Patent ID: 12241825

DETAILED DESCRIPTION

The present disclosure presents technology for detecting microplastics of various sizes present in water, regardless of the transparency of the microplastics. The present disclosure employs a microfluidic chip as a device for capturing and detecting microplastics based on optical technology and presents optimized conditions for the detection of microplastics with various sizes and transparency.

As mentioned earlier in the ‘Background’ section, different apparatuses are necessary for the detection of microplastics with different sizes, and the destructive thermo-analytical method is not suitable for the quantitative detection of microplastics

The optical technology employed in the present disclosure is capable of visualizing the morphology of a sample three-dimensionally without special manipulation (labeling), regardless of the transparency of the sample. This allows for the observation of the shape, structure, size, etc. of the sample with a microscope, by artificially inducing light interference using a polarizer and a polarizing prism and thereby maximizing the contrast of the sample. Whereas the common optical microscope requires labeling, such as fluorescence staining for measurement of a transparent sample, the present disclosure does not require such treatment. The transparency of microplastics is determined by refractive index and absorbance. If the refractive index of microplastics is the same as that of water, they have high transparency, and the transparency of microplastics is also affected by the absorbance, depending on the color of the microplastics.

According to the optical technology of the present disclosure, it is possible to obtain a non-fluorescent image of nanoparticles and accurately observed the transport of plastics of nano- or sub micrometer-sizes with small refractive indices, regardless of transparency. Moreover, the present disclosure enables quantitative analysis of microplastics present in water by counting the number of microplastics through analysis of the images obtained by an optical imaging device.

Optimization of the optical imaging device is required to observe the microplastics having various sizes and transparency, which are present in water, morphologically and quantitatively. The optical imaging device according to the present disclosure employs a bandpass filter in order to reduce chromatic aberration resulting from the difference in refraction angles and maintain light quantity at a predetermined level, and employs a bandpass filter of a specific wavelength range in order to detect nanometer-sized nanoplastics.

In addition, a magnification system is employed to observe microplastics of various sizes and transparency. Although the microplastics of various sizes and transparency can be observed by adjusting the magnification of the objective lens, it becomes very difficult to focus on all microplastics if the magnification of the objective lens is increased. In contrast, if the magnification system is employed between the second polarizer and an image sensing device of the optical imaging device, even the nanometer-sized nanoplastics can be detected while maintaining the focus on the sample.

Furthermore, for the easier observation of a microchannel of the microfluidic chip, it is necessary to dispose the objective lens below the microfluidic chip (inverted type).

In addition to the optimization of the optical imaging device described above, the present disclosure employs a microfluidic chip and a fluid transportation device for real-time morphological and quantitative observation of the microplastics by the optical imaging device.

The microfluidic chip has a microchannel filled with the fluid containing microplastics. Because the optical imaging device focuses on a point in the microchannel, the microplastics included in the fluid, which moves in the microchannel, can be detected. By observing the fluid that flows in the microchannel in real time, it is possible to observe the presence of microplastics morphologically and quantitatively. For accurate morphological and quantitative observation of the microplastics contained in the fluid, the microchannel is designed in consideration of fluid resistance.

The fluid transportation device is a device that supplies the fluid containing microplastics to the microchannel. It is composed of a pressure pump and a flow sensor and can control the transportation speed of the fluid supplied to the microfluidic chip through the pressure pump and the flow sensor.

As described above, the present disclosure allows morphological and quantitative observation of the microplastics with various sizes and transparency, which are present in a fluid, in the microfluidic chip based on optical technology. For this, the present disclosure presents a configuration which optimizes the optical imaging device, the microchannel of the microfluidic chip and the fluid transportation device.

Hereinafter, an apparatus for detecting microplastics based on optical technology according to an exemplary embodiment of the present disclosure will be described in detail referring to drawings.

