Correlation of dielectrophoretic crossover frequency with optical density and plate counts for assessing Staphylococcus aureus concentration analysis

Rapid and accurate assessment of bacterial concentration is essential, yet conventional methods remain constrained by low detection sensitivity at low concentrations with long processing times. Optical density (OD₆₂₅) measurements report a detection sensitivity value of approximately of 93% for high concentrations of \(10⁷ to 10⁸\) CFU/mL. Plate count assays under similar bacteria parameters exhibit 62% and require > 24 h for incubation and colony enumeration. In this study, we introduce the dielectrophoretic (DEP)-based crossover frequency ( f x0 ) method as a quantitative, frequency-based metric for rapid bacterial concentration assessment, varying concentrations of initial, 1:10, 1:100, and 1:1000 representing bacteria parameter of \(10⁵ to 10⁸ CFU/ml\) . The initial concentration, 1.5 × 10⁸ CFU mL, yielded an OD₆₂₅ of 0.12, an average plate count of 320 CFU, and an f x0 of 4.5 MHz, corresponding to the densest bacterial population. At a 1:10 concentration, these values decreased to OD₆₂₅ = 0.08, 220 CFU, and f x0 = 3.23 MHz. Further dilution to 1:100 concentration yielded OD₆₂₅ = 0.05, 186 CFU, and f x0 = 2.50 MHz, while the most dilute sample at 1:1000 concentration showed OD₆₂₅ = 0.011, 80 CFU, and f x0 = 0.71 MHz, reflecting reduced cell density and conductivity. Detection sensitivity analysis from the response normalization equation for OD₆₂₅, plate count, and f x0 experimental achieved values of 53.6%, 59.15%, and 60.69%, respectively. Based on the increasing trend of OD₆₂₅, plate count, and DEP-based f x0 values with respect to each method, we plotted a linear fit , OD₆₂₅ (R 2 = 0.963), plate count (R 2 = 0.949) and DEP-based f x0 (R 2 = 0.981). The plotted line serves as a reference for the expected values of OD₆₂₅, plate count, and DEP-based f x0 at the selected medium conductivity (σₘ) for the following evaluation tests. We introduced high σₘ values of 0.8 S/m, 0.6 S/m, 0.4 S/m, and 0.2 S/m, and low σₘ values of 0.08 S/m, 0.06 S/m, 0.04 S/m, and 0.02 S/m in the evaluation test to observe the deviation between the plotted line of the expected trend and the actual measured values. We calculated the deviations between expected and measured values and produced a mean deviation of 116% for OD₆₂₅, 49% for plate count, and 60% for DEP-based f x0 with p < 0.05, indicating a strong linear relationship between expected values and actual values measured of every method, thus demonstrating trend agreement within the tested conductivity range, while also revealing nonlinear deviations at elevated conductivity. This paper aims to study the correlation between DEP-based f x0 OD₆₂₅ and plate count by assessing the detection sensitivity value of each method, reliability, and evaluation based on linear regression of expected and measured values under the same experimental conditions for Staphylococcus aureus concentration assessment. The results showed that DEP-based f x0 was potentially superior in detection sensitivity, with a conductivity-associated correlation based on linear regression analysis.