# Rapid In-Field Volatile Sampling for Detection of _Botrytis cinerea_ Infection in Wine Grapes
## 2 Results and Discussion
### In-Field Volatile Sampling  
Thermal desorption GC-MS was applied for the in-field volatile sampling using ZIF-8 as absorption materials, and a commercially available material Tenax(r)-TA was used simultaneously for a comparison. In this experiment, the absolute abundances of peak area counts were integrated to compare the extraction efficiency of the two materials due to the restriction of the IS application in the field environment. This sampling experiment was conducted at a local commercial vineyard in an open-air condition with variant temperatures, humidities, and random air movement, compared to the lab-based volatile extraction experiment within a glass container. The purpose of this experiment is to demonstrate the extraction ability of fugal-related metabolites using ZIF-8 and the proof of concept for the correlations between the in-field volatile detection and the _B. cinerea_ infection severities in the grapes. Volatiles related to fungal infection, hexanal, 1-octen-3-ol, 3-methyl-1-butanol, benzaldehyde, 3-octenone, _trans_-2-hexen-1-ol, 1-octen-1-one, 1-hexanol, 3-octanol, 1,5-dimethylnaphthalene, 1-5-dimethyltetralin, benzyl alcohol, and phenylethyll alcohol were readily detected using ZIF-8 and Tenax(r)-TA as absorbent materials (Figure 3). A range of volatile concentrations are evident for the in-field sample results, which reflect the range of _B. cinerea_ infection severities encountered. Generally, ZIF-8 performed better with higher peak area counts for alcohol compounds, 1-octen-3-ol, 3-octanol, benzyl alcohol, and phenyl alcohol. With the formula of zinc(2-methylimidazolate)\({}_{2}\), ZIF-8 is highly hydrophobic and repels adsorption of water vapour before the onset of capillary condensation, and such material was reported to be suitable for use in humid environments [36]. The selective properties of ZIF8 hydrophobic channels playing a significant role for improved affinity for bio-alcohols was demonstrated with analysis of isobutanol [37]. Our results demonstrating increased sensitivity of ZIF-8 compared to Tenax(r)-TA for the absorption of low-molecular-weight alcohols, including 1-octen-3-ol, 1-hexanol, 3-octanol, benzyl alcohol, and phenylethyll alcohol (Figure 3), are supported by prior reports of ZIF-8 selectivity. An exceptionally high capacity of ZIF8 for some alcohols is reported, which is thought to arise from the flexible structural properties of the solid-phase material, thereby increasing selectivity for this chemical class [37]. Another observation is the higher sensitivities of C8 compounds using ZIF-8 as absorbent materials, which are crucial markers for fungal infection. In this experiment, the overall peak areas detected using ZIF-8 were 8.29, 4.65, 13.13, and 18.52 times higher than Tenax(r)-TA for the detection of 3-octenone, 1-octen-3-one, 3-octanol, and 1-octen-3-ol, respectively. The good performance of ZIF-8 for the extraction of _B. cinerea_ related volatiles from in-field samples, including 3-methyl-1-butanol, 3-octanone, 1-octen-3-one, 3-octanol, 1-octen-3-ol, and phenylethyl alcohol, demonstrates the ability to apply this sorbent material to the in situ volatile collection and detection of _B. cinerea_ infection in grapes prior to harvest. This non-destructive sampling method can also apply to other agricultural products and horticultural products that may be subject to fungal infection during prolonged storage or transport periods. A correlation coefficient plot to show the relationship between the grape _B. cinerea_ infection and the detection of volatile compounds is presented in Figure 4. Strong positive correlations were observed between the detection of 1-octen-3-one, 3-octanone, 3-octanol, and 1-octen-3-ol, as well as the detection of 3-methyl-1-butanol, 1-hexanol, 1,5-dimethyltetralin, benzyl alcohol, phenylethyl alcohol, and 1,5-dimethylnaphthalene for in-field results. These volatiles were important for _B. cinerea_ grape infection, and the correlations may be explained by the growth progression of the pathogen.