A method for optical, label-free detection of molecules at ultra-low concentration, particularly as low as zeptomolar concentration

A method for detection of at least one binding event of specific binding pair-forming substances, comprising:

• providing a layer of a first specific binding pair-forming substance on a substrate, said first specific binding pair-forming substance having a density comprised between 102 and 104 per μm2 of said substrate,
• providing an enclosure of said layer of the first specific binding pair-forming substance with a first dielectric medium, the first dielectric medium comprising a first solution having a first pH value and a first ionic strength value,
• rinsing the enclosure for a first period of time with a second dielectric medium comprising a second solution having a second pH value and a second ionic strength value, wherein at least said second pH value is different than said first pH value,
• restoring said first dielectric medium having the first pH value and the first ionic strength value in said enclosure following said rinsing,
• feeding a solution of a second specific binding pair-forming substance to the enclosure of said layer of the first specific binding pair-forming substance to cause an interaction between said first specific binding pair-forming substance and second specific binding pair-forming substance following said restoring the first dielectric medium in said enclosure, and incubating the enclosure for a second period of time, wherein the interaction comprises a binding event of the at least one binding event when the first specific binding pair-forming substance and the second specific binding pair-forming substance provide said specific binding pair,
• detecting a shift in a parameter representative of a dielectric function of the layer of the first specific binding pair-forming substance following said incubating the enclosure for a second period of time, the shift being defined as a variation of the parameter representative of the dielectric function of the layer of the first specific binding pair-forming substance from a first value occurring when said enclosure only includes said first dielectric medium following said restoring said first dielectric medium, and a second value occurring following incubating said enclosure for the second period of time, and
• comparing the shift with a threshold value, whereby when the shift exceeds the threshold value, the at least one binding event between said first specific binding pair-forming substance and second specific binding pair-forming substance has occurred.