**4.1 Sensitivity**

The lowest concentration of analyte that a biosensor can detect is basically its limit of detection (LOD) or sensitivity. To check the occurrence of analyte traces in a sample at analyte concentrations, a biosensor is needed in several environmental tracking and medical applications for dealing with analyte concentrations with a sensitivity as low as nanograms per milliliter (ng/ml), and in some cases, it reaches femtograms per milliliter (fg/ml) [10].
