Immunoassay arrays fabricated by dip-pen nanolithography with resonance Raman detection

Here, we report the first use of resonance Raman scattering for the detection of miniaturized microscale arrays fabricated by dip-pen nanolithography. Antibody arrays for prostate-specific antigen (PSA) were printed, and a sandwich immunoassay was carried out. An enzyme-linked detection antibody was used to provide an insoluble and stable colored microdot in the recommended size range for microarray readers, which could be read with resonance Raman scattering. This gives quantitative detection as well as an improved detection limit and a larger dynamic range than that previously achieved by direct fluorescent detection methods. By Raman mapping across the arrayed area, the microdots were easily detected with very little background signal from surrounding areas. Levels of PSA as low as 25 pg/mL were detected using this method, which could be extended to a large number of useful biomarkers.