Glutathione Immunosensing Platform Based on Total Internal Reflection Ellipsometry Enhanced by Functionalized Gold Nanoparticles

Abstract

An immunosensor to detect small molecules, such as glutathione (GSH), has been developed by combination of ellipsometry and Kretschmann surface plasmon resonance (SPR). The Au thin film used for surface plasmon polariton (SPP) excitation is functionalized with anti-GSH to specifically bind GSH. At low concentrations, the small refractive index changes caused by the low molecular weight of GSH induced only negligible shifts in the plasmon resonant energy during GSH binding. To improve sensitivity, gold nanoparticles (AuNPs) are functionalized with glutathione acting as amplifiers of the antigen-antibody interaction. Changes induced by the AuNP adsorption are monitored using Ψ and Δ ellipsometric functions. After performing competitive assays using solutions containing different concentrations of free GSH and a constant amount of functionalized AuNPs, it was concluded that the resonant energy linearly shifts as the relative concentration of free GSH increases. A detection limit for free GSH in the nanomolar range is found, demonstrating the effectiveness of AuNPs to enhance the sensitivity to immunoreactions in total internal reflection ellipsometry.

Optical biosensors based on ZnO nanostructures: advantages and perspectives. A review

“…García-Marín et al used Al-doped ZnO (AZO) nanolayers in Au SPR biosensor as a passive component to reduce losses in optical signal and provide better adhesion of Au nanostructures [102]. Previously, Au nanoparticles were used as biosensitive layer and ZnO was applied to increase the active surface area and to amplify the SPR signal [41,54].…”

Immunosensing platform based on gallium nanoparticle arrays on silicon substrates

“…GaNPs/Si based immunosensors are developed following the procedure previously described with slight modifications (García-Marín et al 2014). Prior to the functionalization, the GaNPs/Si chips are carefully selected, by measuring the imaginary part of the pseudodielectric function (   i  ) spectra to have the same peak-to-peak amplitude and RPH energy.…”

“…Different immunosensor chips, prepared by the same manner, are incubated for 1 hour in solutions containing increasing concentrations of GSH from 50 to 800 nM. The incubation time is chosen according to previous results obtained in a kinetic study performed between the same antibody and analyte, from which it was concluded that 35 min are enough to ensure that the binding process reaches the equilibrium (García-Marín et al 2014). g/mL) and 50 nM (0.015 µg/mL), calculated as the ratio between three and ten times the standard deviation of the background signal and the sensitivity, respectively.…”

“…In general, those publications that report a lower limit of detection require two functionalization protocols, one for the sensing surface and another one for additional nanostructures that act as signal amplifiers. For instance, the methods described by Stobiecka et al (Stobiecka andHepel 2011) andGarcía-Marín et al (García-Marín et al 2014) use gold nanoparticles to enhance the sensitivity after the previous immobilization of the analyte on the NP surface, which can hinder GSH quantification in more complex matrices.…”

Recent advances in surface plasmon resonance imaging: detection speed, sensitivity, and portability

“…Based on the LSP-SPP coupling-induced enhancement, many ultrasensitive biometric detectors for sensing subtle environmental changes have been demonstrated since the late 1990s [59][60][61][62][63]. In the LSP-SPP coupling configuration, numerical simulation shows that the EM field enhancement is usually the strongest in the gap between the nanoparticle and the film.…”