Direct measurement of the in vitro hemoglobin content of erythrocytes using the photo-thermal effect of the heme group

Blood hemoglobin is an important diagnostic parameter in measuring overall health. The hemoglobin molecule and the iron it contains absorb light energy, leading to thermal changes. This paper presents a new method for determining the hemoglobin concentration of erythrocytes by measuring temperature increases of the heme group when cells are heated by a 532 nm wavelength laser. The advantages of our method are that it determines the hemoglobin content of an entire blood sample without chemical treatments and requires only a small amount of blood (less than 10 μL). A micro scaled platinum resistance temperature detector (Pt RTD) was fabricated using a microelectromechanical system (MEMS) technique that directly measures the temperature changes. The platinum RTD's resistance at 0 °C is 275.32 Ω. For the specific heating of erythrocytes, we used a 0.03 to 9.6 W cm^-2 power tunable diode pumped solid state (DPSS) continuous wave (CW) laser module with a wavelength of 532 nm. When heating human erythrocytes, leukocytes, plasma, and reference solutions, only the temperature of the erythrocytes significantly increased, indicating that our measurement technique can be used to determine hemoglobin concentration. The hemoglobin concentrations for the samples we used were 0.34, 0.67, 1.35, 2.7, 5.4, 8.1, 10.8, 13.5, 16.2, 18.9 and 21.6 g dL^-1. The temperatures measured for each sample were 31.17 ± 1.98, 36.34 ± 3.76, 42.70 ± 4.38, 48.39 ± 6.47, 63.73 ± 3.34, 79.09 ± 9.60, 84.86 ± 1.99, 87.54 ± 9.84, 91.90 ± 5.27, 90.00 ± 3.24 and 95.79 ± 2.66 °C at a 9.6 W cm ^-2 output power of the 532 nm laser at 23 °C. We also provide a theoretical analysis of the temperature increases and investigate their major heat source.