Chiral quantum dots (QDs) are expected to have a range of potential applications in biosensing, labeling, environmental nanoassays, chiral memory, building blocks for the bottomup nanofabrication of chiroptical devices and nanoassemblies, and fluorescent chiral nanoprobes in biomedical and analytical technologies[1,2]. We studied the chiroptical properties of colloidal solution of quantum dots (QDs) which were initially prepared with use of chiral ligands (diaminocyclohexane molecules). We demonstrate completely different circular dichroism (CD) activities of QDs capped with different amount of ligands. We consider that the chiroptical activity is caused by coupling between electric field of the chiral molecules and QDs in case of small amount of ligands. On the contrary, in case of excess amount of ligands, the chiral aggregate of diaminocyclohexane molecules is a significant contributor to the CD activities. Moreover, circularly polarized luminescence (CPL) of chiral QDs is discussed in details. Such optimized design and modulation of chiroptical properties will likely lead to novel applications in chiral biosensing and chiroptical nanomaterials.

References:
1.Mícheál P Moloney, Joseph Govan, Alexander Loudon, Maria Mukhina & Yurii K Gun'ko, Preparation of chiral quantum dots, Nature Protocols 10, 558-573 (2015).
2.U. Tohgha, K. K. Deol, A. G. Porter, S. G. Bartko, J. Kyu Choi, B. M. Leonard, K. Varga, J. Kubelka, G. Muller, M. Balaz, Ligand Induced Circular Dichroism and Circularly Polarized Luminescence in CdSe Quantum Dots, ACS Nano 7 (12), 11094–11102 (2013).

Recent advances in quantitative imaging technology have created new opportunities in life science research and diagnostic medicine.   Faculty members of the Stanford Photonics Research Center have pioneered novel approaches in many areas of the life sciences and medicine:  Neuroscience, Immunology, Pathology, Radiology, Regenerative Medicine, and Protein Engineering.  In my talk I will describe two new applications of quantitative imaging, based on combining several technologies:  novel imaging architectures, high throughput microfluidics, and automated image analysis software.  I will describe an approach which addresses QA/QC challenges in the emerging applications of stem cells in regenerative medicine and will also discuss ultra-high throughput quantitative imaging methods applied to protein engineering.  Both approaches rely on automated analysis of millions of imaged objects to obtain morphological information which can determine, for example, cell phenotype and/or protein function.   We demonstrate how these approaches can provide important information about safety and efficacy of stem cell derived tissue for transplantation, and can be used as part of a very high throughput platform for engineering of proteins with specific desired biological function. 

There is a pressing need for simple, rapid and effective ways of concentrating and capturing bacteria and bacterial spores for detection and identification [1].  Acoustofluidic approaches can act on a large number of cells simultaneously over a relatively wide area, allowing cells to be imaged, concentrated, or captured in a flow-through system. This paper discusses the use of planar ultrasonic resonator systems for high throughput 2D cytometry, for cell concentration and finally for cell capture on functionalized surfaces.  Recent results demonstrate the capture of bacterial spores on antibody functionalized surfaces and it is shown how the same technology can be used to capture cells from more complex fluids such as whole blood. 

Acoustophoretic forces tend to move cells to regions of low acoustic pressure and within planar resonator systems [2] it is generally simplest to generate forces towards the centre of a flow-through chamber as shown in Fig. 1 (a) (a half wave resonance).  Such a half wave mode can be used for particle concentration in low aspect ratio channels [3] but in the wide channels of these resonators the fluid behaviour makes the extraction of a high concentration challenging [4].  Such a half-wave mode can successfully be used to move particles into the focal plane of an imaging system [5].  This approach not only places particles or cells at the imaging focus, but has the additional significant advantage that within a highly laminar flow, all the particles in this optical focal plane will travel through the imaging field at identical velocities, allowing particle tracking during imaging without motion blur.  This has allowed 2D imaging of beads and cells at very high throughputs – up to 200,000 beads per second [5].

A better approach to concentrating bacteria is to force them to a surface rather than to the centre of a channel.  Early acoustic designs for moving particles to a surface were very sensitive to precise layer thicknesses [6], but by using just a thin layer to form the reflector of the device so that the reflection is effectively from the low acoustic impedance air boundary, produces a more robust field [7].  Such an approach for concentrating bacteria, as shown in Fig. 1 (b), can be used to increase the concentration of E. coli by a factor of 60 and at a flow rate of 20 ml/hr [4].

This flow-through concentration requires a further identification stage but a more efficient approach is to detect bacteria of interest within the flow-through chamber itself.  This can be achieved using the approach shown schematically in Fig. 2 in which the machined stainless steel device shown in Fig. 3 incorporates a “thin reflector” that comprises a cover-slip with antibody functionalization for bacterial capture.  Fig. 4 shows an image of a slide with spots functionalized to capture Bacillus globigii (BG) spores using a spore concentration of 105 per ml and a flow rate of 10 ml/hr.  The same approach has also been used successfully to isolate Basophils from diluted whole blood.

