Engineering Grey Nanosystem as Activatable Ratio-colorimetric Probe for Detection of Lead Ions in Preserved Egg

A grey system based on the principle of complementary colors was constructed as an activatable probe for the sensitive and specific ratio-colorimetric detection lead ions (Pb²⁺) in a complex food matrix. This grey system was prepared by mixing purple-red AuNP-capped glutathione (GSH) and green-blue sulfonated pigment green 7 (SPG7), to create the SPG7/AuNP probe. In the presence of Pb²⁺, the strong chelation of Pb²⁺ with GSH could trigger the aggregation of AuNPs, leading to the color activation of SPG7. Hence, the absorbance ratio A_523nm/A_628nm of AuNPs at ∼523 nm and SPG7 at ∼628 nm could be used for highly specific reporting of Pb²⁺ levels with a low detection limit of 0.33 μg/L. Moreover, this probe exhibited promising practical applications in real preserved egg samples with recoveries of 89.2 to 107.5% and relative standard deviations (RSD) in the range of 0.28 to 2.12%, revealing its great potential for harmful substance detection.