Performance of absorption photometry microchip for blood hemoglobin measurement integrated with processing circuits and Si(1 1 0) 45° mirrors

Abstract In this study, advantages of optical path extension in absorption photometry microchip for highly sensitive hemoglobin measurement have been demonstrated. Stability in repetitive measurement is evaluated with real blood samples. Long optical path (5 mm) is realized on the microchip for highly sensitive absorption photometry. Two 45° mirrors are fabricated in ‘Multi-layered smart-MEMS structure’ to form a long optical path. Different type of microchip with different optical path length (0.5 mm) without 45° mirrors was also fabricated for characteristic comparison. Both types of the microchip were evaluated with food color solution, and each characteristic were compared. As a result, effects of optical path extension are clearly shown as detectable lower limit improvement. Furthermore, no adverse effects due to utilization of 45° mirrors were observed. It has been demonstrated that optical path extension with 45° mirrors is very effective to realize highly sensitive measurement in the microchip. Stability in repetitive measurement of the microchip was evaluated with real blood sample for the first time. In repetitive blood sample measurement, slight degradation of photocurrent of photodiode, which corresponds to hemoglobin concentration in the microchip, was observed. It is considered that the degradation is caused by protein adhesion to the surface of the mirrors and the photodiode. However, influence of the degradation can be removed by measurement method of introducing reference solution and sample solution alternately into each channel. Furthermore, normal range of human hemoglobin has been covered with linear range of the microchip. A small coefficient of variation of 0.61% or less was obtained in the measured results. From these results, blood hemoglobin measurement with high sensitivity has been realized with stabilized characteristics in repetitive measurement.