Optical tweezers use focused laser to trap microobjects suspended in the medium to the focal point. They are becoming an indispensable tool in microbiology because of its ability to trap tiny biological particles so that single particle analysis is possible. However, it is still very difficult to trap particles such as DNA molecules that are smaller than the diffraction limit. Although trapping of those is possible by increasing the laser power inversely proportional to the cube of the particle diameter, such high power can cause permanent thermal damages. One of the current solutions to this problem is to intensify the local field by the use of the near-field enhancement coming from nanoplasmonic structures illuminated with lasers. Such solution allows one to use low powered laser and still be able to trap them. In this paper, we present the trapping of a single DNA molecule by the use of the strong field enhancement due to a sub-micrometer sized hole drilled on a gold plate by an e-beam milling process and the trapping is verified by the measurement of the scattering signal that comes from the trapped DNA.
Since the discovery of the trapping nature of laser beam, optical tweezers have been extensively employed to measure
various parameters at micro/nano level. Optical tweezers show exceptional sensitivity to weak forces making it one of
the most sensitive force measurement devices. In this work, we present a technique to measure the stiffness of a
biomaterial at different points. For this purpose, a microparticle stuck at the bottom of the dish is illuminated by the
trapping laser and respective QPD signal as a function of the distance between the focus of the laser and the center of the
microparticle is monitored. After this, microparticle is trapped and manipulated towards the target biomaterial and when
it touches the cell membrane, QPD signal shows variation. By comparing two different QPD signals and measuring the
trap stiffness, a technique is described to measure the stiffness of the biomaterial at a particular point. We believe that
this parameter can be used as a tool to identify and classify different biomaterials.
The introduction and subsequent expression of external DNA inside single living mammalian cell (transfection) can be achieved by photoporation with femtosecond laser. After photoporation, external DNA can be introduced by trapping and successive insertion of DNA coated nanoparticle in the cell using optical tweezers. To maximize the transfection efficiency, one of the major aspects is that the photoporated cell should not be damaged and cell membrane should heal itself immediately or after sometime while the cells are healed in the CO2 incubator. Furthermore, the size of hole created as a result of photoporation should be more than the size of DNA coated nanoparticle to be inserted inside the cell. In this paper, an analysis has been done on single cell of important breast cancer cell lines named MCF-7 and MDAMB231. Size of holes created in cell membrane after photoporation has been measured and the required optimum energy with sustained cell life were determined. Using this analysis, most favorable conditions for maximum transfection efficiency can be determined.
Transfection is the process of introducing DNA into cells so that the introduced DNA will function and produce proteins.
This technique is useful to study the function of various DNA sequences and in the future may lead to gene therapy for
curing genetic diseases. Currently, a number of techniques are available for both population and individual cells
transfection. Although individual cells transfection is less commonly used than the population transfection, it has
benefits because it allows controlled single cell analysis. In this paper, we present a new laser assisted transfection
method for individual cells. In this technique, two lasers are used to perform the transfection procedure and third laser is
used to detect the position of DNA coated nanoparticle which is inserted in the cell. This technique has relatively high
transfection efficiency and good post-transfection cell viability.
Microassembly has been identified as one of critical techniques in innovating the promising era of micro/nano
technology. Several works have been investigated to fabricate various micro-devices such as micro-sensors and microactuators.
Assembly plays an important role for fabricating micro-devices. However, there are only few studies in the
assembly of microparts. In this paper, we present manipulation and assembly of three-dimensional microparts produced
by two-photon polymerization where optical trapping technique was used to manipulate microparts. We show exemplary
microassembly formed by assembling two microparts, a movable female part and a male part fixed on a glass substrate.
Magnetic properties of biological particles are measured in high-gradient magnetic separation (HGMS) analysis, revealing the concentrating process of nucleoprotein particles, ferritin, red blood cells, and eggs. A magnetic force acting on micrometer and submicrometer biological particles having diamagnetic or paramagnetic susceptibility with respect to the solution causes their movement and accumulation in gradient magnetic fields dependent on the values of the magnetic moments. The methods developed enable us to obtain the magnetic moments values of single particles and their assembly directly from magnetic separation and image analyses without assuming the detection of sizes. Our precision methods for the measurement of the capture traveling (magnetic diffusion) time and the accumulation (magnetic sedimentation) radius in HGMS show that it is really possible to determine the weak dia- or paramagnetic shifts of magnetic susceptibility up to 0.7×10-10 (SI units). HGMS analysis of the concentrating process of nucleoprotein granules (microcells, DNA granules, or nucleosome core particles) with polarization microscopy reveals phase transitions for DNA in granules, and separation accumulation of particles enables the determination of the diamagnetic susceptibility and anisotropy properties. Magnetic concentration effects always occur in living systems because micrometer-located gradient magnetic fields inside an organism are strong enough to cause drifts of cellular complexes and organelles of micrometer and submicrometer sizes. We report the appearance of superparamagnetic contamination inside developing shrimp eggs. In the developing shrimps eggs, ferritin aggregates are observed under weak gradient magnetic fields and diaparaferromagnetic changes are detected. A significant interruption of egg development is revealed in such fields.