TY - JOUR
T1 - Biofilm growth monitoring using guided wave ultralong-range Surface Plasmon Resonance
T2 - A proof of concept
AU - Bajaj, Aabha
AU - Abutoama, Mohammad
AU - Isaacs, Sivan
AU - Abuleil, Marwan J.
AU - Yaniv, Karin
AU - Kushmaro, Ariel
AU - Modic, Martina
AU - Cvelbar, Uroš
AU - Abdulhalim, Ibrahim
N1 - Funding Information:
The sensitivity and reliability of an SPR sensor heavily depend upon the penetration depth of the evanescent field, which decays exponentially in the direction normal to the substrate-analyte medium interface. Therefore, small penetration depth limits the reliable detection of cellular entities and multilayered biofilm architecture. For instance, conventional gold SPR substrates exhibit penetration depths up to 200 nm for wavelengths in the visible range, whereas biofilms can grow up to several to tens of micrometer thicknesses (∼100 μm) over weeks. It has been shown that such plasmonic sensors become saturated or fail to assess the concentration and size dependence of the refractive index (Isaacs and Abdulhalim, 2015). To address this issue, we proposed an insulator-metal-insulator (IMI) structure with a long penetration depth of up to a few micrometers or more in the visible range. The bottom insulator layer (e.g. ∼500 nm SiO2) provides a plasmon wave propagating under the metal film and, therefore can be used for reference purposes. The top insulator layer (which can also be ∼500 nm SiO2) acts as a waveguide, so that guided wave SPR modes are excited. Upon specific design of the structure parameters, it was shown that when the resonance angle is close to the critical angle, the penetration depth can become very large, starting from a few micrometers up to tens of micrometers, depending on the wavelength and angle. Under these conditions, the resonance width narrows, indicating long-range propagation (LRSPR) (Jing et al., 2019). Vala et al. (2009) have calculated a 5.5 higher response with LRSPR than conventional SPR for detecting bacteria (Vala et al., 2009). Contrary to standard LRSPR, in which a single insulator layer is buried under the metal layer, the IMI structure provides guided wave long-range (GW-LRSPR) with a larger penetration depth. A few studies have demonstrated that standard LRSPR offers slightly higher penetration depth (Chabot et al., 2012; Shrivastav et al., 2021). Huang et al. (2012) used gold substrate supporting LRSPR to study the connection between Pseudomonas aeruginosa and zwitterionic polymers (Huang et al., 2012). Isaacs and Abdulhalim (2015) have shown computationally and experimentally the need and utility of the IMI design for cell detection as it offers a much greater penetration depth (Isaacs and Abdulhalim, 2015).This work is supported by a joint bilateral project between the Israel Ministry of Science and Technology and the Slovenian Research Agency (ARRS) grant no. NI-0001 and J4-1770. The project is partially funded by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 872662, IPANEMA project.
Funding Information:
This work is supported by a joint bilateral project between the Israel Ministry of Science and Technology and the Slovenian Research Agency (ARRS) grant no. NI-0001 and J4-1770 . The project is partially funded by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 872662 , IPANEMA project.
Publisher Copyright:
© 2023 Elsevier B.V.
PY - 2023/5/15
Y1 - 2023/5/15
N2 - Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100–300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO2–Ag–SiO2) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10−7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO2 surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO2 case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.
AB - Unwelcomed biofilms are problematic in food industries, surgical devices, marine applications, and wastewater treatment plants, essentially everywhere where there is moisture. Very recently, label-free advanced sensors such as localized and extended surface plasmon resonance (SPR) have been explored as tools for monitoring biofilm formation. However, conventional noble metal SPR substrates suffer from low penetration depth (100–300 nm) into the dielectric medium above the surface, preventing the reliable detection of large entities of single or multi-layered cell assemblies like biofilms which can grow up to a few micrometers or more. In this study, we propose using a plasmonic insulator-metal-insulator (IMI) structure (SiO2–Ag–SiO2) with a higher penetration depth based on a diverging beam single wavelength format of Kretschmann configuration in a portable SPR device. An SPR line detection algorithm for locating the reflectance minimum of the device helps to view changes in refractive index and accumulation of the biofilm in real-time down to 10−7 RIU precision. The optimized IMI structure exhibits strong penetration dependence on wavelength and incidence angle. Within the plasmonic resonance, different angles penetrate different depths, showing a maximum near the critical angle. At the wavelength of 635 nm, a high penetration depth of more than 4 μm was obtained. Compared to a thin gold film substrate, for which the penetration depth is only ∼200 nm, the IMI substrate provides more reliable results. The average thickness of the biofilm after 24 h of growth was found to be between 6 and 7 μm with ∼63% live cell volume, as estimated from confocal microscopic images using an image processing tool. To explain this saturation thickness, a graded index biofilm structure is proposed in which the refractive index decreases with the distance from the interface. Furthermore, when plasma-assisted degeneration of biofilms was studied in a semi-real-time format, there was almost no effect on the IMI substrate compared to the gold substrate. The growth rate over the SiO2 surface was higher than on gold, possibly due to differences between surface charge effects. On the gold, the excited plasmon generates an oscillating cloud of electrons, while for the SiO2 case, this does not happen. This methodology can be utilized to detect and characterize biofilms with better signal reliability with respect to concentration and size dependence.
KW - Biofilm
KW - GW-LRSPR
KW - Portable SPR
KW - Surface Plasmon Resonance (SPR)
UR - http://www.scopus.com/inward/record.url?scp=85150822477&partnerID=8YFLogxK
U2 - 10.1016/j.bios.2023.115204
DO - 10.1016/j.bios.2023.115204
M3 - Article
C2 - 36913883
AN - SCOPUS:85150822477
SN - 0956-5663
VL - 228
JO - Biosensors and Bioelectronics
JF - Biosensors and Bioelectronics
M1 - 115204
ER -
