a method and apparatus for the detection and quantification of very low levels of a target analyte using an imaging system is provided . in the case of some analytes such as certain hormones , for example tsh , their levels may be as low as several tens of thousands of molecules per micro liter . these extremely low levels can be measured by using the present invention to count the individual molecules of analyte . the invention also has the advantage of being a primary quantitative method , which is one which needs no standardization .