Introduction. Many countries have developed regulatory lists of banned or restricted cosmetic ingredients for ensuring the safety of cosmetic products. Among the banned substances, dehydroepiandrosterone (DHEA) is an hormone which can affect the biological processes in humans even at a very low level, but it is often illegally added to cosmetic formulations since it has an anti-ageing effect. The aim of this study is to develop a chemiluminescent (CL)-based immunoassay for the detection and quantification of DHEA in cosmetics.

Method. The method involved the development of an integrated lab-on-a-chip platform, the assay was carried out in solution, and the detection was performed inside microwells coupled to a dedicated CL detector.

In this approach, magnetic beads (MBs), used as platform for the competitive immunoassay, were functionalized with anti-DHEA antibodies and were incubated with a solution containing the sample and the peroxidase conjugates of DHEA to provide competition for binding the antibodies. After the washing step, the MBs were added into a black microwell plate with a transparent bottom which was aligned with an array of hydrogenated amorphous silicon photosensors. After the addition of the proper CL substrate, it was possible to monitor the CL signal in real time.

Results. The developed method allowed for the accurate quantification of DHEA down to 20 ppb, and tests were performed on spiked cosmetic samples and suitably pre-treated. 

Conclusion. The proposed assay demonstrated the possibility to exploit a rapid and simple CL-immunoassay for detecting counterfeit at very low level in complex cosmetic matrices. The method can be optimized in the future for different kinds of banned ingredients, allowing the number of target analytes that can be detect into a single analysis to be increased by exercising a multiplexing approach.