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The possibility of lateral extension of conjugation withina covalentlygrafted molecular layer by a scanning probe-based method was tested.A molecular layer derived from ω-(N-pyrrolyl)propanolwas formed on n-type Si(111) surface. Application of large samplebiases greater than ±4 V during conductive atomic force microscope(AFM) scans under vacuum resulted in changes of mechanical and electricalcharacteristics of the molecular layer: the tip–sample conductancewas increased greatly, the friction was reduced significantly, andthe surface potential of the scanned area was increased. The reductionin friction could be attributed to molecular linking formed withinthe layer. The increased conductance suggested extended conjugationamong the pyrrolyl end groups. Therefore, it was inferred that thebiased AFM scan successfully induced local polymerization/oligomerizationwithin the covalently grafted molecular layer. [ABSTRACT FROM AUTHOR]

A label-free, activity-based assay of matrix metalloproteinase (MMP) and its inhibition was demonstrated on peptide-conjugated gold nanoparticles (AuNPs) with nonbiofouling poly(ollgo(ethylene glycol) methacrylate) (pOEGMA) films using time-of-flight secondary ion mass spectrometry (FOF-SIMS). Following surface-initiated atom-transfer radical polymerization of OEGMA on a Si/SiO2 substrate, the MMP activity was determined by analyzing the cleaved peptide fragments using TOF-SIMS on the peptide-conjugated AuNPs. The use of nonbiofouling pOEGMA films in conjunction with AuNPs synergistically enhanced the sensitivity of assays for MMP activity and its inhibition in human serum. The detection sensitivity of MMP-7 in serum was as low as 20 ng mL-1 (1 pmol mL-1), and the half-maximal inhibitory concentration (1C50) of minocycline, which is a MMP-7 inhibitor, was estimated to be 450 nM. It is anticipated that the developed system will be broadly useful for conducting activity-based assays of serum proteases, as well as for screening of their inhibitors, with high sensitivity in a high-throughput manner. [ABSTRACT FROM AUTHOR]