A comprehensive review on the development and state of the art of colorimetric and fluorometric sensor arrays is presented Chemical sensing aims to detect subtle changes in the chemical environment by transforming relevant chemical or physical properties of molecular or ionic species (ie, analytes) into an analytically useful output Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties (eg, mass) The chemical specificity of the olfactory system does not come from specific receptors for specific analytes (eg, the traditional lock-and-key model of substrate-enzyme interactions), but rather olfaction makes use of pattern recognition of the combined response of several hundred olfactory receptors In a similar fashion, arrays of chemoresponsive colorants provide high-dimensional data from the color or fluorescence changes of the dyes in these arrays as they are exposed to analytes This provides chemical sensing with high sensitivity (often down to parts per billion levels), impressive discrimination among very similar analytes, and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, in both the gas and liquid phases Design of both sensor arrays and instrumentation for their analysis are discussed In addition, the various chemometric and statistical analyses of high-dimensional data (including hierarchical cluster analysis (HCA), principal component analysis (PCA), linear discriminant analysis (LDA), support vector machines (SVMs), and artificial neural networks (ANNs)) are presented and critiqued in reference to their use in chemical sensing A variety of applications are also discussed, including personal dosimetry of toxic industrial chemical, detection of explosives or accelerants, quality control of foods and beverages, biosensing intracellularly, identification of bacteria and fungi, and detection of cancer and disease biomarkers

The Optoelectronic Nose: Colorimetric and Fluorometric Sensor Arrays.

Perspectives on oblique angle deposition of thin films: From fundamentals to devices

Porphyrins and related macrocycles have been intensively exploited as sensing materials in chemical sensors, since in these devices they mimic most of their biological functions, such as reversible binding, catalytic activation, and optical changes. Such a magnificent bouquet of properties allows applying porphyrin derivatives to different transducers, ranging from nanogravimetric to optical devices, also enabling the realization of multifunctional chemical sensors, in which multiple transduction mechanisms are applied to the same sensing layer. Potential applications are further expanded through sensor arrays, where cross-selective sensing layers can be applied for the analysis of complex chemical matrices. The possibility of finely tuning the macrocycle properties by synthetic modification of the different components of the porphyrin ring, such as peripheral substituents, molecular skeleton, coordinated metal, allows creating a vast library of porphyrinoid-based sensing layers. From among these, one can...

Porphyrinoids for Chemical Sensor Applications.

http://www.wanglab-tsinghua.com/pdf/2013PMS_321.pdf

Electro-spinning/netting: A strategy for the fabrication of three-dimensional polymer nano-fiber/nets

Environmental Monitoring Ajeet Kaushik,*,†,‡ Rajesh Kumar,*,‡,§ Sunil K. Arya, Madhavan Nair,† B. D. Malhotra, and Shekhar Bhansali‡ †Center for Personalized Nanomedicine, Institute of Neuroimmune Pharmacology, Department of Immunology, Herbert Wertheim College of Medicine, Florida International University, Miami, Florida 33199, United States ‡Bio-MEMS Microsystems Laboratory, Department of Electrical and Computer Engineering, College of Engineering, Florida International University, Miami, Florida 33174, United States Department of Physics, Panjab University, Chandigarh 160014, India Bioelectronics Program, Institute of Microelectronics, A*Star, 11 Science Park Road, Singapore Science Park II, Singapore Department of Biotechnology, Delhi Technological University, Shahbad Daulatpur, Delhi 110042, India

Organic–Inorganic Hybrid Nanocomposite-Based Gas Sensors for Environmental Monitoring

Seven different porphyrin compounds have been investigated as colorimetric gas sensors for a wide range of volatile organic compounds The porphyrins examined were the free base and Mg, Sn, Zn, Au, Co, and Mn derivatives of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine Chloroform solutions of these materials were prepared and changes in their absorption spectra induced by exposure to various organic compounds measured The porphyrins that showed strong responses in solution were selected, and Langmuir-Blodgett films were prepared and exposed to the corresponding analytes This was done to determine whether they are useful materials for solid state thin film colorimetric vapor sensors Porphyrins that readily coordinate extra ligands are shown to be suitable materials for colorimetric volatile organic compound detectors However, porphyrins that already have bound axial ligands when synthesized only show a sensor response to those analytes that can substitute these axial ligands The Co porphyrin displays a considerably larger response than the other porphyrins investigated which is attributed to a switch between Co(II) and Co(III) resulting in a large spectral change

Detection of volatile organic compounds using porphyrin derivatives.

