It is no secret that human mortality resulting from infectious disease is a global concern. According to the World Health Organization infectious diseases, human immunodeficiency virus (HIV) and tuberculosis, rank among the top 10 causes of health-related deaths worldwide. In attempt to lower transmissible infection rates, many efforts have been put forth to better understand, detect, prevent, and treat pathogen infections.
In regards to detection, diagnostic tools for infectious disease have advanced over the years due to the exploitation of biochemical techniques that provide more sensitivity and specificity. To date, the most common diagnostic approach identifies pathogens via antibody-antigen interactions in serological samples using enzyme-linked immunoassays (ELISA). Other diagnostic approaches are molecular techniques including polymerase chain reaction (PCR), an amplification technique that generates deoxyribose nucleic acid (DNA) compliments to a specific nucleic acid sequence. Because the genomes of many pathogens have been sequenced, genetic material of microorganisms can be targeted and amplified when present in patient samples. While these techniques provide sensitive identification, the results often take hours or days to process; thus, procedures that can achieve similar results in less time may serve as better diagnostic tools.
A recently developed technique using nanopore biosensors may allow for pathogen detection in minutes. Biological nanopores are synthesized membranes with spanning protein channels of which an electric current is propagated through. These channels enable small molecules, such as including DNA and small peptides, to travel from one side of the membrane to the other. As analytes travel through the nanopore they create changes, or resistance, in current across the membrane that is proportional to the dimensions of the molecule. The relative dimensions of these molecules can then be used to determine the identification of the analyte.
Interestingly, Dr. Xiyun Guan’s laboratory at the Illinois Institute of Technology in Chicago, Illinois has used nanopore biosensors to identify infectious diseases. Recent studies using this application sought to quantify HIV-1 protease activity, an enzyme needed for HIV to be infectious. Functionally speaking, HIV-1 protease is a protein that cleaves proteins, or substrates, so that they become active. To measure HIV-1 protease activity, the Guan lab used serological samples containing these substrates then noted the current change across the nanopore as the cleaved substrates passed through. Additional studies performed by the Guan lab applied this same principal to detect anthrax toxin, a toxin secreted by Bacillus anthracis, a bacterium that causes anthrax. While this study involved the measurement of DNA complexes that formed in the presence of the bacterium as opposed to peptide cleavage in HIV-1 protease studies, they are two examples of how this system can detect infectious pathogens.
Currently, nanopore biosensors are not being used as diagnostic applications because they lack qualities such as being user friendly or commercially attractive; however, this system could be used to rapidly validate preliminary tests. Ultimately, these studies provide the knowledge needed to generate better diagnostic tools –a critical part of our global efforts to fight infectious disease.