Two-step constructing a p-n heterojunction interfaces for ultrasensitive detection of isopropanol in real stool sample for early colorectal cancer diagnosis and machine learning prediction model

• Isopropanol and para-cresol are considered as one of biomarkers for colorectal cancer. • Iridium oxide and zinc oxide forms a novel p-n heterojunction for isopropanol detection. • Optimized electrodeposition parameters facilitate crystal structure tuning for improved isopropanol detection. • Machine learning model linear discrimination analysis is constructed based upon isopropanol and para-cresol concentration. This research reported a novel p-n junction interface for the enhanced isopropanol detection to tackle the quantitative analysis of headspace volatile organic compounds (VOCs) for real feces sample from colorectal cancer, adenomas and healthy samples in alleviating the uncomfortableness of colonoscopy and false positive in other methods such as genetic related fecal occult blood testing. Iridium oxide and zinc oxide were fabricated according to optimized electrodeposition method and calcination process to further elevate their crystallinity and forming new chemical bond between them. The constructed iridium oxide-zinc oxide p-n junction was used for selective 5 ppm isopropanol detection among 5 ppm methanol, 5 ppm ethanol, 1.6 ppm propan-1-ol, 3.2 ppm buta-1-ol, 80 ppm acetic acid, 106 ppm propanoic acid, and 15 ppm butane-2,3‑dione headspace gases, resulting in an ultrasensitive and selective isopropanol gas sensor. A linear range of 0.0585 ppm to 58.5 ppm isopropanol concentration was constructed with linear product-moment correlation coefficient fitting results of 0.971 for intra-stability test and 0.981 for inter-stability test. The sensitivity is 0.532 and 0.547 for intra- and inter-electrode testing. The proposed sensor possesses CRC pre-screen diagnosis by monitoring isopropanol concentration with a limit of detection (LoD) at 8.32 ppm and limit of quantification (LoQ) at 18.10 ppm. The long-term stability has also been tested up to 90 days. The results demonstrate that the first 30 days the sensor has kept over 90 % of response rate. The as-prepared sensor marks a potential application for real sample screening for CRC disease. A general demonstration for isopropanol oxidation and its mechanism illustration. (A) The electrodeposited ZnO and IrO x isopropanol gas sensing mechanism based on the band gap structure and (B) different ratio of the thikcness of ZnO and anodic IrO x & ZnO and cathodic IrO x .