Minimally invasive detection techniques

Acoustic analysis detects changes in the properties of acoustic waves as they travel at ultrasonic frequencies in piezoelectric materials. The interaction between the waves and the phase-matter composition facilitates chemical selectivity and, thus, the detection of CWA s. These are commonly known as surface acoustic wave (SAW) sensors. Reported studies indicate detection limits as low as 0.01 mg m for organophosphorus analytes within a 2 min analysis [1]. There are several commercially available SAW instruments, which can automatically monitor for trace levels of toxic vapors from G-nerve agents and other CWAs, with a high degree of selectivity. A major advantage of SAW detectors is that they can be made small, portable and provide a real-time analysis of unknown samples. One of the drawbacks of these instruments is that sensitivity and a rapid response time are inversely related. In an ideal instrument, both parameters would be obtained without sacrificing one for the other. 

Another disadvantage is that selective coatings are necessary in order to identify specific chemical analytes. The production of selective polymer films is difficult and these polymer films are susceptible to surface changes, known as dewetting, which leads to a decreased response and instrument performance [2]. As a result, false positives and selectivity issues can occur [1]. 

Prompt gamma ray neutron activation analysis (PGNAA) is a proven method for the identification of chemical warfare agents, which is widely used as a nondestructive technique. 

An interesting application can be found in the literature, from Anikiev and Kolesov [6]. They described an analysis of dumped chemical warfare agents in marine bottom sediments. The method determins the characteristic ratios between primary elements of the marine sediment and 

Sulfur Mustard (oxygen, carbon, nitrogen, phosphorus, sulfur) by electron spectroscopy, and determining the fractionation coefficient for arsenic incorporated into Lewisite relative to scandium using neutron activation analysis. Scandium is used for the estimation of the effects of geochemical factors on the chemical composition of the marine sediment was also described. 

---

Because of minimal sample preparation and minimally invasive approaches Raman spectroscopy has the potential to gain new insights into viral and microbial biochemistry as well as a rapid identification of pathogenic microorganisms. In this chapter the unique potential of several Raman spectroscopic techniques for medical and pharmaceutical issues is discussed, which focus on the analysis of viruses as well as on microbial detection... 

Cepria and coworkers used the voltammetry of immobilized microparticles to detect and quantify the cadmium pigments (e.g., cadmium sulfide and cadmium sulfoselenide) used in artists paints, as well as in glasses, plastics, ceramics, and enamels [141]. For this, a simple, fast and reliable technique was developed that proved to be especially applicable for valuable art objects, as it was minimally invasive and required only nanogram quantities of material (see also Section 6.4.1). For quantification purposes, an abrasive stripping scan was used from + 0.3 V to —1.0 V, following a 10 s pre-treatment step at —1.5 V. The Cd oxidation peak was evaluated with respect to an internal AgCl calibration standard. 

B.C. Wilson, A. Molchovsky, G.J. Czamota, M.D. Sherar, M.C. Kolios, L. Lilge, R.S. Dattani, K.S. Osterman, K.D. Paulsen, P.J. Hoopes (1999). Monitoring tissue response to photodynamic therapy the potential of minimally invasive electrical impedance spectroscopy and high-frequency ultrasound. In Th.J. Dougherty (Ed.), Optical Methods for Tumor Treatment and Detection Mechanisms and Techniques in Photodynamic Therapy VIII (SPIE Proc. Vol. 3592, pp. 73-82). 

---