The present invention relates to a method of capturing, enriching, purifying, detecting or measuring a cell in a sample at a sub-nanogram level comprising providing a nanocomposition, contacting the sample with the nanocomposition to form a mixture solution and allowing the binding of the cell with the nanocomposition, applying a magnetic field to the mixture, and evaluating the presence of or absence of the cell. The nanocomposition is capable of capturing or enriching an analyte at a sub-nanogram level, and comprise a nanostructure operably linked to an analyte-capturing member.