A problem called boson sampling---sampling from the probability distribution of several identical bosons scattered by some linear unitary process---has raised strong interest recently. Despite the simplicity of its structure, boson sampling is a computational hard problem which can not be efficiently simulated on classical computers. By now, several boson sampling experiments have been reported. However, in all of these experiments, boson sampling is realized by implementing the procedure literally instead of being simulated with other systems. It is well known that quantum processes, which are hard to be simulated on classical computers, can be efficiently simulated with controllable quantum devices. In this sense, boson sampling itself should be able to be well simulated with controlled quantum systems. Here we present a method to efficiently simulate boson sampling with qubit systems which are directly applicable to the standard quantum computing model. The two motivations to simulate boson sampling with qubit system are described below. Firstly, the standard quantum computing model is based on qubit system. By simulating boson sampling with qubits, one can run boson sampling on a quantum computer. Secondly, compared with the complex output quantum state that boson sampling process renders, the well-defined multi-qubit output quantum state our method provides is much easier for manipulation and processing. As our method makes the output state of boson sampling more usable, it might help theorists find some new applications for boson sampling. Besides presenting the theory, we have also experimentally demonstrate our scheme using photonic qubits. The experimental results reproduce the probability distribution of boson sampling quite well, which is in accordance with the theoretical expectation.

It is becoming clear that bacteria exist primarily as members of surface-adhered social communities, called biofilms, rather than as free-living individuals. These communities are encased in an extracellular matrix that provides protection from harsh environmental conditions, predation, enables resource sharing, and facilitates intercellular communication. Depending on the local conditions bacteria will transition between these two states and this interplay is fundamental to the ecology and biology of bacteria. The biofilm lifestyle colors all aspects of bacterial interactions with their environment whether attached to a rock in a stream, as an aggregate in activated sludge, or in an infection. To begin understanding biofilm development we visualize the initial encounter bacteria have with surfaces. Here, bacteria undergo a fundamental change in lifestyle, becoming surface-bound. We use cell tracking to link surface motility to surface exploration and colonization. As biofilms mature, growing three-dimensional, we utilize laser scanning confocal microscopy as well as label free imaging techniques to visualize phenotypic changes that occur within biofilms over time and space.

Polymer replication is critical to applications for microfluidics, especially for optofluidics. There's a huge discrepancy between processes used in academia and industry. Due to the limitation of cost and material properties, the PDMS casting is not suitable for large scale manufacture. In order to produce large numbers of devices by replicating a master structure, the micro-injection molding provides efficient and promising chips consist of rigid plastic, which is widely accepted in industry. In this talk, the challenging tooling and process control of micro-injection molding are addressed. Our advanced tooling, molding and welding technology can help customers transform the lab samples into marketable products rapidly.

We demonstrate the intriguing possibility of harnessing phonon sources, in particular, surface acoustic waves (SAW), for synthesizing and manipulating two-dimensional materials. For example, the large surface accelerations associated with the SAW vibration—on the order of 10 million g’s—can be employed for micro/nanoscale material processing, in particular, for debundling carbon nanotube agglomerates. These large mechanical stresses, together with the high intensity electric field inherent in the electromechanical coupling of the acoustic wave during SAW microcentrifugation and nebulisation, can also be used to rapidly exfoliate bulk three-dimensional crystalline transitional metal dichalcogenides such as molybdenum disulphide (MoS₂) into monolayer and few-layer nanosheets with high yield. Finally, the SAW can be exploited for the manipulation of quasiparticles in these two-dimensional materials. For example, we show the possibility for reversibly modulating trion to exciton transition, and their subsequent transport and hence spatial separation within the material.

The assembly process of nanoparticles from individual atoms, and nanostructures from nanoparticles in solution is fundamental for materials engineering and “bottom-up” fabrication of functional nanodevices.

Using dynamic in situ TEM imaging [1-3] in liquids, I will describe how nanoparticles form in solution and how these nanoparticles interact with each other. First, I will discuss how phase separation of a solution containing Au ions into solute-rich and solute-poor phases leads to formation of Au nanocrystal through a pathway that does not follow classical nucleation theory (CNT). Namely, I will show that there are multiple steps that lead to formation of nuclei from which nanocrystals grow [4]. These steps are: 1) phase separation of liquid solution into solute-poor and solute-rich phases, from which 2) an amorphous nanoparticles which serve as a precursor for nuclei emerges. This is followed by 3) crystallization of amorphous nanoparticle into a crystalline nuclei.

