Meena Karve

Invertase inhibition based electrochemical sensor for the detection of heavy metal ions in aqueous system: Application of ultra-microelectrode to enhance sucrose biosensor's sensitivity.

We are reporting fabrication and characterization of electrochemical sucrose biosensor using ultra-microelectrode (UME) for the detection of heavy metal ions (Hg(II), Ag(I), Pb(II) and Cd(II)). The working UME, with 25 microm diameter, was modified with invertase (INV, EC: 3.2.1.26) and glucose oxidase (GOD, EC: 1.1.3.4) entrapped in agarose-guar gum. The hydrophilic character of the agarose-guar gum composite matrix was checked by water contact angle measurement. The atomic force microscopy (AFM) images of the membranes showed proper confinement of both the enzymes during co-immobilization. The dynamic range for sucrose biosensor was achieved in the range of 1 x 10(-10) to 1 x 10(-7)M with lower detection limit 1 x 10(-10)M at pH 5.5 with 9 cycles of reuse. The spectrophotometric and electrochemical studies showed linear relationship between concentration of heavy metal ions and degree of inhibition of invertase. The toxicity sequence for invertase using both methods was observed as Hg(2+)>Pb(2+)>Ag(+)>Cd(2+). The dynamic linear range for mercury using electrochemical biosensor was observed in the range of 5 x 10(-10) to 12.5 x 10(-10)M for sucrose. The lower detection limit for the fabricated biosensor was found to be 5 x 10(-10)M. The reliability of the electrochemical biosensor was conformed by testing the spike samples and the results were comparable with the conventional photometric DNSA method.

Glutaraldehyde activated eggshell membrane for immobilization of tyrosinase from Amorphophallus companulatus: Application in construction of electrochemical biosensor for dopamine

Tyrosinase from a plant source Amorphophallus companulatus was immobilized on eggshell membrane using glutaraldehyde. Among the three different approaches used for immobilization, activation of eggshell membrane by glutaraldehyde followed by enzyme adsorption on activated support could stabilize the enzyme tyrosinase and was found to be effective. K(m) and V(max) values for dopamine hydrochloride calculated from Lineweaver-Burk plot were 0.67 mM and 0.08 mM min(-1), respectively. Studies on effect of pH showed retention of more than 90% activity over a pH range 5.0-6.5. Membrane bound enzyme exhibited consistent activity in the temperature range 20-45 degrees C. Shelf life of immobilized tyrosinase system was found to be more than 6 months when stored in phosphate buffer at 4 degrees C. An electrochemical biosensor for dopamine was developed by mounting the tyrosinase immobilized eggshell membrane on the surface of glassy carbon electrode. Dopamine concentrations were determined by the direct reduction of biocatalytically liberated quinone species at -0.19 V versus Ag/AgCl (3M KCl). Linearity was observed within the range of 50-250 microM with a detection limit of 25 microM.

Conductivity-Based Catechol Sensor Using Tyrosinase Immobilized in Porous Silicon

A conductivity-based catechol biosensor was developed using porous silicon as an immobilization matrix for enzyme tyrosinase. The enzyme was extracted from plant source Amorphophallus companulatus and immobilized in an electrochemically etched surface of p-type silicon. The presence of enzyme in a porous structure and the retention of enzyme activity were confirmed by scanning electron microscopy and spectrophotometric studies, respectively. The principle of the sensor is based on the change in the conductivity of the tyrosinase-entrapped porous silicon matrix. When the entrapped tyrosinase interacted with catechol, the change in the current voltage (I-V) characteristics was obtained, which was proportional to analyte concentration. The analytical characteristics of the sensor including response time, linearity range, lower detection limit, reusability, and storage stability were studied.

Biopolymer-Polyaniline Composite for a Wide Range Ammonia Gas Sensor

This paper reports the wide range ammonia sensing behavior of biopolymer polyaniline composite. The agarose-guar gum-polyaniline (A-G-PANI) composite films were prepared by the in situ synthesis of polyaniline in the biopolymeric matrix. The polyaniline biocomposite exhibits an interpenetrated network structure as confirmed by field emission scanning electron microscopy. The synthesized polyaniline biopolymer composite shows an excellent ammonia sensing behavior over a wide range of 10-90000 ppm (9%). The sensor shows high performance in terms of sensitivity factor (Rgas/Rair) ranging from 1.07 to 34.95 in the entire concentration range. The response time and recovery time of the sensor varies from 2 to 5 min and 5 to 25 min, respectively, with respect to the increase in the concentration of gas. The sensor shows selective response against H2S, ethanol, methanol, and acetone. The enhanced performance of the sensor is attributed to the presence of large number of sites provided by the interpenetrated network structure of polyaniline biocomposite. The electrical circuit model for A-G-PANI is constructed using the electrical impedance spectroscopy, and a probable mechanism is proposed for detection over a wide range.

