Venkata Raghu Mokkapati

Graphene based nanosensor for aqueous phase detection of nitroaromatics

A graphene-based nanosensor was fabricated to selectively detect nitrotriazolone (NTO) molecules with a molecularly imprinted film via simple electrical measurements. Molecularly imprinted polymer comprising chitosan was used as sensitive layer. Gold electrodes for electrical measurements were lithographically fabricated on Si/SiO2 substrate, followed by monolayer graphene transfer and polymeric film coating. Monolayer graphene and molecularly imprinted polymer were characterized by ATR-FTIR, UV-Vis, SEM and Raman spectroscopy. Transfer-length measurements (TLM) indicate that the sensor selectively and linearly responds against aqueous NTO solutions within a wide range of concentration of 0.01–0.1 mg mL−1 that covers the lowest toxic level of NTO determined by USEPA. This nanosensor with embedded electrodes is re-usable and suitable for field applications, offering real-time electrical measurements unlike current techniques where complex analytics are required.

Vitamin C Pretreatment Enhances the Antibacterial Effect of Cold Atmospheric Plasma

Bacterial biofilms are three-dimensional structures containing bacterial cells enveloped in a protective polymeric matrix, which renders them highly resistant to antibiotics and the human immune system. Therefore, the capacity to make biofilms is considered as a major virulence factor for pathogenic bacteria. Cold Atmospheric Plasma (CAP) is known to be quite efficient in eradicating planktonic bacteria, but its effectiveness against biofilms has not been thoroughly investigated. The goal of this study was to evaluate the effect of exposure of CAP against mature biofilm for different time intervals and to evaluate the effect of combined treatment with vitamin C. We demonstrate that CAP is not very effective against 48 h mature bacterial biofilms of several common opportunistic pathogens: Staphylococcus epidermidis, Escherichia coli, and Pseudomonas aeruginosa. However, if bacterial biofilms are pre-treated with vitamin C for 15 min before exposure to CAP, a significantly stronger bactericidal effect can be obtained. Vitamin C pretreatment enhances the bactericidal effect of cold plasma by reducing the viability from 10 to 2% in E. coli biofilm, 50 to 11% in P. aeruginosa, and 61 to 18% in S. epidermidis biofilm. Since it is not feasible to use extended CAP treatments in medical practice, we argue that the pre-treatment of infectious lesions with vitamin C prior to CAP exposure can be a viable route for efficient eradication of bacterial biofilms in many different applications.

Low Concentrations of Vitamin C Reduce the Synthesis of Extracellular Polymers and Destabilize Bacterial Biofilms

Extracellular polymeric substances (EPS) produced by bacteria form a matrix supporting the complex three-dimensional architecture of biofilms. This EPS matrix is primarily composed of polysaccharides, proteins and extracellular DNA. In addition to supporting the community structure, the EPS matrix protects bacterial biofilms from the environment. Specifically, it shields the bacterial cells inside the biofilm, by preventing antimicrobial agents from getting in contact with them, thereby reducing their killing effect. New strategies for disrupting the formation of the EPS matrix can therefore lead to a more efficient use of existing antimicrobials. Here we examined the mechanism of the known effect of vitamin C (sodium ascorbate) on enhancing the activity of various antibacterial agents. Our quantitative proteomics analysis shows that non-lethal concentrations of vitamin C inhibit bacterial quorum sensing and other regulatory mechanisms underpinning biofilm development. As a result, the EPS biosynthesis in reduced, and especially the polysaccharide component of the matrix is depleted. Once the EPS content is reduced beyond a critical point, bacterial cells get fully exposed to the medium. At this stage, the cells are more susceptible to killing, either by vitamin C-induced oxidative stress as reported here, or by other antimicrobials or treatments.

