Aptamer Clicked Poly(ferrocenylsilanes) at Au Nanoparticles as Platforms with Multiple Function[†].

Aptamers are widely used in biosensing due to their specific sensitivity toward many targets. Thus, gold nanoparticle (AuNP) aptasensors are subject to intense research due to the complementary properties of aptamers as sensing elements and AuNPs as transducers. We present herein a novel method for the functional coupling of thrombin-specific aptamers to AuNPs via an anionic, redox-active poly(ferrocenylsilane) (PFS) polyelectroyte. The polymer acts as a co-reductant and stabilizer for the AuNPs, provides grafting sites for the aptamer, and can be used as a redox sensing element, making the aptamer-PFS-AuNP composite (aptamer-AuNP) a promising model system for future multifunctional sensors. The aptamer-AuNPs exhibit excellent colloidal stability in high ionic strength environments owing to the combined electrosteric stabilizing effects of the aptamer and the PFS. The synthesis of each assembly element is described, and the colloidal stability and redox responsiveness are studied. As an example to illustrate applications, we present results for thrombin sensitivity and specificity using the specific aptamer.

Formulation of Antioxidant Composites by Controlled Heteroaggregation of Cerium Oxide and Manganese Oxide Nanozymes.

Antioxidant composites based on nanozymes [manganese oxide microflakes (MnO2 MFs) and cerium oxide nanoparticles (CeO2 NPs)] were formulated by controlled heteroaggregation. The interparticle attraction via electrostatic forces was systematically tuned with surface functionalization by the poly(diallyldimethyl chloride) (PDADMAC) polyelectrolyte. The PDADMAC-coated MnO2 MFs (PMn) were heteroaggregated with oppositely charged CeO2 NPs to generate the Ce-PMn composite, while the PDADMAC-functionalized CeO2 NPs (PCe) were immobilized onto bare MnO2 MFs, resulting in the Mn-PCe composite. Both the adsorption of PDADMAC and the self-assembly of oppositely charged particles resulted in charge neutralization and charge reversal at appropriately high doses. The interparticle force regimes, the aggregation states, and the physicochemical properties of the relevant dispersions were also highly dependent on the dose of PDADMAC, as well as that of PDADMAC-functionalized metal oxides (PMO) enabling the fine-tuning and control of colloidal stability. The individual enzyme-like activity of either metal oxide was not compromised by PDADMAC adsorption and/or heteroaggregation, leading to the formation of broad-spectrum antioxidant composites exhibiting multiple enzyme-like activities such as superoxide dismutase, oxidase, and peroxidase-type functions. The low cost and ease of preparation, as well as controllable colloidal properties render such composites potential enzyme mimicking agents in various industrial fields, where processable antioxidant systems are needed.

Dual functionality of ferrocene-based metallopolymers as radical scavengers and nanoparticle stabilizing agents.

The beneficial redox properties of ferrocene-based polymers have been utilized during in situ preparation of metallic nanoparticles, while such redox features also indicate a great promise in applications as free radical scavengers. Here, colloidal dispersions of an antioxidant nanozyme composed of amidine-functionalized polystyrene latex (AL) nanoparticles, negatively charged poly(ferrocenylsilane) (PFS(-)) organometallic polyions, and ascorbic acid (AA) were formulated. The AL was first functionalized with PFS(-). Increasing the polymer dose resulted in charge neutralization and subsequent charge reversal of the particles. The strength of repulsive interparticle forces of electrostatic nature was significant at low and high doses leading to stable colloids, while attractive forces dominated near the charge neutralization point giving rise to unstable dispersions. The saturated PFS(-) layer adsorbed on the surface of the AL (p-AL nanozyme) enhanced the colloidal stability against salt-induced aggregation without affecting the pH-dependent charge and size of the particles. The joint effect of PFS(-) and the AA in radical decomposition was observed indicating the antioxidant potential of the system. The immobilization of PFS(-) deteriorated its scavenging activity, yet the combination with AA improved this feature. The results indicate that p-AL-AA is a promising radical scavenger since the high colloidal stability of the particles allows application in heterogeneous systems, such as in industrial manufacturing processes, where antioxidants are required to maintain acceptable product quality.

Antioxidant colloids via heteroaggregation of cerium oxide nanoparticles and latex beads.

Antioxidant colloids were developed via controlled heteroaggregation of cerium oxide nanoparticles (CeO2 NPs) and sulfate-functionalized polystyrene latex (SL) beads. Positively charged CeO2 NPs were directly immobilized onto SL particles of opposite surface charge via electrostatic attraction (SL/Ce composite), while negatively charged CeO2 NPs were initially functionalized with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte and then, aggregated with the SL particles (SPCe composite). The PDADMAC served to induce a charge reversal on CeO2 NPs, while the SL support prevented nanoparticle aggregation under conditions, where the dispersions of bare CeO2 NPs were unstable. Both SL/Ce and SPCe showed enhanced radical scavenging activity compared to bare CeO2 NPs and were found to mimic peroxidase enzymes. The results demonstrate that SL beads are suitable supports to formulate CeO2 particles and to achieve remarkable dispersion storage stability. The PDADMAC functionalization and immobilization of CeO2 NPs neither compromised the peroxidase-like activity nor the radical scavenging potential. The obtained SL/Ce and SPCe artificial enzymes are foreseen to be excellent antioxidant agents in various applications in the biomedical, food, and cosmetic industries.

