By designing an ultrathin metasurface, which consists of spatially variant plasmonic structures with engineered geometric Berry phase, it is shown that spin-orbit coupling of light can be utilized to manipulate the SAM dependent focusing of light or the optical vortex beam and rotate the orbital angular momentum of light. More recently, we also demonstrated that the spin dependent metasurface can be applied to design highly efficient optical holograms The metasurface hologram offers the unique opportunity of creating high quality holographic optical patterns with high spatial resolution and broad angle of view, which have important impact in the areas including holographic displays, beam shaping, data storage, optical trapping, optical tweezers and so on.

In nonlinear optical regime, we also provided proof for the first time of the existence of nonlinear geometrical Berry phase in a third harmonic generation process by using a plasmonic nanocross with spatially variant orientation angle. The nonlinear geometric Berry phase is 4θ, where θ is the orientation angle of the nanocross with respect to the x-axis. This nonlinear phase can be continuously tuned by from zero to 2π by simply rotating the in plane orientation angle of the meta-atom.

The use of sunlight to drive organic reactions constitutes a green and sustainable strategy for organic synthesis. Herein, we discovered that the earth-abundant aluminum oxide (Al₂O₃) though paradigmatically known to be an insulator could induce an immense increase in the selective photo-oxidation of different benzyl alcohols in the presence of a large variety of dyes and O₂. This unique phenomenon is based on the surface complexation of benzyl alcohol (BnOH) with the Brønsted base sites on Al₂O₃, which reduces its oxidation potential and causes an upshift in its HOMO for electron abstraction by the dye. The surface complexation of O₂ with Al₂O₃ also activates the adsorbed O₂ for receiving electrons from the photoexcited dyes. This discovery brings forth a new understanding on utilizing surface complexation mechanisms between the reactants and earth abundant materials to effectively achieve a wider range of photoredox reactions.

Circulating tumor cells (CTCs) are cancer cells shed from primary tumor and circulating in the peripheral blood. CTCs initiate secondary tumor colonies and result in more than 90% of cancer death. Isolation and enumeration of CTCs have exhibited promising clinical applications in cancer early diagnosis, prognosis and personalized therapy. However, owing to the extremely low rarity (as low as one CTC in one billion blood cells), CTCs isolation remains a great technical challenge. Current CTCs isolation approaches are based either on their biological properties, including immunoassay, magnetic-activated cell sorting, fluorescence-activated cell sorting, or physical properties, including filtering, inertial microfluidics, deterministic lateral displacement and etc. In general, biology-based techniques are characterized as high purity but low throughput; while physical property based techniques have advantages of low cost and high throughput. In this work, we reported the fabrication of a multilayer crossflow device and demonstrated the capability of isolating CTCs from whole blood based on lateral-flow filtration. The device was consisted of a filter membrane sandwiched between two microfluidic channel layers and fabricated with standard PDMS soft lithography and multilayer bonding technique. A 77.3% filtration efficiency with 4.5um polystyrene beads and a 97% cancer cells recovery rate have been achieved for a single-pass filtration. To further enhance the enrichment ratio(concentration of CTCs prior to filtration over that post-filtration) of CTCs over blood cells, a recirculating filtration system was built by combing the crossflow device with pressure pump and electromagnetic valves. In this system, 1 ml blood sample was treated for 10 times within 40 minutes, with an enrichment ratio of more than 10⁴.

The human eye is an important and yet difficult organ to study in situ. Microfluidic technologies provide the tool to model the human eye and allow the simultaneous observation of cellular behaviors under different physiological conditions. In this talk, I will share some of the conditions that are needed for constructing a physiologically relevant in vitro eye model. The model will be used to study the effects of saccadic eye movement and hydrostatics on the fluidic and cellular behaviors on-chip. The ability to control, observe, measure and monitor the relevant variables on a microfluidic chip enables the potential to understand the physo-chemical and fluid mechanical origins of conditions often observed in the human eye, and suggest new therapeutic and surgical strategies.

Biofilm formation on synthetic membranes, i.e., membrane biofouling, is a major problem encountered in membrane processes for water and wastewater treatment. Quantification of biofouling is often conducted destructively and hence, results only reflect a snapshot of biofouling processes. This limitation is mainly due to the lack of tools that allow us to monitor dynamics of biofouling without the need of dissembling the membrane testing systems. In a recent study, we developed a novel multichannel fluidic membrane biofilm flow cell that enables non-destructive monitoring of biofouling dynamics using confocal laser scanning microscopy (CLSM). As a proof of concept, we used Green Fluorescent Protein (GFP)-tagged Shewanella oneidensis as a model organism and examined its biofilm development on forward osmosis membranes. The temporal profiles of quantitative biofouling parameters were obtained without disrupting the continuous operation of the membrane testing system. We also demonstrated that, combining with fluorescent staining techniques; the dynamics of biofouling by natural, un-tagged bacteria could also be monitored using CLSM without dissecting the membranes. The microfluidic flow cell developed in this study is a promising tool for non-destructive evaluation of antifouling properties of novel membranes.