New electroanalytical applications of self-assembled monolayers
Introduction
Recent developments in the physical chemistry of surfaces can be ascribed essentially to progress in manipulation with single molecular layers. This has led to a chemical approach to nanotechnology [1] that has resulted in numerous applications. Analytical chemistry became one field of application: new methods, for forming molecularly organized structures with pre-defined properties, such as insulating or conductive layers, sensitive layers or layers preventing non-specific adsorption, as well as for forming laterally organized microstructures and nanostructures, can be applied to develop new sensor structures and technologies.
This progress is based mainly on the discovery and the development of self-assembled monolayers of sulfuric compounds (thiols, disulfides) on gold and other solid conductive surfaces [2], [3], [4]. In comparison with Langmuir-Blodgett technology, which was previously the main approach to forming molecular coatings of electrodes, the technology of self-assembly has numerous advantages: (i) self-assembled monolayers are almost free of defects; (ii) self-assembled monolayers are much more stable, especially in water and other solvents; (iii) formation of self-assembled monolayers does not require any complicated set-ups (such as Langmuir-Blodgett troughs and precision lifts) and is less sensitive to impurities; and, (iv) the choice of molecules to be deposited is not limited to water-insoluble amphiphilic compounds.
The main objective of this paper is to provide a short review of the latest achievements in applying self-assembled monolayers to the development of new electroanalytical approaches and devices. The topic is limited to the consideration of electroanalytical methods and self-assembled monolayers of thiol compounds. This reflects the scope of the author's interests, as well as the fact that most applications of self-assembled monolayers in different analytical applications (such as optical, mechano-acoustic, scanning tunneling or atomic force microscopies) exploit only the anchor function of the monolayers as a “molecular glue” for immobilizing different organic molecules, mainly biological or artificial receptors [5], [6], [7], [8], [9], [10], [11], [12]. This approach can now be considered traditional (Fig. 1) and its realization usually does not depend on a particular application. Because of similar considerations, numerous applications of self-assembled monolayers in the design of enzymatic biosensors were also excluded; interested readers are directed to another recent review [13]. Physical and chemical properties of self-assembled monolayers, as well as different examples of technical applications, are also reviewed elsewhere [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28].
Section snippets
Electrical control of metal-thiol binding and electrically-addressable immobilization
The self-assembly of alkanethiols on metal electrodes and the desorption of these self-assembled monolayers from the electrodes are controlled by the electrode potential (Fig. 2). The range of maximal stability of alkanethiol monolayers on gold electrodes is between about 0.2 V and 0.5 V versus a saturated calomel electrode (SCE). The open circuit potential of the gold electrode during thiol deposition is within this stability range [29]; that is why it is usually possible to obtain
Spreader-bar technique: formation of stable, nanostructured, self-assembled monolayers
The most effective technique for forming artificial receptors is based on molecular imprinting, which comprises the formation of a three-dimensional porous polymer, the cavities of which match the molecular structure of the analyte of interest [10], [11], [12], [64], [65], [66], [67], [68], [69]. There have been several attempts to apply the principle of molecular imprinting to forming two-dimensional chemical receptors. The first report was published by J. Sagiv [70] as early as 1980. The
Self-assembled monolayers as selective filters for gas sensors
Extensive electrochemical applications of self-assembled monolayers of thiol compounds started in 1987 after the publication of Finklea et al.[4], who demonstrated strong blocking of Faraday processes by self-assembled monolayers of alkanethiols. The permeability of the self-assembled monolayers to non-ionic substances, especially in gaseous form, was still studied less, probably because of lack of suitable analytical methods [80], [81], [82], [83]. It was shown that self-assembled monolayers
Conclusion
Self-assembled monolayers of thiol compounds have several attractive features that make them useful for a number of analytical applications:
- (i)
their strong binding to gold and many other solid surfaces provides an effective way to use these molecules as primers for immobilization of further organic compounds with different functions, for example biological receptors;
- (ii)
electrical control of the self-assembly can be exploited for the electrically-addressable immobilization of different receptors onto
Acknowledgements
The author is grateful to his colleagues, Th. Hirsch, M. Riepl, M. Vasjari, H. Kettenberger, T. Panasyuk-Delaney, I. Novotny, V. Rehacek and V. Tvarozek, who obtained many of the experimental results described in this review. The author also thanks Professor O.S. Wolfbeis for fruitful discussions.
References (99)
- et al.
Sensors Actuators B
(1991) - et al.
Biosens. Bioelectron
(1997) - et al.
Biosens. Bioelectron
(1996) - et al.
Trends Anal. Chem.
(2000) - et al.
Anal. Chim. Acta
(2001) - et al.
Trends Anal. Chem.
(1999) Biosens. Bioelectron
(1995)- et al.
Trends Biotechnol
(1995) - et al.
Colloids Surf. B
(1999) - et al.
Chem.
(2000)
Chem.
Chem., Interfacial Electrochem
Chem.
Chem.
Chem.
Chem.
Anal. Chim. Acta
Trends Anal. Chem.
Curr. Opin. Biotechnol
Trends Biotechnol
Sens. Actuators, B
Chem.
Electrochim. Acta
Synth. Met
Sens. Actuators B
Appl. Surf. Sci.
Anal. Chim. Acta
Anal. Chim. Acta
Langmuir
Langmuir
Anal. Letters
Anal. Chem.
Adv. Mater.
Acc. Chem. Res.
Ann. N.Y. Acad. Sci.
Electroanal. Chem.
Adv. Mater.
Acc. Chem. Res.
Annu. Rev. Biophys. Biomol. Struct
ChemPhysChem.
Angew. Chem., Int. Ed
Adv. Mater.
Anal. Chem.
Electroanalysis
Langmuir
Mikrochim. Acta
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2018, Sensors and Actuators, B: ChemicalCitation Excerpt :Self-assembly is a widely used surface modification technique for biochemical applications. This technology is usually applied by several driving forces, including electrostatic interactions, coordination bonds, hydrogen bonds, covalent bonds, and ligand bonds [30,31]. Due to the high sensitivity of FBAR, the self-assembled monolayers or multilayers are the most appropriate sensitive coating for the detection of trace gases because of its ultra-small thickness and very fast adsorption of gas molecules.