Conventional electrochemical dissolved oxygen (DO) sensors are expensive as they use platinum in their construction. In addition, these sensors biofoul when used in natural or waste water, which leads to reduced sensitivity and variable performance. Here, we solve these problems by: replacing platinum with hemin as the low-cost alternative for electrocatalysing the oxygen reduction reaction and using silicone rubber [poly(dimethylsiloxane) (PDMS)] functionalized with polyethyleneglycol (PEG) as the anti-biofouling gas permeable membrane to provide selectivity with an increased lifetime. This DO sensor has a sensitivity of 20.7 (μA/cm2)/(mg/L) of DO in a concentration range of 2-7 mg/L. In addition, the common interferences, such as phosphates and nitrates, show minor influence in the DO detection. Furthermore, the PEG functionalization of PDMS membrane reduced biofouling and increased the lifetime of the sensor by 20 times in accelerated biofouling conditions.