2 research outputs found
Effects of Polythiophene Surface Structure on Adsorption and Conformation of Bovine Serum Albumin: A Multivariate and Multitechnique Study
Protein interactions with surfaces
of promising conducting polymers
are critical for development of bioapplications. Surfaces of spin-cast
and postbaked polyÂ(3-alkylthiophenes), regiorandom P3BT, and regioregular
RP3HT are examined prior to and after adsorption of model protein,
bovine serum albumin, with time-of-flight secondary ion mass spectrometry,
atomic force microscopy, and X-ray photoelectron spectroscopy. The
multivariate method of principal component analysis applied to ToF-SIMS
data maximizes information on subtle differences in surface chemistry:
PCA reveals alkyl side chains and conjugated backbones, exposed for
RP3HT and P3BT, respectively. Phase imaging AFM shows semicrystalline
microstructure of RP3HT and amorphous morphology of P3BT films. A
cellular-like pattern of proteins adsorbed on RP3HT develops with
coverage to more uniform overlayer, observed always on P3BT. The amount
of adsorbed protein, determined by XPS as a function of BSA concentration
(up to 10 mg/mL), is ∼21% lower for RP3HT than P3BT (up to
1.1 mg/m<sup>2</sup>). Although PCA differentiates protein from polythiophene,
relative protein surface composition evaluated from ToF-SIMS saturates
rather than increases with amount of adsorbed BSA from XPS. This reflects
ToF-SIMS sensitivity to outermost layer of proteins, enabling multivariate
analysis of protein conformation or orientation. PCA distinguishes
between amino acids characteristic for external regions of BSA adsorbed
to P3BT and RP3HT. These amino acids are identified for P3BT and RP3HT
as hydrophilic and hydrophobic, respectively, by relative hydrophobicity
of amino acid side chains. Alternative identification with BSA domains
fails, pointing to substrate-induced changes in conformation and degree
of denaturation rather than orientation of adsorbed protein
Plasma-Assisted Nanoscale Protein Patterning on Si Substrates via Colloidal Lithography
Selective immobilization of proteins
in well-defined patterns on
substrates has recently attracted considerable attention as an enabling
technology for applications ranging from biosensors and BioMEMS to
tissue engineering. In this work, a method is reported for low-cost,
large scale and high throughput, selective immobilization of proteins
on nanopatterned Si, based on colloidal lithography and plasma processing
to define the areas (<300 nm) where proteins are selectively immobilized.
A close-packed monolayer of PS microparticles is deposited on oxidized
Si and, either after microparticle size reduction or alternatively
after metal deposition through the PS close-packed monolayer, is used
as etching mask to define SiO<sub>2</sub> nanoislands (on Si). C<sub>4</sub>F<sub>8</sub> plasma was used to selectively etch and modify
the SiO<sub>2</sub> nanoislands while depositing a fluorocarbon layer
on the Si surface. The plasma-treated surfaces were chemically characterized
in terms of functional group identification through XPS analysis and
reaction with specific molecules. Highly selective protein immobilization
mainly through physical adsorption on SiO<sub>2</sub> nanoislands
and not on surrounding Si was observed after C<sub>4</sub>F<sub>8</sub> plasma-induced chemical modification of the substrate. The thickness
of the immobilized protein monolayer was estimated by means of AFM
image analysis. The method reported herein constitutes a cost-efficient
route toward rapid, large surface, and high-density patterning of
biomolecules on solid supports that can be easily applied in BioMEMS
or microanalytical systems