Development of silver nanoparticles and aptamer conjugated biosensor for rapid detection of E. coli in a water sample.

A simple, rapid, and sensitive electrochemical biosensor based on a screen-printed carbon electrode (SPCE) was developed for onsite detection of E. coli in real time. This work analyzed the effect of aptamer conjugation and PBS buffer solution on the colloidal stability of the silver nanoparticles (AgNPs). Aggregations of the AgNPs after aptamer conjugation in PBS buffer were observed from the particle size distribution analysis. The AgNP-aptamer conjugation and its affinity towards E. coli (DH5α) were confirmed by UV-visible spectrophotometry, which showed a linear increment in the absorption with increasing E.coli concentration. The screen-printed carbon electrodes were modified by drop-casting of AgNPs, which were used as an effective immobilization platform for E. coli-specific aptamers. The modified electrode's surface modification and redox behavior were characterized using cyclic voltammetry. Finally, E. coli was detected using differential pulse voltammetry with an optimized incubation time of 15 min. The developed biosensors showed a linear decrease in current intensity with an increase in the concentration of E. coli. The biosensor had a relative standard deviation (RSD) of 6.91% (n = 3), which showed good reproducibility. The developed biosensors are highly sensitive and have a limit of detection (LOD) as low as 150 CFU/ml. The biosensor showed good selectivity for E.coli coli when comparing the signal response obtained for bacteria other than E.coli. Also, the biosensor was found stable for four weeks at room temperature and showed high recoveries from 95.27% to 107% during the tap water sensitivity validation.

A novel, efficient and economical alternative for the removal of toxic organic, inorganic and pathogenic water pollutants using GO-modified PU granular composite.

Multicomponent wastewater treatment utilising simple and cost-effective materials and methods is an important research topic. This study has reported the fabrication and utilisation of graphene oxide (GO) embedded granular Polyurethane (PU) (GOPU) adsorbent for the treatment of lead ion (Lead ion (Pb(II)), Methylene blue (MB), and E. coli. PU granules were wrapped with GO flakes to improve hydrophilicity, interaction with polluted water, cation-exchange reaction, and binding of pollutants on its surface. Synthesised GOPU granules were characterised by X-Ray Diffraction (XRD), Raman, Fourier transform infrared (FTIR) spectroscopy, and Scanning electron microscopy (SEM) analysis to ensure the successful synthesis of GO and fabrication of GOPU granules. Further, batch and continuous adsorption processes were studied in different operating conditions to evaluate the performance of GOPU granules in practical applications. The kinetic and isotherm analyses revealed that the adsorption of Lead (Pb(II)) ion and Methylene Blue (MB) dye followed the Freundlich and Langmuir isotherm models, respectively, and they showed good agreement with the Pseudo-second-order kinetic model. The adsorption capacities of GOPU granules for the elimination of Pb(II) and MB dye were about 842 mg/g and 899 mg/g, respectively. Additionally, investigations into the fixed bed column revealed that the adsorption column performed best at a flow rate of 5 mL/min and a bed height of 6 cm. Pb(II) adsorption had a bed uptake capacity (qbed) of 88 mg/g and percentage removal efficiency (%R) of 76%. Similarly, MB adsorption had a bed uptake capacity of 202 mg/g and a percentage removal efficiency of 71%. A systematic invention on antibacterial activity toward E. coli showed that The GOPU granules have a removal efficiency of about 100% at an exposure of 24 h. These findings indicated the possible use of GOPU granules as promising adsorbents for various water pollutants.

Development of glucose oxidase-chitosan immobilized paper biosensor using screen-printed electrode for amperometric detection of Cr(VI) in water.

Hexavalent chromium is a toxic heavy metal getting discharged into the environment and water bodies through various industrial processes. Conventional analysis methods call for expensive equipment and complicated sample pretreatment that made unsuitable for onsite detection. Paper is used as an enzyme immobilization platform because of its property to wick the liquid by capillary action; lightweight, cheap and can be easily patterned or cut according to the requirements for developing biosensor. In this study, enzyme immobilization of glucose oxidase (GOx) on filter paper were examined using three polysaccharides such as chitosan, sodium alginate and dextran for entrapment efficiency, activity and stability of the immobilized enzyme. Among the three, chitosan proved efficient for enzyme entrapment with about 90% efficiency at 0.3% (w/v) chitosan. The stability was checked after 1 week at 4 °C and room temperature, where the chitosan entrapped enzyme retained nearly 97% stability at 4 °C. Enzyme inhibition study of GOx and Cr(VI) was carried out using chronoamperometry shown uncompetitive type of inhibition. A paper-based electrochemical biosensor strip was developed by immobilizing GOx enzyme on filter paper using chitosan as an entrapping agent and associating it with a screen-printed carbon electrode for amperometric measurements. The linear range of detection was obtained as 0.05-1 ppm with the limit of detection as 0.05 ppm for Cr(VI), which is the standard permissible limit in potable water. The relative standard deviation (5.6%) indicates good reproducibility of the fabricated biosensor.

Colorimetric paper bioassay by horseradish peroxidase for the detection of catechol and resorcinol in aqueous samples.

Phenolic compounds such as catechol and resorcinol are toxic and persistent pollutants in the aqueous environment. Detection procedures such as chromatographic and spectrophotometric methods are time-consuming and require sophisticated instruments with skilled manpower. Development of a simple, cost effective, portable and disposable paper based biosensor could be a better alternative to the conventional methods. The present study attempted to develop a paper based biosensor by immobilizing horseradish peroxidase enzyme to detect catechol and resorcinol in aqueous samples. Horseradish peroxidase catalyzes the oxidation of phenolic compounds to semiquinones, which on reaction with a chromogen, 3-methyl 2-benzothiazolinone hydrazine (MBTH) gives faint pink to red color depending on the compound and its concentration in the sample is the basis for biosensing application. Different methods of enzyme immobilization on filter paper like physical adsorption, covalent coupling, and polysaccharide entrapment were executed. The performance of the various enzyme immobilization methods was evaluated by analyzing the developed color intensity using ImageJ software. Entrapment technique is the most effective method of immobilizing enzyme on the filter paper that produces the highest color intensity with better stability. The visible limit of detection (LoD) was observed as 0.45 mM (50 mg/L) for catechol and 0.09 mM (10 mg/L) for resorcinol in aqueous samples.