Agarose–guar gum assisted synthesis of processable polyaniline composite: morphology and electro-responsive characteristics

The present communication reports the development of processable polyaniline (PANI) in the film form via agarose–guar gum (A–G) assisted in situ polymerization of aniline using potassium dichromate as an oxidant. The network structure of A–G not only provides the mechanical support to polyaniline, but also a microporous template, which allows the reinforcement of PANI into nanostructures with an interpenetrated polymer network between PANI and A–G, as evidenced by optical microscopy and SEM. The FTIR and TGA analysis confirms the formation of an agarose–guar gum–polyaniline composite (A–G–PANI) having hydrogen bonding interactions. The A–G–PANI film has better adherence property on the glass substrate as compared with PANI. The A–G–PANI composite shows appreciable DC conductivity in the range of 10−3–10−2 S cm−1 and electrochemical activity, having oxidation–reduction transitions corresponding to polyaniline. It exhibits both ionic and electronic conductivity as confirmed by EIS. The electro-responsive characteristics exhibited by the novel A–G–PANI composite make it a promising electrode material for the construction of chemical sensors and biosensors.

A novel inhibition based biosensor using urease nanoconjugate entrapped biocomposite membrane for potentiometric glyphosate detection

A potentiometric biosensor based on agarose-guar gum (A-G) entrapped bio-nanoconjugate of urease with gold nanoparticles (AUNps), has been reported for the first time for glyphosate detection. The biosensor is based on inhibition of urease activity by glyphosate, which was measured by direct potentiometry using ammonium ion selective electrode covered with A-G-urease nanoconjugate membrane. TEM and FTIR analysis revealed nanoconjugate formation and its immobilization in A-G matrix respectively. The composite biopolymer employed for immobilization yields thin, transparent, flexible membrane having superior mechanical strength and stability. It retains the maximum activity (92%) of urease with negligible leaching. The conjugation of urease with AUNps allows improvement in response characteristics for potentiometric measurement. The biosensor shows a linear response in the glyphosate concentration range from 0.5ppm-50ppm, with limit of detection at 0.5ppm, which covers maximum residual limit set by WHO for drinking water. The inhibition of catalytic activity of urease nanoconjugate by gyphosate was confirmed by FTIR analysis. The response of fabricated biosensor is selective towards glyphosate as against various other pesticides. The biosensor exhibits good performance in terms of reproducibility and prolonged storage stability of 180days. Thus, the present biosensor provides an alternative method for simple, selective and cost effective detection of glyphosate based on urease inhibition.

Development of acid phosphate inhibition-based amperometric biosensor for determination of inorganic phosphate

The present study describes construction of amperometric biosensor for determination of inorganic phosphate (IP) using single enzyme acid phosphatase (ACP). A blend of biopolymers agarose and guar gum was used to immobilize ACP and estimation of inorganic phosphate was carried out electrochemically using substrate L-ascorbic acid-2-phosphate. Enzyme catalyzes substrate hydrolysis and ascorbic acid is formed as a product which shows oxidation peak at +0.08 V. This peak intensity decreases when enzyme electrode is dipped in inorganic phosphate solution prior to monitoring substrate hydrolysis. The response is linear in the range of 1 × 10-6 M to 4 × 10-5 M IP with a detection limit of 5 × 10-7 M. The enzyme sensor was stable over a period of three months with a marginal loss in enzyme activity when stored at 4° C under dry conditions. This single enzyme approach tries to overcome the drawbacks of multi-enzyme system for inorganic phosphate determination yet maintaining sensitivity and selectivity of enzymatic methods. Possible influence of other species coexisting with inorganic phosphate in water samples was investigated. The performance of this single enzyme based biosensor was in good agreement with earlier reports on biosensors for inorganic phosphate determination using multi-enzyme approach.