Elsevier

Talanta

Volume 251, 1 January 2023, 123800
Talanta

Rapid and ultrasensitive solution-based SERS detection of drug additives in aquaculture by using polystyrene sulfonate modified gold nanobipyramids

https://doi.org/10.1016/j.talanta.2022.123800Get rights and content

Highlights

  • A simple ligand exchange protocol was introduced to modify the surface of CTAB Au BPs by polystyrene-sulfonate ligand.

  • The PSS-Au BPs were used to detect the cationic dye molecules in solution-based SERS detection.

  • Multivalent salts were used to investigate their effect on solution-based SERS detection by using PSS-Au BPs.

  • The addition of aggregating agent in colloidal solution improved the SERS signal intensity and limit of detection.

  • The PSS-Au BPs were used for real sample detection of malachite green and methylene blue in fish pond water.

Abstract

In recent years, surface-enhanced Raman spectroscopy (SERS) has been widely used in various fields for the rapid detection of trace-level molecular targets. In this study, we have developed a simple and effective solution-based SERS protocol to improve the activity for the detection of cationic dye molecules in aquaculture. The polystyrene sulfonate functionalized gold nanobipyramids (PSS–Au BPs) were synthesized from the cetyltrimethylammonium bromide (CTAB) reaction system followed by the ligand exchange process. The halide ions-induced aggregation of PSS-Au BPs was carried out by using four type of different salts such as NaCl, NaBr, MgCl2 and MgSO4 to investigate their influence on the SERS activity. The results demonstrate that the ionic strength of the solution has an important impact on the colloidal stability and SERS activity. The PSS-Au BPs show an improved SERS sensitivity at lower concentrations of the aggregating agents in solution-based SERS by detecting the crystal violet (CV) molecules with a limit of detection (LOD) to 3.28 × 10−11 M. Furthermore, to demonstrate the generality of our proposed strategy, trace amounts of three more dyes such as malachite green (MG), methylene blue (MB), and rhodamine 6G (R-6G), as well as other molecules such as thiram and bisphenol-S were also detected. This protocol not only provides a method for rapid on-site detection of trace-level molecules but can also be applied to other SERS-based analysis.

Graphical abstract

Very simple and effective solution-based SERS detection system by using polystyrenesulfonate functionalized Au BPs.

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Introduction

An important application of the plasmonic metal nanoparticles (NPs) is their use in surface-enhanced Raman spectroscopy (SERS). SERS provides structural information of analytes adsorbed on the surface of metal NPs and has extremely high sensitivity compared with ordinary Raman scattering. The SERS effect is due to the enhancement in the local electromagnetic field as hot spots at the nanometric gaps between metal NPs [[1], [2], [3], [4]]. However, the solution-based SERS still meets technological challenges since the mainly used Au colloidal NPs as enhanced substrates show low sensitivity, particularly in weakly adsorbed molecules. In the solution-based SERS protocol, controlling the assembly process or aggregation state with precise inter-particle distance and modification of the surface chemistry of nanoparticles is a critical strategy to improve the SERS activity [[5], [6], [7], [8], [9], [10], [11], [12]].

The self-assembly and aggregation of anisotropic nanostructures such as gold nanobipyramids (Au BPs) may greatly enhance the electromagnetic field because of their sharp edges and tips. During the self-assembly of anisotropic nanostructures, the coupling of localized surface plasmon resonance (LSPRs) leads to further electromagnetic enhancement due to the formation of second-generation hot spots between the gaps and interparticle junctions [[13], [14], [15]]. So far, there have been some reports on the Au nanorods, showing the effectiveness of their assembly and aggregation to generate large electromagnetic fields in the hot spot regions, but reports on Au BPs are still rare [[16], [17], [18], [19]]. The seed-mediated electrochemical synthesis method was used to grow bipyramidal Au nanostructures on indium tin oxide substrates to detect 4-aminothiophenol as probe molecules [20]. Lee et al. reported a graphene laminated Au BPs as a sensitive detection platform for antibiotic molecules [21]. Lee and co-workers used zeolitic imidazolate framework-8-wrapped Au BPs for hydrogen sulfide gas sensing in Raman-silenced regions [22]. Therefore, the halide ions-induced self-assembly and aggregation of Au BPs can be used as an important tool for studying the SERS properties of ordered Au BPs.

