ABSTRACT
Figure 18.1 shows a scheme of the integrated biosensor for detecting total bacterial count. The biosensor contains two parts enveloped in a dark chamber: a home-made sensitive element, and a photomultiplier tube (PMT) used as detector element, which has been previously described (Luo et al. 2009). The former is the key to produce a measurable bioluminescence, and is disposable for the sake of low cost and easy operation. It comprises of a sampler, a cartridge and a microtube which are linked up through a screw thread in a coaxal-suite mode based on the bioluminescence ATP assay combined with a chemical method of ATP extraction. The somatic eliminating reagent, ATP extractant and luminescence reagent are sealed in advance at the swab, the bottom of the cartridge and the microtube, respectively, so that it is no need of an extra reagent when used. Once a sample gets to the sampler through swabbing or dropping, the free ATP or somatic ATP in the sample are hydrolyzed. As the sampler down-spins continuously, the intracellular ATP is released from bacterial cells by the ATP extractant in a few minutes and the residual extractant is subsequently consumed by the neutralizing reagent. When the lowest aluminum foil is
torn, most of the solution containing the intracellular ATP drops into the microtube and the ATP quickly reacts with the luminescence reagent to produce bioluminescence. Then, the bioluminescence signal is translated to relevant electrical signal by the PMT and further detected by a handheld luminometer (Zhou et al. 2008). The bacterial count of the sample could be easily quantifi ed by measuring the bioluminescence according to the relationship between the concentration of the intracellular ATP and the bioluminescence intensity.
