Electrochemical enzymatic biosensor with long-term stability using hybrid mesoporous membrane.

An acetylcholinesterase-immobilized sensor unit was successfully prepared by encapsulating the enzyme within hybrid mesoporous silica membranes (F127-MST). Through a novel combination with tetracyanoquinodimethane, both acetylcholine and organophosphorus pesticides were successfully detected with high sensitivity. Furthermore, we manufactured the working prototype of an enzyme sensor with this sensor unit for detecting dichlorvos, aldicarb and parathion. At present, the detection limit in this working prototype either equaled or surpassed that of others. Also, we have the advantage of increased stability of the enzyme against the outer environment by encapsulation of the enzymes into a silica nanospace. Consequently, acetylcholinesterase immobilized in F127-MST is a practical sensor with high sensitivity, reusability, and storage stability.

Preparation of copper nitride (Cu3N) nanoparticles in long-chain alcohols at 130-200 °C and nitridation mechanism.

In our laboratory, we are studying copper nitride (Cu3N) nanoparticles as a novel conductive ink that is stable to oxidation and can be metallized at low temperature. In this study, Cu3N nanoparticles prepared via the reaction of copper(II) acetate monohydrate with ammonia gas in long-chain alcohol solvents were characterized by X-ray diffraction analysis, transmission electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis. In addition, we used thermogravimetry-differential thermal analysis to compare the thermal decomposition properties of the prepared Cu3N particles and commercially available Cu3N particles. The decomposition temperature of the prepared particles was more than 170 °C lower than that of the commercial particles. We also examined the influences of the reaction temperature and the alkyl chain length of the alcohol solvent on the product distribution of the reaction and the morphology of the particles. Our results indicated that increasing the solvent hydrophobicity and eliminating water from the reaction system by increasing the temperature affected the product distribution. On the basis of an observation of chromatic change of the reaction solvent and an analysis of the byproducts in the alcohol solvent after the reaction, we propose a mechanism for the formation of Cu3N.

Microporous organic-inorganic nanocomposites as the receptor in the QCM sensing of toluene vapors.

We have used novel microporous biphenylene-pillared layered silicates as receptors in a quartz crystal microbalance (QCM) for sensing toluene vapors. The silicate was successfully coated on a QCM electrode modified with 2-aminoethanethiol. The resultant electrode showed quantitative frequency responses due to enhanced adhesion between the silicate and the electrode. The silicate-coated electrodes also performed better than polystyrene-coated electrodes in terms of both sensitivity and reproducibility of the responses for toluene vapors exposures because the silicate has an organically-modified open-framework structure with a high surface area. In addition, the electrodes revealed the higher sensitivity for toluene vapors than those for alcohol vapors, suggesting selectivity toward sensing toluene vapors probably due to the π-π stacking interaction between biphenylene units and toluene molecules. Hence, we anticipate that the materials are promising to be used as receptors in QCM devices for sensing aromatic vapors.

A novel, disposable, screen-printed amperometric biosensor for ketone 3-ß-hydroxybutyrate fabricated using a 3-ß-hydroxybutyrate dehydrogenase-mesoporous silica conjugate.

A disposable amperometric biosensor for ketone 3-ß-hydroxybutyrate (3HB) has been developed successfully. The sensor is based on a screen-printed carbon electrode containing Meldola's Blue (MB) and sensing components containing nicotinamide adenine dinucleotide (NAD(+)) and 3-ß-hydroxybutyrate dehydrogenase (3HBDH) immobilized in mesoporous silica (FSM8.0) using an aqueous photo-cross-linkable polymer matrix of polyvinyl alcohol (O-391), and it requires only a small sample volume of 10 µL for the measurement. The behavior of a resulting biosensor, i.e., 3HBDH-FSM8.0/NAD(+)/MB-SPCE, was examined in terms of NAD(+) concentration for construction, pH, applied potential, operational range, selectivity, and storage stability. The sensor showed an optimum response at a pH of 7.6 and at an applied potential of -50 mV. The determination range and the response time for 3HB were from 30 µM to 8 mM and approximately 30 s, respectively. In addition, the sensor was quite stable and maintained >90% of its initial response after being stored for over 6 months. This result implies that our method provides a novel biosensor for ketone 3-ß-hydroxybutyrate which is easy-to-use, cost-effective, and has good reproducibility, which are vital for commercial purposes.

An enzyme-encapsulated microreactor for efficient theanine synthesis.

A flow-type microreactor containing glutaminase-mesoporous silica composites with 10.6 nm pore diameter (TMPS10.6) was developed for the continuous synthesis of theanine, a unique amino acid. High enzymatic activity was exhibited by the local control of the reaction temperature.

Amperometric L-lactate biosensor based on screen-printed carbon electrode containing cobalt phthalocyanine, coated with lactate oxidase-mesoporous silica conjugate layer.

A novel amperometric biosensor for the measurement of L-lactate has been developed. The device comprises a screen-printed carbon electrode containing cobalt phthalocyanine (CoPC-SPCE), coated with lactate oxidase (LOD) that is immobilized in mesoporous silica (FSM8.0) using a polymer matrix of denatured polyvinyl alcohol; a Nafion layer on the electrode surface acts as a barrier to interferents. The sampling unit attached to the SPCE requires only a small sample volume of 100 µL for each measurement. The measurement of l-lactate is based on the signal produced by hydrogen peroxide, the product of the enzymatic reaction. The behavior of the biosensor, LOD-FSM8.0/Naf/CoPC-SPCE, was examined in terms of pH, applied potential, sensitivity and operational range, selectivity, and storage stability. The sensor showed an optimum response at a pH of 7.4 and an applied potential of +450 mV. The determination range and the response time for L-lactate were 18.3 µM to 1.5 mM and approximately 90s, respectively. In addition, the sensor exhibited high selectivity for L-lactate and was quite stable in storage, showing no noticeable change in its initial response after being stored for over 9 months. These results indicate that our method provides a simple, cost-effective, high-performance biosensor for l-lactate.

Enhancement in thermal stability and resistance to denaturants of lipase encapsulated in mesoporous silica with alkyltrimethylammonium (CTAB).

We assembled a highly durable conjugate with both a high-density accumulation and a regular array of lipase, by encapsulating it in mesoporous silica (FSM) with alkyltrimethylammonium (CTAB) chains on the surface. The activity for hydrolyzing esters of the lipase immobilized in mesoporous silica was linearly related to the concentration of lipase, whereas that of non-immobilized lipase showed saturation due to self-aggregation at a high concentration. The lipase conjugate also had increased resistance to heating when stayed in the silica coupling with CTAB. In addition, encapsulating the enzyme with FSM coupled CTAB caused the lipase to remain stable even in the presence of urea and trypsin, suggesting that the encapsulation prevented dissociation and denaturing. This conjugate had much higher activity and much higher stability for hydrolyzing esters when compared to the native lipase. These results show that FSM provides suitable support for the immobilization and dispersion of proteins in mesopores with disintegration of the aggregates.