Article pubs.acs.org/JAFC
Cite This: J. Agric. Food Chem. 2019, 67, 6642−6649
New Functional TracerTwo-Dimensional Nanosheet-Based Immunochromatographic Assay for Salmonella enteritidis Detection Tong Bu,†,‡ Jianlong Wang,†,‡ Lunjie Huang,§ Leina Dou,‡ Bingxin Zhao,‡ Tao Li,∥ and Daohong Zhang*,‡ ‡
College of Food Science and Engineering, Northwest A&F University, Yangling, Shaanxi 712100, People’s Republic of China School of Food Science and Engineering, South China University of Technology, Guangzhou, Guangdong 510641, People’s Republic of China ∥ Shaanxi Institute for Food and Drug Control, Xi’an, Shaanxi 710065, People’s Republic of China Downloaded via BUFFALO STATE on July 21, 2019 at 21:34:53 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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S Supporting Information *
ABSTRACT: The rapid monitoring of foodborne pathogens by monoclonal antibody (McAb)-based immunochromatographic tests (ICTs) is desirable but highly challenging as a result of the screening obstacle for a superior performance probe, which will greatly determine the capture efficiency of targets and the sensitivity of the immunoassay. In this work, on the basis of twodimensional (2D) nanosheets (including MoS2 and graphene) as the extraordinary capture probe and signal indicator, we fabricated a label-free ICT method for Salmonella enteritidis detection. Especially, without the customarily labeled antibody probe, these 2D versatile probes presented strong capture ability toward bacteria by directly assembling onto the surface of bacteria. An ideal analytical performance with high sensitivity and specificity was achieved by virtue of the novel nanosheet− bacteria−McAb sandwich format. On the basis of MoS2 2D nanosheets as a fabulous probe element, the developed ICT exhibited a lowest detectable concentration of 103 colony-forming units/mL for S. enteritidis and could be well-applied in drinking water and watermelon juice samples. By the smart design, this work removes a series of conditionality issues of traditional double antibody sandwich-based ICTs and can give a new application direction for 2D nanosheet materials in the rapid detection field. KEYWORDS: 2D nanosheets, label-free, immunochromatographic test, Salmonella enteritidis
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INTRODUCTION
needs to face unsatisfactory circumstances, such as organic extracts or complex sample matrices, when detecting targets.8 With the above issues taken into account, the preparation of advanced label-free materials, which can be directly used as efficient adsorbents to bacteria, is advantageous and urgently needed. Very recently, two-dimensional (2D) materials, e.g., graphene, layered boron nitride, and transition metal dichalcogenides (TMDs), have attracted great attention, owing to their unique large surface area, strong surface adsorbing ability, and low cost.9−14 The huge surface of 2D nanosheets can non-selectively interact with bacteria via van der Waals forces, electrostatic and hydrophobic interactions, etc.15 Simultaneously, these outstanding materials have been explored as tools to kill pathogenic microbes through direct contact with the bacteria; sharp edges of nanosheets may induce membrane stress by puncturing or penetrating into the cell membranes, resulting in the morphological destruction of bacterial cells and leakage of intracellular components, such as proteins, phospholipids, RNA, and DNA.16,17 Therefore, the admirable characteristics suggest that these 2D materials (including graphene-based materials and TMD nanosheets)
Bacterial contaminations and infections have always been a major threat to public health and human life.1 The recent outbreaks of diseases continue to highlight the need for diagnostic tools that are affordable, sensitive, simple, and rapid for pathogen detection under challenging circumstances. These demands have led to the popularity of paper-based immunochromatographic tests (ICTs) as the most prominent rapid point-of-care (POC) diagnostic tests.2−4 It is generally known that the efficient capture ability of recognition agents toward targets is an essential prerequisite for all immunoassaybased methods. To achieve this, in the conventional sandwich ICTs, both the signal nanomaterials and the test line (T-line) must be decorated with antibodies (typical affinity ligands) that are able to separately bind two discrete regions of the target.5 In this sandwich format, the binding affinity or interaction strength between a specific antigen and antibody can intrinsically determine the detection performance.6 Unfortunately, the practical applications of ICTs are often limited by some uncontrollable factors of antibodies: (1) complicated cross-linking procedures between antibodies and nanomaterials are still required for probe preparation;7 (2) the binding ability of the antibody is likely to be affected during the labeling process; and (3) the capacity of resistance to rough chemical conditions of the labeled antibody is a key issue that must to be considered because the antibody often © 2019 American Chemical Society
Received: Revised: Accepted: Published: 6642
January 17, 2019 May 6, 2019 May 21, 2019 May 22, 2019 DOI: 10.1021/acs.jafc.9b00374 J. Agric. Food Chem. 2019, 67, 6642−6649
Article
Journal of Agricultural and Food Chemistry
Scheme 1. Relevant Schematic Illustrations of the 2D Nanosheet-Based ICT System: (A) Sonication-Induced Liquid-Phase Exfoliation of 2D Nanosheets in Ethanol Aqueous Solution, (B) Structure of the Test Strip, (C) Combining Process of 2D Nanosheets with S. enteritidis, and (D) Working Principle of the 2D Nanosheet-Based ICT for Rapid Detection of S. enteritidis
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may have potential as label-free bacteria adsorbents to replace traditional probes in the ICT. Herein, on the basis of the above-mentioned thought, with Salmonella enteritidis as a model bacteria, 2D materials, including MoS2 and graphene, were synthesized as crosslinking agents for bacteria capture and applied in the ICT method. This strategy exempted the use of traditional label materials and probes, opening a new application field for 2D materials. With MoS2 taken as an example, S. enteritidis in the sample was first captured by MoS2 and then the MoS2−S. enteritidis complex was selectively immunocaptured by the detection of the monoclonal antibody (McAb) coated on the T-line. The introduction of 2D materials as adsorbents in immunoassays for pathogen detection not only removed a series of troublesome marking steps and inherent disadvantages of the capture antibody probe, providing an unexpected alternative to traditional probes, but also avoided the use of paired McAbs obtained by the time-consuming screening process. The novel ICT format developed here allows for the test of S. enteritidis in spiked drinking water and watermelon juice samples and can push the application of 2D nanosheet materials in POC tests.
MATERIALS AND METHODS
Reagents and Chemicals. The McAb against target S. enteritidis flagellin was prepared in our laboratory as previously reported.18 MoS2 (bulk particle size of
