Electrosynthesized MIPs for transferrin: Plastibodies or nano-filters?

Abstract

Molecularly imprinted polymer (MIP) nanofilms for transferrin (Trf) have been synthesized on gold surfaces by electro-polymerizing the functional monomer scopoletin in the presence of the protein target or around pre-adsorbed Trf. As determined by atomic force microscopy (AFM) the film thickness was comparable with the molecular dimension of the target. The target (re)binding properties of the electro-synthesized MIP films was evaluated by cyclic voltammetry (CV) and square wave voltammetry (SWV) through the target-binding induced permeability changes of the MIP nanofilms to the ferricyanide redox marker, as well as by surface plasmon resonance (SPR) and surface enhanced infrared absorption spectroscopy (SEIRAS) of the immobilized protein molecules. For Trf a linear concentration dependence in the lower micromolar range and an imprinting factor of ~5 was obtained by 2 SWV and SPR. Furthermore, non-target proteins including the iron-free apo-Trf were discriminated by pronounced size and shape specificity. Whilst it is generally assumed that the rebinding of the target or of cross-reacting proteins exclusively takes place at the polymer here we considered also the interaction of the protein molecules with the underlying gold transducers. We demonstrate by SWV that adsorption of proteins suppresses the signal of the redox marker even at the bare gold surface and by SEIRAS that the treatment of the MIP with proteinase K or NaOH only partially removes the target protein. Therefore, we conclude that when interpreting binding of proteins to directly MIP-covered gold electrodes the interactions between the protein and the gold surface should also be considered.

Recent Advances in Electrosynthesized Molecularly Imprinted Polymer Sensing Platforms for Bioanalyte Detection

“…Another popular electropolymer for the development of eMIPs for proteins is scopoletin, which has been used for transferrin [154], Cytochrome P450 [155], and laccase [156]. Stojanovic et al used Scopoletin to form an insulating polymer layer imprinted with human serum albumin (HSA) on a gold electrode [157].…”

How Reliable Is the Electrochemical Readout of MIP Sensors?

“…The most frequently applied method for the characterization of MIP sensors evaluates the diffusional permeability of the polymer layer to a redox marker, such as ferri/ferrocyanide, by cyclic voltammetry, differential pulse voltammetry, square wave voltammetry or electrochemical impedance spectroscopy (Figure 8) [49,56,60,[115][116][117][118][119][120][121]. This approach is simple, cost-effective and highly sensitive.…”

“…All steps of MIP synthesis, and of the measurement, can be analyzed by methods directly indicating the presence of the target molecule in the MIP layer, or by indirect methods evaluating the change in the signal of a marker [1,31,45]. The direct detection of the template molecules by the redox conversion at an electrode [46], intrinsic fluorescence of the target or of a label [47], Raman and FTIR spectroscopy [48] or surface-enhanced infrared absorption (SEIRA) spectroscopy [49] specifically indicate the presence of the template in the MIP during the removal and rebinding of the target. In contrast, surface plasmon resonance (SPR), quartz crystal microbalance (QCM), and capacitor-or thermistor-based sensing systems reflect specific binding, nonspecific adsorption to the polymer surface and other types of changes in the chemical environment [1,33,42,50,51].…”

Generic sensor platform based on electro-responsive molecularly imprinted polymer nanoparticles (e-NanoMIPs)

“…Soluble redox markers were used in combination with MIPs for indirect detection of effects related to polymer-template interactions. Thus, the binding of the template to the imprinted polymer reduces the permeability of redox markers such as ferricyanide to electrodes coated with MIPs, and this can be used to measure the concentration of the analyte 22,23 . This phenomenon, called the "gate effect", is frequently used in sensors and is a result of morphological changes in the polymer triggered by specific interactions of the polymeric layer with the template molecule [24][25][26][27] .…”