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 CO<sub>2</sub> 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.
The simulation of electromagnetic problems using the Finite-Difference Time-Domain method starts with the geometric
design of the devices and their surroundings with appropriate materials and boundary conditions. This design stage is
one of the most time consuming part in the Finite-Difference Time-Domain (FDTD) simulation of photonics devices.
Many FDTD solvers have their own way of providing the design environment which can be burdensome for a new user
to learn. In this work, geometric and material modeling features are developed on the freely available Google SketchUp,
allowing users who are fond of its environment to easily model photonics simulations. The design and implementation of
the modeling environment are discussed.
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.