in this review article, we have discussed a selection of subjects which includes fatal pulmonary diseases especially lung cancer and their mortality statistics, methods of diagnosing these diseases, the importance of early detection, electronic nose technology and particularly the optoelectronic nose, gas sensors and chemical sensing, colorimetric sensor arrays, color sensing mechanisms, types of color sensing elements, statistical analysis and modeling, varieties of target gases studied with colorimetric sensor arrays, materials used within the colorimetric sensor arrays and in addition, in the last section, we mentioned the development of the colorimetric sensor array using advanced nanoparticles and hydrogels, in addition to numerous case studies with the usage of colorimetric sensors, that a summary of their results is collected in table 3. As mentioned above, the development of colorimetric sensors is quite appealing due to their real-time operation, high sensitivity, selectivity, easy visualization, and so forth. The optoelectronic nose, based on pattern recognition of the color changes of colorimetric sensor arrays, has emerged as a versatile technique for the identification of chemically various analytes mixture like breath, which needs to be used to improve the cure rate of diseases. recently optical sensing witnessed rapid development, in sensing materials which include nanotechnology and nanomaterials advantages, in addition to analytical techniques and imaging systems. 
 in
 this review article, we have discussed a selection of subjects which includes fatal pulmonary diseases  
especially
 lung cancer and their mortality statistics, methods of diagnosing these diseases, the importance of early detection, electronic nose technology and  
particularly
 the  
optoelectronic
 nose, gas sensors and chemical  
sensing
, colorimetric sensor  
arrays
, color  
sensing
 mechanisms, types of color  
sensing
 elements, statistical analysis and modeling, varieties of target gases studied with colorimetric sensor  
arrays
, materials  
used
 within the colorimetric sensor  
arrays
 and  
in addition
, in the last section, we mentioned the development of the colorimetric sensor  
array
 using advanced nanoparticles and hydrogels,  
in addition
 to numerous case studies with the usage of colorimetric sensors, that a summary of their results  
is collected
 in table 3. As mentioned above, the development of colorimetric sensors is quite appealing due to their real-time operation, high sensitivity, selectivity, easy visualization, and  
so
 forth. The  
optoelectronic
 nose, based on pattern recognition of the color  
changes
 of colorimetric sensor  
arrays
, has emerged as a versatile technique for the identification of  
chemically
 various  
analytes
 mixture like breath, which needs to be  
used
 to  
improve
 the cure rate of diseases.  
recently
 optical  
sensing
 witnessed rapid development, in  
sensing
 materials which include nanotechnology and nanomaterials advantages,  
in addition
 to analytical techniques and imaging systems.