5.5 Experimental Section
105
Film preparation: Polymer films were prepared by spin-coating polymer solutions
in toluene (conc. 10 mg/ml) onto oxygen plasma cleaned silicon wafers. The samples
were spun at 3000 rpm for 30 s using a P6700 spin coater (Specialty Coating Systems
Inc). All spin-coated samples were annealed at 135 °C for 24 h in vacuum before
analysis. Mean film thickness were determined by a custom-built spectroscopic ellipsometer using a He–Ne (λ = 632.8 nm) laser. The refractive index of the polymer
film was approximated as 1.48.
Hydrolysis: In solution: The polymer films were hydrolyzed in neat trifluoroacetic
acid for 20 min. For gas-phase hydrolysis, the samples were exposed to acid vapors
of 6 M HCl by placing them 10 mm above the liquid surface in a closed beaker.
All experiments were performed at room temperature. At specified time intervals,
samples were removed from the beaker. All hydrolyzed films were rinsed three times
using Milli-Q water, and finally dried in a stream of nitrogen.
Activation of Hydrolyzed Polymer Films. The COOH groups on polymer films
after hydrolysis were activated by immersion in an aqueous solution of 1-ethyl3-(dimethylamino)-propylcarbodiimide (EDC, 1 M) and N-hydroxysuccinimide
(NHS, 0.2 M) for 30 min. The samples were then rinsed with Milli-Q water, dried in
a stream of nitrogen, and used immediately thereafter.
Immobilization of (Bio)Molecules on Polymer Films. For PEG coupling from
solution, the polymer films were immersed into the corresponding PEG-NH 2 solution
(100 μM PEG solution, PB, pH = 7.4). After a reaction time between 5 min and
10 h, the samples were taken out of the corresponding solution and thoroughly rinsed
with Milli-Q water. BSA and PLL were immersed into the corresponding solution
(100 μM, PB, pH = 7.4). DNA immobilization (100 nM) in phosphate buffer was
carried out in the same procedure as for PEG coupling. Afterwards, the hybridization
of target DNA with dye (100 nM) was followed in phosphate buffer. Then the films
were rinsed with PB (pH = 7.4) and Milli-Q water, and dried in a nitrogen stream.
All experiments were carried out at T = 25 ± 2°.
X-ray Photoelectron Spectroscopy (XPS). XPS spectra were recorded on a PHI
Quantum 2000 Scanning ESCA microprobe using a monochromated X-ray beam
(Al-anode); 100 μm diameter/25 watts X-ray beam scanned over 700 μm × 300 μm
area take-off angle of 45°. Atomic concentrations were determined by numerical
integration of the relative peak areas using the Multipak software with supplied
sensitivity factors (C 1s : 0.314; O 1s : 0.733; N 1s : 0.499) [16].
AFM Experiment: The AFM measurements were carried out with a NanoScope X
multimode AFM (Digital Instruments, Santa Barbara, CA) using a 10 μm scanner.
Tapping mode AFM scans were performed with silicon cantilevers/tips (Nanosensors, Wetzlar, Germany) in air. The instrument was operated at frequencies slightly
lower than the natural resonance frequency of the cantilever in air, and the free amplitude was kept constant. The amplitude-damping (setpoint) ratio was adjusted to ≈
0.9.
105
Film preparation: Polymer films were prepared by spin-coating polymer solutions
in toluene (conc. 10 mg/ml) onto oxygen plasma cleaned silicon wafers. The samples
were spun at 3000 rpm for 30 s using a P6700 spin coater (Specialty Coating Systems
Inc). All spin-coated samples were annealed at 135 °C for 24 h in vacuum before
analysis. Mean film thickness were determined by a custom-built spectroscopic ellipsometer using a He–Ne (λ = 632.8 nm) laser. The refractive index of the polymer
film was approximated as 1.48.
Hydrolysis: In solution: The polymer films were hydrolyzed in neat trifluoroacetic
acid for 20 min. For gas-phase hydrolysis, the samples were exposed to acid vapors
of 6 M HCl by placing them 10 mm above the liquid surface in a closed beaker.
All experiments were performed at room temperature. At specified time intervals,
samples were removed from the beaker. All hydrolyzed films were rinsed three times
using Milli-Q water, and finally dried in a stream of nitrogen.
Activation of Hydrolyzed Polymer Films. The COOH groups on polymer films
after hydrolysis were activated by immersion in an aqueous solution of 1-ethyl3-(dimethylamino)-propylcarbodiimide (EDC, 1 M) and N-hydroxysuccinimide
(NHS, 0.2 M) for 30 min. The samples were then rinsed with Milli-Q water, dried in
a stream of nitrogen, and used immediately thereafter.
Immobilization of (Bio)Molecules on Polymer Films. For PEG coupling from
solution, the polymer films were immersed into the corresponding PEG-NH 2 solution
(100 μM PEG solution, PB, pH = 7.4). After a reaction time between 5 min and
10 h, the samples were taken out of the corresponding solution and thoroughly rinsed
with Milli-Q water. BSA and PLL were immersed into the corresponding solution
(100 μM, PB, pH = 7.4). DNA immobilization (100 nM) in phosphate buffer was
carried out in the same procedure as for PEG coupling. Afterwards, the hybridization
of target DNA with dye (100 nM) was followed in phosphate buffer. Then the films
were rinsed with PB (pH = 7.4) and Milli-Q water, and dried in a nitrogen stream.
All experiments were carried out at T = 25 ± 2°.
X-ray Photoelectron Spectroscopy (XPS). XPS spectra were recorded on a PHI
Quantum 2000 Scanning ESCA microprobe using a monochromated X-ray beam
(Al-anode); 100 μm diameter/25 watts X-ray beam scanned over 700 μm × 300 μm
area take-off angle of 45°. Atomic concentrations were determined by numerical
integration of the relative peak areas using the Multipak software with supplied
sensitivity factors (C 1s : 0.314; O 1s : 0.733; N 1s : 0.499) [16].
AFM Experiment: The AFM measurements were carried out with a NanoScope X
multimode AFM (Digital Instruments, Santa Barbara, CA) using a 10 μm scanner.
Tapping mode AFM scans were performed with silicon cantilevers/tips (Nanosensors, Wetzlar, Germany) in air. The instrument was operated at frequencies slightly
lower than the natural resonance frequency of the cantilever in air, and the free amplitude was kept constant. The amplitude-damping (setpoint) ratio was adjusted to ≈
0.9.