Abstract
A simple and rapid distance paper-based analytical device (dPAD) for the detection of lead (Pb) in foods is proposed herein. The assay principle is based on competitive binding between carminic acid (CA) and polyethyleneimine (PEI) to Pb in a food sample. The paper channels were pre-immobilized with PEI, before reacting with a mixture of the sample and CA. Pb can strongly bind to the CA; hence, the length of the red color deposition on the flow channel decreased as a lower amount of free CA bound to PEI. The dPAD exhibited good linear correlation, with ranges of 5–100 µg·mL−1 (R2 = 0.974) of Pb. Although, the limit of detection (LOD) of this platform was rather high, at 12.3 µg·mL−1, a series of standard additions (8.0, 9.0, and 10.0 µg·mL−1) can be used to interpret the cutoff of Pb concentrations at higher or lower than 2 µg·mL−1. The presence of common metal ions such as calcium, magnesium, nickel, and zinc did not interfere with the color distance readout. The validity of the developed dPAD was demonstrated by its applicability to screen the contamination of Pb in century egg samples. The results obtained from the dPAD are in accordance with the concentration measured by atomic absorption spectroscopy (AAS) (n = 9). In conclusion, this proposed dPAD, combined with the standard addition method, could be applied for screening Pb contamination in food matrices. This platform is, therefore, potentially applicable for field measurements of Pb in developing countries, because it is cheap and rapid, and it requires no significant laborious instruments.
Highlights
Introduction iationsCentury egg, otherwise known as preserved egg or Pidan, is one of the famous Chinese and Thai cuisine ingredients because of its unique taste, high nutrition, and affordability.In the manufacturing process, there is likely the misuse of lead oxide, with it being added into the pickling mixture in order to reduce the ripening time and to help improve the texture of the century eggs
It was found that carminic acid (CA) could be moved to the top of the distance paper-based analytical device (dPAD) when the solution was applied, which implies that the CA did not strongly adsorb into the paper channels
The developed dPAD proposed in this study provides superior advantages in terms of simplicity, rapidity, and affordability for screening the contamination of Pb in century eggs
Summary
There is likely the misuse of lead oxide, with it being added into the pickling mixture in order to reduce the ripening time and to help improve the texture of the century eggs. The lead (Pb) content in the pickling mixture could permeate through the eggshells and egg membrane into all parts of the eggs, thereby accumulating in the egg whites and yolks [1,2]. The Pb content in century eggs has become a major safety concern, because food consumption is a major pathway of toxic compounds for human beings [3]. Accumulation of Pb in the human body could damage the nervous system, and the immune system [4].
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