With antibiotic resistance on the rise and expected to be a major health problem in the coming years [1], we are looking for alternative ways to treat bacterial infectious diseases. This work is in the scope of phage therapy, i.e. the use of therapeutic highly specific bacterial viruses called bacteriophages. As with the antibiotic susceptibility test (antibiogram), a phage susceptibility test (phagogram) that allows rapid and reliable testing of phage collections to identify the optimal phage(s) to administer to patients is highly desirable. Accordingly, we show here preliminary results of a new method to perform a phagogram with phages trapped on an optical chip. The system used is a silicon-on-insulator photonic chip containing L3 slotted 2D hollow photonic crystal cavities topped by a micro fluidic system allowing the transport of phages in their vicinity. The light confined in the cavity allows the trapping of nearby objects by gradient forces while the light collected at the output of the chip allows to deduce information about the trapped object. Circular 2D hollow cavities have been used previously to trap bacteria by means of a self-induced back action (SIBA)[2] mechanism and have demonstrated classification, and viability assessment of bacteria[3-5]. By changing the cavities to a linear cavity (SEM Image on figure 1: A) with an optical field (simulated near field intensity of the resonant mode on figure 1: B) more suitable to the trapping of 100 nm size viruses, we obtain photonic cavities allowing to trap phages and to distinguish different phages according to their families.
Bacteriophages, i.e. bacterial viruses, are nowadays considered a promising strategy to fight against bacterial infectious diseases (phage therapy). However, their strong species-specificity requires performing so-called phagograms to select the right phage(s) for the right patient based on the lysis capacity of the tested phages on the infecting strain. Meanwhile, it is crucial to decrease as much as possible the time-to-result delay since mortality often depends on the treatment delivery time. We present an optofluidic chip, composed of microfluidic layers embedding silicon photonic crystal resonant cavities, which allows for strong light localization and, thus, the possibility to optically trap objects at powers lower than the damage threshold of biological entities [1]. Since trapping occurs in the near field of the optical resonator, the object's presence, nature and even residual movement within the trap lead to a direct modification of the resonant frequency of the optical cavity. This process allows for the acquisition of information such as the refractive index and the morphology of the trapped object [2]. With this approach, we achieved the trapping and differentiation of several types of living bacteria [3]. We will show the direct observation of bacteria-bacteriophage lytic interaction in an H2 hollow cavity, whose scanning electron microscope (SEM) image and resonant mode near field intensity are depicted in Fig. 1(A-B), respectively. The transmission signal over time collected from a lytic event of a single Escherichia coli B cell infected by Myoviridae T4 bacteriophages is presented in Fig. 1(C). The insets show the state of the bacterium before and after the lysis.
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