Real – time fluorescence quantitative PCR (qPCR) is a powerful technology widely used in the field of molecular biology, especially in the following aspects:

I. Pathogen Detection

1. Virus Detection
   • It is of crucial importance in the early diagnosis of viral infections. For example, during the COVID – 19 pandemic, real – time fluorescence quantitative PCR was the main method for detecting viral nucleic acids. RNA was extracted from samples such as throat swabs, nasal swabs, or other samples of patients, followed by reverse transcription and qPCR reactions. This technology can accurately detect extremely low – copy – number viral genes, helping to quickly determine whether a patient is infected with the virus, so that isolation and treatment measures can be taken in a timely manner.
   • For other viruses, such as influenza virus, human immunodeficiency virus (HIV), hepatitis B virus (HBV), etc., real – time fluorescence quantitative PCR can also be used to detect viral load. This is very important for assessing the severity of the disease, monitoring the treatment effect, and predicting disease progression. For example, during the treatment of AIDS, regular detection of the HIV viral load can guide doctors to adjust the antiretroviral treatment plan to ensure the effectiveness of treatment.
2. Bacteria Detection
   • It can be used to detect various bacterial pathogens. Take Mycobacterium tuberculosis as an example. It is the pathogen causing tuberculosis. Real – time fluorescence quantitative PCR can quickly and sensitively detect the DNA of Mycobacterium tuberculosis in sputum or tissue samples, contributing to the early diagnosis of tuberculosis. Compared with the traditional bacterial culture method, qPCR significantly shortens the detection time from several weeks to several hours. Moreover, it can detect bacteria that are difficult to culture, improving the diagnostic efficiency.
   • It is also widely used in the detection of food – borne bacteria. For example, detecting harmful bacteria such as Salmonella and Listeria in food to ensure food safety. By processing food samples and performing qPCR detection, it can be quickly determined whether the food is contaminated and the degree of contamination, so as to take timely measures to prevent food – borne illness incidents.
3. Parasite Detection
   • For some parasites that live in the human body or animals, real – time fluorescence quantitative PCR can also play a role. For instance, Plasmodium, which is the pathogen causing malaria. By detecting the DNA of Plasmodium in the blood, qPCR can diagnose malaria patients at an early stage of infection, even before the appearance of symptoms. This is crucial for the prevention and control of malaria, as early treatment can effectively reduce the spread and severity of malaria.

II. Gene Expression Analysis

1. Basic Research
   • In basic research of molecular biology and genetics, real – time fluorescence quantitative PCR is an important tool for studying gene expression patterns. Scientists can understand the role of genes in physiological and pathological processes by comparing the gene expression levels in different tissues, cell types, or developmental stages. For example, in the study of embryonic development, detecting the changes in gene expression at different embryonic stages through qPCR can reveal the key role of genes in organ formation and cell differentiation.
   • It is used to study the response of genes to environmental factors such as drugs, chemicals, and temperature. For example, when studying the response of plants to drought stress, qPCR can be used to detect the changes in gene expression in plants before and after drought treatment, and find genes related to drought resistance, providing a theoretical basis for breeding drought – resistant plant varieties.
2. Disease Research
   • In cancer research, real – time fluorescence quantitative PCR can be used to detect the expression levels of oncogenes and tumor – suppressor genes. For example, detecting the expression of the HER – 2 gene in breast cancer cells. Over – expression of the HER – 2 gene is associated with a poor prognosis of breast cancer. Monitoring the expression of the HER – 2 gene through qPCR can provide important information for the diagnosis, treatment plan selection, and prognosis assessment of breast cancer.
   • It can also be used to study the changes in the expression of immune – related genes in autoimmune diseases. In rheumatoid arthritis, qPCR can detect the expression of inflammation – related genes in the synovial tissue of joints, helping researchers understand the pathogenesis of the disease and find potential therapeutic targets.

III. Genetic Disease Diagnosis

1. Diagnosis of Monogenic Genetic Diseases
   • For many monogenic genetic diseases, such as cystic fibrosis and thalassemia, real – time fluorescence quantitative PCR is an effective diagnostic method. Take thalassemia as an example. It is a hereditary hemolytic anemia caused by defects in globin genes. By detecting the copy number and mutation of globin genes through qPCR, the genotype of thalassemia patients can be accurately diagnosed, providing a basis for genetic counseling and prenatal diagnosis.
   • In the diagnosis of Huntington’s disease, qPCR can detect the mutations and expression changes of genes related to the disease (such as the HTT gene) in patients. This technology can detect gene abnormalities before obvious symptoms appear in patients, which is very important for early screening and diagnosis of people with a family history of genetic diseases.
2. Detection of Chromosomal Abnormalities
   • It can be used to detect chromosomal numerical abnormalities and small – scale structural variations. For example, in prenatal diagnosis, by detecting the genes related to chromosomes in fetal cells through qPCR, chromosomal numerical abnormal diseases such as Down syndrome (trisomy 21 syndrome) and Edwards syndrome (trisomy 18 syndrome) can be detected. Compared with traditional chromosomal karyotype analysis, qPCR is faster, more sensitive, and can detect some small chromosomal deletions or duplications that are difficult to detect by karyotype analysis.