Development And Application Of Dual-trap Raman Tweezers System And Real-time Study Of The Gelatinization Process Of A Single Rice Starch Granule

Optical manipulation and analysis of single particles in a native aqueous medium are extensively applied to biology and physics. Optical tweezers technology has become a hot topic of new method and new instrument in biophysics, because rapid, noninvasive analyses of individual particles held in an optical trap. Raman tweezers is combination of Raman spectroscopy with optical tweezers, it have many merits comparing to traditional microscopic Raman system: Raman tweezers utilize a focused laser to form the gradient force for trapping living cell in the optical trap. This design optimizes the collection optic of Raman scattered and obtains a high ratio of signal to noise. Stray light from the glass slides significantly decreased as a cell is captured about 10 microns upon the slide. So the combination of optical tweezers with optical spectroscopy allows analyses of individual particles held in an optical trap by identifying chemical composition and revealing molecular behavior of the individual particles suspended in complex environments directly. But a single-trap Raman tweezers can only track and analyze one particle or one cell at a given time. It cannot track or detect two or more individual cells and two correlated portions of one cell in the same time. This is a particular problem if we want to monitor dynamic behaviors of the two interacting cells (such as budding cells) in liquid suspension or monitor molecule transportation in different locations within one large cell. In this paper, we report on the first development of a dual-trap laser tweezers Raman spectroscopy system for the manipulation and analysis of multiple individual living cells. Dual-trap laser tweezers Raman spectroscopy (LTRS) is a combination of dual-trap optical tweezers and Raman spectroscopy. We have developed a dual-trap Raman tweezers that allows capture two particles that are separated by a few micrometers using two optical traps and acquire their Raman spectra with an imaging CCD spectrograph simultaneously. A single laser beam from a near-infrared semiconductor diode laser was divided into two beams by a beam-splitter, and then introduced in an inverted microscope to form two optical traps, separated by 5¹0microns. Two individual cells or dielectric particles were trapped in each trap, respectively. The backward Raman scattering light from them were collected with the same objective and then imaged on the entrance slit of an imaging spectrograph, which then were sensed on different rows of a liquid nitrogen-cooled charge-coupled detector (CCD). Dual trap LTRS system allows monitoring dynamic behaviors of the two interacting cells in liquid suspension and monitoring molecule transportation in different locations within one cell. The dual-trap Raman tweezers allows monitoring the dynamic growth of single budding yeast cells during mitosis by monitoring the nucleus and other cellular components. Dynamic germination and heterogeneity in the release of CaDPA of two Bt. thuringiensis spores in a close separation in L-alanine were observed. Dual trap Raman tweezers would find broad applications in monitoring dynamic behaviors of interacting cells.Real-time monitoring the gelatinization process of single rice starch particle by using laser tweezers Raman spectroscopy system under the condition of excessive water and special heating mode is reported in this paper. These Raman spectra of gelatinization process are acquired using an imaging CCD spectrograph and the gelatinization process is remarked by the changes of spectra peak height. The experimental result further confirmed the fact that the band of 477cm^-1 is assigned as skeletal mode. Study on the rate of gelatinization about single rice starch granules is performed by analyzing the C-O-H group related characteristic peaks which locate at the band of 1052, 1083, 1127, 1339 cm^-1. The results demonstrate that the rate of gelatinization accelerates with rising temperature until the end of gelatinization process.