Analyte sensors and sensing methods for detecting creatinine

An analyte sensor comprising:

• a first working electrode and a second working electrode;
• a creatinine-responsive active area disposed on a distal end of the first working electrode, the creatinine-responsive active area comprising a first electron transfer agent, a first polymer, and an enzyme system comprising multiple enzymes that are capable of acting in concert to facilitate detection of creatinine, the enzyme system comprising:
• creatinine amidohydrolase,
• creatine amidinohydrolase, and
• sarcosine oxidase;
• a dielectric layer covering the first working electrode other than the distal end of the first working electrode;
• a first membrane that is permeable to creatinine and overcoats the creatinine-responsive active area, the first membrane comprising polyvinylpyridine-co-styrene;
• an area for oxygen scavenging disposed upon the first membrane and isolated from the first working electrode, the area for oxygen scavenging comprising a second polymer and glucose oxidase as an oxygen scavenger, the glucose oxidase covalently bonded to the second polymer;
• a glucose-responsive active area disposed upon a surface of the second working electrode, the glucose-responsive active area comprising a second electron transfer agent, a third polymer, and glucose oxidase that is covalently bonded to the third polymer;
• and
• a second membrane that is permeable to glucose and overcoats the glucose-responsive active area,
• wherein the sensor is configured to be partially inserted into a tissue such that a distal portion of the sensor is in contact with an interstitial fluid to detect glucose and creatinine in vivo.