Motivated by the necessity of efficient detection of COVID-19 through specific biomarkers, such as ethyl butyrate and heptanal, we performed first principles calculations based on density functional theory (DFT) to explore the sensing mechanism of pure, vacancy-induced, and single atom catalyzed CrX2 (X = Se, Te) monolayers. Both the biomarkers barely bind on pristine CrSe2. However with Se-vacancy (As-doping) suitable adsorption energies of − 1.44 (− 0.70), and − 0.70 (− 0.54) eV were obtained for ethyl butyrate and heptanal, respectively. Te-vacancy (Sn-doping) in CrTe2 resulted in much stronger binding of ethyl butyrate and heptanal with the adsorption energies of − 2.04 (− 2.40), and − 2.90 (− 2.40) eV, respectively. The adsorption of the mentioned biomarkers altered the magnetic and electronic properties of defected CrX2, which were explored through spin-polarized density of states, electrostatic potential and work function calculations. Measurable changes in electronic and magnetic properties confirmed excellent sensing potential of CrX2. Statistical thermodynamics analysis based on Langmuir adsorption model was employed to study the sensing of the biomarkers at different temperature and pressure ranges for real-world application.