a method to produce aqueous droplets in oil and to manipulate the droplets for storage in the microfluidic device for certain amount of time to accumulate detectable amount of product produced by a single copy or plural copies of enzyme enclosed in the droplets , and to detect and measure the biomarkers in the antibody binding assay is disclosed . the method comprises : generation of droplets in the microfluidic device , storage of droplets in the microfluidic device , measurement of activity of a single copy or plural copies of enzyme in the droplets , individual molecule - counting immunoassay using the droplets . applications can include the single molecule counting immunoassay , a platform for extremely high through digital pcr , a platform for directed evolution at individual molecule resolutions , nanoparticles synthesis , biodegradable polymer particle production and single molecule analysis .