Chip-based nanoflow liquid chromatography for on-chip detection of glycated haemoglobin levels

We develop a nanoflow liquid chromatography (LC)microchip integrated with an injection channel, a packed column, a frit and an optical detector cell for the on-chip detection of glycated haemoglobin (HbA_1c)levels. The LC microchip with high bonding strength of 104.2 bar was achieved by the thermoset polyester (TPE)prototyping technique. An electrolysis micropump (EMP)was designed to deliver the mobile phase into the separation channel. The EMP successfully eliminated the electrodes’ delamination via a novel assembly and sealing method of the electrode array. Thus, the lifetime of the EMP was extended to over 480 h and the generated pressure can be up to 84.2 bar, which is sufficient for most on-chip LC. Flow rates (0.36–16.7 μL/min)were measured at different back pressures (6.12–41.66 bar)when the electric current varied from 1 to 10 mA. The nanoflow LC microchip was actuated with the EMP to perform a liquid chromatography–ultraviolet/visible (LC–UV/VIS)analysis of glycated haemoglobin samples from human blood. Haemoglobins, including HbA_1(a+b), HbA_1c and HbA₀ are eluted in this order under the optimised condition. HbA_1c levels can be precisely measured with a very small blood sample volume of 5 nL in a short analysis time of 2 min. The coefficient of variation (c.v.)for three consecutive measurements of HbA_1c levels was between 1.5% and 7.0%. The day-to-day relative standard deviation (RSD)for the retention time of three components was no more than 6.0%. Furthermore, the test results of the on-chip method were consistent with the calibration values with error of 1.9–7.3%.