Optical tweezers offer the unique ability to manipulate particles dispersed in a liquid medium without any mechanical contact. It can trap, move and position a wide variety of living cells and sub-cellular particles. The nature of the technique has led to its predominant use in the fields of medicine and microbiology. On the other hand, different biomedical experiments require the traps with different structures and characteristics. Commercial optical tweezers are very expensive and they can’t meet the demands of some special experiments. In this paper, the authors describe a detailed recipe for fabrication of an inverted optical trap. The system uses a single mode laser with the wavelength of 1064 nm so as not to damage the living organisms. The system has a platform whose temperature is tunable at a range of 20-40°C and can be stabilized by a controller. The system is also has a video device. The significant advantage of the system is low cost and easy to be operated. It especially fits the labs that are short of fund but interested in the application of optical trap in research of living cells. By means of the system, the authors do the experiments on control over the neuronal growth successfully.
Neuronal growth cones navigate over long distances along specific pathways to find their correct targets. The prevailing opinion is that growth cones appear to be guided by four different mechanisms: contact attraction, chemoattraction, contact repulsion, and chemorepulsion. In contrast to existing methods, we use optical trap to guide neuronal growth. The optical trap is a non-contact manipulation technology which is increasingly used for micromanipulation of living cells and organisms. An intense light gradient near the focal region of a near-infrared laser beam gives rise to forces that make possible optical trapping and manipulation of a variety of micron-sized objects. In the developing nervous system, microtubule and actin play a fundamental role. To change the microtubule polymerization by control the density of tubulins or exerting a persistent force on the whole growth cone, we have shown experimentally that we can use optical trap to guide the growth direction of a neuron. In order to guide the neuronal growth direction, a self-contrived optical trap is placed in front of a specific area of the edge of the cell's growth cone. We turned the neuronal growth direction and guided it to the direction we expected. Control over neuronal growth is a fundamental objective in neuroscience and guiding neuronal growth with optical trap may be very important for the formation of neural circuits as well as nerve regeneration.
Optical tweezers are useful tools for use as non-contact micromanipulators of biological cells and organisms. Conventionally, a Gaussian laser mode is used as the trapping beam. In this paper, the authors describe a detailed recipe for construction of a low cost dual optical tweezers. The system is based on a conventional optical microscope and high-order Laguerre-Gaussian beam lasers. The authors studied both Laguerre-Gaussian beam trap and Gaussian beam trap's characteristics. It has been found that the high-order Laguerre-Gaussian beam trap has many significant advantages: the high-order Laguerre-Gaussian beam trap can hold larger particles more stable than Gaussian beam trap; a single Laguerre-Gaussian beam trap is able to catch free cells and hold them together simultaneously, but traditionally only the multi-Gaussian beam optical traps can fulfill the work; the high-order Laguerre-Gaussian beam trap is safer than the Gaussian beam trap. In addition, the high-order mode laser is inexpensive and the low cost system will make this technique more widely accessible to researchers.
Silver halide emulsions with average grain size around 10 nm and red-green-blue sensitivities were prepared in our laboratory. The influences of some preparing conditions on the emulsion grain size and spectral sensitivity were discussed. The emulsions were used to record holographic reflection gratings for investigating their properties in reflection holography. The reflection gratings were processed in a modified AAC developer and modified R-10 bleach. Diffraction efficiencies of the reflection gratings were up to 55% for the exposure of I .8 mJ/cm2 at 633 nm, 55% for the exposure of 2.2 mJ/cm2 at 515 nm and 50%for the exposure of3.3 mJ/cm2 at 458 nm.
Gene-chip as a very useful means of biotechnology has been applied to many research areas such as gene discovery, disease diagnosis and pharmacogenomics etc. , but commercially available gene-chip detection instruments are too expensive to be accepted by common labs. In this paper, a laser confocal scanning system with holographic notch filters used for simple gene-chip detection is presented. The system is mainly composed of an ordinary optical microscope, two holographic notch filters, a He-Ne laser, a digital controlled X-Y platform, a photodetector and a PC. The volume holographic notch filters were fabricated in our lab to substitute for the expensive narrow-band interference excitation filter and the dichroic filter in the conventional confocal detection system. The detection experiment was carried out on the gene-chips hybridized with cy5-labeled targets and the system sensitivity was determined by static measurement. The sensitivity is about 2x10-22mol/µm2, and the resolution is 10µm. The results indicate that the system can be used in primary gene-chip detection.