An Optical Fiber-Based Nanomotion Sensor for Rapid Antibiotic and Antifungal Susceptibility Tests

Abstract

The emergence of antibiotic and antifungal resistant microorganisms represents nowadays a major public health issue that might push humanity into a post-antibiotic/antifungal era. One of the approaches to avoid such a catastrophe is to advance rapid antibiotic and antifungal susceptibility tests. In this study, we present a compact, optical fiber-based nanomotion sensor to achieve this goal by monitoring the dynamic nanoscale oscillation of a cantilever related to microorganism viability. High detection sensitivity was achieved that was attributed to the flexible two-photon polymerized cantilever with a spring constant of 0.3 N/m. This nanomotion device showed an excellent performance in the susceptibility tests of Escherichia coli and Candida albicans with a fast response in a time frame of minutes. As a proof-of-concept, with the simplicity of use and the potential of parallelization, our innovative sensor is anticipated to be an interesting candidate for future rapid antibiotic and antifungal susceptibility tests and other biomedical applications.

Keywords: Optical fiber sensor; antibiotic/antifungal susceptibility test; nanomotion device; two-photon polymerization.

Figure 1

Schematic representation of our proposed optical fiber based nanomotion sensor system, and the working principle of detecting the microorganism nanomotion induced cantilever vibration as an optical interferometer.

Figure 2

Fabrication of a optical fiber-based nanomotion sensor. (a) The schemes and optical images during the cantilever fabrication process under the two-photon polymerization system. Scale bars are 20 μm. (b) Schematic of the cantilever fabrication. (c) The optical spectra of the nanomotion sensor with different lengths of microcavity.

Figure 3

SEM images and mechanical property characterization of the 2PP-printed cantilever. (a) SEM images of the sensing head of our optical fiber based nanomotion sensor and the fluorescence image of the living E. coli stained on the cantilever. Scale bars are 20 μm. (b) The mechanical measurement on the 2PP-printed cantilever showed a spring constant of 0.304 N/m.

Figure 4

Nanomotion detection assay of E. coli susceptible to ampicillin by using the optical fiber nanomotion sensor. (a) Schematic representation of the workflow of this nanomotion detection: bare 2PP-printed cantilever in PBS media; bare cantilever in LB solution; the cantilever attached with E. coli in the LB solution; and the E. coli attached cantilever in LB solution with the addition of ampicillin. (b) Representative deflection signals of the cantilever in culture medium (gray), during the attachment procedure (red), and of the cantilever with attached E. coli before (green) and after drug exposure (black). (c) Variance of the deflection filtered signals. The signal variance was calculated using data from 10-s-long segments and plotted as a function of time. (d) Normalized variance averages after processing for different experimental conditions. The green bar represents the 100% value, determined from the variance values calculated before the exposure to the drug and the black bar the variance average calculated after the exposure to antifungal, which induced a significant reduction in the fluctuations.

Figure 5

Susceptibility assay of C. albicans cells to antifungal caspofungin by using our optical fiber nanomotion sensor. (a) Schematic representation of the detection workflow: bare cantilever in YPD media; the cantilever attached with C. albicans in the YPD solution; and the cantilever with C. albicans attached in YPD medium with 100 μg/mL caspofungin. (b) Representative deflection signals of the cantilever in culture medium (gray) and cantilever with attached yeast before (green) and after drug exposure (black). (c) Variance of the processing deflection signals. The signal variance was calculated using data from 10-s-long segments and plotted as a function of time before (green) and after (black) yeast attachment exposure to the drug. (d) Normalized variance averages for different experimental conditions. The green bar represents the 100% value, determined from the variance values calculated before the exposure to the drug, and the black bar the variance average of the exposure to antifungal, which induced a significant reduction in the fluctuations.