Immobilization of lactate as an electroactive indicator on pencil graphite electrode for the development of a new electrochemical biosensor for the detection of lactate dehydrogenase

A biosensor was developed for the detection of lactate dehydrogenase (LDH) enzyme using a lactate modified pencil graphite electrode (PGE). The sensor relies on the immobilization of the lactate on PGE, and LDH detection is based on the decrease of lactate peak current following oxidation to pyruvate in the presence of LDH. Square wave voltammetric technique was used for the assay of signals in the range of −0.6 to 0.8 V and a frequency of 25 Hz for the determination of LDH. The dependence of the response was investigated in terms of reaction time, washing time and LDH and NAD+ amounts. Also, the electrochemical behavior of LDH treatment on the lactate modified PGE was studied. The electrode showed good selectivity, repeatability and an operational stability of about 90% of its original response for two weeks. Moreover, the sensor displayed a linear response range from 0.36–2.13 U μl−1 for LDH with a detection limit of 0.16 U μl−1. The response time of the LDH-treated lactate modified PGE was found to be 2 s. The relative standard deviation (RSD) obtained was 3.5% (for LDH 0.71 U μl−1 and n = 3).