“Gate Effect” in p-Synephrine Electrochemical Sensing with a Molecularly Imprinted Polymer and Redox Probes

Abstract

The “gate effect” mechanism for conductive molecularly imprinted polymer (MIP) film coated electrodes was investigated in detail. It was demonstrated that the decrease of the DPV signal for the Fe­(CN)6 4–/Fe­(CN)6 3– redox probe with the increase of the p-synephrine target analyte concentration in solution at the polythiophene MIP-film coated electrode did not originate from swelling or shrinking of the MIP film, as it was previously postulated, but from changes in the electrochemical process kinetics. The MIP-film coated electrode was examined with cyclic voltammetry (CV), differential pulse voltammetry (DPV), electrochemical impedance spectroscopy (EIS), and surface plasmon resonance (SPR). The MIP-film thickness in the absence and in the presence of the p-synephrine analyte was examined with in situ AFM imaging. Moreover, it was demonstrated that doping of the MIP film was not affected by p-synephrine binding in MIP-film molecular cavities. It was concluded that the “gate effect” was most likely caused by changes in radical cation (polaron) mobility in the film.

A new voltammetric platform for reliable determination of the sport performance-enhancing stimulant synephrine in dietary supplements using a boron-doped diamond electrode

“…The acquired sensitivities appeared to be almost similar (around 0.017 mA mM À1 ) for both pulse techniques resulting in very close micromolar LOD values. Unquestionably, the data from the scientic literature have mentioned prospective electrochemical sensors based on chemically modied electrode surfaces [22][23][24] with higher sensitivity and lower LODs for SYN determination when compared to the BDD sensor presented herein. However, as also stated in the Introduction, there are some issues and obstacles connected with the preparation of chemically modied electrodes, especially from the viewpoint of procedure time, incorporation of a modier onto the electrode surface, tedious synthesis of modier material, etc.…”

“…The sensor was also applied for the assessment of the SYN amount in Fructus Aurantii samples with adequate results. The "gate effect" mechanism for conductive molecularly imprinted polymer (MIP) lm coated electrodes for indirect electrochemical determination of SYN was investigated by Lach et al 24 For this purpose, the SYN imprinted polythiophene-based lm was deposited via electropolymerization under potentiodynamic conditions. The authors demonstrated that the decrease of the differential pulse voltammetric peak current for the K 4 [Fe(CN) 6 ]/K 3 [Fe(CN) 6 ] redox probe with the increase of the SYN concentration did not originate from swelling or shrinking of the MIP lm.…”

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.…”

Self-Reporting Molecularly Imprinted Polymer with Covalently Immobilized Ferrocene Redox Probe for Selective Electrochemical Sensing of P-Synephrine

“…But both these mechanisms seem to be invalid in the case of electrochemical sensors based on conductive MIP films. We have already demonstrated that a decrease in the DPV current, caused by the appearance in a solution of an analyte, at conductive MIP film-coated electrodes, might originate not from hindering the diffusion of the redox probe through the film but from changes in electrochemical properties of the film itself [15]. Suppose the redox probe diffusion through the MIP film is not a decisive parameter for the faradaic current involving.…”

“…Herein, we propose to deposit an electrochemically self-reporting MIP film and apply it for fabricating selective electrochemical chemosensors determining the target analyte in the (redox probe)-free test solutions (Scheme 1a). For comparing a new self-reporting MIP chemosensor with the traditional ("gate effect")-based chemosensor, a system of the well-known template and functional monomers was purposefully chosen [15]. Accordingly, we used p-synephrine 1 (Section S2 in Supplementary material) as the model template and then as the target analyte [16].…”