The deposition of silica nanoparticles on Escherichia coli bacteria was investigated. The noncovalent interaction between the silanized surfaces and polar components of the biomembrane resulted in a nanobiostructure. This hybrid architecture showed stable conformation characteristics evaluated with different microscopy techniques, such as bright field confocal microscopy and transmission electron microscopy (TEM). Nanobioarchitectures were detected within colloidal dispersions and in the absence of aqueous media. Nanobiointeractions were related to strong polar and hydrogen bridges’ noncovalent interactions. Thus, well-constituted and defined nanobiostructures were observed by bright field confocal microscopy and TEM after their preparation in optimal conditions. However, to evaluate their stability and internanobiostructure interactions, size distributions within variable periods were determined. Variable nanobioaggregate sizes were recorded according to nanoparticles and bacteria concentrations. From single nanolabeled E. coli with well dispersible properties, low bacteria concentrations were observed. In intermediate and high concentrations, different distributions of nanobiostructures were observed in different periods. It was observed that the incorporation of silica nanoparticles into E. coli increased their dispersibility; however, their modified E. Coli membranes with silanized nanosurfaces augmented their internanobiostructure interactions through time. Here, we discuss the dynamics and nanobio-optics properties of E. coli. Their nanobiostructures could not be considered to be static systems; their interactions are regarded as important factors for dispersibility, stability, and effects against additional chemical agents such as antibiotics.
Tunable fluorescent silica nanoparticles (SiO2 NPs) with variable sizes based on fluorescence resonance energy transfer were synthesized. The SiO2 NPs were obtained by the Störber method by varying tetraethyl orthosilicate (TEOS) concentrations and with the incorporation of different concentrations of fluorescein (Fl) and rhodamine B (RhB) conjugated with 3-(aminopropyl)triethoxysilane. We thus recorded homogeneous SiO2 NPs of different sizes. By transmission electron microscopy imaging, the sizes of 200, 280, and 380 nm were determined. The Fl and RhB fluorescent dyes showed well-overlapped emission from the fluorescent energy donor to the energy acceptor with the optimal ratio of quantum yields. By static fluorescence, varied emissions were recorded according to the concentration ratio of the donor–acceptor pair. Increasing intensity values were collected with the addition of higher concentrations of the fluorescent energy donor and decreased fluorescent lifetime decays. By laser fluorescence microscopy, higher enhanced surfaces were produced in the presence of both emitters, as compared with those in the presence of mono-colored SiO2 NPs with optimal excitation with the fluorescent energy donor only. These NPs were well dispersed in polar solvents; however, due to their polar surface and size, higher interactions produced dimeric nanoaggregates. In addition, to evaluate their applications, their depositions were evaluated over modified glass slide substrates for smart light-responsive materials and over Cyanobacteria and Escherichia coli for the development of nanobiostructures with varied optical activities.
The functionalization of the nanoparticle’s (NP) surface is one method for tuning their overall properties to fit targeted applications. We developed a nanosensor based on the specific supramolecular interactions between ß-cyclodextrin (ßCD) nanocavities and organic molecules of biological interests using the metal-enhanced fluorescence effect (MEF) as the detection signal. We grafted ßCD, a typical macrocyclic host molecule that interacts specifically with different organic molecules and changes their physical properties (such as their fluorescence emission intensity), on gold NPs. To evaluate this nanosensor and the effect of the metallic core, we worked with a typical organic molecule, Rhodamine B (RhB), that has a strong association constant with ßCD (5700 M − 1) and is well-known to be quenched in the presence of cyclodextrins (CDs). The results show that, by grafting ßCD on gold NPs, it is possible to increase the sensitivity of RhB detection by 70%, 80%, and 294% when compared with solutions in (1) a phosphate buffer, (2) with ßCD, and (3) with Au NPs, respectively. These results show that the use of a supramolecular system attached to a metallic NP can interact specifically with a dye to enhance its fluorescence emission through the MEF effect. Moreover, this type of nanosystem can overcome the quenching of the signal by the matrix, such in the case of RhB with CDs. Eventually, this concept could be extended to other dyes with different quenching effects. For this reason, this type of nanosensor system could be used in the future to protect and enhance the dye emission of fluorophores in different biological media.
Gold core–shell nanoparticles were synthesized based on metallic cores, variable silica shell spacers covered with modified fluorescent silica layers. Ultraluminescent properties were obtained based on metal-enhanced fluorescence (MEF). Different silica spacers were synthesized to optimize the MEF enhancement factor (MEFEF). An optimal MEFEF was determined equal to 9.5 for shorter silica spacers (d−SiO2−=10 nm). These nanoparticles were deposed on Escherichia coli bacteria at different concentration levels for Bioimaging generation over their surfaces. The best luminescent nanoparticles were deposed on intermediate and higher bacteria concentrations. In the presence of intermediate bacteria concentrations, the ultraluminescent nanoparticles adsorbed showed an increase of 35% to 45% compared with individual nanoparticles. To modify the surface of individual bacteria, diluted samples of bacteria were used in which a 20% decrease in fluorescence emission was measured. In the presence of higher bacteria concentrations, fewer clear and bright images were obtained. At diluted ultraluminescent nanoparticle concentrations, a decrease in brightness and image detail was observed; and in the absence of nanoparticle deposition, no image was recorded. Accordingly, these ultraluminescent gold core–shell nanoparticles have been shown to be useful as platforms for biodetection and tracking applications.
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