Design of a high-performance optical tweezer for nanoparticle trapping

Integrated optical nanotweezers offer a novel paradigm for optical trapping, as their ability to confine light at the nanoscale leads to extremely high gradient forces. To date, nanotweezers have been realized either as photonic crystal or as plasmonic nanocavities. Here, we propose a nanotweezer device based on a hybrid photonic/plasmonic cavity with the goal of achieving a very high quality factor-to-mode volume (Q/V) ratio. The structure includes a 1D photonic crystal dielectric cavity vertically coupled to a bowtie nanoantenna. A very high Q/V ~ 107 (λ/n)−3 with a resonance transmission T = 29 % at λR = 1381.1 nm has been calculated by 3D finite element method, affording strong light–matter interaction and making the hybrid cavity suitable for optical trapping. A maximum optical force F = −4.4 pN, high values of stability S = 30 and optical stiffness k = 90 pN/nm W have been obtained with an input power Pin = 1 mW, for a polystyrene nanoparticle with a diameter of 40 nm. This performance confirms the high efficiency of the optical nanotweezer and its potential for trapping living matter at the nanoscale, such as viruses, proteins and small bacteria

Nanophotonics for bacterial detection and antimicrobial susceptibility testing

Photonic biosensors are a major topic of research that continues to make exciting advances. Technology has now improved sufficiently for photonics to enter the realm of microbiology and to allow for the detection of individual bacteria. Here, we discuss the different nanophotonic modalities used in this context and highlight the opportunities they offer for studying bacteria. We critically review examples from the recent literature, starting with an overview of photonic devices for the detection of bacteria, followed by a specific analysis of photonic antimicrobial susceptibility tests. We show that the intrinsic advantage of matching the optical probed volume to that of a single, or a few, bacterial cell, affords improved sensitivity while providing additional insight into single-cell properties. We illustrate our argument by comparing traditional culture-based methods, which we term macroscopic, to microscopic free-space optics and nanoscopic guided-wave optics techniques. Particular attention is devoted to this last class by discussing structures such as photonic crystal cavities, plasmonic nanostructures and interferometric configurations. These structures and associated measurement modalities are assessed in terms of limit of detection, response time and ease of implementation. Existing challenges and issues yet to be addressed will be examined and critically discussed

Design of an optical trapping device based on an ultra-high Q/V resonant structure

A novel photonic/plasmonic cavity based on a 1-D photonic crystal cavity vertically coupled to a plasmonic gold structure is reported. The design has been optimized to achieve an ultra-high Q/V ratio, therefore improving the light–matter interaction and making the device suitable for optical trapping applications. Accurate 3-D finite element method (FEM) simulations have been carried out to evaluate the device behavior and performance. The device shows Q 1⁄4 2:8 103 and V 1⁄4 4 104ð=nÞ3, which correspond to a Q=V 1⁄4 7 106ð=nÞ3 with a resonance transmission around 50% at R 1⁄4 1589:62 nm. A strong gradient of the optical energy has been observed in the metal structure at the resonance, inducing a strong optical force and allowing a single particle trapping with a diameter less than 100 nm. The device turns out very useful for novel biomedical applications, such as proteomics and oncology

The Evolgate: a method to improve the pullout strength of interference screws in tibial fixation of anterior cruciate ligament reconstruction with doubled gracilis and semitendinosus tendons.

The goal of the study was to investigate the biomechanical properties of a new device for tibial fixation in arthroscopic anterior cruciate ligament reconstruction using doubled semitendinosus and gracilis tendons.Biomechanical study.This study compares the initial pullout strength, stiffness, and failure modes of 7 pairs of 4-strand human semitendinosus and gracilis grafts fixed to porcine tibias using either the Evolgate (Citieffe, Bologna, Italy) or 1 round threaded titanium interference screw. Structural tests of the graft fixation method tibia complexes were performed using a materials testing machine (MTS Bionix 855, Minneapolis, MN) at a strain rate of 50 mm/second.The mean failure load was 1,237 +/- 191 N for the Evolgate and 537 +/- 65 N for the interference screw (P <.05) and the mean stiffness was 168 +/- 37 N/m for the Evolgate and 105 +/- 17 N/m for the interference screws (P < or =.05). Although in all the cases fixed with the Evolgate failure occurred because of tendon rupture inside the tibial tunnel close to the fixation device, in 4 of the 7 cases fixed with interference screws, failure occurred because of tendon slippage at the fixation site.These results indicate that initial pullout strength of hamstring tendon graft interference screw fixation can be significantly increased using the Evolgate. In fact, because the screws purchase only in the cancellous bone, the Evolgate reinforces the walls of the tibial tunnel with a titanium involute, avoiding the loss of fixation strength related to the low density of the cancellous bone of the proximal metaphysis of the tibia

