Nanoscale Silicate Platelets Research Articles

Fabrication of in situ magnetic capturing and Raman enhancing nanoplatelets for detection of bacteria and biomolecules

In situ magnetic capturing and surface-enhanced Raman scattering (SERS) detection techniques can be used for detecting microbial contamination and uremic toxins. Magnetic SERS substrates were fabricated using immobilized gold nanoparticles (AuNPs) and iron-oxide (Fe3O4) nanoparticles on exfoliated nanoscale silicate platelets (NSPs). The prepared magnetic SERS nanosheets (Fe3O4@AuNPs@NSP nanosheets) were able to not only magnetically capture bacteria and biomolecules but also effectively induce the hot-spot effect and enhance the Raman signal by the surface plasmon resonance of the AuNP arrays. The results showed that both the ratio of AuNPs to Fe3O4 nanoparticles and the order of immobilization on the NSP nanosheets are important factors for inducing magnetic capturing behavior and SERS sensitivity. A method that yielded magnetic capturing behavior was to graft AuNPs on NSP nanosheets first, followed by the immobilization of Fe3O4 nanoparticles. Fe3O4@AuNPs@NSP nanosheets prepared using 0.9 mM HAuCl4 displayed the highest magnetic capturing behavior and SERS enhancement effect, showing an optimal interparticle gap. The bacteria (Escherichia coli) were captured and separated by the magnetic SERS substrates using an applied magnetic field, and then the magnetically captured samples were monitored by Raman spectroscopy for rapid SERS detection. Furthermore, the SERS sensitivity increased by ~2 times after magnetic capturing, and the limit of detection for sensing bacteria was below 103 CFU/mL. The novel magnetic SERS substrates provide ultrasensitive, rapid, and reproducible SERS detection for magnetically capturing biomolecules (bacteria, uremic toxins, and parathyroid hormone) and can be applied in environmental, water, and biomedical detection.

Effects of Deoxynivalenol and Mycotoxin Adsorbent Agents on Mitogen-Activated Protein Kinase Signaling Pathways and Inflammation-Associated Gene Expression in Porcine Intestinal Epithelial Cells.

Deoxynivalenol (DON) is the most prevalent mycotoxin in swine feedstuffs. The intestinal epithelial cells represent the first target for the DON. Here, we studied the effects of DON and mycotoxin adsorbent agents on mitogen-activated protein kinase (MAPK) signaling pathways and inflammation-associated gene expression in porcine intestinal epithelial cells (IPEC-J2). Results showed that phosphorylation of MAPK signaling pathways (p38, ERK, and JNK) was increased after treatment of DON or lipopolysaccharide (LPS) in IPEC-J2 cells. The phosphorylation of p38, ERK, and JNK was not further enhanced after co-treatment with DON and LPS. The inos and cox-2 mRNA expression were significantly induced at 6 h after treatment of DON. DON treatment significantly increased the claudin 3 and occludin mRNA expression at 12 h. DON in combination with LPS treatment did not further increase the inflammation and tight junction-associated gene expression. The DON-induced phosphorylation of MAPK signaling pathways was impaired by mycotoxin adsorbent agent (nanoscale silicate platelets and the mixture of montmorillonites and yeast cell walls) treatment, thereby decreasing inflammation and tight junction-associated gene expression. Taken together, these findings demonstrate that DON triggers the inflammation in IPEC-J2 cells by phosphorylation of MAPK signaling pathways and LPS does not further augment the DON-induced inflammatory responses. Mycotoxin adsorbent agents can attenuate DON-induced inflammatory responses in IPEC-J2 cells through modulation of the phosphorylation of p38, ERK, and JNK.

Evaluation of Carbon Dioxide-Based Urethane Acrylate Composites for Sealers of Root Canal Obturation

A new root canal sealer was developed based on urethane acrylates using polycarbonate polyol (PCPO), a macrodiol prepared in the consumption of carbon dioxide as feedstock. The superior mechanical properties and biostability nature of PCPO-based urethane acrylates were then co-crosslinked with a difunctional monomer of tripropylene glycol diarylate (TPGDA) as sealers for resin matrix. Moreover, nanoscale silicate platelets (NSPs) immobilized with silver nanoparticles (AgNPs) and/or zinc oxide nanoparticles (ZnONPs) were introduced to enhance the antibacterial effect for the sealers. The biocompatibility and the antibacterial effect were investigated by Alamar blue assay and LDH assay. In addition, the antibacterial efficiency was performed by using Enterococcus faecalis (E. faecalis) as microbial response evaluation. These results demonstrate that the PCPO-based urethane acrylates with 50 ppm of both AgNP and ZnONP immobilized on silicate platelets, i.e., Ag/ZnO@NSP, exhibited great potential as an antibacterial composite for the sealer of root canal obturation.

