Subcellular resolution mapping of endogenous cytokine secretion by nano-plasmonic-resonator sensor array.

Local extracellular signaling is central for cellular interactions and organizations. We report a novel sensing technique to interrogate extracellular signaling at the subcellular level. We developed an in situ immunoassay based on giant optical enhancement of a tunable nano-plasmonic-resonator array fabricated by nanoimprint lithography. Our nanoplasmonic device significantly increases the signal-to-noise ratio to enable the first time submicrometer resolution quantitative mapping of endogenous cytokine secretion. Our study shows a markedly high local interleukin-2 (IL-2) concentration within the immediate vicinity of the cell which finally validates a decades-old hypothesis on autocrine physiological concentration and spatial range. This general sensing technique can be applied for a broad range of cellular communication studies to improve our understanding of subcellular signaling and function.

Rapid, massively parallel single-cell drug response measurements via live cell interferometry.

A central question in cancer therapy is how individual cells within a population of tumor cells respond to drugs designed to arrest their growth. However, the absolute growth of cells, their change in physical mass, whether cancerous or physiologic, is difficult to measure directly with traditional techniques. Here, we develop live cell interferometry for rapid, real-time quantification of cell mass in cells exposed to a changing environment. We used tunicamycin induction of the unfolded protein stress response in multiple myeloma cells to generate a mass response that was temporally profiled for hundreds of cells simultaneously. Within 2 h, the treated cells were growth suppressed compared to controls, with a few cells in both populations showing a robust increase (+15%) or little change (<5%) in mass accumulation. Overall, live cell interferometry provides a conceptual advance for assessing cell populations to identify, monitor, and measure single cell responses, such as to therapeutic drugs.

Photothermal nanoblade for large cargo delivery into mammalian cells.

It is difficult to achieve controlled cutting of elastic, mechanically fragile, and rapidly resealing mammalian cell membranes. Here, we report a photothermal nanoblade that utilizes a metallic nanostructure to harvest short laser pulse energy and convert it into a highly localized explosive vapor bubble, which rapidly punctures a lightly contacting cell membrane via high-speed fluidic flows and induced transient shear stress. The cavitation bubble pattern is controlled by the metallic structure configuration and laser pulse duration and energy. Integration of the metallic nanostructure with a micropipet, the nanoblade generates a micrometer-sized membrane access port for delivering highly concentrated cargo (5 × 10(8) live bacteria/mL) with high efficiency (46%) and cell viability (>90%) into mammalian cells. Additional biologic and inanimate cargo over 3-orders of magnitude in size including DNA, RNA, 200 nm polystyrene beads, to 2 µm bacteria have also been delivered into multiple mammalian cell types. Overall, the photothermal nanoblade is a new approach for delivering difficult cargo into mammalian cells.

Image patterned molecular delivery into live cells using gold particle coated substrates.

An image-patterned molecular delivery system for mammalian cells is demonstrated by pulsed laser irradiation of gold particles immobilized on a substrate below a cell monolayer. Patterned cavitation bubble nucleation was captured using a time-resolved imaging system and molecular delivery verified by observing the uptake of a membrane-impermeable fluorescent dye, calcein. Delivery efficiency as high as 90% was observed and multiplexed, patterned dye delivery was demonstrated.

A light-induced dielectrophoretic droplet manipulation platform.

We report on a light-actuated, droplet based microfluidic platform enabling two-dimensional (2D) droplet manipulation on an open chamber with a single-side, featureless photoconductive surface. The droplet actuation mechanism is based on recently demonstrated floating electrode optoelectronic tweezers (FEOET), which enable light-induced dielectrophoretic forces to manipulate aqueous droplets immersed in electrically nonconductive oil, with a light intensity as low as 400 microW/cm2. In this paper, we study the shape effect of optical patterns for 2D droplet actuation, and demonstrate light-actuated droplet manipulation functions including 2D droplet transport, merging, mixing, and multidroplet processing, for up to 16 droplets in parallel. Such an open chamber platform also permits easy interfacing and integration with other microfluidic structures, such as wells and close-channel based droplet devices to increase its versatility for biochemical analyses.

Floating electrode optoelectronic tweezers: Light-driven dielectrophoretic droplet manipulation in electrically insulating oil medium.

We report an optical actuation mechanism, floating electrode optoelectronic tweezers (FEOET). FEOET enables light-driven transport of aqueous droplets immersed in electrically insulating oil on a featureless photoconductive glass layer with direct optical images. We demonstrate that a 681 mum de-ionized water droplet immersed in corn oil medium is actuated by a 3.21 muW laser beam with an average intensity as low as 4.08 muWmm(2) at a maximum speed of 85.1 mums on a FEOET device. FEOET provides a promising platform for massively parallel droplet manipulation with optical images on low cost, silicon-coated glass. The FEOET device structure, fabrication, working principle, numerical simulations, and operational results are presented in this letter.