Abstract
As surface plasmon resonance (SPR)-based biosensors are well translated into biological, chemical, environmental, and clinical fields, it is critical to further realize stable and sustainable systems, avoiding oxidation susceptibility of metal films—in particular, silver substrates. We report an enhanced SPR detection performance by incorporating a TiO2 layer on top of a thin silver film. A uniform TiO2 film fabricated by electron beam evaporation at room temperature is an effective alternative in bypassing oxidation of a silver film. Based on our finding that the sensor sensitivity is strongly correlated with the slope of dispersion curves, SPR sensing results obtained by parylene film deposition shows that TiO2/silver hybrid substrates provide notable sensitivity improvement compared to a conventional bare silver film, which confirms the possibility of engineering the dispersion characteristic according to the incidence wavelength. The reported SPR structures with TiO2 films enhance the sensitivity significantly in water and air environments and its overall qualitative trend in sensitivity improvement is consistent with numerical simulations. Thus, we expect that our approach can extend the applicability of TiO2-mediated SPR biosensors to highly sensitive detection for biomolecular binding events of low concentrations, while serving a practical and reliable biosensing platform.
Highlights
Optical detection technologies based on surface plasmon resonance (SPR) are commonly used in a variety of biological, chemical, environmental, and clinical applications because they are very powerful tools for monitoring binding interactions in a label-free manner [1,2,3,4,5]
Based on our recent finding that the sensitivity of SPR biosensor is strongly correlated with its dispersion curve characteristics [21], we show that a TiO2 overlayer is advantageous for engineering the dispersion relation of a silver film
From the previous studies [21,33], the field amplitude at the binding region is greatly correlated with the sensitivity, and, as a quantitative metric of field-matter interaction, nearfield characteristics can be a useful tool to assess the performance of SPR biosensors that address an enhancement of detection sensitivity
Summary
Optical detection technologies based on surface plasmon resonance (SPR) are commonly used in a variety of biological, chemical, environmental, and clinical applications because they are very powerful tools for monitoring binding interactions in a label-free manner [1,2,3,4,5]. Silver can provide a sharper SPR curve as an attractive substrate, the major disadvantage of chemical instability makes it difficult to obtain reliable optical signals and to perform long-time measurements, limiting the practicality of silver-based SPR biosensors [11]. In this respect, several approaches have been suggested to prevent a silver film in SPR biosensors from being oxidized when it is exposed to an oxygen-containing ambience as the commonly biosensing environment. We further discuss the sensitivity improvement by analyzing the near-field distribution and field-matter interactions in the proximity of the TiO2 /silver hybrid substrate
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