Abstract
Chemosensory protein based olfactory biosensors are expected to play a significant role in next-generation volatile organic compound (VOC) detection systems due to their ultra-high sensitivity and selectivity. As these biosensors can perform most efficiently in aqueous environments, the detection systems need to incorporate a gas sampling interface for gas-to-liquid extraction. This interface should extract the VOCs from the gas phase with high efficiency and transfer them into the liquid containing biosensors to enable subsequent detection. To design such a transfer interface, an understanding of the key parameters influencing the gas-to-liquid extraction efficiency of target VOCs is crucial. This paper reports a gas sampling interface system based on a microfluidic open-channel device for gas-to-liquid extraction. By using this device as a model platform, the key parameters dictating the VOC extraction efficiency were identified. When loaded with 30 μL of capture liquid, the microfluidic device generates a gas-liquid interface area of 3 cm2 without using an interfacial membrane. The pumpless operation based on capillary flow was demonstrated for capture liquid loading and collection. Gas samples spiked with lipophilic model volatiles (hexanal and allyl methyl sulfide) were used for characterization of the VOC extraction efficiency. Decreasing the sampling temperature to 15 °C had a significant impact on increasing capture efficiency, while variation in the gas sampling flow rate had no significant impact in the range between 40–120 mL min−1. This study found more than a 10-fold increase in capture efficiency by chemical modification of the capture liquid with alpha-cyclodextrin. The highest capture efficiency of 30% was demonstrated with gas samples spiked with hexanal to a concentration of 16 ppm (molar proportion). The approach in this study should be useful for further optimisation of miniaturised gas-to-liquid extraction systems and contribute to the design of chemosensory protein-based VOC detection systems.
Highlights
The detection of volatile organic compounds (VOCs) has application in a wide range of industries including food, agriculture, health and security
One of the key challenges in using these biosensors in VOC-detection systems is the requirement for an efficient gas sampling interface to transfer the VOCs from the gas phase into the liquid phase
This is because the biosensors are made of proteins which are functional only in aqueous solutions. This problem is further complicated by the physicochemical properties of certain volatile compounds, which are of significant interest in the health and security domains
Summary
The detection of volatile organic compounds (VOCs) has application in a wide range of industries including food, agriculture, health and security. One of the key challenges in using these biosensors in VOC-detection systems is the requirement for an efficient gas sampling interface to transfer the VOCs from the gas phase into the liquid phase This is because the biosensors are made of proteins which are functional only in aqueous solutions. Miniature systems based on open channels that do not rely on any membrane structure have been reported [17,18] These systems provide an effective way to establish a large gas-liquid interface area and eliminate issues related with membranes. The pumpless operation provides simplicity by eliminating the requirement for any external active pressure control system, making it more desirable for field deployable applications By using this device as a model system, the key factors influencing VOC extraction efficiency for lipophilic VOCs were identified. The impact of parameters such as sampling temperature, gas flow rate and chemical modification of the capture liquid composition have been studied
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