Needle-type lactate biosensor.

A needle-type lactate biosensor has been developed for continuous intravascular lactate monitoring. The sensor employs poly(1,3-phenylenediamine) as the inner layer on the platinum electrode in order to eliminate the interference from oxidizable physiological substances. Cross-linking with glutaraldehyde was used for enzyme immobilization. Dithiothreitol was used as the stabilizer of lactate oxidase. PVC (polyvinyl chloride) was chosen as the external diffusion control membrane. Sensor performance was evaluated in vitro and the sensor shows a sensitivity of 10-15 nA/mM, and a linear range from 1 mM to at least 15 mM lactate. Evaluation of the sensor response in blood plasma showed similar sensitivity and linear range as indicated by the calibration curves obtained in buffer solution. The sensor has a short response time of approximately 1 minute. The sensors were operated continuously for 7 days in phosphate buffer containing solution with a concentration at the physiological lactate level. No significant change in sensor sensitivity and its linear range has been observed. Sensors show a minimum change in its performance when stored in buffer at 4 degrees C for at least 9 months.