In situ electrokinetic enhancement for self-assembled-monolayer-based electrochemical biosensing

Abstract

This study reports a multifunctional electrode approach which directly implements electrokinetic enhancement on a self-assembled-monolayer-based electrochemical sensor for point-of-care diagnostics. Using urinary tract infections as a model system, we demonstrate that electrokinetic enhancement, which involves in situ stirring and heating, can enhance the sensitivity of the strain specific 16S rRNA hybridization assay for 1 order of magnitude and accelerate the time-limiting incubation step with a 6-fold reduction in the incubation time. Since the same electrode platform is used for both electrochemical signal enhancement and electrochemical sensing, the multifunctional electrode approach provides a highly effective strategy toward fully integrated lab-on-a-chip systems for various biomedical applications.

Figure 1

(a) Schematics of ACEF for in situ sensor enhancement. (b) Visualization of the ACEF induced 3D vortices with particle trajectories near the concentric electrode surface in high conductivity buffer (σ =1 S/m). (c) The universal electrode design for in situ electrokinetic enhancement and electrochemical pathogen sensing. R, W, and A represent the reference, working, and auxiliary electrodes, respectively. (d) The detection strategy of the electrochemical assay for pathogen detection. The large green circle on top of the alkanethiol SAM represents streptavidin. The small green circle on top of the streptavidin corresponds to the biotin molecule. The small red circle connected to the detector probe corresponds to fluorescein. The yellow square next to the fluorescein corresponds to antifluorescein antibody.

Figure 2

(a) Voltage dependence of the electrochemical sensor signal with in situ ACEF enhancement. A square wave ac signal at 200 kHz was applied across the working and auxiliary electrodes for 5 min. (b) Comparison of the sensor performances using 0.2 nM of synthetic target with and without ACEF enhancement at different times. The applied ac potential was 5 V_pp at 200 kHz. (c) Investigation of the relative importance of ACEF-induced heating with ACEF-induced advection using E. coli clinical isolates at a concentration of 1 × 10⁶ cfu/mL. Three conditions were tested including incubation at room temperature (20 °C), incubation on a hot plate at 30 °C, and ACEF enhancement (square wave at 5 V_pp and 200 kHz) with an incubation time of 8 min. (d) Comparison of the amperometric sensor signal with and without the prehybridization step of the bacterial lysates and detector probes. The incubation time is 8 min.

Figure 3

Comparison of the sensor performance based on diffusion and ACEF enhancement (square wave potential of 5 V_pp and 200 kHz) with an incubation time of 8 min for detecting (a) different concentrations of E. coli clinical isolates in culture media, (b) E. coli in clinical samples urine 105.2 and urine 74 with 4 × 10⁴ cfu/mL and 4 × 10⁶ cfu/mL E. coli, respectively, (c) S. Saprophyticus clinical isolates, and (d) P. aeruginosa clinical isolates.