Gas sensors based on mass-sensitive transducers. Part 2: Improving the sensors towards practical application

Within the framework outlined in the first part of the review, the second part addresses attempts to increase receptor material performance through the use of sensor systems and chemometric methods, in conjunction with receptor preparation methods and sensor-specific tasks. Conclusions are then drawn, and development perspectives for gravimetric sensors are discussed.

Furo[3,2-c]coumarins carrying carbon substituents at C-2 and/or C-3. Isolation, biological activity, synthesis and reaction mechanisms

The isolation, biological activity and synthesis of natural furo[3,2-c]coumarins are presented, covering mainly the developments in the last 35 years. The most relevant approaches toward the synthesis of 2-substituted, 3-substituted and 2,3-disubstituted heterocycles are also discussed, with emphasis on the efficiency of the processes and their mechanisms.

A Quartz Crystal Microbalance Immunosensor for Stem Cell Selection and Extraction

A cost-effective immunosensor for the detection and isolation of dental pulp stem cells (DPSCs) based on a quartz crystal microbalance (QCM) has been developed. The recognition mechanism relies on anti-CD34 antibodies, DPSC-specific monoclonal antibodies that are anchored on the surface of the quartz crystals. Due to its high specificity, real time detection, and low cost, the proposed technology has a promising potential in the field of cell biology, for the simultaneous detection and sorting of stem cells from heterogeneous cell samples. The QCM surface was properly tailored through a biotinylated self-assembled monolayer (SAM). The biotin–avidin interaction was used to immobilize the biotinylated anti-CD34 antibody on the gold-coated quartz crystal. After antibody immobilization, a cellular pellet, with a mixed cell population, was analyzed; the results indicated that the developed QCM immunosensor is highly specific, being able to detect and sort only CD34+ cells. Our study suggests that the proposed technology can detect and efficiently sort any kind of cell from samples with high complexity, being simple, selective, and providing for more convenient and time-saving operations.

Total syntheses of gerberinol I and the pterophyllins 2 and 4 using the Casnati–Skattebøl reaction under different conditions

The total syntheses of the title compounds were achieved from a single coumarin precursor, taking advantage of the temperature-dependent divergent outcomes of the Casnati–Skattebøl reaction.

A three-step synthetic approach to asymmetrically functionalized 4H-cyclopenta[2,1-b:3,4-b']dithiophenes

A convenient and efficient three-step route toward both symmetrically and asymmetrically functionalized 4H-cyclopenta[2,1-b:3,4-b']dithiophenes has been developed. Using this method a broad collection of functionalized bridged bithiophenes can smoothly be accessed. Starting from 3-bromo-2,2'-bithiophene, prepared by Kumada coupling of 2-thienylmagnesium bromide with 2,3-dibromothiophene under Pd(dppf)Cl(2) catalysis, lithiation and subsequent reaction with dialkyl ketones afforded (a)symmetrically dialkylated tertiary alcohol derivatives. By means of final Friedel-Crafts dehydration cyclization in sulfuric acid medium, these derivatives were converted to 4,4-dialkyl-4H-cyclopenta[2,1-b:3,4-b']dithiophenes. Upon replacement of the dialkyl ketone reagent by ethyl levulinate, an ester-functionalized 4H-cyclopenta[2,1-b:3,4-b']dithiophene was prepared, representing an attractive precursor for variously functionalized cyclopentadithiophene compounds.

Landfill siloxane gas sensing using differentiating, responsive phase coated microcantilever arrays

Landfill biogases are being utilized more frequently as a new source of fuel energy. Volatile siloxane compounds usually contained in landfill biogases will form siloxane residues when the gases are burned, which significantly increases abrasion of combustion engines. Research on detection of siloxanes in landfill gas has been active during recent years with the principal analytical technique being gas chromatography/mass spectrometry (GC/MS). In our present work, we introduce a less expensive, compact methodology that employs microcantilever (MC) arrays for sensitive nanomechanical-based gas-phase sensing of the siloxanes. The cantilevers on the MC array were differentially coated on the active, nanostructured side with different responsive phases, and composite responses (magnitude of siloxane-induced MC bending) for four siloxanes were collected that exhibited selective signatures to aid in recognizing each siloxane. Limits of detection (LODs) derived from linear calibration plots were down to the sub-parts-per-million range, a sensitivity that is comparable with that of GC/MS reported by other researchers. Studies were performed in rather inert helium environment and a realistic matrix, and the overall response profiles and LODs were similar for both matrixes. A 5 week long-term reproducibility study illustrates the stability of the MC array. Moreover, the portable character of the MC array setup makes our method a very promising way to facilitate in-field detection of siloxanes in landfill gas in the future.

Conducting polymers in chemical sensors and arrays

The review covers main applications of conducting polymers in chemical sensors and biosensors. The first part is focused on intrinsic and induced receptor properties of conducting polymers, such as pH sensitivity, sensitivity to inorganic ions and organic molecules as well as sensitivity to gases. Induced receptor properties can be also formed by molecularly imprinted polymerization or by immobilization of biological receptors. Immobilization strategies are reviewed in the second part. The third part is focused on applications of conducting polymers as transducers and includes usual optical (fluorescence, SPR, etc.) and electrical (conductometric, amperometric, potentiometric, etc.) transducing techniques as well as organic chemosensitive semiconductor devices. An assembly of stable sensing structures requires strong binding of conducting polymers to solid supports. These aspects are discussed in the next part. Finally, an application of combinatorial synthesis and high-throughput analysis to the development and optimization of sensing materials is described.

Carbon nanotube stabilised emulsions for electrochemical synthesis of porous nanocomposite coatings of poly[3,4-ethylene-dioxythiophene]

The amphiphobic nature of carbon nanotubes allows them to stabilise droplets of water-insoluble monomers dispersed in the aqueous nanotube suspension, leading to a flexible route to electrochemical synthesis of useful nanoporous composites of nanotube doped conducting polymers, and potentially to other chemistry involving reactants incompatible in the same medium.