Figure 5.

Sensitivity of the electrochemical sensor assay as a function of locations of probe hybridization and fluorescein modification. A: Electrochemical sensor results from fivefold serial dilutions of enterococcal cells using capture probe EF207C paired with detector probes EF165D or EF171D modified by fluorescein at the 5′ and 3′ positions, respectively. B: Electrochemical sensor results from fivefold serial dilutions of E. coli cells using capture probe EC434C paired with detector probes EC393C or EC399C modified by fluorescein at the 5′ and 3′ positions, respectively. The dashed horizontal lines indicate current output thresholds for duplicate results significantly greater than negative control (P < 0.01). 3′-Fluorescein modification of the detector probe combined with continuity between the detector and capture probe hybridization sites resulted in a 23-fold improvement in sensitivity of electrochemical sensor assay for detection of enterococci (from 232,000 down to 9900 cells) and E. coli (from 6500 down to 280 cells).