Integrated optical transfection system using a microlens fiber combined with microfluidic gene delivery

Laser-based molecular delivery and its applications in plant science

Lasers enable modification of living and non-living matter with submicron precision in a contact-free manner which has raised the interest of researchers for decades. Accordingly, laser technologies have drawn interest across disciplines. They have been established as a valuable tool to permeabilize cellular membranes for molecular delivery in a process termed photoinjection. Laser-based molecular delivery was first reported in 1984, when normal kidney cells were successfully transfected with a frequency-multiplied Nd:YAG laser. Due to the rapid development of optical technologies, far more sophisticated laser platforms have become available. In particular, near infrared femtosecond (NIR fs) laser sources enable an increasing progress of laser-based molecular delivery procedures and opened up multiple variations and applications of this technique.This review is intended to provide a plant science audience with the physical principles as well as the application potentials of laser-based molecular delivery. The historical origins and technical development of laser-based molecular delivery are summarized and the principle physical processes involved in these approaches and their implications for practical use are introduced. Successful cases of laser-based molecular delivery in plant science will be reviewed in detail, and the specific hurdles that plant materials pose will be discussed. Finally, we will give an outlook on current limitations and possible future applications of laser-based molecular delivery in the field of plant science.

A Comprehensive Review on Intracellular Delivery

Intracellular delivery is considered an indispensable process for various studies, ranging from medical applications (cell-based therapy) to fundamental (genome-editing) and industrial (biomanufacture) approaches. Conventional macroscale delivery systems critically suffer from such issues as low cell viability, cytotoxicity, and inconsistent material delivery, which have opened up an interest in the development of more efficient intracellular delivery systems. In line with the advances in microfluidics and nanotechnology, intracellular delivery based on micro- and nanoengineered platforms has progressed rapidly and held great promises owing to their unique features. These approaches have been advanced to introduce a smorgasbord of diverse cargoes into various cell types with the maximum efficiency and the highest precision. This review differentiates macro-, micro-, and nanoengineered approaches for intracellular delivery. The macroengineered delivery platforms are first summarized and then each method is categorized based on whether it employs a carrier- or membrane-disruption-mediated mechanism to load cargoes inside the cells. Second, particular emphasis is placed on the micro- and nanoengineered advances in the delivery of biomolecules inside the cells. Furthermore, the applications and challenges of the established and emerging delivery approaches are summarized. The topic is concluded by evaluating the future perspective of intracellular delivery toward the micro- and nanoengineered approaches.

A needle-like optofluidic probe enables targeted intracellular delivery by confining light-nanoparticle interaction on single cell

Intracellular delivery of molecular cargo is the basis for a plethora of therapeutic applications, including gene therapy and cancer treatment. A very efficient method to perform intracellular delivery is the photo-activation of nanomaterials that have been previously directed to the cell vicinity and bear releasable molecular cargo. However, potential in vivo applications of this method are limited by our ability to deliver nanomaterials and light in tissue. Here, we demonstrate intracelullar delivery using a needle-like optofluidic probe capable of penetrating soft tissue. Firstly, we used the optofluidic probe to confine an intracellular delivery mixture, composed of 100 nm gold nanoparticles (AuNP) and membrane-impermeable calcein, in the vicinity of cancer cells. Secondly, we delivered nanosecond (ns) laser pulses (wavelength: 532 nm; duration: 5 ns) using the same probe and without introducing a AuNP cells incubation step. The AuNP photo-activation caused localized and reversible disruption of the cell membrane, enabling calcein delivery into the cytoplasm. We measured 67% intracellular delivery efficacy and showed that the optofluidic probe can be used to treat cells with single-cell precision. Finally, we demonstrated targeted delivery in tissue (mouse retinal explant) ex vivo. We expect that this method can enable nanomaterial-assisted intracellular delivery applications in soft tissue (e.g. brain, retina) of small animals.

Micro-optics for microfluidic analytical applications

This critical review summarizes the developments in the integration of micro-optical elements with microfluidic platforms for facilitating detection and automation of bio-analytical applications.

