Development of QCM Trimethylamine Sensor Based on ...

1. Introduction

Biogenic amines are formed by the activity of bacterial amino acid decarboxylase during the degradation processes of proteins, which have a carcinogenic effect on human body and can be used to indicate bacterial contamination. Being one of biogenic volatile amines, trimethylamine is a good target for the detection of biogenic amines to evaluate the quality of meat food products [ 1 3 ]. In human body, trimethylamine is derived from diet either directly from the consumption of foods containing trimethlamine, or by the intake of food containing precursors to trimethylamine such as trimethylamine-N-oxide, choline and L-carnitine. Normally, the flavin-containing monooxygenase isoform 3 (FMO3) enzyme converts fishy-smelling trimethylamine into another molecule that has no odor. If the enzyme is deficient or its activity is reduced, trimethylamine is not processed properly and can build up in the body. As excess trimethylamine is released in a person's sweat, urine, and breath, it causes the strong odor characteristic of trimethylaminuria [ 4 ]. Trimethylamine is also of clinical interest because of its potential to contribute to neurological toxicity and &#;uraemic breath&#; in patients with end-stage renal disease [ 5 ]. Together with triethylamine, trimethylamine is found to be emitted by building materials degraded by microbial growth [ 6 ]. Trimethylamine has an unpleasant smell, and is irritant to the skin, eyes, mucous membranes and respiratory tract [ 7 ].In a word, a rapid, sensitive, low-cost method to detect trimethylamine is meaningful.

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2, 8-

Various analytical methods have been reported in literature to detect trimethylamine [ 1 11 ]. However, all these methods (photometry, gas chromatography, colorimetric analysis, high performance liquid chromatography, ion mobility spectrometry, etc.) are relatively cumbersome, time consuming and require experienced operators.

Polyaniline, a kind of conductive conjugated polymer, has been regarded as a good sensing material due to its advantages of gas sensing ability and optimum performance at room temperature. It has been exploited in thin film sensors for several gas molecules as well as volatile organic compounds [ 12 16 ]. In spite of the various advantages of polyaniline based gas sensors, some fundamental problems, such as long-time instability and irreversibility and low selectivity, still persist [ 17 ]. Usually solubility of polyaniline is a problem to fabrication quality films. We have recently investigated the method to prepare water-soluble polyaniline based on oxidative polymerization. Moreover, the effect of trimethylamine on the conductivity of polyaniline was investigated [ 18 ].

f

) as a function of the mass (Δ

m

) added to the crystal:

Δ f = 2 f 0 2 A ρ q υ q Δ m

(1)

f

is the observed frequency change (Hz),

f

0 is the fundamental resonant frequency of crystal, A is the active area of the crystal (between electrodes),

ρq

is the density of quartz and

υq

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Visual Merchandising: How to Make Standout Product ... is the shear wave velocity in the quartz. Quartz crystal microbalance (QCM) sensors were widely investigated due to their high sensitivity, durability and linearity for mass of the target materials [

QCM sensor can be constructed by coating the surface of a quartz crystal electrode with a film capable of interaction with the environment of interest. The operating principle of QCM sensors is based on the interaction between the surface of a quartz crystal coated with the sensing materials and the target materials. The Sauerbrey equation was developed for oscillation in air and only applies to rigid mass attached to the crystal [ 19 ]. It gives the change in the oscillation frequency of piezoelectric quartz (Δ) as a function of the mass (Δ) added to the crystal:where Δis the observed frequency change (Hz),is the fundamental resonant frequency of crystal, A is the active area of the crystal (between electrodes),is the density of quartz andis the shear wave velocity in the quartz. Quartz crystal microbalance (QCM) sensors were widely investigated due to their high sensitivity, durability and linearity for mass of the target materials [ 20 24 ].

Chemiresistors are the most popular device configuration of gas sensors based on conducting polymer. However, the resistance of chemiresistor is influenced by many ambient factors, and not only determined by the resistance of the conducting polymer sensing film, but also the contact resistance of electrodes. Moreover, other disadvantages for use of chemiresistors are low limit of detection and sensitivity, compared with sensors based on other configurations such as transistors, optic devices and QCMs. For transistor, its preparation and characterization is slightly complicate. The sensitivity of optic sensors is high, but the detecting procedure is complicate. Because QCM is rather sensitive to mass change, adsorbing a very small amount of analyte can be detected through frequency change. Although a number of polymers have been successfully employed in the coating of QCM sensors [ 20 24 ], polyaniline-coated QCM gas sensor has seldom been investigated. Therefore, we attempted to coat a polyaniline film on a quartz crystal surface, to make a low-cost, high-sensitivity and rapid-response QCM trimethlamine gas sensor. The performance of the sensor was investigated.

From the reviews:

"Distinguished by its attention to the practicalities of working with real crystals&#;a lucid and relatively concise account of modern crystal structure solution &#;valuable to anyone who has an interest in crystal structure refinement." The Geological Journal

"The book provides a nice balance between describing the mathematical fundamentals and offering practical advice on how to solve a crystal structure&#; appropriate for an undergraduate audience (particularly in chemistry) and for graduate students or researchers who find they need a better grasp of the subject&#; a very helpful addition to the collection of introductory texts in X-ray crystallography. Especially for its treatment of common errors in the collection of intensity data and in the interpretation of results."

Acta Crystallographica

"Details at great length the inherent pitfalls and errors that one may encounter when calculating crystal structures using new software programs. The author does an excellent job of describing these errors and ways to recognize them when they appear in your calculations." Mineralium Deposita

From the reviews of the second edition:

"This textbook gives a concise introduction to modern crystal structure determination &#; . The theoretical sections are supported by many illustrations, and lay emphasis on a good understanding &#; . The most important data collection techniques &#; are discussed from a practical point of view. Many tips and insights help readers to recognise and avoid possible errors and traps, and to judge the quality of results." (Chimie Nouvelle Societe Royale de Chimie, Vol. 23 (89), juin, )

&#;&#;Crystal Structure Determination&#; gives a concise introduction to the subject, with particular emphasis placed on the manner in which contemporary analysis actually occurs. &#; The strengths of this book are numerous. The presentation is excellent: the diagrams are plentiful and oftenimpressive, and the formatting of the text is very pleasing to the eye. &#; the research chemist with a desire to appreciate more fully a technique that they are likely to use with increasing frequency &#; the book should be a helpful companion.&#; (Andrew Bond, Crystallography News, June, )

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