Patterned poly(acrylic acid)brushes containing metal nanoparticles for peptide detection by surface assisted laser desorption ionization-mass spectrometry

Abstract

Patterned poly(acrylic acid) (PAA) brushes was successfully generated via photolithography and surface-initiated reversible addition-fragmentation chain transfer (RAFT) polymerization of acid as verified by water contact angle measurements and FT-IR analysis. The carboxyl groups of PAA brushes can act as reducing moieties for in situ synthesis of gold nanoparticles (AuNPs), without the use of additional reducing agent. Under the condition investigated, the AuNPs were both in the well dispersed spherical particles (i.d. 18.45 + 2.34 nm) and aggregated Particles with surface coverage of 2.46 x 10-9 mol/cm2. The glass surface-modified PAA brushes immobilized with AuNPs (AuNPs-PAA) can be used as substrate for SALDI-MS analysis which is capable of detecting both small peptide having m/z  600 (glutathione) and large peptides having m/z  (bradykinin, ICNKQDCPILE) within the interference from matrix signal suggesting that AuNPs were stably trapped within the PAA brushes and the carboxyl groups of PAA can serve as internal proton source. By employing AuNPs as the capture probe, the AuNPs-PAA substrate can selectively identify thiol-containing peptides from the peptide mixtures with LOD as low as 0.1 and 0.05 nM for glutathione and ICNKQDCPILE, respectively. The patterned format together with its high sensitivity and selectivity render this newly developed substrate a potential platform for high throughput analysis of other biomarkers especially those with low molecular weight in complex biological samples.