Dual-trap Raman tweezers for probing dynamics and heterogeneity of interacting microbial cells.

We report on development of dual-trap Raman tweezers for monitoring cellular dynamics and heterogeneity of interacting living cells suspended in a liquid medium. Dual-beam optical tweezers were combined with Raman spectroscopy, which allows capturing two cells that are in direct contact or closely separated by a few micrometers and simultaneously acquiring their Raman spectra with an imaging CCD spectrograph. As a demonstration, we recorded time-lapse Raman spectra of budding yeast cells held in dual traps for over 40 min to monitor the dynamic growth in a nutrient medium. We also monitored two germinating Bacillus spores after the initiation with L-alanine and observed their heterogeneity in the release of CaDPA under identical microenvironment.

[Using Raman spectroscopy to analyze apoptosis of gastric cancer cells induced by cisplatin].

Apoptosis of gastric cancer cells induced by cisplatin was investigated using laser Raman spectroscopy. Gastric cancer cells (SGC7901) were treated with 10 microg x mL(-1) cisplatin for 24, 48 and 72 hours, then were divided into two parts, one for fluorescence staining, the other for collection of Raman spectra by means of scanning. The acquired spectra were then preprocessed by background elimination, smoothing, normalization, baseline correction, and peak fitting. Fluorescence staining result showed that the nucleuses from untreated group were uniformly stained, while those from the group treated for 72 hours were densely stained and broken. The spectra results revealed that the intensity of peaks associated with nucleic acid and protein decreased after the cells were incubated with cisplatin for 24, 48 and 72 hours. The intensity of peaks at 783, 1002 and 1343 cm(-1) respectively fell to 52, 64 and 76 percent of the original value after 72 h of treatment, which indicated that cisplatin could induce apoptosis of gastric cancer cells and reduce the amount of nucleic acid and protein in the cells. The above results suggest that Raman spectra can provide abundant information about the changes in materials in cells and serve as an effective method for real time measurement of apoptosis.

[Laser tweezers Raman spectroscopy analysis of liver cancer tissue].

Single cell laser tweezers Raman spectroscopy (LTRS) has been applied to biology field. In the present article, the authors measured the spectra of liver cancer cells, para-cancer cells and normal hepatocytes using single cell laser tweezer Raman spectroscopy (LTRS) system and compared their average spectra changes. The results showed that the laser tweezers Raman spectroscopy could differentiate specimens of different pathological changes from liver tissue studied. The 1 070 and 1 266 cm(-1) peaks obtained from normal hepatocytes were more visible than the same two peaks obtained from liver cancer and para-cancer specimen. The 1 445 cm(-1) peak of normal hepatocytes was higher than that of liver cancer cells and para-cancer cells. It is known that the 1 070 cm(-1) peak represents lipids and nucleic acids, while 1 266 and 1 445 cm(-1) peaks represent lipids and proteins. So, these peak changes may directly reflect the changed biomaterials related to liver carcinogenesis. Thus, single cell laser tweezer Raman spectroscopy may be a nondestructive, rapid and good method to measure and analyze different pathological specimens from liver cancer.

[The effect of abnormal cell shape on the spectral distinguishing of erythrocytes using laser tweezers Raman spectroscopy].

Erythrocyte is a mature blood cell that contains hemoglobin to carry oxygen to the bodily tissues. Erythrocyte, which takes on a biconcave disc that has no nucleus, is flexible and changeful. Erythrocyte is so sensitive to the environment that the shape of cell goes crimpy, even acanthoid. A laser tweezers Raman spectroscopy (LTRS) setup was used to trap single erythrocyte from healthy donors and patients with thalassemia and to collect the Raman scattering of trapping cell. Normal shape, crimpy erythrocytes and acanthoid erythrocytes were tested, and the averaged spectra, and principal component analysis (PCA) which detailed the spectral difference and the change of hemoglobin, were used to evaluate the effects of different cell shape on the spectral distinguishing of erythrocyte. The results reveal that in normal physiological environment the change in cell shape does not effect the spectral distinguishing of abnormal erythrocyte.

[Study of Raman spectra of single carcinoma of nasopharynx cell].

The Raman spectra from carcinoma of nasopharynx cell lines (CNE2) and normal airway epithelial cell lines (HBE) were investigated using a laser tweezers Raman spectroscopy (LTRS). The Raman scattering measurements were obtained from three different places in every single cell. Visual inspection of the spectra shows that the differences observed in spectra of the cancer cells and normal cells are obvious. The peak ratio I1 304/I1 336 is 1.05 for the normal cell and 1.22 for the cancer cell. Using a combination of principal component analysis (PCA) and discriminant function analysis (DFA), the authors are able to predict cancer cells, and normal cells and the DFA is better for single Raman spectrum. The sampling locations did not seriously affect the result of PCA and DFA. PCA and DFA also show that the uniformity of normal cells is better than that of cancer cells. The results indicate that the Raman spectra may offer the experimental basis for colorectal cancer diagnosis.

[Raman micro-spectroscopy of single blood platelets].

The authors collected the Raman spectra of single blood platelets of human, pig, rat and rabbit suspended in saline so-lution by using a laser tweezers Raman spectroscopy (LTRS) setup. A single platelet cell was trapped in the focus of a near-infrared laser beam at 785 nm and the excited Raman spectrum was acquired. For each species, the Raman spectra of up to 20 platelet cells were acquired and were used to perform a principal components analysis (PCA) or a discriminate function analysis (DFA). The average Raman spectra indicate that the vibration bands at 1 524 and 1 157 cm(-1) of human platelets are obviously different from those of the platelets from pig, rat and rabbit. The Raman intensities at 1 157 and 1 524 cm(-1) bands are significantly high for human platelets. The ratio I1 157 / I1 003 of human platelets was 0.795, but those of pig, rat and rabbit were 0.532, 0.502 and 0.485, respectively. In addition, the platelets from four different species can be discriminated with multivariate analysis. These findings demonstrate that the LTRS, combined with multivariate analysis, could be used to rapidly discriminate platelets from various species and may find valuable application in rapid sensing of biochemical changes in a single cell.