Referring toFIG.1, an apparatus for detecting microplastics based on optical technology according to an exemplary embodiment of the present disclosure includes an optical imaging device100, a microfluidic chip200, a fluid transportation device300, an image sensing device10and an image analysis device20.

The optical imaging device100visualizes a sample by improving contrast without pretreatment such as staining, etc. It focuses on a microchannel230equipped in the microfluidic chip200so as to detect microplastics contained in a fluid moving through the microchannel230. The microfluidic chip200provides a space through which the fluid containing microplastics is transported and is disposed above an objective lens117of the optical imaging device100. The fluid transportation device300supplies the fluid containing microplastics to the microchannel230of the microfluidic chips200, and the image sensing device10is disposed at the rear end of the optical imaging device100and senses the image observed by the optical imaging device100. And the image analysis device20counts the number of the microplastics in the image and analyzes the size and shape of the microplastics by analyzing the image sensed by the image sensing device10.

Hereinafter, each component of the apparatus will be described in detail.

First, as shown inFIG.2, the optical imaging device100includes a light source111, a Köhler illumination system112, a bandpass filter113, a first polarizer114, a polarizing prism116, an objective lens117, a second polarizer119and a magnification system120.

Light source111is a source of light for optical analysis. It emits light of a specific wavelength range such as X-ray, UV, visible light, infrared, etc. depending on the analysis method. In the present disclosure, a halogen lamp emitting visible light or a monochromatic LED may be used as the light source111because interference in the visible region is measured by the optical imaging device100. In an exemplary embodiment of the present disclosure, a 250-W halogen lamp was used.

The Köhler illumination system112is one of the methods of specimen inflammation used for optical microscopy. When the Köhler illumination system112is used, the image of the light source111is formed at the back focal plane of the objective lens117and the light from the sample becomes parallel and partially coherent. The Köhler illumination system112can prevent the image of the light source111formed on the sensing device10with the image of the sample and allows uniform illumination for the whole sample. In an exemplary embodiment, the Köhler illumination system112may be configured as a combination of an achromatic doublet lens and a diaphragm. In the present specification, the ‘sample’ refers to a fluid containing microplastics.

The bandpass filter113refers to a device that passes wavelengths within a certain range and blocks or attenuates wavelengths outside the range. Particularly, in the present disclosure, it refers to an optical bandpass filter. The bandpass filter113is used to reduce chromatic aberration resulting from the difference in refraction angles and maintain the light quantity that can be measured by the image sensing device10.

The resolving power of a microscope refers to the minimum distance between resolvable points. It is determined by the diffraction of light and can be expressed by Equation 1. From Equation 1, it can be seen that the resolving power is improved as the wavelength of light is shorter even for the same objective lens117. For this reason, the bandpass filter113which passes only wavelengths within a specific range is used.

d=λ2⁢n⁢sin⁢θ(Equation⁢1)(d is the minimum distance between resolvable points, n is the refractive index, θ is the half angle of the pencil of light illuminated to the sample, and λ is the wavelength of light)

In the present disclosure, a bandpass filter113with a wavelength range of 400-600 nm having a full width at half maximum (FWHM) of 20-30 nm may be used in order to detect microplastics with a size of several hundred nanometers by increasing optical resolution while reducing chromatic aberration and maintaining light quantity. In an example of the present disclosure, a bandpass filter113with a wavelength of 550 nm having a full width at half maximum of 20 nm was used.FIGS.4A-4Dshow the images obtained using the optical imaging device100and the image sensing device10. It can be seen that not only microplastics with a size of 10 μm but also microplastics with a size of 200 nm can be detected.

The first polarizer114is an optical device which passes only a polarized component of one direction and absorbs or reflects other components. It can convert unpolarized light of the light source111to polarized light. In the present disclosure, a linear polarizer is used.

The polarizing prism (differential interference contrast prism)116is an optical device which manipulates polarized light. It is a polarizing prism prepared by joining two orthogonal, birefringent slabs and is disposed at the back focal plane of the objective lens117. The polarizing prism116splits the beam linearly polarized by the first polarizer114into two orthogonal, independent beams, which reflect at the sample (fluid containing microplastics) and are recombined to interfere with each other.

