# Feasibility of Genipin to Evaluate Chitosan Rainfastness for Biopesticide Applications

## TL;DR

This study explores using genipin to assess how well chitosan stays on surfaces after rain, offering a lab-based alternative to field testing for biopesticide applications.

## Contribution

A novel method using genipin and fluorescence microscopy to evaluate chitosan rainfastness without chromophore grafting is proposed.

## Key findings

- High chitosan concentrations are needed for detectable signals on real leaves due to autofluorescence.
- Parafilm® proved to be the most effective model for detecting chitosan after genipin reaction at low concentrations.
- The counter ion's effect on chitosan rain resistance was evaluated using the proposed method.

## Abstract

Chitosan’s effectiveness as an antimicrobial coating for biocontrol depends on its resistance to rain. Unfortunately, to the best of our knowledge, there is currently no satisfactory method for assessing this resistance, which means that field tests have to be carried out to evaluate it in situ, which are difficult to implement and therefore unsuitable for optimizing formulations. This article explores the use of genipin to detect residual chitosan on surfaces after simulated rain, using fluorescence microscopy. A first study on real vine leaves using MacroFluo microscopy was carried out but showed limitations for the intended application, notably due to the requirement for high chitosan concentrations to achieve detectable signals. A semi-quantitative method based on confocal laser scanning microscopy was then developed on model leaves, as real leaves were unsuitable due to their autofluorescence. Among the tested models, Parafilm® proved to be the most effective, showing sufficient fluorescence after reaction with genipin, even at low chitosan concentrations. For the first time, a method that does not require chromophore grafting onto chitosan has been proposed, allowing for the comparison of chitosan solution rainfastness under laboratory conditions. As an application, the effect of the counter ion on chitosan’s rain resistance was evaluated.