Electrochemically synthesized polymers in molecular imprinting for chemical sensing

Abstract

This critical review describes a class of polymers prepared by electrochemical polymerization that employs the concept of molecular imprinting for chemical sensing. The principal focus is on both conducting and nonconducting polymers prepared by electropolymerization of electroactive functional monomers, such as pristine and derivatized pyrrole, aminophenylboronic acid, thiophene, porphyrin, aniline, phenylenediamine, phenol, and thiophenol. A critical evaluation of the literature on electrosynthesized molecularly imprinted polymers (MIPs) applied as recognition elements of chemical sensors is presented. The aim of this review is to highlight recent achievements in analytical applications of these MIPs, including present strategies of determination of different analytes as well as identification and solutions for problems encountered.

Fig. 1

Structural formulas of the most common polymers prepared by electropolymerization. a Electronically conducting polymers: polyacetylene 1, polyphenylene 2, polyphenylenevinylene 3, polypyrrole 4, poly(aminophenylboronic acid) 5, polythiophene 6, polyaniline 7, and polyethylenedioxythiophene 8. b Electronically nonconducting polymers: polyphenylenediamine 9, polyphenol 10, polyaminophenol 11, and polythiophenol 12

Fig. 2

Cumulative number of articles published during the last decade in the field of chemical sensors using the concept of molecular imprinting: 1 all publications on molecularly imprinted polymer based chemical sensors and 2 publications on chemical sensors using molecularly imprinted polymers prepared by electropolymerization. (Data taken from SciFinder)

Fig. 3

Basic mechanism of thiophene electropolymerization. SCE saturated calomel electrode. (Adapted from [68])

Fig. 4

General procedure for molecular imprinting with an electroactive functional monomer and typical signal transduction methods employed in detection

Fig. 5

Illustration of the mechanism of alteration of the effective thickness, d, of a molecularly imprinted polypyrrole (MIPPy) polymer film with electrical potential stimuli. a at equilibrium, the film is not swollen and ingress of caffeine molecules is precluded. b upon application of a positive potential, the polymer swells and opens up all the imprinted cavities for caffeine binding. c under potential pulsing conditions, the effective thickness is smaller in a partially swollen film compared with that of the film in b, which swells over the entire volume. d three-dimensional enlargement of the partially swollen film under a 1-s positive potential pulse (ΔE = 0.6, 0.5, or 0.4 V). The caffeine-imprinted cavities in the swollen outer part (marked by d) are opened up for caffeine binding; however, those embedded inside the nonswollen part near the Au electrode are not. PBS phosphate-buffered saline (Adapted from [94])

Fig. 6

Mechanism of imprinting of molecular cavities featuring sites for recognition of antibiotics, for example, neomycin (NE), through electropolymerization of a 4-thioaniline 13 cross-linked Au nanoparticle composite with 4-mercaptophenylboronic acid 14 as a functional monomer on an Au electrode surface. Mercaptoethanesulfonic acid 15 prevented coagulation of Au nanoparticles. (Adapted from [114])

Fig. 7

Structural formulas of derivatives of thiophene (16–19, 24–27) and carbazole (20–23) used as functional (16–26) and cross-linking (27) monomers for molecular imprinting

Fig. 8

Structural formulas of the porphyrin functional monomers nickel protoporphyrin IX dimethyl ester 28, cobalt(III) tetrakis(2-aminophenyl)porphyrin hydroxide 29, and iron(III) tetrakis(4-aminophenyl)porphyrin chloride 30

Fig. 9

Procedure for preparation of the molecularly imprinted polymer chemosensor for surface plasmon resonance determination of oxytetracycline (OTC) using phenylenediamine (PD) as the functional monomer. (Adapted from [163])