Electrospinning, a simple and versatile method to fabricate nanofibrous supports, has attracted continuous attention in the field of enzyme immobilization. In this study, acetylcholinesterase (AChE) has been successfully immobilized in PVA nanofibers via electrospinning of a mixture of AChE, BSA as an enzyme stabilizing additive and PVA. The maximum activity recovery of immobilized AChE was about 40%. In comparison with free enzyme, the immobilized AChE showed improved stability while retaining a considerable amount of activity at lower pH values. Moreover, the immobilized AChE retained >34% of its initial activity when stored at 30°C for 100 days and retained 70% of its initial activity after ten consecutive reactor batch cycles.

Bioconversion of cellulosic material into glucose needs cellulase enzymes. One of the most important organisms that produces cellulases is Trichoderma reesei, whose cellulose enzymes are probably the most widely used in the industry. However, these enzymes are not stable enough at high pH and temperatures. The optimized synthetic endoglucanase II gene with Pichia pastoris codon preferences was secretary expressed in P. pastoris. Recombinant enzyme characterization showed maximum activity at pH 4.8 and temperature 75 °C, and it demonstrated increasing thermal stability in high temperature. The enzyme maintained its activity in a wide pH range from 3.5 to 6.5. The optimization of fermentation medium was carried out in shaking flasks. Recombinant protein expression at optimum conditions (pH 7, temperature 25 °C, and 1 % methanol induction) for 72 h demonstrated 2,358.8 U/ml endoglucanase activity units. To our knowledge, this is the highest acidic thermophilic endoglucanase activity that is reported in crude intracellular medium in P. pastoris. We conclude that P. pastoris is an appropriate host for high-level expression of optimized endoglucanase gene with improved thermal stability.

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An electrochemical sensor was prepared to detect nicotine by depositing copper nanoparticles (Cu NPs) on the surface of a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes (MWNTs). The modified electrode was characterized by scanning electron microscopy and cyclic voltammetry. The novel-modified sensor exhibited effective electrocatalytic activities toward anodic oxidation of nicotine. Calibration plot showed two linear regions with different sensitivity, 1.121 (r 2 = 0.982) in the range from 1 9 10 -6 to 9 9 10 -5 M and 0.164 (r 2 = 0.982) from 1 9 10 -4 M up to 1 9 10 -3 M. The detection limit was 1 lM. For six parallel detections of 1 mM nicotine, the relative standard deviation was 5.68 %, suggesting that the film-modified electrode had good reproducibility. Experimental parameters affecting the sensor response such as pH, modifier concentration and electrodeposition scan rate were found to be optimum at 7.0, 2 mg mL -1 and 80 mV s -1 , respectively.

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