Three approaches to detection of biological agents based on biological processes will be presented. The first example
demonstrates the use of dendrimers to deliver a membrane-impermeable fluorescent dye into live bacteria, similar to
viral infection and delivery of DNA/RNA into a bacterial cell. The second example mimics collection and capture of
airborne biological particles by the respiratory mucosa through the use of a hygroscopic sensing membrane. The third
example is based on the use of multiple fluorescent probes with diverse functionalities to detect airborne biological
agents in a manner similar to the olfactory receptors in the nasal tract.
Smiths Detection is developing sensors and integrated instruments for rapid detection and identification of airborne biological agents. A biosensor array has been developed that provides real-time detection and classification of microorganisms based on molecular recognition and fluorescence spectroscopy. This biosensor is being integrated with an identification instrument that is based on a novel approach for surface plasmon resonance and light scattering. This device can continuously monitor for up to 20 biological agents and provide identification in 15 minutes or less.
A new approach is presented for real-time detection of bacterial aerosols using a sensing film configured on optical fibers. The sensing film contains nucleic acid-reactive fluorophores immobilized in hydrophilic polymers such as carboxymethylcellulose. Detection is based on changes in the fluorescence emission as a function of cell number deposited on the sensor. The sample is introduced using a nebulizer and the fiber probe, with the sensing film was placed directly inside a bioaerosol chamber. The sensor shows real-time responses to pulses of aerosolized bacteria such as Pseudomonas aeruginosa. The signals from the sensor are dependent on the humidity in the chamber. We have demonstrated that at lower humidities the ithegrated intensity does not provide a clear indication of the presence of bacterial aerosol. However, ftirther analysis shows that the intensity ratio at different wavelengths, for example I525/I560 or I505/I560, does correlate with bacteria concentration. The present detection limit for aerosolized bacteria is 3000 cells/mm2. To our knowledge, there are no previous reports of real-time detection of bacterial aerosols using the sensing film described here. The sensing film remains stable after storage under desiccation and in the dark for extended periods. The sensor also remains stable at room temperature for many hours after removal from the package.
Fiber optic chemical sensors are being developed for on-line monitoring of gases and liquids. The sensors utilize novel porous polymer or glass optical fibers in which selective chemical reagents have been immobilized. These reagents react with the analyte of interest resulting in a change in the optical properties of the sensor. These sensors (or optrodes) are particularly suited to in-situ detection of atmospheric trace contaminants and dissolved gases and chemicals, as may be required for environmental monitoring. Sensors have been demonstrated for low part-per-billion level detection of aromatic hydrocarbons, hydrazines and ethylene. Sensors have also been demonstrated for carbon monoxide ammonia, and humidity. Also, relevant to groundwater monitoring is the development of an integrated pH optrode system for the pH range 4 - 8, with additional optrodes for lower pH ranges.
Several chemical sensors have been developed using plastic optical fibers. Plastic optical fibers offer many advantages over glass fibers, such as high numerical aperture, low-cost, high flexibility, and ruggedness. The sensing segment is made of novel porous polymer fiber, combined with selective chemical indications systems. By careful selection of polymer systems and indicators, the chemical reagents can be covalently bonded to the porous plastic fiber. These sensors can be used to detect a variety of chemical species and to measure various chemical parameters, both in vapor and solution. They provide high sensitivity and stability. Sensor characteristics, including dynamic range, linearity, and response time, can be tailored to meet specific applications by altering the polymer composition and polymerization procedure. A low-cost, compact optoelectronic and data acquisition subsystem has been designed and constructed to interface with the sensor probe. This system employs two- wavelength, solid-state light sources, which allow the system to be calibrated on-line.