Whereas the general optical imaging device uses polarizing prisms for the upper and lower parts of the sample, in the present disclosure, one polarizing prism116is disposed below the objective lens117, and the polarizing prism116is controlled such that bias is applied to the two beams, thereby improving contrast. In the images obtained by the optical imaging device100, a microfluidic chip having a flat bottom is represented as gray, and the microplastics moving in the microchannel230of the microfluidic chips200are represented as a dark grey to bright gray three-dimensional spheres.

In order to fix the position of the polarizing prism116, it is desirable to adjust the microfluidic chip200, rather than the objective lens117, along the z-axis. When microplastics of various sizes are present in the fluid, the microplastics with the smallest size should be focused.

The second polarizer119is an optical device having the same characteristics as the first polarizer114and serves to pass only the beam recombined by the DIC prism. The beam that has passed through the second polarizer119is sensed by the image sensing device10.

The magnification system120is an optical system which magnifies the image of the sample to be analyzed.

In order to detect and count the microplastics, the image of the sample should be magnified by approximately 100 times. In the general microscope system, the image is magnified by increasing the magnifying power of the objective lens117. But, when the magnification of the objective lens117is increased in the present disclosure, the field of view is reduced, making it difficult to measure the microfluidic chip200having a large area. Here, the field of view refers to the range detectable by the image sensing device10.

In addition, the working distance and depth of field are decreased as the magnifying power of the objective lens117is increased. The working distance is the distance between the objective lens117and the sample. A longer working distance is favored for detection of the microplastics contained in the fluid that moves in the microchannel230of the microfluidic chips200. And the depth of field is the distance between the nearest and the furthest objects that are in acceptably sharp focus in an image. If the depth of field is small, it is difficult to detect microplastics of various sizes at once. Accordingly, it is limited in achieving the desired magnification only with the magnifying power of the objective lens117. Therefore, in the present disclosure, the magnification system120is employed in front of the image sensing device10. As a result, it is not necessary to magnify the image excessively such that the resolution is decreased.

In an exemplary embodiment of the present disclosure, the magnification system120may consist of two achromatic doublet lenses and a zoom lens system. In this case, images magnified by 100 and 200 times can be obtained by using 20× and 40× objective lenses117.

In the present disclosure, the optical imaging device100consists of the objective lens117in an inverted type in which the objective lens117is disposed under the measurement object. The microfluidic chip200, which is the measurement object, is disposed of above the objective lens117due to the instrumental structure of the microfluidic chip. The microfluidic chip200is provided with a microchannel230equipped below a substrate prepared from a polymer material, as will be described later. The microfluidic chip is disposed of above the objective lens117for easier observation of the fluid flowing in the microchannel230.

Next, the microfluidic chip200will be described.

Referring toFIG.3AandFIG.3B, the microfluidic chip200has a structure, in which a transparent glass plate and a flow path substrate are coupled, and a microchannel is patterned on the flow path substrate. The microchannel230is equipped in the flow channel substrate220as the flow channel substrate220is excavated partly. The microchannel230formed in the flow channel substrate220is a space through which the fluid containing microplastics moves. Since the objective lens117of the optical imaging device100is disposed below the transparent glass plate210to focus the microchannel230, it is preferred that the lower surface of the microchannel230is located in the same plane as the upper surface of the transparent glass plate210for easy observation. A fluid inlet231and a fluid outlet232are provided at each end of the microchannel230, respectively. The fluid inlet231and the fluid outlet232may be formed in a vertical direction and the microchannel230may be formed in a horizontal direction. The fluid containing microplastics to be detected is supplied through the fluid inlet231, and the fluid is discharged through the fluid outlet232by passing through the microchannel230after the observation has been completed by the optical imaging device100. The fluid containing microplastics that has been discharged through the fluid outlet232is finally separated and removed by a three-way valve30.

