Liyakat Hamid Mujawar

Bacteria and fungi can contribute to nutrients bioavailability and aggregate formation in degraded soils

Intensive agricultural practices and cultivation of exhaustive crops has deteriorated soil fertility and its quality in agroecosystems. According to an estimate, such practices will convert 30% of the total world cultivated soil into degraded land by 2020. Soil structure and fertility loss are one of the main causes of soil degradation. They are also considered as a major threat to crop production and food security for future generations. Implementing safe and environmental friendly technology would be viable solution for achieving sustainable restoration of degraded soils. Bacterial and fungal inocula have a potential to reinstate the fertility of degraded land through various processes. These microorganisms increase the nutrient bioavailability through nitrogen fixation and mobilization of key nutrients (phosphorus, potassium and iron) to the crop plants while remediate soil structure by improving its aggregation and stability. Success rate of such inocula under field conditions depends on their antagonistic or synergistic interaction with indigenous microbes or their inoculation with organic fertilizers. Co-inoculation of bacteria and fungi with or without organic fertilizer are more beneficial for reinstating the soil fertility and organic matter content than single inoculum. Such factors are of great importance when considering bacteria and fungi inocula for restoration of degraded soils. The overview of presented mechanisms and interactions will help agriculturists in planning sustainable management strategy for reinstating the fertility of degraded soil and assist them in reducing the negative impact of artificial fertilizers on our environment.

Hexamethyldisilazane Modified Paper as an Ultra-sensitive Platform for Visual Detection of Hg2+, Co2+, Zn2+ and the Application to Semi-quantitative Determination of Hg2+ in Wastewater

The present article reports the application of hexamethylsilazane (HMDS) modified filter paper for ultrasensitive detection of Hg(2+), Co(2+) and Zn(2+). By chemical vapor deposition of HMDS, a highly hydrophilic filter paper was fabricated to a low wetting (hydrophobic) substrate. The water contact angle (θ) of modified paper was ∼128°, whereas scanning electron and atomic force microscopy confirmed the surface modification. Using chromogenic reagents, a one-step assay for aforementioned ions was demonstrated onto pristine as well as hydrophobic paper. The assay was completed in less than 10 min and the end-result was in form of a color change that could be easily read by the naked eye. The limit of detection on modified paper was 0.5 ppb, which was 5-order of magnitude superior to that observed on pristine paper. The proposed method was successfully applied for semi-quantitative determination of Hg(2+) ions in real wastewater samples.

Styrofoam modified paper as a low-cost platform for qualitative and semi-quantitative determination of Ni2+ ions in wastewater

In the present article we have demonstrated a swift and low-cost method to design hydrophobic paper and its potential applications for the determination of Ni2+ ions in wastewater. Styrofoam was used as a precursor to fabricate pristine filter paper into a low wetting substrate. The water contact angle (θ) of the modified paper was ∼111° whereas atomic force microscopy analysis ensured a uniform coating of the polymer onto cellulose fibers. Metal specific reagent 1-(2-mercaptophenyl)iminomethyl naphthalen-2-ol (MPMN) was manually arrayed and one-step assay for the determination of Ni2+ was demonstrated on the aforementioned substrates. The end-result was observed in the form of a distinct color change which was easily readable via the naked eye. We also quantitated the concentration of Ni2+ ions through flatbed scanning and scoring their pixel gray volume using image analysis software. On Styrofoam modified paper, the limit of detection was improved to 10−2 μg mL−1, which was 3-orders of magnitude lower than that observed on pristine filter paper. The MPMN reagent was highly selective towards Ni2+ in the presence of a high concentration of commonly diverse heavy metals (Ag+, Al3+, As3+, Ba2+, Cd2+, Cr3+, Fe3+, Pb2+ and Mn2+) and some other ions (Na+, Ca2+, K+ and Cl−) in water. Our developed method successfully demonstrated the semi-quantitative determination of Ni2+ ions in tap and municipal wastewater samples. Due to good specificity as well as accuracy towards Ni2+ ions, our low-cost sensor will be useful in point-of-use applications.