Malachite green (MG), crystal violet (CV), and methylene blue (MB) has good effects on preventing and curing fish diseases such as ichthyophthiriasis and saprolegniasis. However, due to the long degradation time of MG and potentially toxic effects on human health, the use of MG in aquaculture is prohibited in many countries such as China, the USA, and Japan. Compared to MG, MB is not restricted from being used in aquaculture in China, mainly because it is less toxic than MG. Although MB is not much hazardous, it can still cause harmful effects on the human body, such as cyanosis, vomiting, quadriplegia, etc. [[23], [24], [25], [26], [27]]. Therefore, the development of fast and accurate analytical methods is essential to monitor the harmful chemical substances in aquaculture.

In this study, a simple, convenient, rapid, and sensitive salt-dependent solution-based aggregation technique was developed to detect fishery drugs in aquaculture using SERS technology. Polystyrene sulfonate functionalized Au BPs (PSS–Au BPs) were obtained through a simple ligand exchange process. In order to study the SERS activity, the Raman active molecules like CV were initially added to the PSS-Au BPs. In the following, the controlled self-assembly and aggregation of PSS-Au BPs were initiated by introducing aggregating agent to form second-generation hot spots between the aggregated PSS-Au BPs, thus enhancing the solution-based SERS detection sensitivity. Our proposed strategy as the halide ions-dependent aggregation of PSS-Au BPs provides a simple, economical, solution-based method to produce NPs ensembles for SERS detection.

Section snippets

Materials

Sodium borohydride (NaBH4), AgNO3 (Silver nitrate, >99%), HAuCl4 (Tetrachloroauric acid, >99%), HCl (Hydrochloric acid, 37%) were purchased from Sigma-Aldrich Co., USA (China Product). Hexadecyltrimethylammonium chloride (CTAC, >99%), cetyltrimethylammonium bromide (CTAB, >99%), citric acid (>99.5%), l-ascorbic acid (AA, >99%), crystal violet (CV), malachite green (MG), methylene blue (MB), and rhodamine 6G (R-6G) were purchased from Aladdin Industrial Corporation, China. Sodium polystyrene

Solution-based SERS detection mechanism

The ultra-sensitive solution-based SERS detection strategy developed in this work is shown in the schematic diagram in Fig. 1. In previous studies, the polyanions ligands were used to modify the surface for the assembly process of the Au nanostructures. However, the influence of interaction between halide ions and polyanions surface ligands on the stability and SERS activity of the Au BPs has not been revealed [11,17,24]. Therefore, PSS coating was preferred to functionalize the surface of

Conclusion

In summary, CTAB-capped Au BPs were used to functionalize the surface of Au BPs by PSS. The monovalent and divalent salts were used as aggregating agents to initiate the aggregation and assembly of PSS-Au BPs for ultra-sensitive and highly quantitative SERS detection. These self-assembled PSS-Au BPs were successfully applied in detecting the cationic dye molecules and natural fishery drug samples. The trace level detection of analytes in solution by using PSS-Au BPs with high sensitivity showed

Author contributions

Muhammad Usman Amin: Done the experimental work, data Formal analysis and writing; Lingwei Li: Methodology and investigation; Ruiyuan Zhang: Analysis and sampling; Jixiang Fang: Supervised the project and conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 21675122, 21874104, 22074115), the Shaanxi Province Key Industries Innovation Chain Project (No. 2019ZDLSF07-08), the Natural Science Foundation of Shaanxi Province (No. 2019JLP-19), and the World-Class Universities (Disciplines) and the Characteristic Development Guidance Funds for the Central Universities.

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