Tetracationic porphyrin (TMPyP) molecules were incorporated into an optically transparent TiO 2 thin film, prepared by Glancing Angle Physical Vapour Deposition (GAPVD), by simple infiltration (at pH 6.4). The preparation of optically transparent TMPyP/TiO 2 composite thin films provides a method for the integration of the porphyrin molecules into photonic devices for direct monitoring of gases. Previously, UV–visible and fluorescence spectral techniques have been used to study the reversible protonation of TMPyP in aqueous solution. The optical spectrum of TMPyP shows an intense Soret band at 423 nm with a 22 nm red shift upon protonation by HCl. The experimental conditions for monitoring the concentration of HCl gas by absorption spectroscopy have been optimized. The maximum absorbance change was observed at the Soret band wavelength. A selected temperature of 80 °C and a 300 s recovery period were found to be the optimum operating parameters (response time t 50  = 16.8 ± 0.7 s). The composite with smaller surface concentration of TMPyP ( Г  = 0.3 ×  10 −9  mol cm −2 ) presented the best detection limit (0.1 ppm). The response of the composite sensor was highly stable for several months.

/pdf/a-transparent-tmpyp-tio2-composite-thin-film-as-an-hcl-3vnp9hdozk.pdf

A transparent TMPyP/TiO2 composite thin film as an HCl sensitive optochemical gas sensor

Comparing zinc and manganese porphyrin LB films as amine vapour sensing materials

Microbubbles are bubbles below 1 mm in size and have been extensively deployed in industrial settings to improve gaseous exchange between gas and liquid phases. The high surface to volume ratio offered by microbubbles enables them to enhance transport phenomena and therefore can be used to reduce energy demands in many applications including, waste water aeration, froth flotation, oil emulsion separations and evaporation dynamics. Microbubbles can be produced by passing a gas stream through a micro-porous diffuser placed at the gas–liquid interface. Previous work has shown that oscillating this gas steam can reduce the bubble size and therefore increase energy savings. In this work we show that it is possible to further reduce microbubble size (and consequently maximise the number of bubbles) by varying the frequency of the oscillating gas supply. Three different microbubble generation systems have been investigated; an acoustic oscillation system and a mesh membrane, a fluidic oscillator coupled to a single orifice membrane and a fluidic oscillator coupled to a commercially available ceramic diffuser. In all three bubble generation methods there is an optimum oscillation frequency at which the bubble size is minimised and the number of microbubbles maximised. In some cases a reduction in bubble size of up to 73% was achieved compared with non-optimal operating frequencies. The frequency at which this optimum occurs is dependent on the bubble generation system; more specifically the geometry of the system, the type micro-porous diffuser and the gas flow rate. This work proves that by tuning industrial microbubble generators to their optimal oscillation frequency will result in a reduction of microbubble size and increase their number density. This will further improve gaseous exchange rates and therefore improve the efficiency of the industrial processes where they are being employed to produce bubbles, leading to a reduction in associated energy costs and an increase in the overall economic and energetic feasibility of these processes.

Minimising microbubble size through oscillation frequency control

Changes in the visible absorption spectra of ten free base porphyrin compounds in solution and thin film form upon exposure to a range of volatile organic compounds have been investigated. The functional groups attached to the phenyl rings varied in their electron donating/withdrawing strength. These porphyrins were studied with a view to determining their suitability for use in the fabrication of an optical based gas sensor. It has been found that the sensitivity of these sensor materials depends upon the electron donating/withdrawing strength of the functional groups attached to the phenyl rings.

Stuart A. Brittle

Papers

Detection of volatile organic compounds using porphyrin derivatives.

A transparent TMPyP/TiO2 composite thin film as an HCl sensitive optochemical gas sensor

Comparing zinc and manganese porphyrin LB films as amine vapour sensing materials

Minimising microbubble size through oscillation frequency control

Tuning free base tetraphenylporphyrins as optical sensing elements for volatile organic analytes