A<unk>  is a substance used as an indicator of a biologic state.  It is a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention.<unk> s validated by genetic and molecular biology methods can be classified into three types.
Type 0 - Natural history markers
Type 1 - Drug activity markers and
Type II - Surrogate markers
It can be any kind of molecule indicating the existence (past or present) of living organisms. In particular, in the fields of geology and astrobiology<unk> s are also known as biosignatures. The term is also used to describe biological involvement in the generation of petroleum.
Biomarker
Tumor marker
Cardiac marker
Nanosensor
Clinical chemistry
Genetic marker
Neurochemistry
Spectroscopy