A selective and highly sensitive fluorescent probe of Hg in organic and aqueous media: The role of a polymer network in extending the sensing phenomena to water environments

This paper describes the preparation of a hydrophilic copolymer membrane with two comonomers: 1-vinyl-2-pyrrolidone (commercial) and a new water insoluble piperazinedione derivative, which is a fluorogenic mercury sensing motif. The dense membrane permitted the fluorogenic detection of Hg²⁺ in aqueous media. The sensitivity of the membrane this cation was significantly high, with a detection limit of 10 ppt. This limit of detection is much lower than that of DMSO/water solutions of the sensing monomer, which is 10 ppb, and significantly lower than the maximum contaminant level (EPA) in drinking water, 2 ppb.     

A novel electrochemiluminescence glucose biosensor based on alcohol-free mesoporous molecular sieve silica modified electrode

In this study, a thin-film glucose electrochemiluminescence (ECL) biosensor was developed. Ru(bpy)₃²⁺ was doped in alcohol-free low-volume shrinkage mesoporous silica sol-gel with PEG-400 as the template, and glucose dehydrogenase (GDH) was immobilized in polymer Resydrol. NADH, which is produced by the reaction of co-enzyme NAD⁺ and glucose catalyzed by glucose dehydrogenase, reacts with immobilized Ru(bpy)₃²⁺ to generate ECL emission. Among the three types of design including two-layer, mixed and sandwich configuration, the sandwich configuration showed the best sensitivity with the calibration range of 25-2000 μM and the limit of detection of 0.5 μM in a flow injection analysis of glucose. The alcohol-free mesoporous sol-gel and the sandwich design made the biosensor potentially applicable in flow-injection analysis of samples.     

NOx adsorption behavior of LaFeO3 and LaMnO3+δ and its influence on potentiometric sensor response

NO_x adsorption behavior on LaFeO₃ (LFO) and LaMnO_3+δ (LMO) was characterized using temperature controlled methods and mass spectrometry. Temperature program desorption revealed decomposition of complex surface species formation when NO or NO₂ was adsorbed on LFO and LMO. LFO exhibited higher adsorption capacity for NO_x species than LMO and was shown to be more active for NO_x surface conversion. Both effects were attributed to the different B-site cations, with iron in LFO in the 3+ valence state, and manganese in LMO in the 3+ and 4+ valence states. Results from diffuse reflectance infrared spectroscopy were used to identify specific nitrite and nitrate species that are formed on the surfaces of LFO and LMO at room temperature. Temperature programmed reaction revealed a complex NO₂ decomposition mechanism to NO and O₂ for LFO and LMO in which the formation of nitrite and nitrate species serve as intermediates below ∼600 °C. NO_x sensing mechanisms were considered and predicted based on the types and quantities of surface species formed.     

Temperature sensor based on the Er green upconverted emission in a fluorotellurite glass

The temperature dependence of the green upconverted emission from the two thermally coupled ²H_11/2 and ⁴S_3/2 levels of the Er³⁺ ion in a fluorotellurite glass has been analyzed as a function of the optically active ion concentration in order to check its availability as a temperature sensor. The infrared-to-green upconverted emission have been observed by the naked eyes after a cw laser diode excitation at 800 nm. The fluorescence intensity ratio between the thermally coupled emitting levels as well as the temperature sensitivity has been experimentally obtained up to 540 K. A better behaviour as a temperature sensor has been obtained for the less Er³⁺ concentrated glass with a maximum sensitivity of 54 × 10⁻⁴ K⁻¹ at 540 K, one of the highest found in rare-earth doped transparent materials.     

Luminescent Eu(III) hybrid sensors for in situ copper detection

In this work we used the sol-gel technique to develop luminescent Eu(III) transparent films deposited on glass slides to build for sensor devices capable of monitoring transition metal ions in aqueous solutions. The films were obtained from a bis(trialkoxysilyl) organic precursor synthesized from the amide of the 2,6-pyridinedicarboxylic acid (DPA) with aminopropyltriethoxysilane (APTES) in the presence or absence of cetyl trimethyl ammonium bromide (CTAB) surfactant as templating agent and triethylethoxysilane (TEOS) as crosslinker. These sensor devices were used to perform in situ quenching experiments by Cu(II), Fe(III), Co(II) and Ni(II) ions. The results indicate that the templated films allow the detection and quantification of these metals down to ppb levels by means of the values of the Stern-Volmer constants. In particular, it was shown that Cu(II) acts as an extremely efficient quencher (K_SV = 3.5 × 10⁵ M⁻¹) when compared with the results obtained for the other metals, opening the possibility to use these devices as potential Cu(II) sensors for actual applications in aqueous media.     

