Corona-induced micro-centrifugal flows for concentration of Neisseria and Salmonella bacteria prior to their quantitation using antibody-functionalized SERS-reporter nanobeads

The use of microcentrifugal flows driven by ionic wind that is generated near a corona needle tip above the level of a small liquid reservoir is a technique to trap suspended bacteria within a few minutes. Gas ions are ejected at the tip of a corona needle to form an ionic wind that can swipe across the liquid/air interface inside a miniaturized reservoir to generate centrifugal vortices. This will drag suspended particles to the center of the reservoir. This article describes a method where antigen-functionalized polystyrene microspheres are first employed to mimic bacteria. The mimetic bacteria were then detected by surface-enhanced Raman scattering (SERS) signal after binding antibody-conjugated nanoaggregate-embedded beads (NAEBs) to antigen-functionalized polystyrene microspheres. The NAEBs were prepared from silica-coated gold nanoparticle aggregates and labeled with Raman reporter molecules. The work demonstrates that the particles can be concentrated at the stagnant point at the bottom of a reservoir containing 60 mu L solution only by ionic wind-driven centrifugal flows. SERS signals were acquired to identify the bacteria-mimicking particles. The ionic wind flows were then applied to trap and concentrate Neisseria and Salmonella bacteria bound with antibody-conjugated NAEBs at the level of 10(6) colony forming units (CFU) per mL (or lower) within 10 min. The NAEBs were preferably labeled with Ethyl violet or fluorescein derivatives. The log-log calibration plot for Neisseria is linear in the 10(4) to 10(6) CFUai...mL(-1) concentration range.