From exogenous to endogenous: Advances in in vivo sampling in living systems

Complex chemicals, either anthropogenically released or naturally produced, exist in the environment and act as exogenous threats to living organisms. Meanwhile, numerous endogenous active components occurring in living organisms are vital indicators of physiological and biological functions. Conventional in vitro sampling methodologies may lack the ability to accurately reveal the processes of exogenous and endogenous substances in living organisms, especially for transient, variable, or unstable compounds. In vivo sampling techniques that impose minimum invasiveness to living systems are promising tools that provide more reliable information of the substances and thus benefit investigations of their behaviors in living organisms. Microdialysis (MD) and solid-phase microextraction (SPME) represent important in vivo sampling techniques with increasing implementations. Herein, we review recent advances in the in vivo sampling of exogenous and endogenous substances with a special focus on studies using MD and SPME techniques. Based on the current status and experience, we discuss existing challenges and future research development perspectives in this field. • Recent advances in vivo sampling of exogenous and endogenous substances with a special focus on studies using MD and SPME techniques are reviewed. • Existing challenges and future research development perspectives of in vivo sampling are discussed.