Conjugation of phages with CdS nanocrystals. An alternative in the development of a new tracer for immunoassays

In this work we develop a new tracer based on phage particles labeled with CdS nanocrystals for the construction of an electrochemical immunoassays. Therefore, M13 phages and CdS nanocrystals stabilized with the 3-mercap-topropionic acid were conjugated. Different routes for binding the CdS nanocrystals to the phage coat were studied. A complete characterization of the new tracer was performed using uv-visible and fluorescence mi-croscopies, and transmission electron microscopy. The tracer was evaluated in the detection and quantification of an herbicide in river water using an electrochemical immunoassay. As a concept proof, molinate herbicide was chosen, which is a derivative of the thiocarbamate family. Excellent analytical parameters were achieved. The performance of CdS nanocrystals-phage was compared to unlabeled phage, where a significant improvement in sensitivity was found. Thus, CdS nanocrystals-phage are presented as an excellent alternative to the markers commonly used in the development of immunoassays.