Nanoelectrode based devices for rapid pathogen detection and identification

Abstract

Developing new and rapid methods for pathogen detection with enhanced sensitivity and temporal resolution is critical for protecting general public health and implementing the food and water safety standards. In this research vertically aligned carbon nanofiber nanoelectrode arrays (VACNF NEAs) have been explored as a sample manipulation tool and coupled with fluorescence, surface enhanced Raman scattering (SERS) and impedance techniques for pathogen detection and identification. The key objective for employing a nanoelectrode array is that the nano-Dielectrophoresis (nano-DEP) at the tip of a carbon nanofiber (CNF) acts as a potential trap to capture pathogens. A microfluidic device was fabricated where nanofibers (~ 100 nm in diameter) were placed at the bottom of a fluidic channel to serve as a ‘point array’ while an indium tin oxide coated glass slide acted as a macroscale counter electrode. The electric field gradient was highly enhanced at the tips of the CNFs when an AC voltage was applied. The first study focused on the capture of the viral particles (Bacteriophage T4r) by employing a frequency of 10.0 kHz, a flow velocity of 0.73 mm/sec, and a voltage of 10.0 Vpp. A Lithenburg type of phenomenon was observed, that were drastically different from the isolated spots of bacteria captured on VACNF tips in previous study. At the lowest employed virus concentration (1 × 10[superscript]4 pfu/mL), a capture efficiency of 60% was observed with a fluorescence microscope. The motivation of the second study was to incorporate the SERS detection for specific pathogen identification. Gold-coated iron-oxide nanoovals labeled with Raman Tags (QSY 21), and antibodies that specifically bound with E.coli cells were utilized. The optimum capture was observed at a frequency of 100.0 kHz, a flow velocity of 0.40 mm/sec, and a voltage of 10.0 Vpp. The detection limit was ~210 CFU/mL for a portable Raman system with a capture time of 50 seconds. In the final study, a real-time impedance method was employed to detect Vaccinia virus (human virus) in the nano-DEP device at 1.0 kHz and 8.0 Vpp giving a detection limit of 2.51 × 10[superscript]3 pfu/mL.