Biofilms occur when the environmental conditions for a bacterium become suboptimal and hostile, leading the bacteria to utilize biofilm as a defensive strategy. In our work, we determined how different wavelengths of light impact biofilm development and how optical tweezers can be used to manipulate the spatial distribution of biofilm and assess its strength. In particular, we investigated the biofilm formation of Bacillus subtilis in a minimum salts glycerol glutamate (MSgg) medium. Understanding biofilm formation and control strategies is critical because of its effect on human health and the potential for novel biomaterials in future biodegradable technology.
DNA has a helical arrangement, consisting of hundreds of millions of base pairs, whose length and configuration depend on the type and origin of DNA. In this work, we investigate the differences in the linear and nonlinear optical properties of circular-shaped plasmid DNA, small-stranded lambda DNA, and extra-long strands of strawberry DNA under the illumination of a 532 nm laser. We compare the linear absorption spectra of each type of DNA and determine the possible damage to DNA after 1 hour of exposure to high-power green laser. Surprisingly, linear absorption spectra and electrophoresis did not detect any significant damage to all 3 types of DNA. Then we use the Z-scan method to determine the nonlinear absorption and nonlinear index of refraction for each DNA. Our results showed that DNA is a moderately nonlinear photonic material with nonlinear coefficients similar to organic polymers.
In response to a hostile environment, some bacteria form a biofilm by secreting a glue-like matrix called extracellular polymeric substance (EPS) that functions as a physical barrier. In this work, we study the biofilm formation of Bacillus subtilis within minimal biofilm-promoting media (MSgg) and how optical trapping affects bacteria aggregation and biofilm formation. We demonstrate that a laser with a low absorbent wavelength can be used to manipulate biofilm and aggregate bacteria without causing significant photodamage. Whereas, even at low power, a laser with a high absorbent wavelength disrupts biofilm formation and causes significant photodamage to trapped bacteria.
The number of microplastics in aquatic environments is increasing rapidly in recent years and making ocean microplastics one of the major environmental problems. In our research, we focus on the isolation of nature-found microplastics by collecting sand from Los Angeles beaches. Since the optical studies of nature-found microplastics are nontrivial, we generate a standard database by creating and studying different types of irregular-shaped lab-made microplastics using optical tweezer setup. The created database is used to characterize the optical properties of nature-found microplastics. We are planning to apply these results to investigate microplastic interactions with ocean microplankton at a cellular level.
Biofilm is produced when a bacteria’s environment becomes hostile and uses biofilm as protection from the environment. In this work, we investigate the biofilm formation of Bacillus subtilis bacteria within minimal biofilm-promoting media (MSgg media) and how optical trapping affects bacteria aggregation and biofilm development. In low-nutrition media, B. subtilis secretes a glue-like substance and ultimately forms a biofilm. We use an optical tweezers system to observe bacteria division, reorganization, aggregation, and clustering with and without optical trapping. The study of optically controlled biofilm formation enables us to create novel models for inducing and suppressing biofilm development with lasers.
The conservation of optical properties of light through scattering media allows the transmission of high bandwidth information. In this work, we utilize the nonlinear self-trapping and self-guiding of a laser beam to form several centimeters long self-arranged biological waveguides in suspensions of sheep red blood cells. To increase the range of transmitted wavelength through the scattering media, a pump/probe-type nonlinear coupling has been implemented, where the self-formed waveguide conducts weaker light at different wavelengths. Finally, we demonstrate the conservation of polarization state and orbital angular momentum of the transmitted light through these biological waveguides. The ability to create waveguides and maintain optical properties after multiple scattering events may lead to improvements in communication bandwidth with low loss through scattering media and allow development of new biomedical devices.
The conservation orbital angular momentum and polarization for beams propagating through scattering bio-soft matter enables multiplexed signaling. By utilizing nonlinear optical effects in the scattering bio-soft-matter, we investigate the conservation of polarization and OAM through self-trapping and pump/probe coupled waveguides of light in sheep red blood cell suspensions at 532 nm and 780nm wavelengths. This study provides a basis for further exploration into optical signaling in soft matter systems.
