ABSTRACT
In this chapter, an “electronic dog nose” based on surface plasmon resonance (SPR) and an antigen-antibody interaction for security and safety is described. For the SPR sensor to detect explosives, the vapor or particles of the target substances must be dissolved in a liquid. Therefore, we have developed not only sensor surfaces but also antibodies, sampling processes for explosives, and a protocol for the measurement of explosives on the SPR sensor. 19.1 Introduction
19.1.1 Explosive DetectionSince the terrorist attacks in the United States on September 11, 2001, concerns about terrorist attacks have increased in Japan. Dogs
trained to detect explosives were deployed at Narita Airport, Japan, in preparation for the organization of the 2002 FIFA World Cup. Currently, explosive detection systems such as explosive detection dogs, metal detectors, and X-ray inspection apparatus are mainly used to detect explosives. These systems have various advantages and disadvantages depending on the situation. For example, explosive detection dogs are mobile and have high sensitivity to odors emanating from bombs.1 However, a dog’s sensitivity depends on its physical condition, and a dog cannot concentrate on the search for explosives for more than 2 h. The training of dogs is expensive, and dog handlers also require extensive training. Metal detectors are used to detect metal fragments in bombs but often react to metals unrelated to explosives. X-ray inspection apparatus are used to check the shapes of items in baggage. Although X-ray inspection apparatus are the most effective security systems for airports, they are large and cannot be moved easily. Therefore, to overcome these drawbacks, a novel detection system for explosives with mobility, sensitivity, and reliability is required to supplement the above types of detection system.Hence, we combined an SPR analytical instrument, an antigen-antibody interaction, and a sampling method to develop a prototype portable explosive sensor that operates similarly to a dog’s nose. 19.1.2 Concept of Electronic Dog NoseFigure 19.1 shows the concept of the electronic dog nose,2 in which an SPR sensor is adopted as the sensing device. It has high sensitivity and a relatively small size. An antigen-antibody interaction is utilized for the highly selective sensing of chemical substances contained in bombs. Chemical substances must be in solution for antigen-antibody interactions to occur. Thus, explosives must be dissolved for measurement using the SPR sensor and to induce the antigen-antibody interaction regardless of the sampling method.Figure 19.2 shows the elements in the electronic dog nose used for the highly sensitive detection of explosives. We developed two types of sampling method. One involves a surface area of a luggage, in which a bomb is hidden, and the other involves the collection of vapor using an air pump and its concentration at a preconcentrator consisting of an adsorbent and a tube. Both methods are required to dilute the collected molecules in a buffer solution. Two fabrication
methods were used for the sensor surface: One involved physical adsorption and the other used using self-assembled monolayers (SAMs). We chose to develop SAM-based sensor surfaces to improve the stability of sensing in the field.
