We
report the reversible aggregation of silver nanoparticle (AgNP)
assemblies using the combination of a cationic arginine-based peptide
and sulfur-capped polyethylene glycol (PEG). The formation and dissociation
of the aggregates were studied by optical methods and electron microscopy.
The dissociation of silver clusters depends on the peptide sequence
and PEG size. A molecular weight of 1 kDa for PEG was optimal for
the dissociation. The most important feature of this dissociation
method is that it can operate in complex biofluids such as plasma,
saliva, bile, urine, cell media, or even seawater without a significant
decrease in performance. Moreover, the peptide–particle assemblies
are highly stable and do not degrade (or express of loss of signal
upon dissociation) when dried and resolubilized, frozen and thawed,
or left in daylight for a month. Importantly, the dissociation capacity
of PEG can be reduced via the conjugation of a peptide-cleavable
substrate. The dissociation capacity is restored in the presence of
an enzyme. Based on these findings, we designed a PEG-peptide hybrid
molecule specific to the Porphyromonas gingivalis protease RgpB. Our motivation was that this bacterium is a key pathogen
in periodontitis, and RgpB activity has been correlated with chronic
diseases including Alzheimer’s disease. The RgpB limit of detection
was 100 pM RgpB in vitro. This system was used to
measure RgpB in gingival crevicular fluid (GCF) samples with a detection
rate of 40% with 0% false negatives versus PCR for P. gingivalis (n = 37). The combination of PEG-peptide and nanoparticles
dissociation method allows the development of convenient protease
sensing that can operate independently of the media composition.