Facile Fabrication of Flexible Electrodes and Immobilization of Silver Nanoparticles on Nanoscale Silicate Platelets to Form Highly Conductive Nanohybrid Films for Wearable Electronic Devices.

This study investigated films with remarkably high electrical conductivity after they were easily prepared from organic/inorganic nanohybrid solutions containing an organic polymeric dispersant and two-dimensional nanoscale silicate platelets as the inorganic stabilizer dispersed with silver nanoparticles. Transmission electron microscopy shows that the production of silver nanoparticles synthesized by the in situ chemical reduction of AgNO3 in an aqueous solution by N,N-dimethylformamide results in an average silver nanoparticle diameter of circa 20 nm. Thin films of silver nanoparticles were prepared on a 1-μm-thick film with a low sheet resistance of 8.24 × 10−4 Ω/sq, achieved through the surface migration of silver nanoparticles and prepared by sintering at 300 °C to form an interconnected network. This was achieved with a silver nanoparticle content of 5 wt%, using nanoscale silicate platelets/polyoxyethylene-segmented polyimide/AgNO3 at a weight ratio of 1:10:35. During sintering, the color of the hybrid film changed from gold to milky white, suggesting the migration of silver nanoparticles and the formation of an interconnected network. The results show promise for the fabrication of novel silver-based electrocardiogram electrodes and a flexible wireless electrocardiogram measurement system for wearable electronics.

Effect of Nanoscale Silicate Platelets on Azoxystrobin-resistant Isolates of Botrytis cinerea from Strawberry In Vitro and In Vivo

The inhibitory effect of nanoscale silicate platelets modified with different surfactants, i.e., NSS1450 and NSS3150 was evaluated for spore germination and mycelial growth of azoxystrobin-resistant (AR) and -sensitive (AS) Botrytis cinerea isolates from strawberry. The treatments with NSS1450 at the concentration of more than 50 mg/L significantly reduced spore germination by 99.2-100.0% for AR isolates and by 100.0% for AS isolates. In contrast, NSS3150 failed to show an inhibition for the spore germination of AR B. cinerea isolates. In another test, NSS1450 at concentrations higher than 500 mg/L could reduce mycelial growth by 60.2-100.0% and 93.8- 100.0% for AR and AS isolates, respectively, while NSS3150 showed similar inhibition on the spore germination. Further, NSS1450 at the concentrations between 500 to 1000 mg/L and accompanied with a fungicide, azoxystrobin, demonstrated high inhibitory rate 93.8 to 100.0% inhibition) in AR and AS isolates of B. cinerea. Under scanning electron microscope, the NSS1450 at the concentration of 1000 mg/L affected the morphologies of spores and mycelia in shrinking. The disease severity on strawberry leaves was 8.3% after 13 days incubation when treated with NSS1450 at 24 h after the pathogen inoculation. Moreover, spraying the mixture solution of 100 mg/L NSS1450 and 100 mg a.i./L azoxystrobin at 24 h after or before pathogen inoculation showed significantly efficacy compared with inoculation pathogen only. The results indicated that the silicate nanoplatelets after modification by a proper surfactant or NSS1450 had the potentials for treating gray mold disease although further studies are still needed under greenhouse and field conditions.

First Observation of Physically Capturing and Maneuvering Bacteria using Magnetic Clays.

A new class of nanohybrids composed of structurally exfoliated silicate platelets and magnetic iron oxide nanoparticles was synthesized and shown to be capable of capturing microbes in liquid microbiological media. Nanoscale silicate platelets with an approximate thickness of 1.0 nm were prepared from the naturally occurring mineral clays montmorillonite and mica; these clays yielded platelets with lateral dimensions on the order of 80-100 nm and 300-1000 nm, respectively. The magnetic Fe3O4 nanoparticles, approximately 8.3 nm in diameter, were coated in situ onto the silicates during the synthesis process, which involved the coprecipitation of aqueous Fe(2+)/Fe(3+) salts. Owing to the high surface area-to-volume ratios and the presence of ionically charged groups (i.e., ≡SiO(-)Na(+)), the silicate nanoplatelets exhibited intense noncovalent bonding forces between Fe3O4 nanoparticles and the surrounding microorganisms. The Fe3O4-on-nanoplatelet nanohybrids enabled the entrapment of bacterial cells in liquid microbiological media. These captured bacteria formed bacterial aggregates on the order of micrometers that became physically maneuverable under a magnetic field. This phenomenon was demonstrated with Staphylococcus aureus in liquid microbiological media by physically removing them using a magnetic bar; in two experimental examples, bacterial concentrations were reduced from 10(6) to 10(2) and from 10(4) to 10(0) CFU/mL (colony formation unit/mL con). Under a scanning electron microscope, these bacteria appeared to have rough and wrinkled surfaces due to the accumulated silicate platelets. Furthermore, the external application of a high-frequency magnetic field completely destroyed these aggregated microbes by the magnetically induced heat. Hence, the newly developed nanohybrids were shown to be viable for physically capturing microbes and also for potential hyperthermia treatment applications.

