Bioluminescent sensor for naphthalene in air: Cell immobilization and evaluation with a dynamic standard atmosphere generator

A dynamic atmosphere generator with a naphthalene emission source has been constructed and used for the development and evaluation of a bioluminescence sensor based on the bacteria Pseudomonas fluorescens HK44 immobilized in 2% agar gel (107 cell mL−1) placed in sampling tubes. A steady naphthalene emission rate (around 7.3 nmol min−1 at 27 °C and 7.4 mL min−1 of purified air) was obtained by covering the diffusion unit containing solid naphthalene with a PTFE filter membrane. The time elapsed from gelation of the agar matrix to analyte exposure (“maturation time”) was found relevant for the bioluminescence assays, being most favorable between 1.5 and 3 h. The maximum light emission, observed after 80 min, is dependent on the analyte concentration and the exposure time (evaluated between 5 and 20 min), but not on the flow rate of naphthalene in the sampling tube, over the range of 1.8–7.4 nmol min−1. A good linear response was obtained between 50 and 260 nmol L−1 with a limit of detection estimated in 20 nmol L−1 far below the recommended threshold limit value for naphthalene in air.