The present invention relates to a biochip scanning method and apparatus using phase changes and more particularly to a biochip detection method and apparatus using phase changes based on reflectance detection, wherein a laser beam is radiated to a biochip having immobilized probes placed thereon to cause a phase change in a phase change layer located under the biochip and the reflectance on the phase change layer according to the phase change is detected to allow reproduction or recording of bio information on the biochip.
The following is a basic principle of the detection method using phase changes according to the invention. Ge2Sb2Te5 (GST) is a phase change optical recording material that is widely used as a recording medium for Digital Versatile Disks (DVDs), Phase change Random Access Memory (PRAM), or the like. The GST has the characteristics of reversible phase changes between amorphous and crystalline states. Information is optically written or erased using the reversible phase change characteristics of the GST, thereby obtaining information that is required for the invention.
The invention also relates to a biochip detection method using phase changes and more particularly to a biochip detection method using phase changes based on resistance detection, wherein the resistance between two electrodes connected respectively to both ends of a phase change layer including a bio spot where a phase change occurs is measured so that it is possible to easily detect phase changes in the biochip.
A conventional biochip is constructed by attaching biomolecule probes such as DNA or protein to be analyzed to a substrate. This makes it possible to analyze gene expression patterns, gene defects, protein distribution, and reaction patterns in a sample. The biochip can be classified according to the type of attachment of probes into a microarray chip with probes being attached to a solid substrate and a lab-on-a-chip with probes being attached to a micro-channel. That is, the biochip includes a substrate on which biological materials such as nucleic acid is fixed. A well known biochip is a DNA chip. The DNA chip includes a substrate on which DNAs are fixed. A protein chip includes a substrate on which proteins are fixed.
A system for detecting whether or not target molecules have been bound to immobilized probes on a substrate is required to determine whether or not target molecules that can be bound to probes are present on a sample of the biochip.
A general method to read information from the biochip is to detect the intensity of light emitted from fluorescent materials included in probe molecules. A typical method is laser-induced fluorescence detection. In this method, a laser is used as an excitation light source of a wavelength to be absorbed by the fluorescent material. The laser radiates a laser beam to bring the fluorescent material into an excited state. The system detects the intensity of fluorescent light that the fluorescent material emits when it returns to the ground state. The strength of binding of immobilized probes to target probes (i.e., bio information) can be determined from the intensity of the fluorescent light. Quantitative analysis can be performed by attaching fluorescent materials to a DNA or protein sample in the above manner.
The most frequently used apparatus for detecting fluorescent light using the laser-induced fluorescence detection method is a confocal laser scanning system. The confocal laser scanning system uses laser as a light source and receives a fluorescent signal emitted from a sample using a photomultiplier tube, which is a special detector, and converts it into a digital image using an A/D converter.
The following is an example of the DNA chip detection method. A DNA sample is mostly labeled with a fluorescent dye and is then reacted with probes on a DNA chip for gene analysis and a fluorescent material remaining on the surface of the chip is detected using a confocal microscope or a CCD camera (see U.S. Pat. No. 6,141,096).
However, it is difficult to design a small-size system according to this optical detection method. This method also does not support digital outputs. Thus, many studies have been done to develop a new detection method that provides detection results using electrical signals.
Many research institutes including the Clinical Micro Sensor have studied a method to electrochemically detect DNA hybridization using metal compounds which are susceptible to oxidation and reduction (see U.S. Pat. Nos. 6,096,273 and 6,090,933). In this method, when DNAs are hybridized, they form a complex, together with a compound containing metal which is susceptible to oxidation and reduction, and the complex is then electrochemically detected (see Anal. Chem., Vol. 70, pp. 4670-4677, 1998; J. Am. Chem. Soc., Vol. 119, pp. 9861-9870, 1997; Analytica Chimica Acta, Vol. 286, pp. 219-224, 1994; Bioconjugate Chem., Vol. 8, pp. 906-913, 1997). However, this electrochemical method also has a disadvantage in that it requires special labeling.
Intensive studies have also been carried out to develop an analysis method without using fluorescent dyes or any other markers. Examples of the developed method include a method to measure a difference in mass before and after binding using a quartz crystal microbalance (see Anal. Chem., Vol. 70, pp. 1288-1296, 1998) and an analysis method using Matrix Assisted Laser Desorption Ionization (MALDI) mass spectrometry (Anal. Chem., Vol. 69, pp. 4540-4546, 1997, U.S. Pat. No. 6,043,031).
In another method, a difference of even one base can be analyzed using a micro-fabricated cantilever which is a mechanical sensor type for measuring the molecular binding force before and after binding of DNA probes and target molecules (see Science, Vol. 288, pp. 316-318, 2000; Proc. Natl. Acad. Sci. USA, 98, 1560, 2001).
In the biochip scanner using the above laser-induced fluorescence detection method, fluorescent signals emitted from fluorescent dyes are weak depending on detection conditions, environmental changes, or the like. Thus, to detect the fluorescent signals, it is necessary to use an expensive, highly sensitive detector such as a photomultiplier tube (PMT) and a large number of optical parts such as a dichroic filter and an emission filter, which are required for highly accurate detection. This leads to an increase in the cost of the scanner. The detection conditions are also harsh. These are obstacles to the generalization of the biochip scanner.
In the case of DNA chip detection, it is also necessary to very accurately detect deflection of cantilever beams. This requires additional equipment such as laser, thereby increasing equipment and financial losses.