Aptamer-Controlled Reversible Inhibition of Gold Nanozyme Activity for Pesticide Sensing

This study addresses the need for rapid pesticide (acetamiprid) detection by reporting a new colorimetric biosensing assay. Our approach combines the inherent peroxidase-like nanozyme activity of gold nanoparticles (GNPs) with high affinity and specificity of an acetamiprid-specific S-18 aptamer to detect this neurotoxic pesticide in a highly rapid, specific, and sensitive manner. It is shown that the nanozyme activity of GNPs can be inhibited by its surface passivation with target-specific aptamer molecules. Similar to an enzymatic competitive inhibition process, in the presence of a cognate target, these aptamer molecules leave the GNP surface in a target concentration-dependent manner, reactivating GNP nanozyme activity. This reversible inhibition of the GNP nanozyme activity can either be directly visualized in the form of color change of the peroxidase reaction product or can be quantified using UV–visible absorbance spectroscopy. This approach allowed detection of 0.1 ppm acetamiprid within an assay time of 10 min. This reversible nanozyme activation/inhibition strategy may in principle be universally applicable for the detection of a range of environmental or biomedical molecules of interest

Role of the Templating Approach in Influencing the Suitability of Polymeric Nanocapsules for Drug Delivery: LbL vs SC/MS

Polymer nanocapsules play an increasingly important role for drug delivery applications. Layer-by-layer (LbL) templated synthesis has received the widest attention to fabricate polymer nanocapsules. However, for drug delivery applications, the LbL approach may not necessarily offer the optimum nanocapsules. We make the first attempt to compare the LbL approach with a more recently developed solid core/mesoporous shell (SC/MS) templated approach in context of their suitability for construction of sub-500 nm sized capsules for drug delivery applications. The nanocapsules of chitosan, poly­(allylamine hydrochloride) (PAH), and poly­(sodium 4-styrenesulfonate) (PSS) are fabricated using LbL and SC/MS templating approaches and loaded with curcumin, a model lipophilic anticancer drug. The influence of the templating approach on capsule aggregation, polymer loading, drug loading, cellular uptake, and therapeutic efficacy against MCF-7 breast cancer cells is compared in an effort to identify the most suitable fabrication method and polymer material for drug delivery applications. In combination, among different tested nanocapsules, chitosan nanocapsules fabricated using the SC/MS approach are found to be the most promising candidate that demonstrates the optimum cytotoxic efficiency and significant potential for drug delivery

Fine-Tuning the Antimicrobial Profile of Biocompatible Gold Nanoparticles by Sequential Surface Functionalization Using Polyoxometalates and Lysine

<div><p>Antimicrobial action of nanomaterials is typically assigned to the nanomaterial composition, size and/or shape, whereas influence of complex corona stabilizing the nanoparticle surface is often neglected. We demonstrate sequential surface functionalization of tyrosine-reduced gold nanoparticles (AuNPs^Tyr) with polyoxometalates (POMs) and lysine to explore controlled chemical functionality-driven antimicrobial activity. Our investigations reveal that highly biocompatible gold nanoparticles can be tuned to be a strong antibacterial agent by fine-tuning their surface properties in a controllable manner. The observation from the antimicrobial studies on a gram negative bacterium <i>Escherichia coli</i> were further validated by investigating the anticancer properties of these step-wise surface-controlled materials against A549 human lung carcinoma cells, which showed a similar toxicity pattern. These studies highlight that the nanomaterial toxicity and biological applicability are strongly governed by their surface corona.</p> </div

SEM micrographs of <i>E. coli</i> bacterial cells before (A) and after treatments with AuNPs^Tyr (B), AuNPs^Tyr@PTA (C), AuNPs^Tyr@PTA-Lys (D), AuNPs^Tyr@PMA (E) and AuNPs^Tyr@PMA-Lys (F).

<p>Scale bars correspond to 1 μm and the regions of damage in treated bacterial cells have been shown by arrows.</p

Schematic representation of the summary outcome of this work showing increase in antimicrobial activity of AuNPs after their sequential functionalization with POMs and lysine.

<p>Schematic representation of the summary outcome of this work showing increase in antimicrobial activity of AuNPs after their sequential functionalization with POMs and lysine.</p

UV-visible absorbance spectra (A) and TEM images of AuNPs^Tyr (a), AuNPs^Tyr@PTA (b), AuNPs^Tyr@PTA-Lys (c), AuNPs^Tyr@PMA (d) and AuNPs^Tyr@PMA-Lys (e) with scale bars of 50 nm.

<p>The UV-vis absorbance spectra of pristine PTA and PMA molecules are also shown. Particle size distribution histograms (B-F) correspond to TEM images shown in (a-e), respectively. </p

Dose-dependent cytotoxicity profile of AuNPs^Tyr (1), AuNPs^Tyr@PTA (2) and AuNPs^Tyr@PTA-Lys (3) against A549 human lung carcinoma cells.

<p>Dose-dependent cytotoxicity profile of AuNPs^Tyr (1), AuNPs^Tyr@PTA (2) and AuNPs^Tyr@PTA-Lys (3) against A549 human lung carcinoma cells.</p

Schematic representation of tyrosine-mediated synthesis of gold nanoparticles (AuNPs^Tyr), followed by their sequential surface functionalization with POMs (PTA or PMA) and lysine (Lys).

<p>Schematic representation of tyrosine-mediated synthesis of gold nanoparticles (AuNPs^Tyr), followed by their sequential surface functionalization with POMs (PTA or PMA) and lysine (Lys).</p

Antibacterial profile of PTA and PMA functionalized materials against <i>E. coli</i> are shown in Panels A and B, respectively.

<p>Curves 1 and 2 correspond to control bacterial cells (1) and AuNPs^Tyr (2), respectively. Curves 3 and 4 correspond to AuNPs^Tyr@PTA (3A), AuNPs^Tyr@PTA-Lys (a), AuNPs^Tyr@PMA (3B) and AuNPs^Tyr@PMA-Lys (4B). Doses on the x-axis correspond to either W (Panel A) or Mo (Panel B), except in curves 2, where it corresponds to equivalent amount of Au as that present in respective curves 4.</p

Protocols for obtaining immobilized cells for SEM.

<p>(A) Add cell suspension into the PDMS chamber. (B) Apply electric field and immobilize cells between the microelectrodes. Immobilized cell density can be adjusted by varying the electric field application period. (C) Dry the suspension with a lint-free cotton wipe. (D) Add media containing chemicals into the PDMS chamber for cell treatment. (E) Dry the medium with a lint-free cotton wipe. (F) Add dehydration solutions to the PDMS chamber. (G) Dry the dehydration solutions with a lint-free cotton wipe. Turn off the electric field and leave the sample for 10 minutes at room temperature to let the remained medium evaporate. (H) The sample is ready for SEM when all liquid is evaporated. Scale bar is 100 µm.</p