First evidence of singlet oxygen species mechanism in silicate clay for antimicrobial behavior

Nanoscale silicate platelets (NSPs) from the natural silicate clay minerals were shown to have antimicrobial ability through physical trapping mechanism. The NSP could inhibit the growth of drug-resistant species such as methicillin-resistant Staphylococcus aureus and silver ion-resistant Escherichia coli. We further found that the NSP generated singlet oxygen species under ultraviolet irradiation. This is the first time to report the ability of generating singlet oxygen species by the platelets of ca. 80×80×1nm in geometric shape. The ability to emit singlet oxygen species of the NSP clay provides an explanation for “physical trapping” antimicrobial mechanism.

Nanohybrids of Silver Particles on Clay Platelets Delaminate Pseudomonas Biofilms

To evaluate the effectiveness of novel nanohybrids, composed of silver nanoparticles and nanoscale silicate platelets, to clear Pseudomonas aeruginosa biofilms. The nanohybrids were manufactured from an in situ reduction of silver salts in the silicate platelet dispersion, and then applied to biofilms in vitro and in vivo. In reference to the biocidal effects of gentamycin, the nanohybrids mitigated the spreading of the biofilms, and initiated robust cell death and exfoliation from the superficial layers of the biofilms in vitro. In vivo, the nanohybrids exhibited significant therapeutic effects by eliminating established biofilms from infected corneas and promoting the recovery of corneal integrity. All of the evaluations indicate the high potency of the newly developed silver nanoparticle/nanoscale silicate platelet nanohybrids for eliminating biofilms.

Selective SERS Detecting of Hydrophobic Microorganisms by Tricomponent Nanohybrids of Silver–Silicate-Platelet–Surfactant

Nanohybrids consisting of silver nanoparticles (Ag), clay platelets, and a nonionic surfactant were prepared and used as the substrate for surface-enhanced Raman scattering (SERS). The nanoscale silicate platelets (SP) (with dimensions of 100 × 100 nm(2) and a thickness of ∼1 nm) were previously prepared from exfoliation of the natural layered silicates. The tricomponent nanohybrids, Ag-SP-surfactant (Ag-SP-S), were prepared by in situ reduction of AgNO3 in the presence of clay and the surfactant. The clay platelets with a large surface area and ionic charge (ca. 18 000 sodium ions per platelet) allowed for the stabilization of Ag nanoparticles in the range of 10-30 nm in diameter. With the addition of a nonionic surfactant such as poly(oxyethylene) alkyl ether, the tricomponent Ag-SP-S nanohybrids possessed an altered affinity for contacting microorganisms. The particle size and interparticle gaps between neighboring Ag on SP were characterized by TEM. The surface tension of Ag-SP and Ag-SP-S in water implied different interactions between Ag and hydrophobic bacteria ( Escherichia coli and Mycobacterium smegmatis ). By increasing the surfactant content in Ag-SP-S, the SERS peak intensity was dramatically enhanced compared to the Ag-SP counterpart. The nanohybrids, Ag-SP and Ag-SP-S, with the advantages of varying hydrophobic affinity, floating in medium, and 3D hot-junction enhancement could be tailored for use as SERS substrates. The selective detection of hydrophobic microorganisms and larger biological cells makes SERS a possible rapid, label-free, and culture-free method of biodetection.

Clay films with variable metal ions and self-assembled silicate layer-void nanostructures

The naturally occurring silicate clays with sodium counter-ions were exfoliated into nanoscale silicate platelets (NSP-ONa) and subsequently exchanged with various metal ions including lithium(I), potassium(I), magnesium(II), calcium(II), and aluminum(III) to afford silicate platelets with the corresponding metal counter-ions (NSP-OM, M = metal counter-ion). In solution, their ionic properties were characterized by measuring zeta potentials over pH to reveal the electrokinetic shifting from −50 mV to −5 mV. The gelling behavior was shown to be low at a concentration of 4 wt% for M = monovalent Na+, K+, and Li+; and 7 wt% for M = multivalent Mg2+, Ca2+, and Al3+. Under the process of solution coating and evaporating, the silicate platelets self-assembled into thin films of 20–100 μm in thickness with the exception of NSP-OAl. The regularity of the clay's self-assembled nanostructure increases as the valence of the metal counter-ion decreases. The nanostructures of the silicate films were further characterized by wide angle X-ray diffraction, density/void measurement, and scanning electron microscopy. These findings of NSP-OM and their self-assembled nanostructures formation were for the first time recorded and suggested for new film fabrications by bottom-up technology.

