Israel Sánchez-Barragán

Room temperature phosphorescence optosensing of benzo[a]pyrene in water using halogenated molecularly imprinted polymers

A selective optosensor for benzo[a]pyrene (BaP) determination in water samples, using a molecularly imprinted polymer (MIP) for the recognition of the analyte, has been developed. Detection was based on measurements of the native strong room temperature phosphorescence (RTP) emission from the BaP recognized by the MIP. The non-covalent MIP was synthesized using BaP as a molecular template. Different halogenated-bisphenol A compounds were compared as precursors in the polymerization (thus ensuring the presence of a heavy atom, required to induce RTP emission from the analyte). In the developed optosensor, samples are injected in a flow system and the analyte is on-line retained onto the polymeric material. In the absence of oxygen (using sodium sulfite as the oxygen scavenger) the heavy atom present in the MIP structure induced analytically useful RTP emission from the recognized BaP. After measurement of the luminescent emission, the sensing material can be easily regenerated by passing 2 mL of methanol over the MIP. The optosensor demonstrated a very high selectivity for BaP determination in water even in the presence of other luminophores that could be non-specifically adsorbed onto the MIP surface. Under optimal experimental conditions, a benzo[a]pyrene detection limit of 10 ng L(-1) (20 mL sample injection volume) was achieved with good reproducibility (a RSD of 3% was obtained for 1 microg L(-1) BaP). Finally, the proposed optosensor was successfully applied to the analysis of spiked natural water with BaP.

Design of a low-cost optical instrument for pH fluorescence measurements

This paper describes the electronic design and the performance of a low-cost fiber-optic instrument for pH fluorescent measurements. The chemical sensing phase consists of an organic pH indicator (mercurochrome) immobilized in a sol-gel matrix placed at the end of a fiber optic by means of a steel grid. The active phase was excited by means of a high-intensity blue light-emitting diode. The light signal was modulated to avoid external interference. Fluorescence emission is detected by a low-cost photodiode. To avoid drifts in excitation light emission intensity, a ratiometric measurement was proposed. To perform such measurements, two fiber-optic measurement channels were used. One of them was employed to measure only the pH indicator fluorescent emission intensity. The second channel was employed to measure only the intensity of the excitation light reflected by the sensing phase. The ratio between both signals is only proportional to pH and proved to be independent of excitation light intensity. The sensor is useful over the pH range of 4-8, providing highly reliable results

Direct and rapid discrimination of aflatoxigenic strains based on fibre-optic room temperature phosphorescence detection

An innovative analytical methodology for the rapid identification of aflatoxin-producing moulds belonging to Aspergillus genus is presented here. The procedure is based on the measurement, using a fibre-optic luminometer, of the room temperature phosphorescence (RTP) emitted by aflatoxins produced by isolated aflatoxigenic strains, cultured in a special culture medium consisting of malt extract agar modified with beta-cyclodextrin and sodium deoxycholate for RTP induction. Unequivocal detection of the presence of aflatoxins in the culture medium is achieved within the first 36 h of incubation at 32 degrees C, owing to the selectivity and sensitivity of the RTP emission, as compared with the minimum of 72 h needed using a conventional microbiological method. In a first step, the capability of aflatoxin standard solutions to emit analytically useful RTP was evaluated. In this line all experimental conditions were optimised for in vitro induction of RTP from aflatoxins. In a second step, a simple analytical test was developed and it has been evaluated for the rapid identification of aflatoxigenic strains, as a discriminating assay from non-aflatoxigenic strains based on the measurement of experimental RTP emission observed. Confirmation of aflatoxin production on the studied culture plates was accomplished by means of an HPLC/fluorescence reference method.

Iodinated molecularly imprinted polymer for room temperature phosphorescence optosensing of fluoranthene

A novel molecularly imprinted polymer (MIP) of high interest for room temperature phosphorescence (RTP) sensing systems is described; the synthesized MIP contains iodine as internal heavy atom in the polymeric structure and its applicability for RTP sensing of fluoranthene at microg L(-1) levels is demonstrated.

Solid-supported room temperature phosphorescence from aflatoxins for analytical detection of Aspergillus spp. strains

A simple, direct and rapid analytical methodology for the detection of aflatoxin producing Aspergillus spp. strains based on the measurement of room temperature phosphorescence from aflatoxins is presented here.

Ratiometric Methods For Optical Fiber Instrumentation Based On Luminescence Sensors

The optical fiber instruments in analytical applications are usually based on a luminescence chemical sensor. Direct intensity measurements of the luminescence emission are, due to their simplicity, a very common measuring principle. Consequently, many optical fiber devices are based on the intensity measurement of the luminescence emission. Unfortunately, direct luminescent intensity measurements suffer from a series of non-analyte fluctuations, which make them inappropriate for the development of precise instrumentation. An alternative for solvents this trouble is to measure the lifetime of luminescence emission. In that case the drawback is an increase in the complexity of the measurement. A ratiometric measurement can solve many of the trouble previously exposed. When the excitation light interacts with a luminescence chemical sensor different optical emissions take place. Some of these emissions are analyte dependent and they are employed to extract the quantitative information required. The rest of emissions are usually considered like noise that can reduce the accuracy. With a ratiometric scheme this noise, or background light, is converted in a useful signal that can improve the accuracy of the measurement. In this paper we proposed two new ratiometric methods specially designed to be implemented with optical fiber instrumentation. The potential of our proposed ratiometric methods to overcome such problems of accuracy in luminescent sensing will be evaluated. The correct election of the methodologies with respect to the analytical performance of the chemical sensor will be also analyzed.