Development of ultraviolet-polymerizable enzyme pastes: Bioprocess applications of screen-printed L-lactate sensors

The development of an amperometric L-lactate-specific enzyme electrode fabricated entirely using screen-printing technology is described, The sensor is based on immobilization of lactate oxidase from Pediococcus sp, by printing and subsequent UV irradiation within a polymerizable paste containing different supplements, The sensor optimization is described with respect to the most important features, such as composition and viscosity of the paste, stability, optimum pH and analytical range, The sensor was applied in a flow-through chamber within a flow injection (FI) system based on dialysis to off-line and on-line bioprocess monitoring of Geotrichum candidum cultivations in complex media, The sensor exhibited good operational stability; 4200 single injections (60 measurements per hour) led to a decrease of only 8.7%, the standard deviation being <1% (n = 60), Using an FI system with direct sample injection (3 x 10(-5) l sample injection volume), the detection limit was 2 x 10(-8) mol l(-1) and the linear range extended up to 1 x 10(-3) mol l(-1). The linear range of the dialysis-based FI system extended from 5.5 x 10(-4) to 5 x 10(-2) mol l(-1). The correlation between results obtained by analysis of diluted off-line bioprocess samples with the amperometric device and with a homogeneous photometric assay using lactate dehydrogenase was r = 0.985, By on-line injection analysis of undiluted complex fermentation broth over a period of 12 h prior to the inoculation, no significant loss of sensor response was observed, which demonstrates the good operational stability of the system even with complex real samples, Additional investigations indicated the necessity for pH conformity of the sample and standard solutions.