S. Xiong

Nanometer-precision linear sorting with synchronized optofluidic dual barriers

Researchers explore loosely overdamped system with extreme low stiffness for nanoparticle sorting with nanometer precision. The past two decades have witnessed the revolutionary development of optical trapping of nanoparticles, most of which deal with trapping stiffness larger than 10−8 N/m. In this conventional regime, however, it remains a formidable challenge to sort out sub–50-nm nanoparticles with single-nanometer precision, isolating us from a rich flatland with advanced applications of micromanipulation. With an insightfully established roadmap of damping, the synchronization between optical force and flow drag force can be coordinated to attempt the loosely overdamped realm (stiffness, 10−10 to 10−8 N/m), which has been challenging. This paper intuitively demonstrates the remarkable functionality to sort out single gold nanoparticles with radii ranging from 30 to 50 nm, as well as 100- and 150-nm polystyrene nanoparticles, with single nanometer precision. The quasi-Bessel optical profile and the loosely overdamped potential wells in the microchannel enable those aforementioned nanoparticles to be separated, positioned, and microscopically oscillated. This work reveals an unprecedentedly meaningful damping scenario that enriches our fundamental understanding of particle kinetics in intriguing optical systems, and offers new opportunities for tumor targeting, intracellular imaging, and sorting small particles such as viruses and DNA.

Sculpting nanoparticle dynamics for single-bacteria-level screening and direct binding-efficiency measurement

Particle trapping and binding in optical potential wells provide a versatile platform for various biomedical applications. However, implementation systems to study multi-particle contact interactions in an optical lattice remain rare. By configuring an optofluidic lattice, we demonstrate the precise control of particle interactions and functions such as controlling aggregation and multi-hopping. The mean residence time of a single particle is found considerably reduced from 7 s, as predicted by Kramer’s theory, to 0.6 s, owing to the mechanical interactions among aggregated particles. The optofluidic lattice also enables single-bacteria-level screening of biological binding agents such as antibodies through particle-enabled bacteria hopping. The binding efficiency of antibodies could be determined directly, selectively, quantitatively and efficiently. This work enriches the fundamental mechanisms of particle kinetics and offers new possibilities for probing and utilising unprecedented biomolecule interactions at single-bacteria level.Optical trapping is a versatile tool for biomedical applications. Here, the authors use an optofluidic lattice to achieve controllable multi-particle hopping and demonstrate single-bacteria-level screening and measurement of binding efficiency of biological binding agents through particle-enabled bacteria hopping.

Nanoparticles sorting and assembly based on double-axicon in an optofluidic chip

This paper presents a novel optofluidic system for nanoparticle sorting by using interference patterns generated through a double-axicon. The tightly confined Bessel beam is used to sort the 200-nm and 500-nm polystyrene nanoparticles massively and simultaneously by adjusting the flow rate and the laser power. Additionally, 2-μm polystyrene particles are assembled into a 2D array by utilizing the discrete interference pattern. This system first utilizes the interference patterns based on the on-chip double-axicon, and integrates the sorting and assembly abilities into a single chip. It has a great potential in bacterial and DNA sorting and cell assembly.

Cavitation in confined spaces

Cavitation phenomena in real world are typically confined by one or more boundaries. Confining cavitation in small channels allows to study their interaction with cells, the formation of emulsions, and even sonochemical reactions in far greater detail as it would be possible in the bulk. However, it was expected that boundary layers will hinder bubble collapse more and more as the structure sizes are reduced. In this presentation the channel size is reduced even further, thus from microfluidic to nanofluidic channels. In microfluidic channels cavitation bubbles are generated with focused laser pulses and with acoustic waves. Acoustic cavitation in micrometer sized allows the formation of homogeneous emulsions, rapid rupture of cells (yeats and bacterias), and the dispersion of nanoparticles. While laser induced cavitation bubbles allow the study of bubble dynamics and bubble interaction in nanofluidic channels. In particular we will present experimental results on the dynamics of single bubbles and bubble...

Controllable particle hopping in optofluidic lattice for antibody screening and binding efficiency measurement

Particle patterning and hopping has attracted much attention owing to their extensive involvement in many physical and biological studies. Here, by configuring an intriguing Optofluidic, we are able to pattern 500 nm particles into a 2D array in the flow stream. We also achieve a 2D patterning of cryptosporidium in the microchannel. By investing particle-particle interactions, we studies the long ignored new particle hopping mechanisms, and used them to screen antibodies. Our observed particle hopping in the flow stream completes the family of particle kinetics in optofluidic potential wells and inspires new minds in the develop new light fields in the microchannel. The 2D patterning of particles facilites the parallel culture and study of multiple biological samples in the flow stream.

