of SERS active substrates capable of, for instance, probing the molecular arrangement of drugs within biomimetic systems, [12] simultaneous detection of tryptophan, phenylalanine, urea, and melamine, [13] detection of methenamine in foodstuffs, [14] 4-mercapto-pyridine, [15] benzenethiol, [16] and graphene oxide (GO). [17] Herein, we propose a simple yet very effective photocatalytic method that uses an LbL assembled film of TiO 2 nanoparticles (TiO 2 NP) to simultaneously act as a photocatalyst and immobilization platform for Ag nanoparticles (AgNPs) aiming at SERS applications.…”

An Electrochemical Sensor for the Detection of Cu2+ Based on Gold Nanoflowers‐modifed Electrode and DNAzyme Functionalized Au@MIL‐101 (Fe)

“…To ensure the sensitivity of the electrochemical sensor, various functional nanomaterials are usually employed for signal amplification [13][14][15]. As one of the research hotspots in recent years, metal-organic frameworks (MOFs) have been used in many fields, such as catalysis [16], supercapacitors [17], adsorption and separation [18], and sensing [19][20][21]. Tang and coworkers have developed a series of MOF-based Immunosensors for fluorescent or colorimetric determination [22,23].…”

Encapsulation of live cells by metal-organic frameworks for viability protection

“…Among the chosen materials reported, metal-organic frameworks (MOFs) [16][17][18], a type of crystalline material constructed with metal ions or metal clusters and organic ligands, have attracted the most attention because of their porous structures, diversity of precursors, and convenient synthesis [19][20][21]. Several materials [22][23][24] and semiconductors [25][26][27] of different sizes and shapes have been coated with MOFs to form composite materials. In addition, some biological macromolecules, such as proteins [28][29][30], enzymes [31][32][33][34][35][36], and cells [37,38], have been coated with MOFs under mild conditions, which is critical for the maintenance of their biological activity.…”