Antibiotic resistance kills an estimated 700,000 people each year worldwide and experts predict that this number could hit 10 million by 2050. Rapid diagnostics would play an essential role in the fight against this alarming phenomenon by improving the way in which antibiotherapy is used, notably by stopping the unnecessary use of antibiotics. Clinical microbiology has relied on culture as the standard method for characterizing pathogens over the past century. This process is time-consuming and requires large biomasses. In this context, single-cell monitoring would be a significant breakthrough compared to Petri dishes culture. A first step was achieved by the demonstration of single bacterium trapping by optical tweezers and integrated photonics. Here, the nondestructive real-time state monitoring of a single alive trapped bacterium is demonstrated. In order to achieve this, a two-laser setup was developed to simultaneously trap and monitor a single bacterium in the near-field of a nanobeam microcavity. While the first laser is used to excite the optical field tweezing the bacterium, the second laser probes the cavity resonance spectrum. The bacterium optical interaction with the resonant cavity mode allows to assess the bacterium state in real time when subjected to an antibacterial agent (antibiotics, alcohol, temperature). Confronted to standards culture-based methods, this optical label-free approach yields relevant information about bacterial viability, without time-consuming culture or staining.
Those results evidence that on-chip devices operating at telecom wavelength may greatly enhance the monitoring of bacteria in the near future leading to major improvements in health care diagnosis and patient treatments.
The development of methods for the rapid analysis of pathogenic bacteria or viruses is of crucial interest in the clinical diagnosis of infectious diseases. In the last decade, optical resonators integrated with microfluidic layers arose as promising tools for biological analysis, notably thanks to their ability to trap objects with low powers, beneath the damage threshold of biological entities, and with a small footprint. Moreover, the resonant nature of optical cavities allows for the simultaneous acquisition of information on the trapped objects, thanks to the feedback effect induced by the specimen on the trapping field itself.
Here we report on the trapping and on the Gram-type differentiation of seven types of living bacteria in an optofluidic system based on an optical cavity consisting in a large hole in a 2D silicon photonic crystal membrane. The hollow nature of the resonant cavity results in a large overlap between the confined field and the hollow volume, allowing for a maximum interaction between the trapping field and the trapped cell. The optical cavity was excited at the resonance wavelength and the shift induced by the trapped bacteria was analysed. To test the trapping capabilities of our structure, we investigated seven types of bacteria, featuring different morphologies, Gram-types and mobilities (presence or absence of flagella). The analysis of the resonance shift yielded Gram typing in a label-free and not destructive way, due to differences in the refractive index and in the deformability of the cell wall. In particular, Gram negative bacteria showed a larger shift.
Near-field optical forces arise from evanescent electromagnetic fields and can be advantageously used for on-chip
optical trapping. In this work, we investigate how evanescent fields at the surface of photonic cavities can efficiently trap
micro-objects such as polystyrene particles and bacteria. We study first the influence of trapped particle’s size on the
trapping potential and introduce an original optofluidic near-field optical microscopy technique. Then we analyze the
rotational motion of trapped clusters of microparticles and investigate their possible use as microfluidic micro-tools such
as integrated micro-flow vane. Eventually, we demonstrate efficient on-chip optical trapping of various kinds of bacteria.