Ultracompact high-sensitivity biosensing based on regenerable laminated bio-conjugation in integrated photonic circuits

Biosensor based on micro-ring resonator platform has attracted much attention owing to its high sensitivity for identifying various toxins in the environment. Among various bio-toxins, Botulinum neurotoxin (BoNT) are one type of poisonous substances causing the life-threatening neuroparalytic disease and probably used as biological weapon. In our study, a silicon based micro-ring resonator is designed, fabricated and demonstrated to detect BoNT in water sources. First, the capture antibody is labelled on the surface of silicon waveguide for capturing BoNT. The amount of BoNT bound on the surface results in the change of the effective refractive index. As a result, the concentration of toxins can be sensed based on the resonant shift response. Before involving the detection antibody in the assay, the BoNT concentration can be detected in the range from 200 ng/mL to 1 μg/mL. For further improving LOD, a signal enhancement strategy is to use biotin conjugated detection antibody to form a sandwich structure, and then to bind streptavidin-HRP and biotin conjugated anti-HRP antibody. LOD can be improved to 30 ng/mL after linking the detection antibody. After associating with the layer-by-layer structure composed by HRP and anti-HRP antibody on the sandwich assay, LOD can be improved to several pg/mL. Based on this strategy, the process of signal enhancement is flexible to achieve target LOD. And it also can be regenerated and reused after a cycle of detection. Therefore, this platform shows a high potential to apply for robust, realtime and high sensitive detection for various bio-toxins in water sources.

Single Gold Nanoparticle Trapping using an Optofluidic Chip

We present an optofluidic chip for the trapping and separation of single gold nanoparticles (60–100 nm). Size and refractive index of a gold nanoparticle are determined by the trapping position using Drude and Mie theories.

Particle trapping and hopping in an optofluidic fishnet

Particle jumping between optical potentials has attracted much attention owing to its extensive involvement in many physical and biological experiments. In some circumstances, particle jumping indicates escaping from the optical trap, which is an issue people are trying to avoid. Nevertheless, particle jumping can facilitate the individual trap in each laser spot in the optical lattice and enable sorting and delivery of nanoparticles. Particle hopping has not been seen in fluid because Fluidic drag force dramatically reduce the dwell time of particle or break the potential well. Here, we observe particle hopping in the microchannel by three reasons, e.g., particle collision or aggregation, light disturbing by pretrapped particle and fake trapping position. We show that commonly ignored particle influence to the light could create a new isolated trapping position, where particle hops to the adjacent potential well. The hopping happens in an optofluidic fishnet which is comprised of discrete hotspots enabling 2D patterning of particles in the flow stream for the first time. We also achieve a 2D patterning of cryptosporidium in the microchannel. Our observed particle hopping in the flow stream completes the family of particle kinetics in potential wells and inspires new interests in the particle disturbed optical trapping. The 2D patterning of particles benefits the parallel study of biological samples in the flow stream and have potential on cell sorting and drug delivery.

Sorting and measurement of single gold nanoparticles in an optofluidic chip

Gold nanoparticles have sparked strong interest owing to their unique optical and chemical properties. Their sizedependent refractive index and plasmon resonance are widely used for optical sorting, biomedicine and chemical sensing. However, there are only few examples of optical separation of different gold nanoparticles. Only separating 100-200 nm gold nanoparticles using wavelength selected resonance of the extinction spectrum has been demonstrated. This paper reports an optofluidic chip for sorting single gold nanoparticles using loosely overdamped optical potential wells, which are created by building optical and fluidic barriers. It is the first demonstration of sorting single nanoparticles with diameters ranging from 60 to 100 nm in a quasi-Bessel beam with an optical trapping stiffness from 10−10 to 10−9 N/m. The nanoparticles oscillate in the loosely overdamped potential wells with a displacement amplitude of 3–7 μm in the microchannel. The sizes and refractive indices of the nanoparticles can be determined from their trapping positions using Drude and Mie theory, with a resolution of 0.35 nm/μm for the diameter, 0.0034/μm and 0.0017/μm for the real and imaginary parts of the refractive index, respectively. Here we experimentally demonstrate the sorting of bacteria and protozoa on the optofluidic chip. The chip has high potential for the sorting and characterization of nanoparticles in biomedical applications such as tumour targeting, drug delivery and intracellular imaging.

Study of nano/micro jets generated by laser-induced bubbles in thin films

The paper presents a liquid jet in thin films (height varies from micro to nanometers) and the study of its dynamics under the effects of the thin films dimension and viscosity. Furthermore, the penetrating jet velocity is investigated in terms of the laser energy and the distance between the laser focus and the targeted gas bubble surface. In the microchannel, strong shear stress ruptures part of the gas bubble and Rayleigh-Plateau instability further shattered it into small bubbles. On the other hand, in the nanochannel, the nanojets accelerate liquids with thickness of hundreds of nanometers.