The flow channel substrate220equipped with the microchannel230is made of a polymer material such as PDMS. The flow channel substrate220equipped with the microchannel230, the fluid inlet231and the fluid outlet232may be prepared by embossing-patterning a silicon substrate to form the microchannel230, the fluid inlet231and the fluid outlet232through photolithographic and etching processes and then pouring a polymer solution, e.g., a PDMS solution, onto the embossing-patterned silicon substrate. After the flow channel substrate220is prepared, the surface of the microchannel230, the fluid inlet231and the fluid outlet232may be treated hydrophilically or hydrophobically, if necessary.

The optical imaging device100is focused on the microchannel230. For easier focusing of the objective lens117, it is desired to set the ratio of the height and width of the microchannel230at 1:2-1:3 in consideration of the fluid resistance defined by Equation 2. If the ratio of the height and width of the microchannel230is smaller than 1:2, it is difficult to focus the objective lens117. And, if it is larger than 1:3, the fluid flow becomes too slow.FIGS.5A,5B and5Cshows the images of microplastics with a size of 2 μm (FIG.5A), 1 μm (FIG.5B) and 200 nm (FIG.5C) flowing in the microchannel230with a diameter of 50 μm, which were obtained by the optical imaging device100and the image sensing device10.FIG.6shows the image of the apparatus for detecting microplastics based on optical technology prepared according to an exemplary embodiment of the present disclosure.

R=12⁢η⁢L1-0.63(h/w)⁢1h3⁢w(Equation⁢2)(R is fluid resistance, h is the height of the microchannel230, w is the width of the microchannel230, L is the length of the microchannel230, and η is the viscosity of the fluid)

Next, the fluid transportation device300includes a pressure pump310, a flow sensor320, an air compressor330and a tube340. The air compressor330stores the fluid containing microplastics, and the fluid containing microplastics is supplied via the tube340to the microchannel230through the fluid inlet231of the microfluidic chip200.

The flow rate of the fluid supplied to the microfluidic chip200is controlled by the pressure pump310and the flow sensor320. The pressure pump310applies pressure to the microfluidic chip200. The flow rate of the fluid may be controlled by controlling the operation of the pressure pump310. The flow sensor320serves to measure the flow rate of the fluid flowing in the tube340. The operation of pressure pump310is controlled based on the flow rate of the fluid measured by the flow sensor320.

Next, the image sensing device10is a device that is equipped at one side of the optical imaging device100and senses the beam that has passed through the magnification system120of the optical imaging device100. In an exemplary embodiment, it may consist of an image sensor such as CCD, CMOS, CIS, etc., a digital single-lens reflex camera, etc.

The image analysis device20counts the number of microplastics contained in the image and analyzes the shape and size of the microplastics by analyzing the image sensed by the image sensing device10.

The apparatus for detecting microplastics based on optical technology according to an exemplary embodiment of the present disclosure may further include a pretreatment device400.

The pretreatment device400is a device which removes impurities contained in the fluid to be analyzed by pretreating the fluid. In order to remove the impurities contained in the fluid, the pretreatment device400may be configured as an organic pollutant-removing device, a separation membrane or a combination thereof. The organic pollutant-removing device removes organic pollutants contained in the fluid through a chemical or biological process, and the separation membrane separates the impurities from the microplastics through concentration and based on the difference in density.

[Detailed Description of Main Elements]10: image sensing device20: image analysis device30: three-way valve100: optical imaging device111: light source112: Köhler illumination system113: bandpass filter114: first polarizer115: beam splitter116: polarizing prism117: objective lens118: reflecting mirror119: second polarizer120: magnification system200: microfluidic chip210: transparent glass plate220: flow channel substrate230: microchannel231: fluid inlet232: fluid outlet300: fluid transportation device310: pressure pump320: flow sensor330: air compressor340: tube400: pretreatment device