Ultrasensitive colocalization detection based on plasmonic nanolithography with molecular-overlapped optical near-fields

The detection sensitivity of surface plasmon resonance (SPR) biosensors has been improved by employing colocalization of spatial distribution of electromagnetic near-fields and detection molecules. We have used plasmon nanolithography to achieve light-matter colocalization on triangular nanoaperture arrays and optimized array configurations to improve colocalization efficiency. Streptavidin-biotin interactions were measured to validate the concept. It was confirmed that colocalized distributions of target binding and localized near-fields produced larger optical detection sensitivity. The colocalized detection was also shown to come with wider dynamic range than noncolocalized detection. The effective limit-of-detection of colocalized measurements was on the order of 30 pM. The colocalized detection sensitivity was estimated to be below 1 fg/mm² in a 100-nm deep evanescent area, an enhancement by more than three orders of magnitude over conventional SPR sensor.