Femtosecond Laser Fabrication of Cavity Microball Lens (CMBL) inside a PMMA Substrate for Super-Wide Angle Imaging

Since microlenses have to date been fabricated primarily by surface manufacturing, they are highly susceptible to surface damage, and their microscale size makes it cumbersome to handle. Thus, cavity lenses are preferred, as they alleviate these difficulties associated with the surface-manufactured microlenses. Here, it is shown that a high repetition femtosecond laser can effectively fabricate cavity microball lenses (CMBLs) inside a polymethyl methacrylate slice. Optimal CMBL fabrication conditions are determined by examining the pertinent parameters, including the laser processing time, the average irradiation power, and the pulse repetition rates. In addition, a heat diffusion modeling is developed to better understand the formation of the spherical cavity and the slightly compressed affected zone surrounding the cavity. A micro-telescope consisting of a microscope objective and a CMBL demonstrates a super-wide field-of-view imaging capability. Finally, detailed optical characterizations of CMBLs are elaborated to account for the refractive index variations of the affected zone. The results presented in the current study demonstrate that a femtosecond laser-fabricated CMBL can be used for robust and super-wide viewing micro imaging applications.

Fabrication of embedded microball lens in PMMA with high repetition rate femtosecond fiber laser

Embedded microball lenses with superior optical properties function as convex microball lens (VMBL) and concave microball lens (CMBL) were fabricated inside a PMMA substrate with a high repetition rate femtosecond fiber laser. The VMBL was created by femtosecond laser-induced refractive index change, while the CMBL was fabricated due to the heat accumulation effect of the successive laser pulses irradiation at a high repetition rate. The processing window for both types of the lenses was studied and optimized, and the optical properties were also tested by imaging a remote object with an inverted microscope. In order to obtain the microball lenses with adjustable focal lengths and suppressed optical aberration, a shape control method was thus proposed and examined with experiments and ZEMAX® simulations. Applying the optimized fabrication conditions, two types of the embedded microball lenses arrays were fabricated and then tested with imaging experiments. This technology allows the direct fabrication of microlens inside transparent bulk polymer material which has great application potential in multi-function integrated microfluidic devices.

The optical fiber tip: an inherently light-coupled microscopic platform for micro- and nanotechnologies

The flat tip of an optical fiber is a unique and unconventional platform for micro and nanotechnologies. The small cross-section and large aspect ratio of the fiber provide an inherently light-coupled substrate that is uniquely suited to remote, in vivo and in situ applications. However, these same characteristics challenge established fabrication technologies, which are best suited to large planar substrates. This review presents a broad overview of strategies for patterning the flat tip of an optical fiber. Techniques discussed include self-assembly, numerous lithographies, through-fiber patterning, hybrid techniques, and strategies for mass manufacture, while the diverse applications are discussed in context throughout.

The grab-and-drop protocol: a novel strategy for membrane protein isolation and reconstitution from single cells

Samples of cell membrane were non-destructively removed from individual, live cells using optically trapped beads, and deposited into a supported lipid bilayer mounted on an S-layer protein-coated substrate.

Femtosecond optical transfection of individual mammalian cells

Laser-mediated gene transfection into mammalian cells has recently emerged as a powerful alternative to more traditional transfection techniques. In particular, the use of a femtosecond-pulsed laser operating in the near-infrared (NIR) region has been proven to provide single-cell selectivity, localized delivery, low toxicity and consistent performance. This approach can easily be integrated with advanced multimodal live-cell microscopy and micromanipulation techniques. The efficiency of this technique depends on an understanding by the user of both biology and physics. Therefore, in this protocol we discuss the subtleties that apply to both fields, including sample preparation, alignment and calibration of laser optics and their integration into a microscopy platform. The entire protocol takes ~5 d to complete, from the initial setup of the femtosecond optical transfection system to the final stage of fluorescence imaging to assay for successful expression of the gene of interest.

