The component that is responsible for pungency taste of the chilli is capsaicin. Chilli hotness is proportional to the capsaicin concentration, which can be determined based on the colour changes of Gibbs reagent when reacting with capsaicin in an alkaline medium. Immobilisation of Gibbs reagent onto silica nanoparticles (approximately 80 nm in size) was carried out to construct a new optical sensor for the direct and rapid determination of capsaicin in chilli fruits. The optical sensor was based on a clear colour change of the sensor from white to blue when exposed to capsaicin. A good response was found towards capsaicin concentrations in the range of 25.0-300.0 ?M with detection limit of 18.6 ?M in an alkaline medium of pH 10. The results were reproducible with a good relative standard deviation (RSD) in the range of 2.3-5.3%. Silica nanoparticles as a matrix of immobilisation for Gibbs reagent enhanced the sensor performance in terms of response time (30 s), sensitivity, and detection limit compared to immobilisation matrix such as XAD beads evaluated in this study. The presence of small amount of interfering compounds in the chilli fruit had no significant effect on the sensor response. The optical capsaicin sensor was successfully developed and applied to the chilli samples and demonstrated comparable results with the HPLC standard method. Copyright � 2016 American Scientific Publishers All rights reserved.

The characteristics of a potentiometric biosensor for the determination of permethrin in treated wood based on immobilised cells of the fungus Lentinus sajor-caju on a potentiometric transducer are reported this paper. The potentiometric biosensor was prepared by immobilisation of the fungus in alginate gel deposited on a pH-sensitive transducer employing a photocurable acrylic matrix. The biosensor gave a good response in detecting permethrin over the range of 1.0-100.0 ?M. The slope of the calibration curve was 56.10 mV/decade with detection limit of 1.00 ?M. The relative standard deviation for the sensor reproducibility was 4.86%. The response time of the sensor was 5 min at optimum pH 8.0 with 1.00 mg/electrode of fungus L. sajor-caju. The permethrin biosensor performance was compared with the conventional method for permethrin analysis using high performance liquid chromatography (HPLC), and the analytical results agreed well with the HPLC method (at 95% confidence limit). There was no interference from commonly used organophosphorus pesticides such as diazinon, parathion, paraoxon, and methyl parathion.

Background: A novel optical sensor for the rapid and direct determination of permethrin preservatives in treated wood was designed. The optical sensor was fabricated from the immobilisation of 2,6-dichloro-p-benzoquinone-4-chloroimide (Gibbs reagent) in nafion/sol-gel hybrid film and the mode of detection was based on absorption spectrophotometry. Physical entrapment was employed as a method of immobilisation.Results: The sensor gave a linear response range of permethrin between 2.56-383.00 ?M with detection limit of 2.5 ?M and demonstrated good repeatability with relative standard deviation (RSD) for 10 ?M at 5.3%, 100 ?M at 2.7%, and 200 ?M at 1.8%. The response time of the sensor was 40 s with an optimum response at pH 11.Conclusions: The sensor was useful for rapid screening of wood or treated wood products before detailed analysis using tedious procedure is performed. The validation study of the optical sensor against standard method HPLC successfully showed that the permethrin sensor tended to overestimate the permethrin concentration determined. � 2013 Arip et al.; licensee Chemistry Central Ltd.