Antibody‐Capped Mesoporous Nanoscopic Materials: Design of a Probe for the Selective Chromo‐Fluorogenic Detection of Finasteride

The synthesis of capped mesoporous silica nanoparticles (MSN) conjugated with an antibody (AB) as a gatekeeper has been carried out in order to obtain a delivery system able to release an entrapped cargo (dye) in the presence of a target molecule (antigen) to which the conjugated antibody binds selectively. In particular, MSN loaded with rhodamine B and functionalized on the external surface with a suitable derivative of N‐(t‐butyl)‐3‐oxo‐(5α,17β)‐4‐aza‐androst‐1‐ene‐17‐carboxamide (finasteride) have been prepared (S1). The addition of polyclonal antibodies against finasteride induced capping of the pores due to the interaction with the anchored hapten‐like finasteride derivative to give a MSN–hapten–AB nanoparticle S1‐AB. It was found that the addition of capped material S1‐AB to water solutions containing finasteride resulted in displacement of the antibody, pore uncapping and entrapped‐dye release. The response of the gated material is highly selective, and only finasteride, among other steroids, was able to induce a significant uncapping process. Compared with finasteride, the finasteride metabolite was able to release 17 % of the dye, whereas the exogen steroids testosterone, metenolone and 16‐β‐hydroxystanozolol only induced very little release of rhodamine B (lower than 10 %) from aqueous suspensions containing sensing solid S1‐AB. A detection limit as low as 20 ppb was found for the fluorimetric detection of finasteride. In order to evaluate a possible application of the material for label‐free detection of finasteride, the capped material was isolated and stored to give final sensing solid S1‐AB‐i. It was found to display a similar behavior towards finasteride as to that shown by freshly prepared S1‐AB; even after a period of two months, no significant loss of selectivity or sensitivity was noted. Moreover, to study the application for the detection of finasteride in biological samples, this “aged” material, S1‐AB‐i, was tested using commercially available blank urine as matrix. Samples containing 70 and 90 % blank urine were spiked with a defined amount of finasteride, and the concentration was determined using capped S1‐AB‐i. Recovery ranges from 94 % to 118 % were reached. Antibodies as gatekeepers: Novel capped mesoporous silica nanoparticles (MSN) using antibodies as gatekeepers have been prepared in order to detect finasteride. In the presence of these particles (S1‐AB), displacement of the antibody takes place, uncapping the pores and relea