Aminopyrene functionalized mesoporous silica for the selective determination of resorcinol

High sensitivity Schottky junction diode based on monolithically grown aligned polypyrrole nanofibers: Broad range detection of m-dihydroxybenzene

Aligned p-type polypyrrole (PPy) nanofibers (NFs) thin film was grown on n-type silicon (100) substrate by an electrochemical technique to fabricate Schottky junction diode for the efficient detection of m-dihydroxybenzene chemical. The highly dense and well aligned PPy NFs with the average diameter (∼150-200 nm) were grown on n-type Si substrate. The formation of aligned PPy NFs was confirmed by elucidating the structural, compositional and the optical properties. The electrochemical behavior of the fabricated Pt/p-aligned PPy NFs/n-silicon Schottky junction diode was evaluated by cyclovoltametry (CV) and current (I)-voltage (V) measurements with the variation of m-dihydroxybenzene concentration in the phosphate buffer solution (PBS). The fabricated Pt/p-aligned PPy NFs/n-silicon Schottky junction diode exhibited the rectifying behavior of I-V curve with the addition of m-dihydroxybenzene chemical, while a weak rectifying I-V behavior was observed without m-dihydroxybenzene chemical. This non-linear I-V behavior suggested the formation of Schottky barrier at the interface of Pt layer and p-aligned PPy NFs/n-silicon thin film layer. By analyzing the I-V characteristics, the fabricated Pt/p-aligned PPy NFs/n-silicon Schottky junction diode displayed reasonably high sensitivity ∼23.67 μAmM(-1)cm(-2), good detection limit of ∼1.51 mM with correlation coefficient (R) of ∼0.9966 and short response time (10 s).

Porphyrin-embedded silicate materials for detection of hydrocarbon solvents

The development of porphyrin-embedded mesoporous organosilicate materials for application to the detection of volatile hydrocarbon solvents is described. Design of the receptor and optical indicator construct begins with parallel selection of the porphyrin indicator and design of the mesoporous sorbent. For the porphyrin indicator, high binding affinity and strong changes in spectrophotometric character upon target interaction are desired. The sorbent should provide high target binding capacity and rapid binding kinetics. A number of porphyrin/metalloporphyrin variants and organosilicate sorbents were evaluated to determine the characteristics of their interaction with the targets, benzene, toluene, and hexane. The selected porphyrin candidates were covalently immobilized within a benzene-bridged sorbent. This construct was applied to the detection of targets using both fluorescence- and reflectance-based protocols. The use of red, green, and blue (RGB) color values from the constructs in a highly simplified detection scheme is described.

Biomimetic sensor for certain phenols employing a copper(II) complex

A new dimeric Cu(II) complex [Cu(mu(2)-hep)(hep-H)](2).2PF(6) (1) containing a bidentate (hep-H = 2-(2-hydroxyethyl)pyridine) ligand was synthesized and characterized by single crystal X-ray diffraction studies. Each Cu ion in 1 is in a distorted square pyramidal geometry. Further 1 is used as a modifier in the construction of a biomimetic sensor for determining phenols [phenol (Phe), resorcinol (Res), hydroquinone (HQ), and catechol (Cat)] in phosphate buffer by using cyclic voltammetry (CV), chronocoulometry, electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and square wave voltammetry (SWV). DPV has been proposed for trace determination of Phe and Res while SWV for HQ and Cat. The method has been applied for the selective and precise analysis of Phe in commercial injections, Res in hair coloring agents, HQ in photographic developers and cosmetics, and Cat in tea samples and guarana tablets. The calibration curves showed a linear response ranging between 10(-6) and 10(-8) M for all four of the analytes with detection limits (3sigma) of 1.04 x 10(-8), 2.31 x 10(-8), 1.54 x 10(-8), and 0.86 x 10(-8) M for Phe, Res, HQ, and Cat, respectively. The lifetime of the biomimetic sensor was 200 days at room temperature (at least 750 determinations). The catalytic properties of 1-CPE were characterized by chronoamperometry and were found to be in good agreement with Michaelis-Menten kinetics.

Mesoporous Silicate Materials in Sensing

Mesoporous silicas, especially those exhibiting ordered pore systems and uniform pore diameters, have shown great potential for sensing applications in recent years. Morphological control grants them versatility in the method of deployment whether as bulk powders, monoliths, thin films, or embedded in coatings. High surface areas and pore sizes greater than 2 nm make them effective as adsorbent coatings for humidity sensors. The pore networks also provide the potential for immobilization of enzymes within the materials. Functionalization of materials by silane grafting or through cocondensation of silicate precursors can be used to provide mesoporous materials with a variety of fluorescent probes as well as surface properties that aid in selective detection of specific analytes. This review will illustrate how mesoporous silicas have been applied to sensing changes in relative humidity, changes in pH, metal cations, toxic industrial compounds, volatile organic compounds, small molecules and ions, nitroenergetic compounds, and biologically relevant molecules.