A miniaturized flow-injected thermal biosensor was developed for the d
etermination of urea and L-lactate in undiluted blood in 1-mu L sample
s. The sensor employed a small enzyme column constructed of stainless
steel tubing and microbead thermistors. Urease and lactate oxidase/cat
alase were separately immobilized onto controlled-pore glass beads, wh
ich, in turn, were charged into the enzyme column. With a flow rate of
70 mu L/min, linear analytical ranges from 0.2 to at least 50 mmol/L
and 0.2 to 14 mmol/L were obtained for urea and lactate, respectively.
The relative standard deviations (CVs) for measurements of analyte in
buffer were 0.91% for urea and 1.84% for lactate. For urea in whole b
lood, the CV for 50 determinations was 4.1%. Contrived samples contain
ing various concentrations of urea and L-lactate in whole blood were d
etermined with this sensor and with a spectrophotometric method. Compa
risons of the results gave correlation coefficients of 0.989 and 0.984
for 30 blood urea and 30 blood lactate assays in concentrations rangi
ng from 4 to 20.9 mmol/L and from 1.7 to 12.7 mmol/L, respectively.