Microfluidic chip-capillary electrophoresis with dynamic multi-segment standard addition for rapidly identifying nephrolithiasis markers in urine

Abstract

A microchip-CE device was fabricated for bed-side monitoring of nephrolithiasis biomarkers in urine by incorporating on-chip continuous passive mixing and standard addition to reduce sample matrix interference, increase sample throughput and eliminate accessories for active mixing. Under optimized conditions with buffer containing 20mM borate and 0.5mM CTAB at pH 10.3, sample and standards injected electrokinetically at -350V for 10s for online mixing in a Y-merging flow microchannel prior to CE separation and UV detection at 210nm, both inhibitors (citrate, CA) and promoters (oxalate, OA and uric acid, UA) for nephrolithiasis can be separated and determined in human urine in a single run completed within 10min after a simple 50-fold sample dilution and filtering. Satisfactory working ranges from 0.13-40, 0.25-40 and 0.025-40mM, LOD 2.6, 6.1 and 0.7μM, repeatability (%RSD, n=5) for migration time 1.40, 1.43, 0.47 and peak area 4.46, 6.10, 1.98, respectively, for CA, OA and UA are obtained for urine samples. The use of on-chip standard addition is shown to improve repeatability of the migration time, assist the identification of nephrolithiasis markers from difficult samples with noisy baseline and enlarge the working range for nephrolithiasis marker determination. The device developed can be used for both routine and emergency monitoring to deliver results on demand for bedside monitoring and public health protection. It provides an early detection of nephrolithiasis to enable timely treatments, ease anxiety of parents for neonates consuming suspected contaminated food, and quick results for patients in a critical condition. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.