Coumarin meets fluorescein: a Förster resonance energy transfer enhanced optical ammonia gas sensor

Abstract

This study focuses on the development of an optical ammonia gas sensor, the sensing mechanism of which is based on Förster resonance energy transfer (FRET) between coumarin and fluorescein. The dyes were immobilized into an organically modified silicate matrix during polymerizing methyltriethoxysilane with trifluoropropyltrimethoxysilane on a poly(methyl methacrylate) substrate. The resulting dye-doped xerogel films were exposed to different gaseous ammonia concentrations. A logarithmic decrease of the coumarin fluorescence emission band at 442 nm was observed with increasing gaseous ammonia concentrations, which was due to enhanced FRET between coumarin and fluorescein. The coumarin/fluorescein composition was optimized in order to obtain the best ammonia sensitivity. First experiments in a flow cell gas sensor setup demonstrated a sensitive and reversible response to gaseous ammonia.

Carbon Dots and Fluorescein: The Ideal FRET Pair for the Fabrication of a Precise and Fully Reversible Ammonia Sensor

“…Indeed, the calculated LODNH3 (as the extrapolated concentration at which the signal is three times the averaged standard deviation of the readouts) resulted to be 110 ppb. Hence, the proposed sensor reduces by roughly three order of magnitudes the limit of detection obtained by the previous FRET pair evaluated by our group (i.e., 115 ppm) [8]. This result so far represents the lowest limit of detection of any optical ammonia sensor published in literature.…”

“…The response time of the sensors calibrated on the fluorescein emission peak (defined as the time required to achieve 95% of the stable fluorescence intensity) shows a relatively sharp response time of 8 ± 2 min in adsorption and 15 ± 2 min in desorption upon exposure to 20 ppm of ammonia, which represent a noticeable improvement if compared to our previous work [8], where even the thinnest sol-gel coating showed a relatively longer response time (i.e., 18 ± 2 min). Thus, the deposition of a sol-gel layer onto the electrospun fiber (localized either directly on the fiber or in the surroundings of several entangled fibers) increases the overall accessible surface area.…”

“…Although fluorescein is well-known to increase its emission peak at higher pH values [8][9][10], such remarkable sharp response to ammonia cannot be exclusively ascribed to the fluorescein pH behavior. Indeed, as it has been observed by studying the FRET behavior in solution, a prominent increase in FRET efficiency from 85 to 88% is observed when 10 v/v % of 0.1 M NH4OH solution in water is added to the mixture.…”

Electrical and gas sensing properties of novel cobalt(II), copper(II), manganese(III) phthalocyanines carrying ethyl 7-oxy-4,8-dimethylcoumarin-3-propanoate moieties

“…According to the best of our knowledge, there is no report on coumarinophthalocyanine applications as gas sensors except the report on optical ammonia sensors by Widmer and coworkers [36] and carbondioxide sensors by Altun and coworkers [37]. Therefore, this report will be the first for ethyl 7-oxy-4,8-dimethylcoumarin-3-propanoate bearing phthalocyanines as conductometric n-butyl acetate and ammonia sensors.…”

Micro- and nanostructured sol-gel-based materials for optical chemical sensing (2005–2015)

“…The sensor system 50 h dCO 2 response is depicted in Fig. 9 [130]. Dye leaching, pH, ionic strength and alkali ions interferences were prevented by employing protective Teflon layer which was deposited on the top of the sensing layer.…”