Graphene-Based Sensor for Detection of Bacterial Pathogens.

Microbial colonization to biomedical surfaces and biofilm formation is one of the key challenges in the medical field. Recalcitrant biofilms on such surfaces cause serious infections which are difficult to treat using antimicrobial agents, due to their complex structure. Early detection of microbial colonization and monitoring of biofilm growth could turn the tide by providing timely guidance for treatment or replacement of biomedical devices. Hence, there is a need for sensors, which could generate rapid signals upon bacterial colonization. In this study, we developed a simple prototype sensor based on pristine, non-functionalized graphene. The detection principle is a change in electrical resistance of graphene upon exposure to bacterial cells. Without functionalization with specific receptors, such sensors cannot be expected to be selective to certain bacteria. However, we demonstrated that two different bacterial species can be detected and differentiated by our sensor due to their different growth dynamics, adherence pattern, density of adhered bacteria and microcolonies formation. These distinct behaviors of tested bacteria depicted distinguishable pattern of resistance change, resistance versus gate voltage plot and hysteresis effect. This sensor is simple to fabricate, can easily be miniaturized, and can be effective in cases when precise identification of species is not needed.

A Sustainable Approach for the Green Synthesis of Silver Nanoparticles from Solibacillus isronensis sp. and Their Application in Biofilm Inhibition.

The use of bacteria as nanofactories for the green synthesis of nanoparticles is considered a sustainable approach, owing to the stability, biocompatibility, high yields and facile synthesis of nanoparticles. The green synthesis provides the coating or capping of biomolecules on nanoparticles surface, which confer their biological activity. In this study, we report green synthesis of silver nanoparticles (AgNPs) by an environmental isolate; named as AgNPs1, which showed 100% 16S rRNA sequence similarity with Solibacillus isronensis. UV/visible analysis (UV/Vis), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and Fourier-transform infrared spectroscopy (FTIR) were used to characterize the synthesized nanoparticles. The stable nature of nanoparticles was studied by thermogravimetric analysis (TGA) and inductively coupled plasma mass spectrometry (ICP-MS). Further, these nanoparticles were tested for biofilm inhibition against Escherichia coli and Pseudomonas aeruginosa. The AgNPs showed minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of 3.12 µg/mL and 6.25 µg/mL for E. coli, and 1.56 µg/mL and 3.12 µg/mL for P. aeruginosa, respectively.

Graphene coated magnetic nanoparticles facilitate the release of biofuels and oleochemicals from yeast cell factories.

Engineering of microbial cells to produce high value chemicals is rapidly advancing. Yeast, bacteria and microalgae are being used to produce high value chemicals by utilizing widely available carbon sources. However, current extraction processes of many high value products from these cells are time- and labor-consuming and require toxic chemicals. This makes the extraction processes detrimental to the environment and not economically feasible. Hence, there is a demand for the development of simple, effective, and environmentally friendly method for the extraction of high value chemicals from these cell factories. Herein, we hypothesized that atomically thin edges of graphene having ability to interact with hydrophobic materials, could be used to extract high value lipids from cell factories. To achieve this, array of axially oriented graphene was deposited on iron nanoparticles. These coated nanoparticles were used to facilitate the release of intracellular lipids from Yarrowia lipolytica cells. Our treatment process can be integrated with the growth procedure and achieved the release of 50% of total cellular lipids from Y. lipolytica cells. Based on this result, we propose that nanoparticles coated with axially oriented graphene could pave efficient, environmentally friendly, and cost-effective way to release intracellular lipids from yeast cell factories.