Method of particle detection, apparatus therefor, method of forming particle concentration difference in dispersion liquid, and apparatus therefor

#The present invention relates to a method of particle detection, an apparatus therefor, a method of forming a particle concentration difference in a dispersion liquid, and an apparatus therefor and more particularly, to a method of particle detection, an apparatus therefor, a method of forming a particle concentration difference in a dispersion liquid, and an apparatus therefor, regarding first and second particles having different diameters.

#The manipulation and process of a microscopic object has been especially focused on recently relative to nanotechnology and biotechnology. The microscopic object of the order of micrometers can be manipulated under a microscope by a laser beam without being touched by use of a laser tweezers, and it can be processed by laser ablation and a polymerization reaction of the laser. However, it is difficult to bring the microscopic object and another object together or to inject another object into the microscopic object even by combining the above techniques. Since a shock wave (laser-induced shock wave) generated by focusing the laser beam in a liquid by an objective lens of a microscope can highly accelerate the object, it is regarded as effective energy to perform an operation requiring high energy.

#Here, techniques regarding the above are disclosed in Japanese Unexamined Patent Publication No. 2003-210159, Japanese Unexamined Patent Publication No. 2003-344260, Japanese Unexamined Patent Publication No. 2005-144538, Japanese Unexamined Patent Publication No. 2005-335020, Japanese Unexamined Patent Publication No. 2005-287419, Japanese Unexamined Patent Publication No. 2005-168495, and Appl. Phys. Lett., 84, 2940 (2004), Appl. Phys. A, 79, 795 (2004).

#FIG. 1 is a schematic diagram showing a time change of the fluorescent intensity at a position apart from a shock wave generation point based on a concentration distribution change by a laser-induced shock wave;

#FIG. 2 is a schematic view showing an apparatus;

#FIG. 3 is a schematic view showing a focused position of a laser beam;

#Embodiments of the present invention will be described with reference to the drawings hereinafter. First, a description will be made of a principle. A shock wave can be generated in a dispersion liquid by focusing a laser beam in the dispersion liquid by use of a pulse laser such as a Nd:YAG laser having a Q-switch, a light collection optical system such as a microscope, and water. First particles having a first diameter and second particles having a second diameter larger than the first diameter are dispersed in the dispersion liquid. A change occurring in the dispersion liquid can be measured by any method as long as the absorption, fluorescence, and refractive index can be optically detected and another property change in the dispersion liquid can be detected in a time region from nanoseconds to microseconds at high speed. In addition, an observation position is to be several micrometers to millimeters apart from the focused position. In addition, according to the present invention, it is assumed that particles having a diameter of several nanometers is migrated on a time scale of several nanoseconds.

#It is thought that the particles are accelerated hydrodynamically by the propagation of the shock wave generated through light absorption and plasma generation at the focused point. At this time, since the larger particle, that is, the particle having a larger diameter is more accelerated, it is considered that the viscosity at a shock wave front becomes high due to high pressure, and viscosity resistance is generated when the shock wave passes the particles, so that the particle are accelerated. Here, the shock wave front is a front surface of the propagation of the shock wave. In addition, since the particle having a small diameter is not accelerated, it is considered that the elastic collision of the shock wave does not occur. Thus, the difference of the particle size can be identified due to this size dependency. In addition, the propagation speed of the shock wave front is 2000 to 2200 m/s. This speed is higher than a migration speed in the electrophoresis method and the dielectrophoresis method.

#The principle of the present invention will be described further in detail. Here, a time change of measured fluorescent intensity can be understood as follows. FIG. 1 is a schematic diagram showing a time change of the fluorescent intensity at a focused position (x0) of an observing excitation light source positioned apart from a shock wave generation point based on a concentration distribution change by the laser-induced shock wave. In FIG. 1, a vertical axis designates the concentration of the dispersion liquid, and a horizontal axis designates a distance (x) from the shock wave generation point. In addition, the function shown by a solid line is an observation region function (F(x)) in FIG. 1. Here, the observation region function is a function showing the distribution of the fluorescent intensity in an observation region from a position (x) in an excitation light axis direction centered around the focal position (x0) of the excitation light source when the space distribution of the concentration is monitored by the fluorescence.