Quartz crystal microbalance design

Fig. 12.19. Design of the quartz crystal microbalance for electrochemistry, showing the applied electric field and external contact.

Compact chemical sensors can be broadly classified as being based on electronic or optical readout mechanisms [28]. The electronic sensor types would include resistive, capacitive, surface acoustic wave (SAW), electrochemical, and mass (e.g., quartz crystal microbalance (QCM) and microelectromechanical systems (MEMSs)). Chemical specificity of most sensors relies critically on the materials designed either as part of the sensor readout itself (e.g., semiconducting metal oxides, nanoparticle films, or polymers in resistive sensors) or on a chemically sensitive coating (e.g., polymers used in MEMS, QCM, and SAW sensors). This review will focus on the mechanism of sensing in conductivity based chemical sensors that contain a semiconducting thin film of a phthalocyanine or metal phthalocyanine sensing layer. 

Section 14.2.1 on XPS has been revised to reflect the current state of commercial instrumentation. Spectroelectrochemistry, briefly introduced in Chapter 5, has been expanded upon in Chapter 15, with commercial instrumentation and examples. Probes based on quartz crystal microbalance response are covered. The radical new pH meter design using calibration-free, easily stored, extremely robust, voltammetric-based probes with surfaces of anthroquinone-bonded multiwaUed carbon nanotubes, introduced in March 2013 by SENOVA Systems, is described. 

Various physical transducers can be used to detect interaction of the immobilized DNA probe with the analyte. Commonly used detection systems include optical (MarvUc, 1997 Jordan, 1997 Lee, 2001), electrochemical (Wang, 2001 Palecek, 2001) or mass sensitive devices (Storri, 1998 Ebara, 2000). Considering the growing number of potential applications, simphcity and low cost are some of the major design parameters in both microarray and other biosensor apphcations. Therefore, increased attention has been given to relatively simple detection or sensing techniques such as fluorescence measurements. This method offers faster assays without the need for specific substrate properties such as in the mass-sensitive quartz-crystal microbalance (Storri, 1998 Ebara, 2000) or in more complex optical techniques such as surface plasmon resonance (Jordan, 1997 Lee, 2001). 

Other electrochemical biosensors may be utilized for the design of BioETs mainly one can think of using conductimetric and/or impedimetric enzyme-based biosensors that might be utilizable as the others above. However, there remain the fields of optical sensing and gravimetric sensing (employing quartz crystal microbalance, bulk or surface acoustic wave devices), two fields rarely used up to now in conjunction with biosensors. [10]... 

---