Research Article: Aptamer-based fluorometric determination of Salmonella Typhimurium using Fe3O4 magnetic separation and CdTe quantum dots

Date Published: June 19, 2019

Publisher: Public Library of Science

Author(s): Junan Ren, Gang Liang, Yan Man, An Li, Xinxin Jin, Qingju Liu, Ligang Pan, Yogendra Kumar Mishra.


Based on the high sensitivity and stable fluorescence of CdTe quantum dots (QDs) in conjunction with a specific DNA aptamer, the authors describe an aptamer-based fluorescence assay for the determination of Salmonella Typhimurium. The fluorescence detection and quantification of S. Typhimurium is based on a magnetic separation system, a combination of aptamer-coated Fe3O4 magnetic particles (Apt-MNPs) and QD-labeled ssDNA2 (complementary strand of the aptamer). Apt-MNPs are employed for the specific capture of S. Typhimurium. CdTe QD-labeled ssDNA2 was used as a signaling probe. Simply, the as-prepared CdTe QD-labeled ssDNA2 was first incubated with the Apt-MNPs to form the aptamer-ssDNA2 duplex. After the addition of S. Typhimurium, they could specifically bind the DNA aptamer, leading to cleavage of the aptamer-ssDNA2 duplex, accompanied by the release of CdTe QD-labeled DNA. Thus, an increased fluorescence signal can be achieved after magnetic removal of the Apt-MNPs. The fluorescence of CdTe QDs (λexc/em = 327/612 nm) increases linearly in the concentration range of 10 to 1010 cfu•mL-1, and the limit of detection is determined to be 1 cfu•mL-1. The detection process can be performed within 2 h and is successfully applied to the analysis of spiked food samples with good recoveries from 90% to 105%.

Partial Text

Bacterial infection is a major problem for human health because of their toxin system and probable antibiotic resistance [1,2]. Salmonella Typhimurium (S. Typhimurium) is one of the most important prevalent pathogens in humans, causing diarrhea, fever, and abdominal cramps [3,4]. This salmonellosis is mostly related to contaminated foods that mainly originate from animal sources, including poultry eggs, milk, beef, and raw food, and non-animal foods, such as fruits, vegetables, and spices [5]. Currently, S. Typhimurium is considered a key concern in many countries, such as the US, China, Europe, and Japan. Therefore, it is important to develop a method that can detect S. Typhimurium rapidly, accurately and sensitively for food quality control.

In this paper, we report a magnetic separation system-based fluorescence sensing strategy to detect and quantify S. Typhimurium with high sensitivity and selectivity. QD-ssDNA2 was incubated with Apt-MNPs to form an aptamer-complementary DNA duplex as a detection probe. Upon addition of S. Typhimurium, QD-ssDNA2 is replaced by the bacteria and released from the Fe3O4 MNPs, accompanied by the release of CdTe QD-labeled ssDNA2, resulting in a significantly increased fluorescence intensity. The difference in fluorescence intensity can be used to sensitively detect S. Typhimurium, with a low detection limit of 1 cfu•mL-1. Furthermore, the fluorescence sensor was also successfully applied to detect S. Typhimurium in water and milk. In addition, the aptamer and QD-modified complementary sequences are more cost-effective and more stable than antibodies, and the assay can capture targets with magnetic beads and use fluorescence to quantify S. Typhimurium simultaneously within 2 h. In conclusion, the sensing assay has the potential to be further extended to on-site screening of pathogenic bacteria S. Typhimurium-related food contamination and other pathogenic bacteria targets by changing the aptamer and cDNA.