Comparative study of block copolymer-templated localized surface plasmon resonance optical fiber biosensors: CTAB or citrate-stabilized gold nanorods

Abstract

Block copolymer (BCP) brush-like layer absorbed on optical fibers are shown to address the longstanding challenge of forming dense and well-dispersed gold nanorods (AuNRs) films on highly curved surface, allowing the development of real-time localized surface plasmon resonance (LSPR) biosensors for antigen-antibody interaction. This method requires only solution-based manufacturing processes and a plasma cleaning step to self-assemble AuNRs with various aspect ratios on the optical fibers. Because AuNRs capped with cetyltrimethylammonium bromide (CTAB) have been problematic for biosensing applications due to their cytotoxicity and displacement difficulty in the construction of biosensors, citrate-stabilized AuNRs were prepared from CTAB-stabilized AuNRs via surfactant exchange. For comparison, both a poly(styrene)-b-poly(acrylic acid) (PS-b-PAA) BCP template with CTAB-stabilized AuNRs and a poly(styrene)-b-poly(4-vinyl pyridine) (PS-b-P4VP) BCP template with citrate-stabilized AuNRs were employed for the fabrication of the optical fiber biosensor. The LSPR spectral analysis results demonstrate that the sensitivity of the sensor produced by the PS-b-P4VP templating method was 1.5 times better than that of the sensor produced by the PS-b-PAA templating method, which was due to the improved surface coverage and reduced aggregation of nanoparticles. The detection limit of the PS-b-P4VP-templated sensor for human IgG was 0.6 nM. Furthermore, for citrate-stabilized AuNRs, the PS-b-P4VP templating method also led to a better surface morphology and higher sensitivity as compared to the standard particle absorption methods using alkoxysilanes or polyelectrolytes on identical fibers. The simplicity of the fabrication process and the far superior optical performance of the PS-b-P4VP-templated LSPR optical fiber sensor illustrate the ability to regulate the detection range by tuning the aspect ratios of the AuNRs, and demonstrate its application prospects as a real-time biosensor without cytotoxicity.