Sensitive Bacterial Detection via Dielectrophoretic-Enhanced Mass Transport Using Surface-Plasmon-Resonance Biosensors

The performance of surface plasmon resonance (SPR)-based bacterial biosensors is often compromised as a result of diffusion-limited mass transport of bacteria to the sensing surface. In this work, dually functional interdigitated electrodes (IDEs) were developed to sustain SPR and increase bacterial mass transport through external application of dielectrophoresis (DEP). IDEs were defined into 50 nm Au films with fixed electrode gaps (EG = 5 μm) and varied electrode widths (EW = 10, 20, and 100 μm), referred to as interdigitated SPR (iSPR) chips. The iSPR chips with EW = 100 μm effectively supported SPR, with comparable sensitivity to those of conventional SPR chips. The surfaces of iSPR chips (EW = 100 μm) were modified with mannose to target the FimH adhesin of Escherichia coli and increase cellular adhesion. An LOD of ∼3.0 × 102 CFU/mL E. coli was achieved on mannosylated iSPR chips under positive-DEP conditions, which is about a 5 order of magnitude improvement compared with those of mannosylated conventional SPR chips without DEP. Furthermore, secondary antibody amplification enabled selective enhancement of dilute (103 CFU/mL) E. coli suspensions, whereas no amplification was observed for concentrated (108 CFU/mL) nontarget (Staphylococcus epidermidis) bacterial suspensions. The results presented here indicate the great potential of the incorporation of DEP into SPR biosensors for rapid, sensitive, and specific detection of bacteria with broad applications in areas of biomedical diagnostics, environmental monitoring, food safety, and homeland security.