Determination of methotrexate in spiked human blood serum using multi-frequency electrochemical immittance spectroscopy and multivariate data analysis

This article describes an attempt to develop a sensor based on multi-frequency immittance spectroscopy for the determination of methotrexate (MTX) in blood serum using gold electrodes modified with antibodies. The attachment of antibodies was monitored with electrochemical immittance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The EIS measurements of MTX resulted in a data matrix of size 39 × 55. The data were analysed using multivariate data analysis and showed a concentration dependence and time dependence that could be separated. This allowed the calculation of a multivariate calibration model. The model showed good linear behavior on a logarithmic scale offering a detection limit of 5 × 10⁻¹² mol L⁻¹. - Highlights: • Determination of methotrexate (MTX) in spiked blood serum using a biosensor; gold electrodes modified with antibody. • Electrode surface modification was performed by introducing reagents while the electrodes were mounted in a flow cell. • The electrode modification was monitored using electrochemical immittance spectroscopy and X-ray photoelectron spectroscopy. • The method offered a wide linear working range with 8 orders of magnitude and a detection limit of 5 × 10^-12 mol L^-1.