In colloidal suspensions with nonlinear optical techniques, it is possible to overcome strong scattering effects and form a self-induced waveguide of light. Previous studies of dielectric, metallic, and biological colloidal suspensions show waveguide formation for spherical, elliptical, and disc-like particles. In all the previous works, the particle can be approximated as a spherical particle. In this work, we study light propagation and the possibility to form a waveguide with long helical-shaped particles. In our study, we extract the strawberry DNA using the CTAB protocol, resuspend DNA in DI water, and study the possibility to form biological waveguides in DNA suspensions at different wavelengths. Since extracted DNA are very long helical-shaped strands, which coil with each other, DNA displays a "topologically frustrated" inability to move and can’t form a typical biological waveguide.
Optical signaling through bio-soft matter is an emerging area of interest for biomedical applications. However, modern communication protocols require high capacity OAM, Polarisation and wavelength multiplexed signaling. Utilizing nonlinear optical effects, we investigate the conservation of polarization and orbital angular momentum through self-trapping and pump/probe coupled waveguides of light in sheep red blood cell suspensions at 532 nm and 780nm wavelengths. This study provides a basis for future exploration for signaling in soft matter systems.
The ability to fabricate your own microfluidic devices provides flexibility to alter the exact design of the device as the project develops. Here we present a concise fabrication process of reusable microscope-compatible microfluidic devices for biophotonic applications. The method requires commonly available components, such as a 3D printer or 3D pen, heat plate, sonicator, PDMS, and acetone. For high NA objective’s measurements, a cover glass can be inserted and replaced from the main microfluidic chamber. For our studies of the controlled bacterial biofilm formation, a laser beam is also delivered from the side of the microfluidic device with a fiber-coupled laser or from the bottom through an objective.
In this work, we study how to grow biofilms and control their growth with optical trapping techniques. In low nutrition media Bacillus subtilis (NCIB 3610) secretes extracellular polymeric substance (EPS), glue-like substance, and ultimately form a biofilm. To observe cells aggregation into clusters and the dynamics of controlled biofilm formation, we utilize an optical tweezers system built around a commercial inverted microscope. A highly focused near-infrared laser beam generated by our optical tweezers attracts cells toward the center of the laser beam, where they are trapped into clusters.
The conservation of optical properties as a beam propagates through a scattering media is important to creating more complex optically induced structures and the transmission of high bandwidth information. By utilizing the nonlinear optical effect in the scattering bio-soft-matter, we investigate the conservation of polarization and orbital angular momentum through self-trapping and pump/probe coupled waveguides of light in sheep red blood cell suspensions at 532 nm and 780nm wavelengths. The ability to maintain these properties after multiple scattering events may lead to improvements in communication bandwidth with low loss.
The ability to use a wide range of wavelengths for deep penetration is important in order to target or avoid absorption bands of the biological media. By utilizing the nonlinear optical effect in the scattering bio-soft-matter, we demonstrate the self-trapping and guiding of light in sheep red blood cell suspensions for a range of different wavelengths. By pump-probe type coupling, biological waveguides formed at one wavelength can effectively guide a wide spectrum of light at low power. Finally, we investigate propagation and guiding of non-Gaussian beams in biological suspensions.
The ability to use a wide range of wavelengths for deep penetration is important in order to target or avoid absorption bands of the biological media. By utilizing the nonlinear optical effect in the scattering bio-soft-matter, we demonstrate the self-trapping and guiding of light in sheep red blood cell suspensions and bacterium suspensions for a range of different wavelengths. By master/slave-type coupling, biological waveguides formed at one wavelength can effectively guide a wide spectrum of light at low power. Finally, we investigate propagation and guiding of optical vortex beams in biological suspensions.
Using light, living cells can be manipulated to form several centimeter long waveguide structures, capable of guiding light through scattering media. Here, we will discuss some results of self-trapping and guiding of light in biological suspensions of different cells, including cyanobacteria, E. coli, and red blood cells. A forward-scattering theoretical model is developed which helps understand the experimental observations. Formed waveguides can provide effective guidance for weaker light through scattered bio-soft-matter. The ability to transmit light through turbid fluids with low loss could open up the possibilities for deep-tissue imaging, as well as noninvasive treatment and diagnostics.
