6.4 Non-specific Adsorption (NSA)
115
6.4 Non-specific Adsorption (NSA)
It is established that the PEG grafting density, in addition to the molar mass, is an
important factor for the inhibition of NSA of various types of biomolecules [27].
As shown above, the grafting density of PEG 500 -NH 2 on PNHSMA films can be
conveniently controlled by changing the reaction (stamp–film contact) time. The
effectiveness of blocking the polymer layer against covalent coupling (and/ or NSA)
of solution-borne nucleophiles was consequently tested as a function of PEG 500 -NH 2
grafting thickness with fluoresceinamine and with dye-labeled BSA by fluorescence
microscopy. Figure 6.3 shows the decrease of the fluorescence emission intensity of
fluoresceinamine and BSA, respectively, on PNHSMA films for different PEG 500 -
NH 2 grafting thicknesses. Without any PEG coating, strong fluorescence emission
was observed in both cases indicating a significant coverage of the corresponding
fluorescent adsorbate. Increasing reaction times in the reactive μCP step using a
featureless stamp (i.e., increasing thickness of the grafted PEG 500 -NH 2 layers) were
found to lead to a significant reduction of adsorbate coverage. For the maximum
PEG 500 -NH 2 grafting thickness of 1.8 nm, the ratio of the observed fluorescence
emission intensity vs. the background fluorescence of neat PNHSMA was found to
be only 1.5. Hence it can be concluded at this point that the grafted PEG layers with
1.8 nm thickness inhibit the immobilization of fluoresceinamine and BSA effectively.
Fig. 6.3 Plots of integrated fluorescence emission intensity (the PEG thickness was determined by
ellipsometry for each coupling time) of PEG-functionalized PNHSMA films treated with a fluoresceinamine; b BSA for 30 min followed by rinsing with PB buffer (pH 7.4) and drying versus
reaction (stamp–film contact) time/ PEG thickness. The insets show representative fluorescence
microscopy images acquired for the corresponding samples (image size: 145 × 145 μm 2 )
115
6.4 Non-specific Adsorption (NSA)
It is established that the PEG grafting density, in addition to the molar mass, is an
important factor for the inhibition of NSA of various types of biomolecules [27].
As shown above, the grafting density of PEG 500 -NH 2 on PNHSMA films can be
conveniently controlled by changing the reaction (stamp–film contact) time. The
effectiveness of blocking the polymer layer against covalent coupling (and/ or NSA)
of solution-borne nucleophiles was consequently tested as a function of PEG 500 -NH 2
grafting thickness with fluoresceinamine and with dye-labeled BSA by fluorescence
microscopy. Figure 6.3 shows the decrease of the fluorescence emission intensity of
fluoresceinamine and BSA, respectively, on PNHSMA films for different PEG 500 -
NH 2 grafting thicknesses. Without any PEG coating, strong fluorescence emission
was observed in both cases indicating a significant coverage of the corresponding
fluorescent adsorbate. Increasing reaction times in the reactive μCP step using a
featureless stamp (i.e., increasing thickness of the grafted PEG 500 -NH 2 layers) were
found to lead to a significant reduction of adsorbate coverage. For the maximum
PEG 500 -NH 2 grafting thickness of 1.8 nm, the ratio of the observed fluorescence
emission intensity vs. the background fluorescence of neat PNHSMA was found to
be only 1.5. Hence it can be concluded at this point that the grafted PEG layers with
1.8 nm thickness inhibit the immobilization of fluoresceinamine and BSA effectively.
Fig. 6.3 Plots of integrated fluorescence emission intensity (the PEG thickness was determined by
ellipsometry for each coupling time) of PEG-functionalized PNHSMA films treated with a fluoresceinamine; b BSA for 30 min followed by rinsing with PB buffer (pH 7.4) and drying versus
reaction (stamp–film contact) time/ PEG thickness. The insets show representative fluorescence
microscopy images acquired for the corresponding samples (image size: 145 × 145 μm 2 )