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 nm² 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

mRNA levels of <i>VEGF-A, TGF-β1</i> and <i>IL-6</i> in different treatment groups during wound healing.

<p>AgNP/NSP treatment also modulates the expression of cytokine mRNAs in wounded skin. The levels of <i>VEGF-A</i>, <i>TGF-β1</i> and <i>IL-6</i> mRNA expression from mice of different treatment groups in both acute thermal injury at day 7 (a) and excision wound at day 15 (b) were examined by RT-PCR. Relative band intensities of different groups were calculated by a densitometer and are demonstrated by the values under the bands. The data shown are representative of three independent experiments.</p

Wound healing rates on (a) acute burn model (b) excision wound model and the photographs of wound appearance on day 5 after (c) acute burn injury and (d) excision injury.

<p>The rate of infected wound healing was compared in animals treated with staphylococcus only (Staph), staphylococcus and NSP (Staph+NSP), staphylococcus and Poly-Ag (Staph+Poly-Ag), staphylococcus and AgNP/NSP (Staph+AgNP/NSP), staphylococcus and Aquacel® (Staph+AQ), staphylococcus and silver sulfadiazine (Staph+SS), and control (untreated). The results are expressed as the mean ± SD from three independent experiments in each group. *<i>P</i><0.05, comparison between AgNP/NSP and the other 6 groups at each time point; † <i>P</i><0.05, comparison between SS treatment with the untreated, Staph, Staph+NSP, and Staph+Poly-Ag groups; ‡ <i>P</i><0.05, comparison between AQ treatment with the untreated, Staph, Staph+NSP, and Staph+Poly-Ag groups; # <i>P</i><0.05, comparison between NSP treatment with untreated, Staph and Staph+Poly-Ag groups; § <i>P</i><0.05, comparison between Poly-Ag treatment with untreated and Staph groups. All the comparisons were confirmed by Student’s <i>t</i> test.</p

Cytotoxicity toward the human foreskin fibroblast (Hs68) cell line after 12 h of incubation with AgNP/NSP, polymer dispersed AgNP (Poly-Ag) and silver sulfadiazine (SS) using the MTT assay (a).

<p>The values are expressed as the mean ± SD from 4 independent experiments. DNA damage in Chinese hamster ovary (CHO) cells by the comet assay showed the average lengths of the cell tails after incubation with different concentrations of AgNP/NSP and Poly-Ag (b). Data are shown as the mean ± SD (at least 200 cell tails were counted in each sample). *<i>P</i><0.05 at each concentration, Student’s <i>t</i> test.</p

Cytokine profile of wound healing.

<p>Serum levels of VEGF-A, TGF-β1 and IL-6 from mice of different treatment groups in both acute thermal injury at day 7 and excision wound at day 15 were examined by ELISA method.</p><p>Results are expressed as the mean (pg/ml) ± standard deviation (SD) from three independent experiments of each group.</p>*<p>Statistically significant as compared to the Staph group (<i>P</i><0.01, Student’s <i>t</i> test).</p