Immobilization of Streptavidin on a Plasmonic Au-TiO2 Thin Film towards an LSPR Biosensing Platform

Abstract

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 TiO2 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-TiO2 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-TiO2 thin films were activated with O2 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-TiO2 thin films have the potential to be used as an LSPR platform for label-free biosensors.

Chitosan Micro-Membranes with Integrated Gold Nanoparticles as an LSPR-Based Sensing Platform

“…According to the IUPAC definition [ 30 ], the LOD value was estimated in this case to be 1.339 RIU, corresponding to a 0.007 RIU shift from the water reference. The sensitivity of the nanoplasmonic membrane is similar to magnetron-sputtered nanocomposite thin film containing Au NPs dispersed on a titanium dioxide (TiO 2 ) matrix [ 7 ]. Apparently, the incorporation of the Au NPs on various solid matrices (i.e., chitosan and TiO 2 ) promotes the emergence of sensing ability, even at a considerably low RIS value.…”

“…Apparently, the incorporation of the Au NPs on various solid matrices (i.e., chitosan and TiO 2 ) promotes the emergence of sensing ability, even at a considerably low RIS value. In fact, Au-TiO 2 nanoplasmonic thin film, with sensitivity around ~33 nm/RIU, has been reported as a suitable sensing platform for biosensing detection [ 6 , 7 ]. In turn, Majdi et al [ 31 ] reported colloidal chitosan-gold nanoparticles with an established RIS value of 60 nm RIU −1 , determined by fitting of the LSPR band shift vs. the refractive index of several glycerol solutions.…”

“…Both the intensity and peak location of the LSPR band are highly dependent on the NSTs’ shape, size, and composition, as well as the refractive index (RI) of the surrounding medium [ 2 , 3 ]. Changes in the gas or liquid nano-environment and analyte binding to the plasmonic NSTs cause a resonance peak shift due to a refractive index change, which can be used and explored for label-free and real-time detection of gases [ 4 ], liquids [ 5 ], and (bio)molecules [ 6 , 7 ]. LSPR platforms offer label-free, sensitive, rapid, robust, and versatile analyte detection, being, therefore, a desirable detection technology for a variety of biosensing applications such as biomedical [ 8 ], environmental [ 9 ], agricultural [ 10 ], and food industry [ 11 ] applications, among others.…”

Critical Issues on the Surface Functionalization of Plasmonic Au-Ag/TiO2 Thin Films with Thiolated Oligonucleotide-Based Biorecognition Elements

“…In a previous study, the functionalization of Au/TiO 2 thin films was reported, aiming at the production of sensitive LSPR-based optical transducers [36]. Streptavidin and biotin conjugated with horseradish peroxidase (HRP) were chosen as the model receptoranalyte to prove the efficiency of the immobilization method and to demonstrate the potential of the LSPR-based biosensor.…”

Functional Nanomaterials for Sensing and Detection

“…Localized surface plasmon resonance (LSPR)-based sensors are a very promising type of optical biosensor for label-free detection. In another contribution, J. Borges et al developed a plasmonic Au-TiO 2 thin film and demonstrated its potential use as an LSPR platform for label-free biosensors [ 6 ]. Fluorescence-based detection is one of main sensing techniques, and S. J Park et al fabricated a nitrogen and phosphorus co-doped carbon dot/silver nanoparticle nanocomposite for a fluorescence sensor, which could sensitively detect metformin hydrochloride with high selectivity [ 7 ].…”