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Signal amplification in time-resolved fluorometry.

A frequent question among clinical biochemists is how sensitive analytical techniques should be in the context of clinical diagnostics. Currently, the analyte concentrations usually encountered in clinical chemistry range from 10−3 to 10−12 mol/L. By far, the most sensitive nonamplification techniques used in the clinical laboratory are based on noncompetitive immunological assays. Is there any need for measuring analytes at even lower concentrations? The answer is likely yes. Once the methodologies for measuring even lower concentrations of analytes are developed and our knowledge of the many new candidate biological markers that likely will be discovered through the Human Genome Project is more complete, we may be interested in or need to measure analyte concentrations that are 1/10th to 1/100th of those currently measured. Hence, we should continually pursue the development of methodologies that can reach the ultimate sensitivity, i.e., detection of single molecules.

In other areas of laboratory medicine, e.g., microbiology, single pathogen particles (e.g., viruses and bacteria) have diagnostic significance. We should not forget that the measurement of a single molecule in a very small fraction of the total blood volume may mean that the whole organism could contain relatively large numbers of such pathogenic or abnormal constituents. When the analytes are nucleic acids (DNA …