Combination of Cold Atmospheric Plasma and Vitamin C Effectively Disrupts Bacterial Biofilms

Cold atmospheric plasma (CAP) is increasingly used in medical applications for eradication of bacterial and tumor cells. CAP treatment devices, known as plasma jet pens, produce reactive oxygen and nitrogen species at atmospheric pressure and room temperature. The produced reactive species are concentrated in a small and precisely defined area, allowing for high precision medical treatments. CAP has been demonstrated as very effective against planktonic bacterial cells. Unfortunately, bacterial cells in biofilms are typically aggregated and protected by dense exopolymeric matrix, synthesized and secreted by the bacterial community. The main limitation in using CAP against bacterial biofilms is the thick protective matrix of extracellular polymers that shields bacterial cells within this complex architecture. CAP has also been shown to effectively eradicate tumor cells, but the main current limitation is the susceptibility of the surrounding healthy tissues to higher doses. We have recently demonstrated that vitamin C, a natural food supplement, can be used to destabilize bacterial biofilms and render them more susceptible to the CAP killing treatment. Here we discuss the possible impact that a pre-treatment with vitamin C could have on CAP applications in medicine. Specifically, we argue that vitamin C could enhance the effectiveness of CAP treatments against both the bacterial biofilms and some selected tumors.

NaB integrated graphene oxide membranes for enhanced cell viability and stem cell properties of human adipose stem cells

Here we present the integration of boron (NaB) with graphene oxide (GO) to develop a new class of membranes which are biocompatible and cost-effective for cell and tissue culture studies. Ethanol (EtOH) assisted the uniform dispersion of GO flakes on top of a glass substrate. We investigated the effect of a GO + NaB membrane on the growth and proliferation of hASCs. hASCs showed better cell viability on NaB integrated GO membranes compared to their respective controls. The concentrations of NaB and GO are 0.02% and 1/20 of stock (0.024%) respectively. To our knowledge this is the first time that enhanced cell proliferation and attachment ability of hASCs with NaB integrated GO membranes has been observed. Our study provides a platform for the development of 3D-GO scaffold systems combined with NaB in tissue engineering.

Gold Nanoparticles in Diagnostics and Therapeutics for Human Cancer

The application of nanotechnology for the treatment of cancer is mostly based on early tumor detection and diagnosis by nanodevices capable of selective targeting and delivery of chemotherapeutic drugs to the specific tumor site. Due to the remarkable properties of gold nanoparticles, they have long been considered as a potential tool for diagnosis of various cancers and for drug delivery applications. These properties include high surface area to volume ratio, surface plasmon resonance, surface chemistry and multi-functionalization, facile synthesis, and stable nature. Moreover, the non-toxic and non-immunogenic nature of gold nanoparticles and the high permeability and retention effect provide additional benefits by enabling easy penetration and accumulation of drugs at the tumor sites. Various innovative approaches with gold nanoparticles are under development. In this review, we provide an overview of recent progress made in the application of gold nanoparticles in the treatment of cancer by tumor detection, drug delivery, imaging, photothermal and photodynamic therapy and their current limitations in terms of bioavailability and the fate of the nanoparticles.

Effect of polymer type on characterization and filtration performances of multi-walled carbon nanotubes (MWCNT)-COOH-based polymeric mixed matrix membranes

ABSTRACT Multi-walled carbon nanotubes (MWCNTs) can be used for the fabrication of mixed matrix polymeric membranes that can enhance filtration perfomances of the membranes by modifying membrane surface properties. In this study, detailed characterization and filtration performances of MWCNTs functionalized with COOH group, blended into polymeric flat-sheet membranes were investigated using different polymer types. Morphological characterization was carried out using atomic force microscopy, scanning electron microscopy and contact angle measurements. For filtration performance tests, protein, dextran, E. coli suspension, Xanthan Gum and real activated sludge solutions were used. Experimental data and analyses revealed that Polyethersulfone (PES) + MWCNT-COOH mixed matrix membranes have superior performance abilities compared to other tested membranes.