Improved Fabrication of Polymeric Optical Fiber Tweezers for Single Cell Detection

Abstract

A new fabrication method of polymeric optical fiber tweezers with a multi-mode tip is presented. Preliminary results show higher robustness, improved ability for 2D trapping and differentiation of particles based on back-scattering analysis.

<p>Optical fiber-based sensing method for nanoparticle detection through supervised back-scattering analysis: a potential contributor for biomedicine</p>

“…It is also important to note that perturbations can arise during the photopolymerization lenses fabrication method, therefore modifying the modal field distribution along each lens. Some reflection from the core/cladding of the fiber boundary can also arise during the process 19. Therefore, all these interdependencies could lead to some degree of variability on the scattering collecting performance of the different lenses fabricated using the selected probes fabrication method.…”

“…The spherical lens on the top of an optical fiber used to tightly focus the laser beam was fabricated through a self-guided photopolymerization method previously developed by our lab in collaboration with Soppera and colleagues 22–25. According to previous studies also conducted by our lab,18,19,21 these lenses are able to simultaneously trap and capture enough information through the light scattered by the trapped particle to identify its type, for particles with diameters above 1 µm. However, considering that the total optical force exerted on a given particle results from the sum of the scattering and the gradient forces, and that both depend on the particle diameter, the optical trapping of nanoparticles (with diameters below 1 µm and, therefore, beyond the light diffraction limit) is not expected 26.…”

“…The strong decrease of trapping forces with the nanoparticle radius is not compatible with its stable immobilization 26. Although the trapping of nanoparticles using this type of lenses is not expected, taking into account its geometry and properties, there is previous evidence that they are able to capture significant information for the detection of nanostructures 18,19,21. Thus, the same fabrication method as the one employed to fabricate the spherical lenses for simultaneous trapping and sensing in our previous studies was applied here.…”

“…The signal processing procedure applied here was already successfully adopted in previous studies to differentiate types of microparticles, bacteria, and cells 18,19,21. It consists of a sequence of stages that were applied to each acquisition with a duration of 60 seconds considering each fiber tool position and solution from Table 1, resulting in a dataset composed of short-term signal portions of 2 seconds (please consult Figure 3 for a scheme explaining all the steps performed since signal acquisition to class differentiation).…”

“…The signal was, at first, filtered using a Butterworth high-pass filter with a cutoff frequency of 500 Hz to remove low-frequency interferences, since the input laser signal was modulated using a 1 kHz sinusoidal function. This type of filter was already successfully applied in previous microparticles type differentiation problems using the light scattered by the immobilized target by optical trapping 18,19,21,28. In order to standardize comparisons, the z -score for each 60-seconds acquisition for each fiber location acquisition and solution was computed, by subtracting the mean over the 60-seconds signal to each signal value and dividing the obtained result by the SD of the whole 60-seconds acquisition.…”