Biomedical Optics Laboratory | Dr. Yong-Qing Li
ECU Biomedical Optics Laboratory includes a bio-optics lab (room E212), a photonics lab (E211a), a microbiology lab (room E217) and a machine/electronics lab (room E211b) located in the Howell Science Complex building. The optics laboratory is well equipped with three optical tables, lasers/optics, a diamond-anvil cell for high pressure study, and houses three modified research DIC/phase-contrast/fluorescence mircosopes, two bench laser Tweezers and Raman spectroscopy (LTRS) setups, and a Raman and fluorescene imaging setup for the single cell studies. The microbiology lab is equipped for spore/bacteria preparation, storage, and treatment. The machine/electronics lab is equipped for making mechanic and electronic parts.
The major equipment includes three inverted DIC and phase-contrast microscope (Nikon TE2000 and TiS, Olympus IX81), atomic force microscope (easyScan 2, Nanosurf), two spectrometers (Jobin Yvon Triax320), two TE-cooled CCD detector (Princeton Instruments, PIXIS), two EMCCD (Andor DU-897), and two near-infared diode lasers (785nm/1500mW), two ultrafast pulsed lasers (Coherent 900-D and 900-P) for Raman microscopy and multi-photon microscopy, two solid-state green lasers (Coherent Verdi-10) used for the excitation source and optical pulling and two single photon detectors. The lab is also equipped with a XY motorized stage and vortex phase plate for the solid-phase Raman cytometry.
The capabilities include Laser tweezers and Raman spectroscopy system of biological particles suspending in liquid and in air with a size ranging from 0.2 to 100 microns; Confocal micro-Raman spectroscopy and Raman imaging for biological and chemical analysis; Differential interference contrast/fluorescence microscopes; Atomic force microscope; Automated imaging spectrometer for laser Raman spectroscopy from 200 to 2000 nm; Ultrafast pulsed laser sources tunable from 700 to 980 nm, pulse width of 100 fs or 1ps, power up to 1.0W at a repetition rate of 76 MHz, synchronized repetition. Pulse picker with EOM selects femto or pico second pulses with a rate from 1.0 kHz to 250 kHz. Electronic multiplying CCD with single photon counting capability; high power laser scissor (up to 1.0J per pulse).
The research goal of our lab is to apply the principles and techniques of quantum optics for the detection, identification, and manipulation of fundamental biological processes at the level of single cells and single molecules. The current research includes Raman tweezers, optical pulling and trapping of airborne particles, and monitoring dynamic biological process of single living cells.
1. Optical pulling of airborne particles over 10 meters
Optical pulling is the attraction of objects back to the light source using optically induced “negative forces.” It is commonly expected that when illuminated by a collimated laser beam, an object will be accelerated along the light propagation direction by radiation pressure. The idea of using optical beam to attract objects back to the light source is counterintuitive and has long been attractive to scientists. We demonstrate that micron-sized absorbing objects can be optically pulled and manipulated over a meter-scale distance in air with a collimated laser beam based on negative photophoretic force.
2. Pulling and lifting macroscopic objects by light
In Maxwell’s theory of electromagnetic waves, light carries energy and momentum and the exchange of the energy and momentum in light-matter interaction generates optically-induced forces acting on material objects. Although optical forces have been widely applied for the manipulation of microscopic objects, they are usually unnoticeable on macroscopic objects because the magnitude of optical forces is generally much weaker than the gravitational force (FG) of the large objects. There are two types of optically-induced forces. One is radiation pressure force (FRP) arising from direct momentum transfer between the object and the incident light, which is in pN or nN range and is not enough to lift large objects. The other is photophoretic or radiometric force (FRM) due to photo-heating effect, in which the photon energy of the incident light is first converted into the thermal energy of the object and then asymmetrical momentum transfer between the heated object and the surrounding gas molecules produces FRM, which can be several orders of magnitude larger than the radiation force FRP. We directly observe light-induced attractive forces that allow pulling and lifting centimeter-sized objects off the ground by a light beam. This large force (~4.4 μN) allows rotating a motor with four-curved vanes (up to 600 rpm). Optical pulling of macroscopic objects may find nontrivial applications for solar radiation-powered near-space propulsion systems.
3. Raman tweezers
It is the combination of Nobel-Prize winning optical tweezers and Raman spectroscopy, which allows capturing and manipulating a single biological particle including cell, bacterium and virus and allows acquiring the Raman spectroscopy of the trapped particles. Raman tweezers can provide biochemical composition of a single living cell without chemically interfering it and the measured vibrational energy levels can be used as fingerprints for identification of biological cells.
4. Monitor dynamic biological process of single cells and cellular heterogeneity by live-cell microscopy and spectroscopy
The ability to monitor biological dynamics of individual cells and explore cellular heterogeneity is of particular interest to single-cell microbiology. Bulk-scale measurements report only average values for the population and are not capable of determining the contributions of individual heterogeneous cells. It is possible to use micro-Raman tweezers to monitor dynamic biological process and cellular explore heterogeneity based on measuring the molecular vibration frequencies from the scattered light. As an example, we studied on the real-time detection of kinetic germination and heterogeneity of single Bacillus thuringiensis spores in an aqueous solution by monitoring the calcium dipicolinate (CaDPA) biomarker with laser tweezers Raman spectroscopy (LTRS). Germination is the process by which a dormant spore returns to its vegetative state when exposed to suitable conditions. In our experiment, a single B. thuringiensis spore was optically trapped in a focused laser beam and its Raman spectra were recorded sequentially in time after the exposure to a nutrient-rich medium, so that the CaDPA amount inside the trapped spore was monitored during the dynamic germination process.
Fig.1 (a) Time-lapse Raman spectra of a single trapped Bacillus thuringiensis spore after exposure to the TSB growth medium and the corresponding DIC images. Curve A is for 0 min from the time when the spore was captured in the optical trap; B for 29 min; C for 30 min; D for 31min; and E for 40 min. (b) Intensities of the 1016 cm-1 CaDPA band of five individual Bt spores as a function of the incubation time.