Gas sensors allow the monitoring of the chemical environment of humans, which is often crucial for their
wellbeing or even survival. Miniaturization, reversibility, and selectivity are some of the key challenges for
serial use of chemical sensors. This tutorial review describes critical aspects when using nanomaterials as
sensing substrates for the application in chemiresistive gas sensors. Graphene has been shown to be
a promising candidate, as it allows gas sensors to be operated at room temperature, possibly saving large
amounts of energy. In this review, an overview is given on the general mechanisms for gas-sensitive
semiconducting materials and the implications of doping and functionalization on the sensing
parameters of chemiresistive devices. It shows in detail how different challenges, like sensitivity, response
time, reversibility and selectivity have been approached by material development and operation modes.
In addition, perspectives from the area of data analysis and intelligent algorithms are presented, which
can further enhance these sensors' usability in the field.