A method of making a plasmon-resonance biosensor includes conjugating precious metal nanorods with form factor at least 1.5 with a biological probe material. Microfluidic chambers of volume under 0.025 microliter are formed over a substrate, and an aqueous suspension of the conjugated nanorods is injected into the chambers. The nanorods are organized in rows and aligned in long dimension along the rows. The biosensor is configured to be read by obtaining an optical absorption spectrum upon exposure to the analyte. The biosensor includes precious metal nanorods organized in rows with long dimension approximately parallel to the rows. The nanorods are conjugated with biological probes capable of binding to an analyte, the probes may be an aptamer, an antibody, a protein-nucleic acid (PNA), a complimentary DNA, or an enzyme having a binding site.