Optical-Antenna-Enhanced LED Biochips for Femtomolar Detection of Protein Biomarkers

The ability to detect protein biomarkers at the single-molecule level represents the ultimate sensitivity in disease diagnostics and has profound societal benefits, including the early detection of cancer and Alzheimer's disease. Typical digital immunosensing assays rely on bulky laser or halogen light sources, which hinder the development of miniaturized and low-cost point-of-care testing devices. This study demonstrates a novel single-molecule biosensing platform that integrates plasmonic optical antennas, comprising gold nanoparticles coupled to a gold film, with an inexpensive LED chip. The concept of enhancing the platform's limit of detection (LOD) was realized by improving the signal-to-noise ratio (SNR) between the scattering light of the plasmonic antenna and the background emission from the working LED chip, resulting in an optimized SNR of 2.67 dB. Consequently, the quantification detection of human IL-6 was achieved with an LOD of 2.01 fg/mL, showing performance similar to that of a current single-molecule detection platform. These findings demonstrate a portable and low-cost single-molecule detection platform that may drive further advances in the field.