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 μL 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 10⁶ 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 10⁴ to 10⁶ CFU⋅mL⁻¹ concentration range. [Figure not available: see fulltext.]