Understanding the interaction of capping molecules with
inorganic
nanozymes to modulate catalytic activity is of great interest because
it could bring them one step closer to natural enzymes. This study
demonstrates the ability of l-cysteine (Cys) to modulate
the enzymatic activity of nanozymes by varying their thickness on
nanoparticle surfaces. The Cys-functionalized Ru nanoparticles in
chain-like two-dimensional nanostructures (Cys-Ru NSs) with excellent
peroxidase-like activity were synthesized using a one-pot wet chemical
method. Surprisingly, Cys tunes the peroxidase-like activity of Cys-Ru
NSs at a specific concentration. Furthermore, Cys excels at controlling
the surface properties of Ru nanoparticles, which induces nanoparticle
self-assembly and improves colloidal dispersion and stability. A colorimetric
assay for lysophosphatidylcholine (LPC) detection was developed by
combining hydrogen peroxide produced by enzymatic oxidation of LPC
with Cys-Ru NS-catalyzed 3,3′,5,5′-tetramethylbenzidine
oxidation. The colorimetric assay demonstrated a broad linear detection
range of 10–800 μM with a regression constant of 0.99
and a limit of detection of 10 μM. These colorimetric changes
can be seen with the naked eye. In addition, the assay showed good
specificity and 106.1–118.1% recovery of LPC from spiked human
serum samples. The present Cys-Ru NS-based LPC assay is an excellent
way to overcome the shortcomings of existing LPC assays, which does
not require expensive equipment, skilled technicians, and lengthy
analysis times.