Polyethersulfone membrane printed with 1-(2-pyridylazo)-2-naphthol (PAN) sensor for sensitive enrichment and rapid determination of Zn2+ in water

A facile approach for the rapid and sensitive detection as well as determination of Zn2+ ions in water has been developed. The method was based upon the use of a polyethersulfone membrane printed with 1-(2-pyridylazo)-2-naphthol (PAN) as a novel platform for rapid enrichment of Zn2+ ions. Atomic force microscopy, scanning electron microscopy and goniometer studies were performed to understand the PES characteristics. The end result for Zn2+ determination was visually noticeable via a distinct colour change on the membrane surface from 10−3 μg mL−1 onwards, with a linear dynamic range of 10−1 to 102 μg mL−1. The specificity of the proposed sensor was improved by masking common interfering ions towards Zn2+ in water. The developed platform is robust enough to withstand slight changes in pH, temperature and volume, confirming its applicability in point-of-use testing. The proposed membrane-based sensor provides better performance compared to the similar assay executed on a pristine filter-paper platform with a maximum limit of detection of only up to 101 μg mL−1. The developed sensor was satisfactorily applied for the analysis of Zn2+ ions in tap- and wastewater samples without pretreatment with an acceptable relative standard deviation (RSD) ≤ ±2.9%. The precision of the proposed method was also estimated for inter- and intra-day replicates (n = 5) at various concentrations and RSD values of less than 11.0% were achieved. Statistical treatment using t- and F-tests of the results of the developed sensor with those obtained by the standard method reflected no significant differences in the precision.

A versatile optical assay plate fabricated from e-waste and its application towards rapid determination of Fe3+ ions in water

A novel approach for reusing e-waste towards the design of low-cost analytical tools/devices has been presented. An optical assay plate with cone-shaped wells was fabricated, which can serve as a versatile tool for rapid assays. In the present study, we have demonstrated the application of the assay plate towards the sensitive detection and precise determination of Fe3+ ions using highly selective 2-hydroxy-1-naphthaldehyde (HyNA) reagent. The proposed method was optimized against common analytical parameters, e.g. base diameter, analyte volume, solution temperature and pH. At the optimal experimental conditions, the repeatability of the signal intensity values in various wells was confirmed with an acceptable standard deviation (based on 3 s), relative standard deviation (5.1) and RSD (±7.1%). A good limit of detection (based on 3 s/b = 1.8 μM) and limit of quantification (based on 10 s/b = 5.4) of total Fe3+ ions and linear dynamic range (18–900 μM) were successfully achieved. In the absence of the fabricated plate, the assay performance showed 50% reduction in the signal density and a higher limit of detection (i.e., 90 μM). Due to its high selectivity and negligible interference, the proposed method was successfully applied for the detection and precise determination of Fe3+ ions in tap and marine water samples.

A Highly Structured 1,10-Phenanthroline Arrayed Hydrophobic Sulfone Membrane Platform for the Rapid Determination and Speciation of Fe2+/Fe3+ Ions in Water

An optical assay for the rapid determination and chemical speciation of Fe2+/Fe3+ species has been proposed for the first time on a polyether sulfone (PES) membrane platform. The small pore size and low wettability (θ ∼82°) of the membrane disallowed the dissipation of analyte droplets on the surface, thus localizing it onto nanoliter arrayed 1,10-phenanthroline spots. Under optimized conditions and within ∼5 min, an acceptable limit of detection (0.1 μg mL-1) and linear dynamic range (1 - 100 μg mL-1) were achieved. The proposed method was also successfully applied for indirect determination of Fe3+ ions in synthetic samples after reduction to Fe2+ using SO2. The performance of the proposed sensor was validated for its robustness and stability. Due to high selectivity and accuracy, the method was satisfactorily applied for the analysis of Fe2+/Fe3+ species in marine water samples. The proposed method is an easy and low-cost system coupled with good reproducibility and ruggedness, applicable for point-of-use testing.

Poly(methyl methacrylate) modified cellulose fibers patterned with highly selective chromogenic reagent for rapid and trace determination of Co2+ in water

A simple one-step assay for the trace determination of Co2+ was developed on filter paper modified with solubilized polymethyl methacrylate (PMMA) and arrays of 3-[(2-mercapto-vinyl)-hydrazono]-1,3-dihydro-indol-2-one (MHDI) reagent. The paper modified with a thin film of PMMA transformed its surface wettability from hydrophilic (θ ∼ 0°) to hydrophobic (θ ∼ 92°). Goniometry and scanning electron microscopy confirmed modification of cellulose fibers. On a low-wetting surface, analyte droplet could be confined onto the MHDI spot, allowing visual detection of 1 μM concentration of Co2+ within 10 min. The limit of detection (LOD) was three orders of magnitude superior to that of a similar assay executed on unmodified paper. The established method is the first of its kind for Co2+ determination with a wide linear dynamic range (101 to 104 μM) coupled with good reproducibility, ruggedness and point-of-use testing. Due to high selectivity towards Co2+ and minimum interference from diverse ions, the developed probe was successfully applied for the trace analysis of Co2+ in tap and industrial wastewater samples. The established method was successfully validated using ICP-OES analysis. The proposed assay could be compared favorably to most of the reported methods for Co2+ determination in terms of ease, cost-effectiveness and analysis time. The recoveries from the recognized method were >90%, confirming its potential use for sensing Co2+.