NIR Raman spectroscopic investigation of single mitochondria trapped by optical tweezers.

Raman spectroscopy is a vibration spectroscopic technique that has been widely used to probe biochemical changes of biological sample such as tumor tissue, blood cells, bacteria and yeast. Here, we applied near-infrared Raman spectroscopy to analyze the chemical composition changes of intact or swollen mitochondria induced by calcium ions. We used a confocal Laser Tweezers Raman Spectroscopy (LTRS) system that combined optical trapping and near infrared Raman spectroscopy to confine a single mitochondrion and consequently measure its Raman spectra following the addition of calcium ion solution. We analyzed Raman spectra of mitochondria isolated from rat liver, heart muscle and kidney, respectively. The major Raman peaks at 1654, 1602, 1446, 1301 and 1226 cm(-1) were observed from individual intact mitochondria. We examined the differences in near infrared spectra between intact and Ca(2+) damaged mitochondria. We found that after the exposure of the intact mitochondria to the 100 muM Ca(2+) solution the band of 1602 cm(-1) decreased very rapidly in the first period and then disappeared after 30minutes, while the intensities of the phospholipids and protein bands changed slowly in the first period and then suddenly disappeared, corresponding to the Ca(2+) induced swelling process. These results demonstrate the potential of LTRS technique as a valuable tool for the study of bioactivity and molecular composition of mitochondria.