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.

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A molecularly imprinted polymer (MIP) is a synthetic polymer that provides specific cavities for its analyte. In this study, the MIP specific to carminic acid, an insect-derived pigment, has been synthesized using methacrylic acid (MAA) and 4-vinyl pyridine (4Vpy) as monomers and ethylene glycol dimethacrylate (EDGMA) as a cross-linker. The imprinted surface particles were characterized by Scanning Electron Microscope (SEM). The rough surface of the synthesized MIP represented the specific binding site for carminic acid. The paper-based MIP polymerization was performed by pre-treatment the cellulose paper with aminopropyltriethoxysilane (APTES) before polymerization with the MIP solution. The novel membrane-grafted MIP exhibits good performance for selective recognition with the target carminic acid, which can be demonstrated by the imprinted factor of 1.94 as compared to those of nonimprinted polymer. According to the Scatchard analysis, it was estimated that there are two types of binding strategy, including high and low affinity, which corresponded to the Ka of 1.24x103 mM and 0.10 x103 mM, respectively. It was thus preliminary concluded that the membrane-grafted MIP fabricated in this study has the potential to be implemented in many applications such as extraction and pre-concentration.