Sheraz Kalim

Photothermal nanoblade for large cargo delivery into mammalian cells

We report a photothermal nanoblade that utilizes a metallic nanostructure to harvest laser pulse energy and convert it into a localized explosive vapor bubble, which rapidly punctures a lightly-contacting cell membrane via high-speed fluidic flows and induced transient shear stress. Integrating the metallic nanostructure with a micropipette, the nanoblade generates a micron-sized membrane access port for delivering concentrated cargo (5×108 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, 200 nm polystyrene beads to 2 µm bacteria have been delivered into multiple cell types.

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.

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.

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.

Biomechanics of Single Cells and Cell Populations

Cells form the basic unit of life. Their health and activities can be quantified by a multitude of biochemical and biophysical techniques that measure responses to external or internal stimuli. Many experimental approaches attempt to integrate molecular mechanisms with changes in the mechanical properties of cells, such as visocoelasticity and compliance, to link cell function with structure. An emerging view of cellular heterogeneity is that even within homogenous cell populations, individual cells may exhibit unique behavioral characteristics that deviate significantly from the population average. Here, several approaches for quantifying biophysical cellular responses are briefly reviewed and linked to specific underlying molecular mechanisms. We succinctly describe each approach and then elaborate on a new interferometer-based method for higher-throughput biophysical analysis of single cells within populations.

Light image patterned molecular delivery into live cells using gold particle coated substrate

Light-patterned molecular delivery into cells is demonstrated by pulsed laser irradiation of gold particles immobilized on the substrate below a cell monolayer. Molecular delivery is verified by observing the uptake of membrane-impermeable fluorescent dye.

A Novel Single-Cell Surgery Tool Using Photothermal Effects of Metal Nanoparticles

We demonstrate a novel single-cell surgery tool that integrates photothermal effects of gold nanoparticles with microcapillary techniques. A transient hole opening of the cell membrane at the tip of the micropipette was accomplished using laser-induced localized heating of nanoparticles. A control experiment using a conventional glass pipette of the same size without gold nanoparticles is also performed to exclude the effect of direct laser heating. This device has the potential to enable minimum cell damage during operation and provides a direct and convenient access to the cell interior without exerting large mechanical stress to fragile cells.

Molecular Delivery Into Live Cells Using Gold Nanoparticle Arrays Fabricated by Polymer Mold Guided Near-Field Photothermal Annealing

A massively-parallel molecular delivery system for mammalian cells is demonstrated by pulsed-laser irradiation of a gold nanoparticle array situated below a cell monolayer. This system is capable of high throughput and spatially-targeted delivery into desired areas of a cell culture by designing the laser irradiation pattern. Rapid fabrication of gold nanoparticle arrays over large areas (>1 mm2 ) is achieved by polymer mold guided near-field photothermal annealing.Copyright

Light-Driven Microfluidic Platforms for Droplet-Based Biochemical Analysis

We report on two light-induced droplet actuation mechanisms, floating electrode optoelectronic tweezers (FEOET) and lateral field optoelectrowetting (LOEW), for manipulating aqueous droplets immersed in oil on a featureless photoconductive surface with an open chamber configuration. Droplet functions including transporting, merging, mixing, and splitting, and multi-droplet manipulation have been accomplished. Droplet manipulation in FEOET is based on light-induced dielectrophoretic forces in an electrically insulating medium such as oil. It has been shown that oilimmersed aqueous droplets can be actuated by a light beam with an intensity as low as 400 μW/cm2 in FEOET. However, due to the weak force generated by the DEP-based droplet actuation, the droplet moving speed is limited to hundreds of μm/s and performing other droplet manipulation functions such as splitting and injection is challenging on FEOET. On the other hand, LOEW-based droplet actuation is realized by modulating the interfacial surface tension of a droplet on a hydrophobic surface through a light-induced electrowetting effect. Since surface tension provides large forces than DEP on a droplet with a diameter from mm to hundreds of μm, LOEW allows transporting droplets at a speed in the range of cm/s and performing droplet-based functions such as splitting and injection. The open chamber configuration of these platforms provides flexibility in integration with other microfluidic components such as external reservoirs and tubing for broad chemical and biochemical applications.