Lactic acid is a simple and effective indicator for estimating physiological function. Rapid and sensitive detection of lactic acid is very useful in clinical diagnosis. However, the concentration of lactic acid in the physiological state is too low to be detected using traditional Raman spectroscopy. We applied silver colloidal nanoparticles-mediated surface-enhanced Raman spectroscopy (SERS) for rapid identification and quantification of lactic acid. The standard SERS spectra of lactic acid were defined and the 1395 cm −1 band intensity was used for quantification from 0.3 to 2 mM (R 2 = 0.99). In clinical blood sample measurement, the ultrafiltration (cutoff value 5 kDa) can efficiently reduce background fluorescence to improve SERS performance. We established identical and optimal procedure by adjusting reaction time and volume ratio of serum and nanoparticles to obtain high SERS reproducibility. Finally, we showed that silver colloidal nanoparticles-mediated SERS technique was successfully applied to detect lactic acid at physiological concentrations in the blood.

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Blood lactic acid concentration is an important indicator for physiological functions. To develop a rapid and sensitive measurement technique for monitoring blood lactic acid may provide a useful tool in clinical diagnosis. We proposed to develop a microdialysis surface-enhanced Raman spectroscopy (microdialysis-SERS) approach to filter/reduce interference from other large metabolites in blood and enhance the detection sensitivity for blood lactic acid. In this study, a microdialysis probe was constructed using 13 kDa cut-off dialysis membrane. The dialysate was mixed with 50 nm Ag colloidal nanoparticles automatically in a micro-fluid chamber for SERS detection under blood microdialysis of Sprague-Dawley rat. The linear range of SERS-lactic acid measurement is 10 -5~3 x10 -4 M with R 2 value of 0.99. The optimal mixing flow rate of nanoparticles is 18 µl/min under microdialysis at constant flow rate (2 µl/min). Real time lactic acid monitoring in vivo also has been demonstrated using microdialysis-SERS system.