Next, I will highlight the role of intermolecular forces between nanoparticles in solution and describe their role in the assembly of nanostructures from individual nanoparticle building blocks (bottom-up approach) [5]. Specifically, I will show how the balance between repulsive hydration force and attractive van der Waals (vdW) force results in a metastable nanoparticle-pair which promotes their subsequent attachment to each other [5]. I will also describe the dynamics of how capillary forces, interfaces and linker molecules aide in the assembly of nanoparticles [6-7].

Finally, I will conclude by describing our recent work where we track the nanoscale dynamics of wet-etch (top-down approach) processes to shape nanomaterials.

These findings highlight the role of solvent mediated physical and chemical forces in material synthesis and self-assembly of nanoparticles. Our observations also emphasize the importance of direct nanoscale observation in uncovering previously unknown intermediate states that are pivotal for synthesis and self-assembly.

References:

[1] M. J. Williamson, R. M. Tromp, P. M. Vereecken, R. Hull, F. M. Ross, Nature Materials 2 (2003), p. 532.

[2] H. Zheng, R. Smith, Y. Jun, C. Kisielowski, U. Dahmen, A. P. Alavisatos, Science 324 (2009), p. 1309.

[3] U. Mirsaidov, H. Zheng, D. Bhattacharya, Y. Casana, P. Matsudaira, Proc. Natl. Acad. Sci. U.S.A. 109 (2012), p. 7187.

[4] N. D. Loh, S. Sen, M. Bosman, S. F. Tan, J. Zhong, C. Nijhuis, P. Kral, P. Matsudaira, U. Mirsaidov, Nature Chemistry 9 (2017), p.77 .

[5] U. Anand, J. Lu, N. D Loh, Z. Aabdin,  U. Mirsaidov, Nano Lett. 16 (2016), p. 786.

[6] G. Lin, X Zhu, U. Anand, Q. Liu, J. Lu, Z. Aabdin, H. Su, U. Mirsaidov, Nano Lett. 16 (2016), p. 1092.

[7] G. Lin, S. W. Chee , S. Raj, P. Kral, and U. Mirsaidov, ACS Nano 10, p. 7443-7450 (2016).

Drinking water quality is critical for all countries while a more challenging problem in many developing countries. In the worldwide well accepted standard for drinking water quality, setup by U.S. Environmental Protection Agency (EPA), a single harmful bacterium cannot be allowed in tap water. However, the EPA recommended standard testing method is still based on the conventional approach of antibody-bacterium conjugation. An immunological detection method, such as ELISA, operated in a biological lab, needs a skillful operator with a cycle taking about 24 hours. It certainly cannot meet the requirements of today’s fast changing living environment. Especially currently we are very concern about food, water and air poisoning and contamination. Thus rapid identification of bacterial species in single bacterium level becomes very crucial.

The measurement of physical parameters, the length, width, the ratio of them and the refractive index of bacteria species were reported by Liu et al. with the approach of refractometry [1]. Our presentation reports latest efforts in investigation of optical scattering patterns of single bacterium of three species, namely E. coli, Shigella flexneri, and Bacillus subtilis under acoustic focusing. These optical scattering patterns were obtained with a customized a prototype system including a customized laser illumination module and a scattering pattern recording module. Representative scattering patterns of a single bacterium flowing through a microfluidic channel are displayed in Fig. 1. As their average physical dimensions still have some differences though having overlapping, their scattering patterns also have differences. But low signal to noise ratio and size non-uniformity of bacteria of the same species, as well as waterborne impurity microbial from 0.8 mm to 3 mm make the optical patterns not reliable for bacterial identification.

We have also measured four strains of E. coli with their scattering patterns are displayed in Fig. 2 which show almost identical scattering patterns. Thus, it is concluded that bacteria species and strains cannot be identified reliably from only physical parameters mentioned above. These parameters can enrich our knowledge to bacteria species in different time points of their life cycle, but not enough to distinguish them in single bacterium level.

To address this problem, we have proposed a fluo-scattering detection system with a schematic drawing is shown in Fig. 3. The approach combines the fluorescence detection of immuno-labeling of bacterium with specific antibody, like what illustrated in Fig. 4, with the optical scattering module to increase the identification efficiency. Fig. 5 shows our preliminary result of differentiation of E. coli (O114) labeled with SyBr gold and 2 mm polystyrene beads. While Fig. 6 shows differentiation of Bacillus spore with unknown waterborne impurity microbial.

With more fluorescence detection channels are built in the fluo-scattering detection system, it has high potential to be able to differentiation 3 to 4 species/strains of bacteria.

We here propose a new experimental technique to modulate cortical neuronal activities by a combination of laser light irradiation and electrical microstimulation in the tissue slice perfused with artificial cerebro-spinal fluid. This technique enables one to both excite and inhibit the neuron populations in a spatially confined manner.