Metal organic framework wrapped gold nanourchin assembled on filter membrane for fast and sensitive SERS analysis
Graphical abstract
Introduction
Surface enhanced Raman scattering (SERS) is a powerful analytic tool with promising application in various branches of analytical science [1,2]. An efficient substrate plays a dominated role in determining its sensing performance [[3], [4], [5], [6]]. Recently, integrating Au or Ag nanostructures with other functional materials with magnetic, catalytic, porous, or flexible properties becomes a hot topic [[7], [8], [9], [10], [11], [12], [13]]. Specifically, hybrids of Au/Ag nanostructures with metal organic frameworks (MOFs) receive considerable attention [[14], [15], [16], [17], [18], [19]]. The introduction of MOF not only improves sensitivity, but also endows the substrate with proper selectivity and makes it possible to detect analyte with low affinity to Au/Ag substrate owning to the tunable pore size, strong adsorption ability, and chemical enhancement effect of MOF [9]. Therefore, developing novel Au/Ag-MOF hybrid substrate is important and interesting for practical SERS analysis.
Despite the advantages of various hybrid substrate of Au/Ag-MOFs in SERS application, there is also many challenges and great space to be explored. (1) Most work use spherical particles to construct MOF-Au/Ag hybrid [20,21], and few involves anisotropic particles, which may produce higher enhancement ability [22]; (2) to increase signal, Au/Ag particles are densely decorated onto MOF [21,23], which blocks the pores of MOF and brings uncontrolled aggregation; (3) longtime incubation from 30 min to 10 h is needed to improve SERS signal in typical immersion detection mode [21,[24], [25], [26]], which leads to low efficiency; (4) these MOF based substrates easily precipitate in solution or random aggregate on matrix (typically glass or silicon slide [20,21,[25], [26], [27]]), leading to poor signal reproducibility. On the other hand, filtration is a simple and effective way to separate or enrich molecules, and MOFs have intrinsic advantage for filtration, separation and enrichment [28]. However, the combination of MOF based hybrid substrate with filtration for SERS detection has not been reported.
In this study, gold nanourchins (GNUs) wrapped with metal organic framework (GNU@MOF) was prepared and assembled on filter membrane to achieve fast and sensitive SERS analysis. The combination of GNU and MOF (MIL-100(Cu)) provides higher enhancement than that of GNU or MOF in traditional immersion detection mode with detection time 60 min. To improve sensing efficiency, GNU@MOF was assembled on a filter membrane to develop a filtration type substrate GNU@MOF-F by simple filtration operation. For this substrate, the interaction time of substrate with analyte was greatly reduced from 60 min to less than 1 min (about 10 s). Interestingly, the SERS signal obtained on GNU@MOF-F is comparable or even stronger than those obtained on typical immersion mode substrate (GNU@MOF-I), and the signal reproducibility was also greatly improved. The GNU@MOF-F was used to detect toxic dye MG in standard solution and MB in lake water sample, which shows one or two orders of magnitude lower detection limit than that of GNU@MOF-I (60 min) or GNU@MOF-I (10 s). Moreover, the GNU@MOF-F can be reused at least 3 times without obvious signal attenuation.
Section snippets
Reagents
Chloroauric acid (HAuCl4), trisodium citrate dihydrate (Na3Cit), silver nitrate (AgNO3), L-dopa, polyvinylpyrrolidone (PVP, K30), aluminum chloride hexahydrate (AlCl3·6H2O), copper(II) chloride dihydrate (CuCl2·2H2O), nickel chloride hexahydrate (NiCl2·6H2O), methylene blue (MB), and malachite Green (MG) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All reagents were used as received without further processing. Deionized water (ρ ≥ 18.2 MΩ cm) was produced by a
Preparation and characterization of GNU@MOF
Branched gold or silver nanostructures often provide stronger SERS signal than their spherical counterpart. So, GNUs prepared by our previous Ag seed mediated method was used in this study. The GNU displays an urchin-like morphology (Fig. 1a) with many nano-thorns on its surface (Fig. 1b). The EDX result reveals the product is mainly composed of C, Au and a little Ag (Fig. 2a). Element C is from the reductant L-dopa as its oxidant product can adsorb onto GNU in a similar way to that of
Conclusions
Gold nano-urchin wrapped with metal organic framework MIL-100(Cu) was assembled onto filter membrane to form a new filtration type SERS substrate GNU@MOF-F. The substrate with dense and uniform hot-spots can achieve fast and sensitive SERS molecule sensing within 1 min by simple filtration, which shows higher SERS signal, lower detection limit, improved reproducibility and higher efficiency than traditional immersion method for molecule sensing. For practical application, the GNU@MOF-F was used
CRediT authorship contribution statement
Fugang Xu: Conceptualization, Project administration, Writing - review & editing, Methodology. Wenjuan Shang: Investigation, Formal analysis, Writing - original draft. Guangran Ma: Software, Writing - review & editing. Yongmei Zhu: Data curation. Meijuan Wu: Formal analysis.
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgement
This work is supported by the National Natural Science Foundation of China (21665011, 21705063).
Fugang Xu received his Ph.D. degree in the Changchun Institute of Applied Chemistry, Chinese Academy of Science, China. He is now working in the College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang, China. His research interest is the preparation of hybrid materials for surface enhanced Raman and electrochemical detection.
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Fugang Xu received his Ph.D. degree in the Changchun Institute of Applied Chemistry, Chinese Academy of Science, China. He is now working in the College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang, China. His research interest is the preparation of hybrid materials for surface enhanced Raman and electrochemical detection.
Guangran Ma received her Ph.D. degree in Jiangxi Normal University, China. She is now working in the Analytical and Testing Center of Jiangxi Normal University. Her research interests focus on preparation of porous materials for surface enhanced Raman and electrochemical detection.
Yongmei Zhu is a senior experimentalist in the Analytical and Testing Center, Jiangxi Normal University, Nanchang, China. Her research interests is medical analysis using Raman and chromatography method.
Wenjuan Shang is studying for her master degree in the College of Chemistry and Chemical Engineering, Jiangxi Normal University. Her research interests mainly focus on the fabrication of MOF based SERS active nanostructure for bio-chemical analysis.
Meijuan Wu is studying for her master degree in the College of Chemistry and Chemical Engineering, Jiangxi Normal University. Her research interests focus on the preparation of micro- and mesoporous metal organic framework for chemical analysis by electrochemical methods.