Photonic hydrogel sensors

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified

Molecular Design and Engineering of Photonic Crystal Hydrogels for Biosensing Applications

The rise of personalized medicine, increasing threat of bioterrorism, and growing concern of environmental pollutants necessitates the development of alternative biosensing techniques. Towards this end, we investigated the utility of using chemically and structurally modified photonic hydrogels for optical biosensing applications. Photonic crystal hydrogels are comprised of a crystalline colloidal array polymerized into a stimuli-responsive hydrogel. The crystalline colloidal array is comprised of highly charge nanoparticles that self-assemble into a photonic crystal that Bragg diffracts. The hydrogel is designed to undergo a volume transition in the presence of a target analyte. Altering the hydrogel volume in turn alters the lattice spacing of the photonic crystal, causing the diffraction peak to shift. Initially, we explored the use of photonic hydrogels for the detection of enzymatic phosphorylation through the fabrication of kinase-responsive optically diffracting materials. The responsive nature of the hydrogel was confirmed via diffraction measurements and was seen to exhibit a time- and dose-dependent response. A theoretical model for swelling in ionic polymer networks was then utilized to elucidate the key parameters that modulate response sensitivity. The determined parameters were experimentally tuned and a detection limit of 0.1 U/µL was achieved in a 2 h reaction time. We then developed a photonic hydrogel approach for DNA detection. Via hybridization events with a complementary probe strand, we were able to detect down to picomole amounts of a target p53 sequence. Moreover, we demonstrated that this approach could readily detect a single base pair mutation in the target strand. We further showed that this approach is sensitive to epigenetic changes through the detection of a fully methylated form of the target sequence. Lastly, we developed a high-throughput glucose- and ethanol-responsive photonic crystal hydrogel for monitoring microbial fermentation. A platform was developed for the fabrication of photonic hydrogels in 96-well plates to allow for rapid detection and the response sensitivity tuned through blending a thermally responsive polymer with hydrophilic and hydrophobic co-monomers. The 96-well platform was then used as a high-throughput method to monitor ethanol production during fermentation growth of Saccharomyces cerevisiae

Paderwski, the story of a modern immortal,

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Advantage of a broad focal zone in SWL: Synergism between squeezing and shear

Objective: The focal zone width appears to be a critical factor in lithotripsy. Narrow focus machines have a higher occurrence of adverse effects, and arguably no greater comminution efficiency. Manufacturers have introduced new machines and upgrades to broaden the focus. Still, little data exists on how focal width plays a role in stone fracture. Thus, our aim was to determine if focal width interacts with established mechanisms known to contribute to stone fracture. Method: A series of experiments were undertaken with changes made to the stone in an effort to determine which is most important, the shock wave (SW) reflected from the back end of the stone (spallation), the SW ringing the stone (squeezing), the shear wave generated at surface of the stone and concentrated in the bulk of it (shear), or SWs generated from bubble collapse (cavitation). Shock waves were generated by a Dornier HM3-style lithotripter, and stones were made from U30 cement. Baffles were used to block specific waves that contribute to spallation, shear, or squeezing, and glycerol was used to suppress cavitation. Numerical simulation and high-speed imaging allowed for visualization of specific waves as they traveled within the stone. Results: For brevity, one result is explained. A reflective baffle was placed around the front edge of a cylindrical stone. The proximal baffle prevented squeezing by preventing the SW from traveling over the stone, but permitted the SW entering the stone through the proximal face and did not affect the other mechanisms. The distal baffle behaved the same as no baffle. The proximal baffle dramatically reduced the stress, and the stone did not break (stone broke after 45±10 SWs without the baffle and did not break after 400 SWs when the experiment stopped). The result implies that since removing squeezing halted comminution, squeezing is dominant. However, there is much more to the story. For example, if the cylindrical stone was pointed, it broke with the point on the distal end but not with the point on the proximal end. In both cases, squeezing was the same, so if squeezing were dominant, both stones should have broken. But the pointed front edge prevents the shear wave. The squeezing wave and its product - the shear wave - are both needed and work synergistically in a way explained by the model. Conclusions: A broad focus enhances the synergism of squeezing and shear waves without altering cavitation's effects, and thus accelerates stone fracture in SWL. © 2007 American Institute of Physics

Assessing the mechanism of kidney stone comminution by a lithotripter shock pulse

Comminution of axisymmetric stones by a lithotripter shock wave was studied experimentally and theoretically. In experiments, shock waves were generated by a research electrohydraulic lithotripter modeled after the Dornier HM-3, and stones were made from U-30 cement. Cylindrical stones of various length to diameter ratios, stones of conical shape, and stones with artificial cracks were studied. In other cases, baffles to block specific waves that contribute to spallation or squeezing were used, and glycerol was used to suppress cavitation. The theory was based on the elasticity equations for an isotropic medium. The equations were written in finite differences and integrated numerically. Maximum compression, tensile and shear stresses were predicted depending on the stone shape and side-surface condition in order to investigate the importance of the stone geometry. It is shown that the theoretical model used explains the observed position of a crack in a stone. The theory also predicts the efficiency of stone fragmentation depending on its shape and size, as well as on the presence of cracks on the stone surface and baffles near the stone. © 2005 American Institute of Physics

Photonic Crystal Kinase Biosensor

We have developed a novel biosensor for kinases that is based on a kinase-responsive polymer hydrogel, which enables label-free screening of kinase activity via changes in optical properties. The hydrogel is specifically designed to swell reversibly upon phosphorylation of a target peptide, triggering a change in optical diffraction from a crystalline colloidal array of particles impregnated into the hydrogel. Diffraction measurements, and charge staining, confirmed the responsive nature of the hydrogel. Moreover, the change in diffraction of the hydrogel upon treatment with kinase exhibited a time- and dose-dependent response. A theoretical model for ionic polymer networks describes the observed optical response well and can be used to quantify the extent of phosphorylation