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Title: Label-free SERS detection of Salmonella Typhimurium on DNA aptamer modified AgNR substrates

item CHEN, JING - University Of Georgia
item Park, Bosoon
item HUANG, YAO-WEN - University Of Georgia
item ZHAO, YIPING - University Of Georgia
item KWON, YONGKUK - Animal And Plant Quarantine Agency

Submitted to: Journal of Food Measurement and Characterization
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2017
Publication Date: 6/2/2017
Citation: Chen, J., Park, B., Huang, Y., Zhao, Y., Kwon, Y. 2017. Label-free SERS detection of Salmonella Typhimurium on DNA aptamer modified AgNR substrates. Journal of Food Measurement and Characterization. doi:10.1007/s11694-017-9558-6.

Interpretive Summary: Salmonellae are a group of pathogenic bacteria that have been frequently associated with foodborne outbreaks. There are an estimated 1.2 million cases of salmonellosis each year, causing 16,000 hospitalizations and 500 deaths. Salmonella Typhimurium is a serotype that causes the largest number of foodborne outbreaks. In addition, some strains of Salmonella Typhimurium also display high virulence and drug-resistance. Therefore, timely detection of Salmonella Typhimurium from food has become an urgent need for food safety. Since conventional methods for Salmonella detection rely on laborious procedures and often take 4-7 days to complete, rapid methods such as polymerase chain reaction (PCR) have been under intense investigation for many years and have achieved high sensitivity. Nevertheless, molecular-based methods face some restraints, particularly when detecting pathogens from real food samples, due to the need for sample pre-enrichment and presence of PCR-inhibitors in these matrices. Therefore, the development of rapid alternative methods is still demanding. Surface enhanced Raman scattering is an optical technique that amplifies the signal of Raman scattering using nanostructured metal materials. Using the SERS spectra, various bacterial species or even strains can be differentiated. In this study, we report an aptamer-based, label-free SERS technique for detection of Salmonella Typhimurium. The anti-S. Typhimurium aptamer is covalently attached to the highly uniform silver nanorod (AgNR) array substrates, and the SERS spectra are compared before and after the substrates are exposed to either whole cells or cell fragments of S. Typhimurium and control bacteria.

Technical Abstract: A straightforward label-free method based on aptamer binding and surface enhanced Raman specstroscopy (SERS) has been developed for the detection of Salmonella Typhimurium, an important foodborne pathogen that causes gastroenteritis in both humans and animals. Surface of the SERS-active silver nanorod array substrates is modified with anti-S. Typhimurium DNA aptamer and a spacer molecule, mercaptohexanol, and exposed to S. Typhimurium and non-specific control bacteria. SERS spectra of S. Typhimurium whole cell samples show significantly higher intensity ratios of the '' = 725 and 680 cm-1 peaks (I725/I680) compared to the negative and blank controls. In contrast, when lysed bacterial cell components (supernatant, cell pellets, and mixture) are used, the I725/I680 ratios of S. Typhimurium samples are significantly lower than those of the negative controls but higher than those of the blank controls. In both cases, S. Typhimurium can be distinguished from the other samples using principle component analysis. The observed spectral differences may be attributed to the conformational changes in the aptamer DNA when it binds to its target bacteria, but further studies are needed to confirm this hypothesis.