Enhancing silver nanoparticle and antimicrobial efficacy by the exfoliated clay nanoplatelets

The antimicrobial efficacy of silver nanoparticles (AgNP) is enhanced by using the exfoliated clay nanoscale silicate platelets (NSP) as the supports. The NSP were in the dimension of 80 nm × 80 nm × 1 nm and were derived from the exfoliation of natural clays such as sodium montmorillonite. Increasing the amount of NSP addition at the relative Ag/silicate composition ratios from 0.5/99.5 to 50/50 w/w significantly altered the particle size AgNP from 3.6 nm to 35 nm in diameter. Evaluation of antibacterial activities for these nanohybrids demonstrated the effect of the amount of NSP support and Ag size on inhibiting the growth of dermal pathogens including Gram-positive and Gram-negative bacteria. Scanning electron microscope observations further revealed the interaction of the AgNP/NSP nanohybrids in contact with individual bacteria surface. The tailoring of the AgNP/NSP nanostructures has largely affected the bacterial surface interaction by NSP adherence and hence the antimicrobial efficacy.

Effect of grafting architecture on the surfactant-like behavior of clay-poly(NiPAAm) nanohybrids

A new class of clay-polymer nanohybrids was synthesized by grafting poly(N-isopropylacrylamide) (PNiPAAm) on the edge of nanoscale silicate platelets (NSPs) through covalently bonded linkers to form various architectures. The inherent ionic character of NSPs and the organic moieties of isopropyl amide in PNiPAAms impart surface active properties to the nanohybrids. Surface tension and particle size measurements were used to determine the critical micelle concentrations (CMCs) of the nanohybrids. It was found that PNiPAAm brushes grafted onto NSPs with the single-headed linkers are loosely packed and can expand easily in water causing inter-hybrid interactions. In contrast, PNiPAAm brushes grafted onto NSPs with the double-headed linkers may alternatively exhibit intra-hybrid interactions and the hybrids tend to exist in a dispersed state. Consequently, the latter has a higher CMC than the former. In addition, the CMC can be tailored by adjusting the grafting density of the linkers on the NSP surfaces. The densely grafted nanohybrids exhibit close inter-hybrid contact resulting in a lower CMC than that for the sparsely grafted nanohybrids. Molecular simulations were also performed to study the effects of the polymer-grafted architecture and the density of the linkers on the micellar behavior of NSP-PNiPAAm hybrids. The simulation results were found to be in good agreement with the experimental observations. Thus, it is possible to control the surface active properties and aggregation of the clay-PNiPAAm hybrids by manipulating the organic grafting architectures of the silicate platelets.

Nanohybrids of Silver Particles Immobilized on Silicate Platelet for Infected Wound Healing

Silver nanoparticles supported on nanoscale silicate platelets (AgNP/NSP) possess interesting properties, including a large surface area and high biocide effectiveness. The nanohybrid of AgNP/NSP at a weight ratio 7/93 contains 5-nm Ag particles supported on the surface of platelets with dimensions of approximately 80×80×1 nm3. The nanohybrid expresses a trend of lower cytotoxicity at the concentration of 8.75 ppm Ag and low genotoxicity. Compared with conventional silver ions and the organically dispersed AgNPs, the nanohybrid promotes wound healing. We investigated overall wound healing by using acute burn and excision wound healing models. Tests on both infected wound models of mice were compared among the AgNP/NSP, polymer-dispersed AgNPs, the commercially available Aquacel, and silver sulfadiazine. The AgNP/NSP nanohybrid was superior for wound appearance, but had similar wound healing rates, vascular endothelial growth factor (VEGF)-A levels and transforming growth factor (TGF)-β1 expressions to Aquacel and silver sulfadiazine.

Fine Dispersion and Property Differentiation of Nanoscale Silicate Platelets and Spheres in Epoxy Nanocomposites

Silica spheres (with an averaged diameter of 10 nm) and silicate platelets (approximately 100×100×1 nm3 in dimension) were allowed to disperse in polyoxypropylene-triamine (400 g/mol molecular weight), then cured with the epoxy resin diglycidyl ether of bisphenol-A (DGEBA). With 1–5 wt % loading of these inorganic silicates, the cured epoxies exhibited high hardness, transparency, and a low thermal expansion coefficient. These silicate platelets also enhance the epoxy hardness from the pristine 2H to 4H while adding only 0.5 wt %. By comparison, if the spherical silica is used, a similar hardness can only be achieved by loading as high as 5 wt % of the silica. The high aspect-ratio and fine dispersion of the platelet silicates were found to be important factors in influencing the cured epoxy’s properties. In addition, a TEM micrograph shows that the silicate platelets are well-dispersed and have a unique self-arranged lamellar orientation.