The detection of toxic insecticides is a major scientific and technological challenge. In this regard, imidacloprid is a neonicotinoid that is a systemic insecticide that can accumulate in agricultural products and affect human health. This work aims to study the properties of chitosan–TiO2 nanocomposites in which nanoparticles with high surface area serve as molecular recognition sites for electroanalytical imidacloprid detection. We show that the best sensitivity to imidacloprid was obtained using a modified electrode with a chitosan–TiO2 nanocomposite with a 40 wt.% of TiO2 nanoparticles. By using a three-phase effective permittivity model which includes chitosan, TiO2, an interface layer between nanoparticles and a matrix, we showed that nanocomposites with 40 wt.% of TiO2 the interface volume fraction reaches a maximum. At higher nanoparticle concentration, the sensitivity of the sensor decreases due to the decreasing of the interface volume fraction, agglomeration of nanoparticles and a decrease in their effective surface area. The methodology presented can be helpful in the design and optimization of polymer-based nanocomposites for a variety of applications.

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A new disease of the fruit tree Jocote de Corona (Spondias purpurea L.) was observed in El Salvador, Central America. The symptoms included small chlorotic leaves, highly proliferating shoots, and shortened internodes. Absence of sweet pulp in fruits made them inedible, causing considerable yield losses for farmers. The disease etiology was investigated using polymerase chain reaction with phytoplasma-specific primers, sequencing, and phylogenetic analysis. We obtained no amplification products from symptomless plants, whereas all tests were positive from plants with symptoms. Phylogenetic analysis indicated that this phytoplasma clustered in the 16S rIII group, the type member of which is X-disease phytoplasma. This is the first report of a phytoplasma associated with Jocote de Corona disease in El Salvador and Central America.