This work presents an adsorption model based on the Sips isotherm for sensing different concentrations of DNA with open gate AlGaN/GaN high electron mobility field effect transistors (HEMTs). Probe-DNA was immobilized on the transistor gate before the application of target-DNA. Concentrations of 10-15 to 10-6 mol/L were tested. The sensor has a detection limit of 10-12 mol/L and saturates after the addition of 10-8 mol/L target-DNA.

Extended research has been developed in the use of wheat straw (WS) as biomass for the production of biofuels (bioethanol), including the processes of degradation of cellulose by enzymatic systems. For centuries, Cellulose has been used by man; however, its enormous potential as a renewable energy source was recognized only after the discovery of cellulose degrading enzymes (cellulases). A wide variety of microorganisms can produce cellulolytic enzymes under appropriate culture conditions and among these microorganisms are filamentous fungi of the genera Trichoderma, Aspergillus, Penicillium and Fusarium. The purpose of this study was to produce cellulase enzyme from previously isolated and characterized filamentous fungi. Cellulytic fungi belonged to Aspergillus flavus, Aspergillus niger, Aspergillus oryzae, Penicillium chrysogenum, Penicillium sp., and Trichoderma harzianum. All these strains were preserved by lyophilization and also kept in sterile media (sand and soil) at 4 °C. The production of cellulases by submerged fermentation was performed in a Mandels mineral medium. The nitrogen sources were urea and ammonium sulfate. Glucose alone was used in the pre-inoculum, and dried and ground wheat straw was used in the fermentation as carbon sources. Subcultures of spore suspensions were incubated with orbital stirring (120 rpm) at 30 °C for 48 hours and used as inoculum for submerged fermentation with wheat straw as substrate in mineral medium with an initial pH of 5. Activity cellulase was determined by the method of 3,5-dinitrosalicylic acid (DNS). The results showed that wheat straw have potential for use as a substrate in the production of cellulases. Aspergillus niger showed the highest enzymatic activity from the cellulase produced 0.051 FPU (filter paper units) after 96 hours of fermentation.

Public health and environmental protection concerns provoked by phenolic compounds pollution impose the development of sensitive, rapid and cost effective methods for in situ phenols monitoring. Given that biosensors based techniques could face these challenges, a variety of such devices was suggested and applied for phenolic compounds quantification. Their majority are based on the polyphenol oxidase (PPO) catalyzed phenols oxidation to catechol and then, to quinones, coupled with the registration of the quinones reduction current. Nevertheless, quinoid products polymerization involving electrode passivation corrupts the biosensors operational stability. Thus, to avoid this drawback, in this work is proposed another approach for phenolic compounds quantification based on the electrochemical detection of the oxygen depletion during PPO catalyzed catechol oxidation using a Clark type electrode with a disposable active enzyme membrane. The oxygen probe was modified in comparison to the commercial ones: its flat front allowed ensuring a good contact with the active enzyme membrane and the gold multicathode uniformly dislocated on the surface of the flat front permitted eliminating O2 diffusional constraints. The active enzyme membrane was prepared by drop-coating of a mixture of PPO and gelatin onto a gelatin-saturated cellulose filter. A linear calibration graph for catechol determination was obtained in the range up to 0.7 mM with a slope of 0.902 μA/mM, at pH 6.5 and ambient temperature. The steady-state response to catechol of the biosensor was reached in 120 s. The biosensor had an excellent reproducibility (RSD<3%) due to the reliable enzyme immobilization technique, allowing the preparation of active enzyme membranes with identical characteristics. The proposed biosensor provided stable response and free of interferences measurements since the unique possible electrochemical reaction is O2 reduction. Another biosensor advantage is associated with the use of disposable prefabricated active enzyme membranes.

This investigation introduces a new very simple and efficient approach for QCM sensor response amplification, developed for hydrolases activity determination. For this purpose, the QCM crystal surface was modified with nanoparticles loaded enzyme substrate. During the enzymatic substrate degradation, the heavier nanoparticles were also released from the sensitive layer together with the substrate degradation products. Nanoparticles removal resulted in QCM signal amplification due to the higher nanoparticles specific mass compared with the specific mass of the substrate.

The suggested concept was successfully applied for creating of simple biosensing platforms for trypsin and lipase activity determination in real time using respectively SiO2 nanoparticles loaded olive oil and Ag nanoparticles loaded gelatin as enzyme substrates. Up to 10 times amplification of the QCM signal was reached applying the proposed approach compared with the common one.