Photonic nanojet focusing for hollow-core photonic crystal fiber probes

Large-pitch kagome-lattice hollow-core photonic crystal fibers (HC-PCFs) offer appealing optical properties for beam delivery and remote sensing. However, focusing their optical mode on a submicrometer spot can be challenging due to the large mode diameter and low numerical aperture of these fibers. Here, we demonstrate that a 30 μm latex microsphere directly set at the HC-PCF end-face provides an efficient means to focus the fiber mode down to a spot of 540 nm full width at half-maximum thanks to a photonic nanojet effect. The system is used for fluorescence imaging and direct laser writing on a thin absorbing layer. Potential applications include inspection of semiconductor wafers, photolithography, laser surgery, fluorescence sensing, or optical transfection.

Hollow-core photonic crystal fiber probe for remote fluorescence sensing with single molecule sensitivity

Current optical fiber probes for fluorescence spectroscopy struggle with large luminescence background and low detection sensitivities that challenge the detection of fluorescent molecules at sub-micromolar concentration. Here we report the demonstration of a hollow-core photonic crystal fiber (HC-PCF) probe for remote fluorescence sensing with single molecule sensitivity down to nanomolar concentrations, where both the excitation and fluorescence beams are counter-propagating through the same fiber. A 20 μm polystyrene microsphere is used to efficiently excite and collect the fluorescence from the sample solution thanks to a photonic nanojet effect. Compared to earlier work with silica fibers, the new HC-PCF-microsphere probe achieves a 200x improvement of the signal-to-noise ratio for a single molecule detection event, and a 1000x reduction of the minimum detectable concentration. The device is implemented with fluorescence correlation spectroscopy to distinguish between molecules of similar fluorescence spectra based on the analysis of their translational diffusion properties, and provides similar performance as conventional confocal microscopes.

Optical fiber-based photomechanical gene transfer system for in vivo application

We developed an optical-fiber-based photomechanical gene transfer system for endoscopic or catheter-based application. A fiber tip with a laser-absorbing film covered with a transparent plastic disk for plasma confinement was attached to a quartz fiber; the film was irradiated with nanosecond laser pulses transmitted through the fiber to generate photomechanical waves (PMWs). Characteristics of PMWs emitted from the fiber tip were examined to confirm the necessary conditions for gene transfer. We then attempted to transfer reporter genes to the rat skin as a test tissue in vivo with the fiber system, and the results showed significantly high protein levels and spatially selective pinpoint gene expressions in the tissue.

Enhancement and optimization of plasmid expression in femtosecond optical transfection

Cell transfection using femtosecond lasers is gaining importance for its proven ability to achieve selective transfection in a sterile and relatively non-invasive manner. However, the net efficiency of this technique is limited due to a number of factors that ultimately makes it difficult to be used as a viable and widely used technique. We report here a method to achieve significant enhancement in the efficiency of femtosecond optical transfection. The transfection procedure is modified by incorporating a suitable synthetic peptide containing nuclear localization and DNA binding sequences, assisting DNA import into the nucleus. We achieved a 3-fold enhancement in the transfection efficiency for adherent Chinese Hamster Ovary (CHO-K1) cells with this modified protocol. Further, in the presence of this biochemical reagent, we were able to reduce the required plasmid concentration by ~70% without compromising the transfection efficiency. Also, we report for the first time the successful photo-transfection of recently trypsinised cells with significantly high transfection efficiency when transfected with modified plasmid. This paves the way for the development of high throughput microfluidic optical transfection devices.

Optical transfection using an endoscope-like system

Optical transfection is a powerful method for targeted delivery of therapeutic agents to biological cells. A tightly focused pulsed laser beam may transiently change the permeability of a cell membrane to facilitate the delivery of foreign genetic material into cells. We report the first realization of an endoscope-like integrated system for optical transfection. An imaging fiber (coherent optical fiber bundle) with ∼ 6000 cores (pixels) embedded in a fiber cladding of ∼ 300 μm in diameter, produces an image circle (area) of ∼ 270 μm diam. This imaging fiber, with an ordered axicon lens array chemically etched at its exit face, is used for the delivery of a femtosecond laser to the cell membrane for optical transfection along with subcellular resolution imaging. A microcapillary-based microfluidic system for localized drug delivery was also combined in this miniature, flexible system. Using this novel system, a plasmid transfection efficiency up to ∼ 72% was obtained for CHO-K1 cells. This endoscope-like system opens a range of exciting applications, in particular, in the targeted in vivo optical microsurgery area.