Method for label-free detection of femtogram quantities of biologics in flowing liquid samples

Abstract

Rapid (∼10 min) measurement of very low concentration of pathogens (∼10 cells/mL) and protein (∼fg/mL) has widespread use in medical diagnostics, monitoring bio-threat agents, and in a broader context as a research method. For low-level pathogen, we currently use culture enrichment methods and, thus, rapid analysis is not possible. For low protein concentration, no direct method is currently available. We report here a novel macrocantilever design whose high-order resonant mode near 1 MHz exhibits mass detection sensitivity of 10 cells/mL for cells and 100 fg/mL for protein. The sensor is 1 x 3 mm and uses a piezoelectric layer for both actuation and sensing resonance. Sample is flowed (∼1 mL/min) past the antibody-immobilized sensor, and as antigen binds to the sensor, resonance frequency decreases in proportion to antigen concentration. The sensor showed selectivity to the pathogen even though copious nonpathogenic variant was simultaneously present. © 2007 American Chemical Society.