Biological samples often have various absorption bands that need to be either targeted or avoided in opto-fluidic micromanipulation or biomedical imaging. With nonlinear optics, it is possible for light to self-induce a waveguide. However, the desired wavelengths may not be suitable to exhibit nonlinear self-guiding due to the absorption bands or the light-bioparticle interaction is not strong enough. Here we study formation of waveguides in red blood cell suspensions for a range of different wavelengths. We utilize nonlinear optical response for self-trapping of a laser beam, forming light guides in RBCs suspended in a phosphate buffer solution. To improve the number of usable light wavelengths over purely self-guided propagation, we use the master-slave relation, in a manner similar to the pump-probe experiment: a master beam creates a waveguide first in a scattering bio-soft-matter suspension over a few centimeters, and then a “slave” beam uses this waveguide to propagate through the medium. The slave beam, injected simultaneously, has no appreciable nonlinear self-action itself but experiences the master waveguide akin to an optical fiber. This new approach can provide a path to guide a wide range of wavelengths, including those in the absorption bands at lower power so as not to damage the sample. The fact that we can guide a wide range of wavelengths may bring about new applications in medicine and biology, for instance, in developing alternative solutions to transmit energy and information through scattering media, as needed in deep-tissue imaging, treatment and diagnostics.
Understanding the deformability and associated biomechanical properties of red blood cells (RBCs) is crucial for many pathological analysis and diagnosis of human diseases. In such endeavors, optical tweezers have played an active role over the past decades. Here, we study the RBC deformability by employing a novel “tug of war” (TOW) optical tweezers consist of a pair of elongated diverging accelerating beams that can stably trap and stretch a single RBC under different osmotic conditions without any tethering or mechanical movement. With a viscous drag method, we compare directly the trapping force at different states of RBCs, and find that even one arm of the TOW tweezers can apply a force of over 18pN with only 100mW laser power, more than 2 times stronger than that from the Gaussian trap at the same condition. Without the need of two independent controls as in a conventional dual trap, the spacing between the two TOW traps can be increased conveniently from 0 to over 9m, resulting in nearly 15% of cell deformation. We obtain the shear modulus of the RBCs in different osmotic conditions, with the largest value of 3.36±0.95pN/μm in the hypertonic case, and compare with those previously reported results. Our work may bring about a new photonic tool for the study of biomechanical properties of living cells, promising for applications such as distinguishing healthy and diseased cells.
We design and demonstrate multi-trap tug-of-war (TOW) optical tweezers with object-adapted optical potentials for trapping and manipulating asymmetric particles and biological samples such as mutant bacterial cells. While dual TOW tweezers can effectively trap rod-shaped objects and even stretch them laterally, triangular TOW tweezers enable in-plane trapping of larger asymmetric objects which do not necessarily have mirror symmetry. When trapping with the dual TOW tweezers, we previously demonstrated that they are more stable than Gaussian beam-based dual traps, and the strong lateral pulling forces from the TOW optical tweezers can stretch and even break apart cellular clusters. Here we show multi-trap TOW (with 3 and 4 arms) optical tweezers can be employed to control and manipulate mutant Sinorhizobium meliloti bacterial cells, which are typically multi-pronged. We discuss the advantage of such TOW beam-based optical tweezers over traditional Gaussian beam-based holographic tweezers, and the potential applications of these TOW tweezers in studying cellular viscoelasticity, biomechanics, motility, and intercellular interactions.
In typical colloidal suspensions, the corresponding optical polarizability is positive, and thus enhanced scattering takes place as optical beams tend to catastrophically collapse during propagation. Recently, light penetration deep inside scattering suspensions has been realized by engineering dielectric or plasmonic nanoparticle polarizibilities. In particular, we have previously demonstrated two types of soft-matter systems with tunable optical nonlinearities - the dielectric and metallic colloidal suspensions, in which the effects of diffraction and scattering were overcome, hence achieving deep penetration of a light needle through the suspension.
In this work, we show that waveguides can be established in soft matter systems such as metallic nanosuspensions through the formation of plasmonic resonant solitons. First, we show that, due to plasmonic resonance, a 1064nm laser beam (probe) would not experience appreciable nonlinear self-action while propagating through 4cm cuvette containing the metallic nanosuspension of gold spheres (40nm), whereas a 532nm laser beam (pump) can readily form a spatial soliton due to nonlinear self-trapping. Second, we demonstrate effective guidance of the probe beam, which would otherwise diffract significantly through the nanosuspensions, due to the soliton-induced waveguide from the pump beam. Such guidance was observed when the power of the probe beam was varied from 20mW to 500mW at constant pump beam power, with more pronounced guidance realized from lower to higher probe beam power. Interestingly, due to the presence of the probe beam, the pump beam undergoes self-trapping at an even lower power. These results may bring about the possibility of engineering plasmonic soliton-based waveguides for many applications.
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