Bee-based sensor using apis mellifera for detection of Andrographis paniculata volatile compounds

Honey bees can be trained to be sniffer bees due to the presence of high number of odorant receptors (170 odorant receptors) in their heads. This unique characteristic enables them to detect scent down to part per trillion level. In this study, localized honey bees (Apis mellifera) were trained by using the method of classical Pavlovian conditioning. The proboscis extension reflex (PER) of sniffer bees towards the target odor was observed and recorded. The phytochemical profile of Andrographis paniculata (A. paniculata) was constructed using headspace solid-phase microextraction coupled with gas chromatography integrated with mass spectrometer method. The volatile marker compounds were identified. The sniffing capacity of the sniffer bees was determined by varying the heating temperature from 50-120 °C, the weight of plant material from 20-100 mg and the percentage (20-100%) of the target herbal sample in the mixture of A. paniculata and Clinacanthus nutans (C. nutans). C. nutans is an herbal plant which is morphologically similar to A. paniculata and it also belongs to the Acanthaceae family. The efficiency, accuracy and sensitivity of sniffer bees were analyzed and validated statistically. The success rate of sniffer bees for heating temperatures was approximately 90 %. The success rate for minimum weight of plant sample, 20 mg was 50 %. The success rate percentage of target herbal sample increased when the percentage of A. paniculata was proportionally increased. Compounds such as caryophyllene, ß-elemene, 3,3-dimethylhexane, apiol, 6,10,14-trimethyl-2-pentadecanone and dihydroactinidiolide were detected in the gaseous mixture. The kinetics of volatile marker compounds released from the plant samples were studied to predict the concentrations of the volatile marker compounds for sniffer bee detection at 85 ?. Second-order and two-site kinetic models were selected because of the kinetic data of these volatile marker compounds fitted well to these models (R2 > 0.9)

Sniffer bees as a reliable tool for Andrographis paniculata detection

Honey bees of Apis mellifera could be trained to be highly reliable sniffers for the detection of Andrographis paniculata using the classical Pavlovian conditioning training method with high success rate, > 80% based on the proboscis extension reflex as a positive response to the presence of the herb. The success rate of sniffer bees was found to be in a temperature dependent manner, but not significantly affected by the heating duration (5–110 min). The variance of 7.7% success rate was observed for the heating temperature ranged 50–120 °C with the highest success rate (92.7%) at 100 °C. This could be due to the content of signature compounds released from the heated herbal samples. Three signature compounds such as dihydroactinidiolide, apiol and 6,10,14-trimethyl-2-pentadecanone were proposed to be the volatile marker of the herb since their concentrations changed in accordance with the temperature profile and success rate of sniffer bees. The volatile compounds were extracted by divinylbenzene and carboxen coated polydimethylsiloxane fiber in the headspace of solid phase micro-extraction before analyzed by GC–MS for identification. Almost 50% success rate could be achieved using the minimum amount of 20 mg herbal samples. High selectivity of the sniffer bees has also been proven by no response to another morphologically similar herb, Clinacanthus nutans which was also heat-treated in the similar manner. The sniffer bees also showed to exhibit 80% success rate to detect A. paniculata mixed with 50% C. nutans as interference in a mixture