David K. Daniel

Enzyme based Biosensor for Heavy Metal Ions Determination

ABSTRACT Sol-gel-immobilized-urease conductometric biosensor on a thick film interdigitated electrode was developed. The biosensor can be used for heavy metal ions determination in liquid samples. The biosensor exhibited good response to changes in urea concentration within the range of 1mM to 15 mM. After standardizing the sensor for Urea, the biosensor has been used to determine the heavy metal ions of different concentrations. The concentration range of Urea that can be detected by using this sensor is 1mM to 15mM.The heavy metals range is from 0.1mM to 10mM. Among the three metals used, the amount of inhibition is found to be more in Cadmium, then Copper and then Lead. The sensitivity is 1 mM in spectrophotometric technique and 5 mM in electrical method. The described sensor is tested for synthetic effluents in laboratory conditions. By further refinement, it can be used to test real industrial samples.

ENZYME BASED SENSOR FOR DETECTION OF UREA IN MILK

ABSTRACT Enzyme based sensor for detection of urea in milk was constructed using a piezo-electric sensor, which measures the pressure of the gas, evolved in the sample. The sensor showed linear behavior for varying concentrations of urea in the samples. The time response of the sensor was evaluated and liquid to gas ratio of 1:2.5 was found to give satisfactory output by the sensor. The results indicate that this technique can be effectively used to detect urea levels in milk.

CARBON DIOXIDE FIXATION BY CHLORELLA MINUTISSIMA BATCH CULTURES IN A STIRRED TANK BIOREACTOR

ABSTRACT Increasing concentrations of CO2 in the atmosphere is causing severe environmental destruction to the earth. To capture the excess CO2, its microalgal sequestration is increasingly being explored. This technique could become a profitable industry that would help mitigate global warming and produce a large number of value-added products like pigments, carotenoids, carbohydrates, lipids, etc. In this regard, three microalgal strains viz., Calothrix sp., Spirulina platensis and Chlorella minutissima were studied for their growth characteristics. Based upon the kinetic parameters, possible by-products, tolerance to CO2, etc., the best strain was selected for further studies. The optimum pH, photoperiod, nitrate concentration and light intensity for this strain were experimentally determined. Also, studies were conducted with and without baffles, with varying aeration rates and with two different impellers and i.e., marine propeller and disc turbine impeller, in the presence of air alone and a mixture containing air with 15% CO2. Among the three strains studied, C. minutissima was found to be the best strain for further work. It has maximum biomass productivity at pH 6, photoperiod of 14 h light:10 h dark cycles, 5 g/l nitrate and 6000 lx light intensity. Runs with baffles yielded higher biomass. Marine propeller gave better biomass yields in both runs i.e., with and without additional CO2. Also, the optimum aeration rate was determined to be 1 lpm. The carbohydrate, lipid, protein, chlorophyll and carotenoid content of the biomass were estimated.

Biosensor to Detect Chromium in Wastewater

ABSTRACT A urease based biosensor for the determination of chromium ions in wastewater using modified sol gel immobilization technique was developed. Crude urease from Dolichos uniflorus immobilized on non woven cellulose swab was used as the bio recognition element. The maximum velocity (Vm) decreased from 10.62 mM/min for the free urease to 3.28 × 10−3 mM/min for the immobilized urease, while the change in the saturation constant (Km) was from 20.044 mM to 22.049 mM. The performance of the sensor was evaluated and the factors affecting inhibition and immobilization of the enzyme were investigated. The sensor was operational when used for six times after which the operational stability reduced by 6%. The sensor could be stored for four days after which the storage stability decreased by 2%. The activity of the immobilized urease was restored up to 12% of its original activity after inhibition by chromium. The biosensor developed showed high reproducibility when tested with water samples.

Lipase‐catalyzed esterification of palmarosa oil

The present study was carried out with free lipase to study the conversion of geraniol of palmarosa oil to geranyl acetate using acetic acid as acyl donor. The significant factors such as temperature, enzyme concentration and molar ratio of the reactants were investigated for their effects on the ester conversion. A temperature of 60°C and 50 μL of the enzyme solution were found to give the best results for 75 mM of each substrate. The percentage of esterification estimated by both gas chromatographic analysis (which indicated product formation) and titrimetry (which showed acid consumption, i.e. ester formed) was found to be in good agreement. A mechanism for the reaction was proposed, involving nonlinear inhibition studies (inhibition by acid), validation of the reaction and prediction of the kinetic parameters using polymath. Substrate inhibition with dead end complex of acetic acid was found to represent the kinetic data.

Progress in enzyme inhibition based detection of pesticides

The previous few decades have seen the development of biosensors and their use in monitoring of pesticides in food and environmental samples. Although inhibition‐based biosensors have been subject of several recent research works, their performance characteristics greatly depend on the type of immobilization and the presence of interfering compounds in the samples. Moreover, sensitivity, detection limits, and rapidity of the response are few of the other major features that need to be investigated further if they are to become operationally user‐friendly. This review will highlight research carried out in the past on biosensors that are based on enzyme inhibition for determination of organophosphorus compounds and carbamate pesticides.

Effect of carbon dioxide on the rheological behavior of submerged cultures of Chlorella minutissima in stirred tank reactors

The objective of this study was to quantify the effect of algal biomass concentration on the rheology of the algal culture broth. Batch cultivations of Chlorella minutissima were carried out with air and carbon dioxide in a stirred tank bioreactor with a working volume of 1.8 L. The apparent viscosity of the culture broth was significantly affected by the cell mass concentrations in the bioreactor. Culture broth containing 50 g/L cell mass from air fed was found to exhibit an apparent viscosity of 1.52 mPa.s. The apparent viscosity of the carbon‐dioxide‐fed cultivations was found to increase by 20% at a shear rate of 100 s−1. The flow behavior of the system was adequately described by the Herschel–Bulkley model with a small yield stress.