Detection of protein analytes via nanoparticle-based bio bar code technology.

We describe a new format for the recently introduced bio bar code technology, which improves the dose response over 10,000-fold and thereby makes this technique analytically useful. Unlike other ultrasensitive protein detection methods, such as immuno-PCR or immuno-RCA, the bio bar code technique does not employ any enzymes to achieve detection limits in the attomolar range. By sandwiching a target between a magnetic bead and an amplifier nanoparticle, a multiplicity of bar code oligonucleotides are released for each captured target analyte. These surrogate bar code targets are then hybridized to microarrays and detected with silver-amplified gold nanoparticle probes. Using PSA detection as a model, we demonstrate a linear dose response over at least 4 orders of magnitude in both target concentration and concomitant signal and a 1000-fold improvement in detection limit compared to the best ELISA system.