Immobilization of streptavidin on a plasmonic Au-TiO2 thin film towards an LSPR biosensing platform

• Published in: Nanomaterials (Basel, Switzerland) Switzerland), 2022-05, Vol.12 (9), p.1526
• Main Authors: Pereira-Silva, Patrícia, Meira, Diana I., Costa-Barbosa, Augusto, Costa, Diogo, Rodrigues, Marco S., Borges, Joel, Machado, Ana V., Cavaleiro, Albano, Sampaio, Paula, Vaz, F.
• Format: Article
• Language: English
• Subjects: Argon plasma; Au-TiO2 thin film; Binding sites; Biosensors; Biotecnologia Industrial; Biotin; Contact angle; Electromagnetism; Engenharia dos Materiais; Engenharia e Tecnologia; Enzyme-linked immunosorbent assay; Enzymes; Gold; Horseradish peroxidase; Immobilization; LSPR detection; Nanocomposites; Nanoparticles; Oxygen plasma; Peroxidase; Plasma etching; plasmonic biosensor; Plasmonics; Proteins; Refractivity; Science & Technology; Sensors; Silicon wafers; Streptavidin; streptavidin–biotin; Surface plasmon resonance; Thin films; Titanium; Titanium dioxide
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano12091526

Optical biosensors based on localized surface plasmon resonance (LSPR) are the future of label-free detection methods. This work reports the development of plasmonic thin films, containing Au nanoparticles dispersed in a TiO 2 matrix, as platforms for LSPR biosensors. Post-deposition treatments were employed, namely annealing at 400 °C, to develop an LSPR band, and Ar plasma, to improve the sensitivity of the Au-TiO 2 thin film. Streptavidin and biotin conjugated with horseradish peroxidase (HRP) were chosen as the model receptor–analyte, to prove the efficiency of the immobilization method and to demonstrate the potential of the LSPR-based biosensor. The Au-TiO 2 thin films were activated with O 2 plasma, to promote the streptavidin immobilization as a biorecognition element, by increasing the surface hydrophilicity (contact angle drop to 7°). The interaction between biotin and the immobilized streptavidin was confirmed by the detection of HRP activity (average absorbance 1.9 ± 0.6), following a protocol based on enzyme-linked immunosorbent assay (ELISA). Furthermore, an LSPR wavelength shift was detectable (0.8 ± 0.1 nm), resulting from a plasmonic thin-film platform with a refractive index sensitivity estimated to be 33 nm/RIU. The detection of the analyte using these two different methods proves that the functionalization protocol was successful and the Au-TiO 2 thin films have the potential to be used as an LSPR platform for label-free biosensors. Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020, UIDB/04050/2020, and UID/EMS/00285/2020, and by the projects NANO4BIO: POCI-01-0145-FEDER-032299, with FCT reference PTDC/FIS-MAC/32299/2017, and CO2Plasmon, with FCT reference EXPL/CTM-REF/0750/2021. Patrícia Pereira-Silva, Diana I. Meira, and Diogo Costa acknowledge FCT for their Ph.D. scholarships, 2020.08235.BD, SFRH/BD/143262/2019, and SFRH/BD/136279/2018, respectively. Augusto Costa-Barbosa also acknowledges FCT for his Ph.D. scholarships SFRH/BD/133513/2017 and COVID/BD/152169/2021. The authors would like to express their gratitude to Nuno P. Barradas (C2TN, University of Lisbon) and Eduardo Alves (IPFN, University of Lisbon) for RBS measurements and analysis.