Influence of pH on particle size and sensing response of chemically synthesized chromium oxide nanoparticles to alcohols

Nanoparticles of chromium oxide have been synthesized by following a co-precipitation route at various pH values of the precursor solution. Structural and morphological analysis were carried out by using XRD and TEM techniques which revealed that the size of nanoparticles synthesized at pH 9 was smaller as compared to those synthesized at other pH values. The thick films of synthesized samples were deposited on alumina substrate and their sensing response to methanol, ethanol and isopropanol was investigated at different operating temperatures. It was observed that all the sensors gave optimum response at 250 °C. It has been observed that sample prepared at pH 9, being a collection of smallest particles as compared to other samples, exhibited high sensing response to alcohol vapour. Sensor response of all the samples tested was significantly higher towards isopropanol vapour than towards methanol or ethanol.In the present study the effect of particle size on intergranular activation energy has been studied as well. It was found that smaller particles possess high activation energy and exhibit higher sensing response as compared to that of larger particles. This type of study may help in the selection of particle suitable for gas sensing.     

Water pre-adsorption effect on room temperature SnO2 nanobelt ethanol sensitivity in oxygen-deficient conditions

The water adsorption effects on room temperature ethanol sensitivity of a SnO₂ single crystal nanobelt was studied. SnO₂ nanobelt showed better electrical conductivity in air than in vacuum. The current increased linearly with relative humidity in air and with water concentration in vacuum. In the presence of water vapor, the SnO₂ nanobelt electrical response was quite different, depending on the H₂O and C₂H₅OH molecules adsorption sequence. The current response to ethanol gas increased substantially when water was pre-adsorbed. However, no change was found without water pre-adsorbtion. This interesting behavior is ascribed to competition between the H₂O and C₂H₅OH molecules trying to adsorb on oxygen sites at the tin oxide surface. Dissociated water acts as the surface conduction channel resulting in better conductivity, while ethanol is physisorbed without water pre-adsorption. Based on this sensing mechanism, SnO₂ nanobelt can be used as a highly efficient ethanol detector in humid air.     

Aging fingerprint characterization of beer using electronic nose

In this work, attempts were made in order to characterize the change of aroma of alcoholic and non alcoholic beers during the aging process by use of a metal oxide semiconductor based electronic nose. The aged beer samples were statistically characterized in several classes. Linear techniques as principal component analysis (PCA) and Linear Discriminant Analaysis (LDA) were performed over the data that revealed non alcoholic beer classes are separated except a partial overlapping between zones corresponding to two specified classes of the aged beers. A clear discrimination was not found among the alcoholic beer classes showing the more stability of such type of beer compared with non alcoholic beer. In this research, to classify the classes, two types of artificial neural networks were used: Probabilistic Neural Networks (PNN) with Radial Basis Functions (RBF) and FeedForward Networks with Backpropagation (BP) learning method. The classification success was found to be 90% and 100% for alcoholic and non alcoholic beers, respectively. Application of PNN showed the classification accuracy of 83% and 100%, respectively for the aged alcoholic and non alcoholic beer classes as well. Finally, this study showed the capability of the electronic nose system for the evaluation of the aroma fingerprint changes in beer during the aging process.     

Adjacent assembly of self-assembled monolayers for the construction of selective bio-platforms

Selective patterning of bio-substances onto solid platforms is of increasing importance in many areas and widely used for various applications ranging from bio-sensing to cell and tissue engineering. In this study, a new fabrication scheme for the construction of highly selective bio-platforms is presented. The method is based on a direct patterning of poly(ethyleneglycol) (PEG) bio-inert layers on a conducting indium tin oxide (ITO) substrate using electron beam lithography and subsequent assembly of modified amine reactive layers onto the exposed areas. The process is found to create very high “surface contrast” between adhesive and repulsive regions onto the substrate. The platforms are shown to be enable efficient for selective adsorption of a variety of bio-substances including protein arrays, latex beads, and single cells. The high resolution of the technique makes it also applicable for the construction and deposition of bio-structures at the sub-micron scale. The reported technique employs standard lithography and surface chemistry processes, which makes it useful and easy to adopt for a variety of applications and other conductive substrates.