Detection of low molecular weight toxins using optical phase detection techniques

Abstract

Optical methods based on recording a phase shift of electromagnetic waves offer high sensitivity for detection of bio-reactions. The method of Total Internal Reflection Ellipsometry (TIRE), which records simultaneously two parameters Ψ and ∆ related, respectively, to the amplitudes and phases of p-and s-components of polarized light, was exploited here for detection of mycotoxins (T-2, zearalanone, and aflatoxin). The TIRE direct label-free immunoassay enables detecting the above mycotoxins in sub-ppb concentrations in water as well as in food extracts. Further enhancement of sensitivity can be achieved with the use of SiO 2 /Si 3 N 4 /SiO 2 planar waveguides operating as polarization interferometers (PI).

Detection of Aflatoxin B1 with a Label-Free Ellipsometry Immunosensor

“…The maximal thickness increment (at saturation) is about 1.5 nm which is larger than expected for binding rather small molecules of aflatoxin (having linear dimensions of 0.5×0.8 nm). Similar observations were reported earlier for T-2 mycotoxins (5.5 nm thickness increase) [13], zearalenone (2.5-2.7 nm) [17], and nonylphenol (25 nm) [14]. The explanation of this fact lies in the hydrophobicity of investigated molecules and thus their abilities to form aggregates in aqueous solutions when the original stock solution of mycotoxins in methanol was diluted in water.…”

“…3 is typical for immune reactions and similar to those observed earlier for other mycotoxins [13,14,17]. The linear range is quite narrow (from 0.4 ng/ml to 40 ng/ml) which appeared to be typical for monoclonal antibodies [13].…”

“…The above results of TIRE direct immunoassay for aflatoxin B1 are compared here with the data obtained previously for T-2 [11] and zearalenone [17]. The experimental procedures in [11,17] were similar to those described in this work.…”

“…The steady-state single spectral scans were carried out using a large number of rotations (from 500 to 1,000) of compensator followed by averaging the values of y and Δ obtained; such measurements provide highly accurate data for further fitting and the evaluation of the thickness of adsorbed molecular layers. Dynamic spectra data have higher noise level due to the small number of turns (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) of compensator and perhaps due to the light scattering on turbid solution and air bubbles in the cell. Because of the variation in the refractive index of solutions injected in the cell, dynamic spectral measurements are not suitable for data fitting; however, they were used for detection of relative changes in y and Δ and the investigation of affinity of the immune reactions.…”

“…This allows the use of a label-free and cost-effective direct immunoassay format [13,14] in which the molecules of toxins are binding to specific antibodies immobilised on the surface. The method of TIRE was successfully utilised earlier for detection of different low molecular weight toxins, such as herbicides atrazine and simazine [11], mycotoxins T-2 [13] and zearalenone [17], and alkylphenols (nonylphenol) [14]. The achieved detection limit for the above toxins was down to 0.1 ng/ml for T-2 mycotoxins.…”