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Fipronil (FIP), a broad-spectrum phenylpyrazole insecticide, is highly toxic and threatens human health and ecological balance. Developing convenient, rapid, portable analytical technology for on-site and high-frequency testing of FIP is essential to reduce its damage. Herein, a monoclonal antibody (Clone F-3F6) against FIP, with high affinity and specificity, was produced using a novel immunogen, FIP-BSA, which was simply and directly synthesized by conjugating FIP with bovine serum albumin (BSA). Among the previously reported antibodies, F-3F6 acts more specifically against FIP. The FIP metabolites fipronil desulfinyl, fipronil sulfide, and fipronil sulfone showed lower cross-reactivity, and other pesticides were not recognized. To achieve high-frequency and on-site measurements of FIP, an evanescent wave fluorescence biosensor was built by integrating evanescent wave fluorescence technology, a functionalized fiber bioprobe, and a fluorescence-labeled F-3F6 antibody. The detection limit of FIP was 0.032 μg/L. The detection results of real milk and water samples showed that all the coefficients of variation were less than 10%, and the recovery ranged from 90 to 120%. The high reusability and stability of functionalized fiber bioprobe enables the accurate, cost-effective, high-frequency, and facile quantitative detection of FIP. This highly specific and reliable evanescent wave fluorescence biosensor will be well suited to the sensitive and high-frequency on-site analysis of only FIP in food. [ABSTRACT FROM AUTHOR]

Thermoacoustic instability and lean blowout are monitored in propane/air flames in a swirl-stabilized combustor using a novel tunable diode-laser sensor for gas temperature using wavelength-scanned laser absorption of two neighboring water vapor transitions near 1.4 [micro]m. Although the gas composition and temperature are not uniform along the sensor line of sight, temperature oscillations and fluctuations are clearly identified in the fast Fourier transform power spectra of the time-resolved data. Detailed experiments are conducted to optimize the position of the sensor line of sight in the flame for thermoacoustic instability and lean-blowout sensing. The output of the sensor is used to suppress the thermoacoustic oscillations in a phase-delay feedback control system, and acoustic modulation of the intake air flow suppresses the temperature oscillations by more than 7 dB. The low-frequency temperature fluctuations measured by the tunable diode-laser sensor increase sharply as the flame approaches lean blowout. The intensity of these low-frequency fluctuations is used to detect the proximity to lean blowout and can be used as a control variable for active lean blowout suppression without knowing the lean-blowout fuel/air ratio limit. The tunable diode-laser sensor results are compared with traditional pressure and emission sensors, and the tunable diode-laser sensor is found to offer several advantages, including better spatial resolution and insensitivity to background acoustic noise and flame emissions. DOI: 10.2514/1.24774

Tunable diode laser absorption measurements at high pressures by use of wavelength-modulation spectroscopy (WMS) require large modulation depths for optimum detection of molecular absorption spectra blended by collisional broadening or dense spacing of the rovibrational transitions. Diode lasers have a large and nonlinear intensity modulation when the wavelength is modulated over a large range by injection-current tuning. In addition to this intensity modulation, other laser performance parameters are measured, including the phase shift between the frequency modulation and the intensity modulation. Following published theory, these parameters are incorporated into an improved model of the WMS signal. The influence of these nonideal laser effects is investigated by means of wavelength-scanned WMS measurements as a function of bath gas pressure on rovibrational transitions of water vapor near 1388 nm. Lock-in detection of the magnitude of the 2f signal is performed to remove the dependence on detection phase. We find good agreement between measurements and the improved model developed for the 2f component of the WMS signal. The effects of the nonideal performance parameters of commercial diode lasers are especially important away from the line center of discrete spectra, and these contributions become more pronounced for 2f signals with the large modulation depths needed for WMS at elevated pressures. OCIS codes: 120.0120, 120.1740, 300.0300, 300.1030, 300.6260, 300.6380.