Salimi and Hosseini (2021) | • Sensor array system with 19 commercial metal oxide gas sensors | • 87 subjects were included in the experiment• The classification of data was more detailed | • Large amount of data processing• The test process took a long time | [31] |
Di Gilio et al. (2020) | • e-nose with 10 gas sensors for breath detection• Feature extraction algorithms used PCA classifier | • Large number of LC patients (115) and healthy controls (153) were selected for the study with good accuracy | • Sensitivity and specificity are not mentioned | [26] |
Chen et al. (2020) | • e-nose was constructed by metal-ion-induced assembly of graphene oxide• Feature extraction algorithms used PCA classifier | • Better sensitivity and specificity of 95.8% and 96%, respectively• Economical and low power consumption sensor array | • Only four VOCs were mainly analyzed, namely acetone, isoprene, hydrothion, and ammonia | [111] |
Kononov et al. (2019) | • Sensor array system with six metal oxide chemoresistance gas sensors• Classifier-used k-nearest neighbor (k-NN), logistic regression, and linear discriminant analysis (LDA) | • The solid-state sensors keep the sensors stable for long time• Sensitivity, specificity, and accuracy of 95%, 100%, and 97.2%, respectively | • The details about current smokers, past smokers, and nonsmokers are not given• Unreasonable control group selection | [112] |
Chang et al. (2018) | • e-nose with seven metal oxide semiconductor gas sensors for breath detection• Used LDA | • Low cost• 85 subject samples were selected | • Accuracy, sensitivity, and specificity are only 75%, 79%, and 72%, respectively• Smokers were not selected | [113] |
Masuda et al. (2015) | • LC diagnosis system based on self-made SnO2 nanosheet combined with SnO2 nanoparticles and noble metal catalysts | • The functional sensor system showed an excellent detection limit of 1-nonanal, an LC biomarker | • Only 1-nonanal is tested• Still in the sensor development stage | [47] |
Zhang et al. (2017) | • e-nose with 14 gas sensors for breath detection (including metal oxide gas sensors)• Feature extraction algorithms used LDA classifier and fuzzy k-NN | • Sensitivity, specificity, and accuracy of 91.58%, 91.72%, and 91.59%, respectively | • Only 37 subjects were included for the study | [40] |
Itoh et al. (2016) | • Combined SnO2-based metal oxide metal gas sensor with GC | • Gas sensor only needs to detect the concentration of a certain VOC• Good analytical capability• Enough testing samples | • Cumbersome and high cost | [46] |
Güntner et al. (2016) | • Sensor array with four nanostructured and highly porous Pt-, Si-, Pd-, and Ti-doped SnO2 sensing films by FSP | • Stability, high selectivity, low detection limit, and average error | • No further development and testing results | [33] |
Blatt et al. (2007) | • Sensor array system with six highly sensitive metal oxide gas sensors (fabricated by SACMI S.C.) and fuzzy k-NN and genetic algorithm | • Low cost, small size, and short response• Accuracy, sensitivity, and specificity of over 90% | • No external factors such as smoking were considered | [18] |