Design of hybrid biocatalysts by controlled heteroaggregation of manganese oxide and sulfate latex particles to combat reactive oxygen species.

The preparation of an antioxidant hybrid material by controlled heteroaggregation of manganese oxide nanoparticles (MnO2 NPs) and sulfate-functionalized polystyrene latex (SL) beads was accomplished. Negatively charged MnO2 NPs were prepared by precipitation and initially functionalized with poly(diallyldimethylammonium chloride) (PDADMAC) polyelectrolyte to induce charge reversal allowing decoration of oppositely charged SL surfaces via simple mixing. The PDADMAC-functionalized MnO2 NPs (PMn) aggregated with the SL particles leading to the formation of negatively charged, neutral and positively charged (SPMn) composites. The charge neutralization resulted in rapidly aggregating dispersions, while stable samples were observed once the composites possessed sufficiently high negative and positive charge, below and above the charge neutralization point, respectively. The antioxidant assays revealed that SL served as a suitable substrate and that the PDADMAC functionalization and immobilization of MnO2 NPs did not compromise their catalase (CAT) and superoxide dismutase (SOD)-like activities, which were also maintained within a wide temperature range. The obtained SPMn composite is expected to be an excellent candidate as an antioxidant material for the efficient scavenging of reactive oxygen species at both laboratory and larger scales, even under harsh conditions, where natural antioxidants do not function.

Composite materials based on heteroaggregated particles: Fundamentals and applications.

Homoaggregation of dispersed particles, i.e., aggregation of particles of the same shape, charge, size, and composition, is a well-studied field and various theoretical and experimental approaches exist to understand the major phenomena involved in such processes. Besides, heteroaggregation of particles, i.e., aggregation of particles of different shape, charge, size, or composition, has attracted widespread interest due to its relevance in various biomedical, industrial, and environmental systems. For instance, heteroaggregation of plastic contaminant particles with naturally occurring solid materials in waters (e.g., clays, silica and organic polymers) plays an important role in the decontamination technologies. Moreover, nanofabrication processes involving heteroaggregation of particles to prepare novel composite materials are widely implemented in fundamental science and in more applied disciplines. In such procedures, stable particle dispersions are mixed and the desired structure forms owing to the presence of interparticle forces of various origins, which can be tuned by performing appropriate surface functionalization as well as altering the experimental conditions. These composites are widely used in different fields from sensing through catalysis to biomedical delivery. The present review summarizes the recent progresses in the field including new findings regarding the basic principles in particle heteroaggregation, preparation strategies of heteroaggregated structures of different morphology, and the application of the obtained hybrid composites. Such information will be very helpful to those involved in the design of novel composites consisting of different nano or colloidal particles.

Nanocomposite-based dual enzyme system for broad-spectrum scavenging of reactive oxygen species.

A broad-spectrum reactive oxygen species (ROS)-scavenging hybrid material (CASCADE) was developed by sequential adsorption of heparin (HEP) and poly(L-lysine) (PLL) polyelectrolytes together with superoxide dismutase (SOD) and horseradish peroxidase (HRP) antioxidant enzymes on layered double hydroxide (LDH) nanoclay support. The synthetic conditions were optimized so that CASCADE possessed remarkable structural (no enzyme leakage) and colloidal (excellent resistance against salt-induced aggregation) stability. The obtained composite was active in decomposition of both superoxide radical anions and hydrogen peroxide in biochemical assays revealing that the strong electrostatic interaction with the functionalized support led to high enzyme loadings, nevertheless, it did not interfere with the native enzyme conformation. In vitro tests demonstrated that ROS generated in human cervical adenocarcinoma cells were successfully consumed by the hybrid material. The cellular uptake was not accompanied with any toxicity effects, which makes the developed CASCADE a promising candidate for treatment of oxidative stress-related diseases.

Masking specific effects of ionic liquid constituents at the solid-liquid interface by surface functionalization.

Ion specific effects of ionic liquid (IL) constituents on the surface charge and aggregation properties of two types of particles (positively charged amidine (AL) and polyimidazolium-functionalized sulfate (SL-IP-2) latexes) were investigated in IL solutions containing different anions and the 1-butyl-3-methylimidazolium cation. For the AL systems, the affinity of IL anions to the particle surface followed the sequence chloride < bromide < nitrate < acetate. The critical coagulation concentration values decreased in the same order indicating that ion specific adsorption determines the surface charge density and the extent of the repulsive interparticle forces. In contrast, no tendencies were observed for the SL-IP-2 particles, i.e., both charge and aggregation features were insensitive to the type of anions. This surprising behavior sheds light on that surface functionalization with the polyimidazolium compound effectively masks interfacial ion specific effects. These results indicate new possible routes to the design of processable particle dispersions in ILs irrespective of their composition.