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4 Reactive Thin Polymer Films as Platforms for the Immobilization …
techniques. However, an important part of the biosensor design is the (bio)chemical
nature of the interfacial layer at the sensor surface, which affords specific biorecognition reactions with high affinity-binding sites. Surface chemical reactions are
similarly important for various biological applications [3], such as the fabrication of
gene [4, 5] or protein chips [6].
Self-assembled monolayers (SAMs) have been successfully applied as platform
for the fabrication of sensing surfaces in biosensors [7]. The limitation of these films
is that they can only provide a 2D architecture of affinity-binding sites on the surface
and hence limited surface coverages (see Chap. 2). In these and related approaches,
the ability to introduce versatile chip interfaces and to control the immobilization of
biomolecules represents a crucial point due to the interplay of organization on the
molecular scale and reactivity in the confinement of organized organic thin films
[8]. These effects result in difficulties to achieve high densities of immobilized
biomolecules in their functional or optimized oriented form.
As an alternative method to obtain reactive platforms, the deposition of polymeric materials onto solid substrates receives increasing attention [9]. Using electrografting, Jérôme et al. have prepared reactive surfaces bearing activated ester
groups, which are highly reactive toward nucleophiles. This reactivity makes the
electrografted coating appropriate for anchoring of a large variety of molecules
[10]. Other polymer-based systems and approaches [11] to overcome the mentioned
intrinsic limitations of 2D platforms comprise hydrogels [12], dendrimers [13],
hyperbranched polymers [14], chemical vapor deposition approaches [15], selfassembled polyelectrolyte multilayers [16], plasma polymers [17], and polymer
brushes obtained by grafting-from approaches.
In Chap. 3, the analysis of hydrolysis reactions of simple reactive PNHSMA
ultrathin films and related SAMs showed that the reaction proceeds also into the
surface-near region of the polymer films (<10 nm depth), implying an enhanced
coverage of immobilized guest molecules in coupling reactions compared to SAMs.
In addition, the reaction kinetics may be significantly retarded for SAMs due to more
pronounced confinement. Hence reactive coatings based on PNHSMA may allow
one to couple many more (bio)molecules per unit area compared to a monolayer
(Scheme 4.1). PNHSMA and related polymer films, such as polystyrene-b-poly(tertbutyl acrylate) (see Chaps. 3 and 5), can be easily obtained, e.g., by spin-coating. The
film thickness of such polymer films can be precisely adjusted (via concentration of
the polymer solution and/or the spinning speed) so that quenching of fluorescence
due to energy transfer to the underlying metal substrate [18] can be avoided during
signal detection. Thus, an optimum sensitivity enhancement in, e.g., surface plasmon
resonance-enhanced fluorescence spectroscopy (SPFS), can be achieved [19].
In this chapter, the investigation of thin PNHSMA films as platforms for the
coupling of biomolecules for potential application in robust, high-loading biosensors is discussed. The coupling of PEG 500 -NH 2 , proteins (BSA), and probe DNA,
as well as its hybridization with target DNA, was studied to confirm an increased
(bio)molecular loading on the one hand and controlled swelling and layer stability on
the other hand. These properties render PNHSMA and related polymer films suitable
for applications involving the immobilization of biomolecules with high molecular
4 Reactive Thin Polymer Films as Platforms for the Immobilization …
techniques. However, an important part of the biosensor design is the (bio)chemical
nature of the interfacial layer at the sensor surface, which affords specific biorecognition reactions with high affinity-binding sites. Surface chemical reactions are
similarly important for various biological applications [3], such as the fabrication of
gene [4, 5] or protein chips [6].
Self-assembled monolayers (SAMs) have been successfully applied as platform
for the fabrication of sensing surfaces in biosensors [7]. The limitation of these films
is that they can only provide a 2D architecture of affinity-binding sites on the surface
and hence limited surface coverages (see Chap. 2). In these and related approaches,
the ability to introduce versatile chip interfaces and to control the immobilization of
biomolecules represents a crucial point due to the interplay of organization on the
molecular scale and reactivity in the confinement of organized organic thin films
[8]. These effects result in difficulties to achieve high densities of immobilized
biomolecules in their functional or optimized oriented form.
As an alternative method to obtain reactive platforms, the deposition of polymeric materials onto solid substrates receives increasing attention [9]. Using electrografting, Jérôme et al. have prepared reactive surfaces bearing activated ester
groups, which are highly reactive toward nucleophiles. This reactivity makes the
electrografted coating appropriate for anchoring of a large variety of molecules
[10]. Other polymer-based systems and approaches [11] to overcome the mentioned
intrinsic limitations of 2D platforms comprise hydrogels [12], dendrimers [13],
hyperbranched polymers [14], chemical vapor deposition approaches [15], selfassembled polyelectrolyte multilayers [16], plasma polymers [17], and polymer
brushes obtained by grafting-from approaches.
In Chap. 3, the analysis of hydrolysis reactions of simple reactive PNHSMA
ultrathin films and related SAMs showed that the reaction proceeds also into the
surface-near region of the polymer films (<10 nm depth), implying an enhanced
coverage of immobilized guest molecules in coupling reactions compared to SAMs.
In addition, the reaction kinetics may be significantly retarded for SAMs due to more
pronounced confinement. Hence reactive coatings based on PNHSMA may allow
one to couple many more (bio)molecules per unit area compared to a monolayer
(Scheme 4.1). PNHSMA and related polymer films, such as polystyrene-b-poly(tertbutyl acrylate) (see Chaps. 3 and 5), can be easily obtained, e.g., by spin-coating. The
film thickness of such polymer films can be precisely adjusted (via concentration of
the polymer solution and/or the spinning speed) so that quenching of fluorescence
due to energy transfer to the underlying metal substrate [18] can be avoided during
signal detection. Thus, an optimum sensitivity enhancement in, e.g., surface plasmon
resonance-enhanced fluorescence spectroscopy (SPFS), can be achieved [19].
In this chapter, the investigation of thin PNHSMA films as platforms for the
coupling of biomolecules for potential application in robust, high-loading biosensors is discussed. The coupling of PEG 500 -NH 2 , proteins (BSA), and probe DNA,
as well as its hybridization with target DNA, was studied to confirm an increased
(bio)molecular loading on the one hand and controlled swelling and layer stability on
the other hand. These properties render PNHSMA and related polymer films suitable
for applications involving the immobilization of biomolecules with high molecular