A Lateral Flow Strip Based on a Truncated Aptamer-Complementary Strand for Detection of Type-B Aflatoxins in Nuts and Dried Figs.

Wenlei Zhai,Meng Wang,Xia Fan,He Wang,Zhilei Zhao,Ailiang Chen,Xiaoyuan Feng

doi:10.3390/toxins12020136

Abstract

Type-B aflatoxins (AFB1 and AFB2) frequently contaminate food, especially nuts and fried figs, and seriously threaten human health; hence, it is necessary for the newly rapid and sensitive detection methods to prevent the consumption of potentially contaminated food. Here, a lateral flow aptasensor for the detection of type-B aflatoxins was developed. It is based on the use of fluorescent dye Cy5 as a label for the aptamer, and on the competition between type-B aflatoxins and the complementary DNA of the aptamer. This is the first time that the complementary strand of the aptamer has been used as the test line (T-line) to detect type-B aflatoxins. In addition, the truncated aptamer was used to improve the affinity with type-B aflatoxins in our study. Therefore, the lengths of aptamer and cDNA probe were optimized as key parameters for higher sensitivity. In addition, binding buffer and organic solvent were investigated. The results showed that the best pair for achieving improved sensitivity and accuracy in detecting AFB1 was formed by a shorter aptamer (32 bases) coupled with the probe complementary to the AFB1 binding region of the aptamer. Under the optimal experimental conditions, the test strip showed an excellent linear relationship in the range from 0.2 to 20 ng/mL with a limit of detection of 0.16 ng/mL. This aptamer-based strip was successfully applied to the determination of type-B aflatoxins in spiked and commercial peanuts, almonds, and dried figs, and the recoveries of the spiked samples were from 93.3%−112.0%. The aptamer-complementary strand-based lateral flow test strip is a potential alternative tool for the rapid and sensitive detection of type-B aflatoxins in nuts and dried figs. It is of help for monitoring aflatoxins to avoid the consumption of unsafe food.

Highlights

Type-B aflatoxins, including aflatoxin B1 and B2 (AFB1 and aflatoxin B2 (AFB2) ), produced by Aspergillus species, have the highest toxicity among mycotoxins that seriously threaten the health of humans and animals [1].Toxins 2020, 12, 136; doi:10.3390/toxins12020136 www.mdpi.com/journal/toxinsAflatoxin B1 (AFB1) is highly carcinogenic, mutagenic, and teratogenic, as reported by the International Agency for Cancer (IARC) [2]
The aim of our study was to find suitable complementary strands to achieve a balance between reduced affinity to aptamer and high efficiency of hybridization with truncated aptamer, and develop a fluorescent lateral flow strip based on a truncated aptamer-complementary strand for rapid and sensitive detection of type-B aflatoxins in nuts and dried figs
The remaining aptamer was combined with the poly T (Table 1) of the control line, as shown in Figure 1a-2, which resulted in a higher fluorescence value of the test-line and a lower fluorescence value of the control line

Summary

Introduction

Type-B aflatoxins, including aflatoxin B1 and B2 (AFB1 and AFB2 ), produced by Aspergillus species, have the highest toxicity among mycotoxins that seriously threaten the health of humans and animals [1].Toxins 2020, 12, 136; doi:10.3390/toxins12020136 www.mdpi.com/journal/toxinsAFB1 is highly carcinogenic, mutagenic, and teratogenic, as reported by the International Agency for Cancer (IARC) [2]. Type-B aflatoxins, including aflatoxin B1 and B2 (AFB1 and AFB2 ), produced by Aspergillus species, have the highest toxicity among mycotoxins that seriously threaten the health of humans and animals [1]. Consumption of nuts and dried fruits is one of the most important contributors to human exposure to mycotoxins, especially AFB1 [4]. To ensure food safety and protect human health, many countries and regions in the world have set maximum allowable limits for AFB1 in nuts and dried figs, which are typically set as 2–8 μg/kg by the European Union [5], and 5–20 μg/kg by China [6]. A recent survey showed that the nuts and dried figs collected from China were seriously contaminated by AFB1 , with the highest levels of

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