  Physical limit of molecular sensing has been extensively studied in
biological systems. Biosensors are engineered equivalents of molecular sensors
in living systems and play critical role in disease diagnosis and management.
Investigation into the physical limits of biosensors could have major
beneficial impact on early disease diagnosis. Here, we present an extension of
the classical works on molecular sensing limits of living systems to the realm
of biosensors. Two approaches are proposed to estimate concentration with noisy
biosensors. We find a trade-off between precision and accuracy.
