QCM sensor

An early example of an MIP-QCM sensor was a glucose monitoring system by Malitesta et al. (1999). A glucose imprinted poly(o-phenylenediamine) polymer was electrosynthesized on the sensor surface. This QCM sensor showed selectivity for glucose over other compounds such as ascorbic acid, paracetamol, cysteine, and fructose at physiologically relevant millimolar concentrations. A unique QCM sensor for detection of yeast was reported by Dickert and coworkers (Dickert et al. 2001 Dickert and Hayden 2002). Yeast cells were imprinted in a sol-gel matrix on the surface of the transducer. The MIP-coated sensor was able to measure yeast cell concentrations in situ and in complex media. A QCM sensor coated with a thin permeable MIP film was developed for the determination of L-menthol in the liquid phase (Percival et al. 2001). The MIP-QCM sensor displayed good selectivity and good sensitivity with a detection limit of 200 ppb (Fig. 15.7). The sensor also displayed excellent enantioselectivity and was able to easily differentiate the l- and D-enantiomers of menthol. 

Figure 15.7 Response of the molecular imprinted polymer quartz crystal microbalance (MIP-QCM) sensor to monoterpene analogues ( ) L-menthol, (A) D-menthol, ( ) citronel-lol, (A) citronellal, and (O) menthone. Reprinted from Percival et al. (2001). Copyright 2001 American Chemical Society.

Fig. 3 Relative mass change with time of the QCM sensors featuring MIP-PMMA and NIP-PMMA blend films at 30 °C for sorhed vapours of (a) toluene and (b) 1,4-xylene. At zero time the toluene or 1,4-xylene vapour is passed and at the time of 60 min nitrogen gas is passed (1,1 ) 1,4-xylene-MIP-PMMA, (2, 2 ) toluene-MIP-PMMA, (5,5 ) NIP-PMMA (adapted from [113])...

A variety of chemical gas sensors are or could be used in electronic nose instruments. So far, successful results have been reached with conductive polymer (CP) sensors, metal oxide semiconductor (MOS) sensors, metal oxide semiconductor field effect transistor (MOSFET) sensors, quartz crystal microbalance (QCM) sensors, and infrared sensors. 

The QCM sensors [5] have gained popularity because they are operated at room temperature and allow combinations of selective layers different to those of MOS, MOSFET and PC sensors. The QCM measures physical mass of the analyte by recording the change in frequency of a quartz crystal when the analyte binds to it. Layers of gas chromatographic stationary phases and natural or synthetic lipids can discriminate between alcoholic drinks, perfume and flavor odorants. 

QCM Sensors Coated with Lecithin and Activated Carbon... 

Quartz crystal microbalance (QCM) sensors that are coated with lecithin and activated carbon can be used to detect environmental pollutants with high recognition ability. The pollutants are detected from a measurable change in crystal oscillator frequency, which is caused by a small increase in mass deposited on... 

Figure 1. QCM sensor response of an atrazine-imprinted polyactylic acid towards a pulse of 3 ppb atrazine in water.

The characteristics of QCM sensors containing mono- or multilayered DNA probe constructed by direct chemical bonding, avidin-biotin interaction or electrostatic adsorption on polyelectrolyte films were compared by Zhou et al. [60]. The use of the polyethyleneimine adhesion, glutaraldehyde cross-linking (PEI-Glu) method to immobilize hepatitis B virus DNA onto gold QCM quartz crystals, enabling the sensor to be regenerated five times, was reported by Hu and co-workers [61],... 

Contact angle measurements were conducted on a FT A 100 contact angle meter for Si02-coated QCM sensor crystals that were immersed in a solution of 0.25mM wfAFP or PVP for 60 min, then rinsed with MQ-water and dried by compressed air. Three independent measurements were done for each sample. 

In this entry, we focus on the discussion of the platform technology for electrochemical sensors, metal oxide semiconductive (MOS) sensors, and piezoelectric based quartz crystal microbalance (QCM) sensors. There are other types of chemical sensors, such as optical sensors, Schottky diode based sensors, calorimetric sensors, field-effect transistor (FET) based sensors, surface acoustic wave sensors, etc. Information of these specific sensors can be found elsewhere and in current journals on sensor technologies. Because of the increasing importance of microfabricated sensors, a brief discussion of microsensors is also given. 

Fig. 4 shows the adsorption isotherm of n-propanol on the QCM sensor at room temperature. The observed trend of the n-propanol film thickness as a function of partial pressure is consistent with the general characteristic of the alcohol adsorption isotherm observed for other systems. The inset in Fig. 4 gives the approximate thickness of the adsorbed alcohol layer on the QCM sensor measured at a partial pressure of 90 10% to the saturation pressure of each alcohol. The actual alcohol thickness on the clean, hydrophilic silicon oxide surface would be slightly larger than that on gold. 

Fig. 2. Measuring set-up (A) photograph of the piezoelectric device and flow system, the inset shows the cell holding the quartz sensor (B) sample QCM sensor with 10 MHz base frequency (as used throughout the described experiments) (C) cross-section through the piezo-cell showing the two rubber O-rings holding the quartz plate, only one side of the sensor is in contact with the fluid (D) cross-section of the cell used for combined piezoelectric and amperometric measurements, the lid also hold a titanium wire electrode and the Ag/AgCI reference electrode.

Further examples of acoustic sensors modified with zeolites include a QCM sensor with silver-exchanged ZSM-5 that responds selectively to acetone (in diabetic s breath) in the ppm-range,ll 16] principal component analysis of multiple QCM-sensor responses (with LTA, MFI, SOD) for the detection of NO/SO2 mixtures,[117] MFI-zeolite-coated microcantilevers with ppm-sensitivity for Freon detection [118,119] and other zeolite-coated cantilevers for humidity sensing.[120]... 

When using QCM sensors in liquid media one faces a considerably more involved situation. The behavior of QCRs under these conditions diverges essentially from that in vacuum or gaseous media. Most important is the significant dissipation of acoustic energy due to liquid contact, which translates to energy lost from the electrical circuit. The oscillation is significantly... 

A vast majority of (bio)chemical QCM sensors involve AT-cut quartz. Experiments are usually performed at a certain frequency and AT-cut crystals provide the larger frequency shift. However, BT-cut quartz can be considered as an interesting alternative, if, e.g., a certain crystal thickness is required for mechanical stability. As discussed already, the limited temperature insensitivity of BT-cut crystals plays a minor role in sensor applications because temperature maintenance is usually required anyway. 

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