Amongst the various microorganisms found as contaminants in food and water samples, Escherichia coli (E. coli) is one of the most predominant bacteria observed. The presence of the various strains of E. coli, pathogenic or non-pathogenic, in either food or water samples serves as an indicator of faecal contamination and helps to determine the hygienic condition, potability and safety of a given water or food sample for consumption. Although several conventional microbial analytical methods and the more advanced biochemical and molecular biology based methods exist for detection of E. coli, these are laden with several limitations. Nanotechnology offers cheaper, more reliable, quicker and more sensitive detection platforms for screening and/or enumerating the load of E. coli in a given sample. The present review outlines in brief the conventional methods available for E. coli detection enlisting the drawbacks of the same. Against this background, nanotechnology-based sensing systems developed for detection and capturing of E. coli so far have been highlighted. The most commonly developed nanosensors employ gold or silver nanoparticles with magnetic nanobeads also being currently employed for sensor development. Further, the evolution of green nanoparticle technology and its application in E. coli sensing has been explored with various examples of carbon dots, graphitic carbon nitride, glycopolymers and rice husk ash being cited. Furthermore, the development of nanosensors for E. coli using bimetallic nanoparticles has also been reviewed. These nanobased sensors have proved to exhibit high sensitivities and low detection limits for E. coli. However, approaches to enhance the sensitivity to detection even further lower limits and provide nanosensors as multifunctionalized detection tools for multiple pathogenic strains are underway.

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A simple, facile co-precipitation technique was successfully used to synthesize the pure, and Mn-doped SnO 2 nanoparticles (NPs) and characterized by X-ray diffraction (XRD), Fourier Transform Infrared (FT-IR)), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy and photoluminescence (PL). XRD analysis indicated that the prepared samples have the pure tetragonal structure of SnO 2. The doping of Mn on SnO 2 surface enhances the crystallite size of the SnO 2 NPs. The polycrystalline in nature SnO 2 nanoparticles was confirmed by SAED pattern. FT-IR analysis illustrates the presence of stretching vibration of the O-Sn-O bond in both SnO 2 and Mn-doped SnO 2 NPs. SEM and TEM analysis shows that the SnO 2 particles are spherical in shape and are uniformly dispersed inside the nanocomposite matrix. The average particle size of SnO 2 in pure SnO 2 and Mn-doped SnO 2 NPs was determined as~14 and 12 nm respectively. The optical analysis confirmed a redshift by doping Mn on SnO 2. The band gap energy for pure SnO 2 and Mn-doped SnO 2 NPs are 3.14 eV to 2.87 eV, respectively. The visible emission was observed from PL analysis. Photocatalytic activity of the pure SnO 2 and Mn-doped SnO 2 are tested using Rhodamine B (RhB) dye as a model compound under UV light. The results revealed that the Mn-doped SnO 2 NPs exhibited higher efficiency than pure SnO 2 for the degradation of RhB dye and furthermore with increasing the amount of Mn doping further enhanced the degradation rate of R hB dye. The synthesized samples present good reusable stability. Dielectric loss of the prepared pure and Mn-doped SnO 2 NPs exhibited a linear trend at higher frequency domain. Increased dopant amount reduced the ac conductivity which is attributed to the particle size effect with the presence of the impurities.

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