Rigorous design of an ultra-high Q/V photonic/plasmonic cavity to be used in biosensing applications

A hybrid device based on a 1D PhC dielectric cavity vertically coupled to a plasmonic slot is proposed for use in biosensing applications. Under efficient coupling conditions between the Bloch mode in the 1D PhC dielectric cavity and the surface plasmon polaritons mode in the metal slot, an ultra-high Q/V ratio (similar to 10(7)(lambda/n)(-3)) has been achieved with a remarkable resonance transmission T (=47%), due to high spectral and spatial confinement in the cavity. The rigorous design process of the cavity, including the influence of geometrical and physical parameters on its performance, has been carried out using the 3D Finite Element Method. A strong light-matter interaction was observed, making the photonic-plasmonic cavity suitable for biosensing and, in particular, for optical trapping of living matter at nanoscale, such as proteins and DNA sections, as required in several biomedical applications. (C) 2015 Elsevier Ltd. All rights reserved

Biomechanics of anterior cruciate ligament reconstruction using twisted doubled hamstring tendons

We studied the biomechanical properties of a twisted doubled semitendinosus and gracilis graft. We applied an un-axial load in order to reproduce the kinematics of a reconstructed anterior cruciate ligament (ACL). A modified cryo-jaw clamp system was used to minimize soft tissue slippage. The lower grip, after fixation of the free ends of the tendons, was rotated 45degrees, translated 1 cm, and bent 40degrees, simulating a knee sprain. The graft was tested to failure using a servohydraulic machine. The specimen from one knee of seven unembalmed cadavers was assigned to the untwisted (parallel) bundles group, while its pair was assigned to the twisted group. For the parallel bundles group, the mean maximum load was 1709.3+/-581.9 N, for the twisted group 2428.3+/-475.4 N (P<0.05). The mean stiffness was respectively 213.6+/-72.4 N/mm and 310.3+/-97.3 N/mm (P=0.08). Although caution should be used in extrapolating the results to clinical estimates of the strength of hamstring grafts, the results of the present study could justify the use of twisted semitendinosus and gracilis bundles in ACL reconstruction

A modified Cryo-Jaw for in vitro biomechanical testing of tendons

The purpose of this study was to develop a new device, which represents a modification of the Cryo-Jaw described by Riemersa and Schamhardt and modified by Hamner et al., for in vitro biomechanical testing of tendons which allows the lower clamp to move in every direction and thus simulate a pathological dislocation of the knee. Tendons are fixed to the device by freezing the clamped part with dry ice. After fixation of their free ends. the lower clamp was rotated 45, translated 1 em, and angled 40 to simulate a knee sprain, Various configurations of bundles were tested: parallel, twisted, and braided. Tests were performed on 10 paired bovine bifurcated digital extensor tendons and 6 paired human hamstring tendons. Grafts were then tested to failure subjected to impulsive load, using a servohydraulic machine. The highest ultimate load recorded for parallel bundles was 4662 +/- 565.71 N for bovine bifurcated digital extensor tendons, and 3057 +/- 475.44 N for human hamstring tendons. In any case, the tendons ruptured midway, well clear of the frozen part; in no case was slippage of the tendons observed. Thus the device proposed allows one to test what happens to the graft of an ACL reconstructed knee during physiological and pathological movements because it can be easily displaced in every direction

Design of a high-performance optical tweezer for nanoparticle trapping

Integrated optical nanotweezers offer a novel paradigm for optical trapping, as their ability to confine light at the nanoscale leads to extremely high gradient forces. To date, nanotweezers have been realized either as photonic crystal or as plasmonic nanocavities. Here, we propose a nanotweezer device based on a hybrid photonic/plasmonic cavity with the goal of achieving a very high quality factor-to-mode volume (Q/V) ratio. The structure includes a 1D photonic crystal dielectric cavity vertically coupled to a bowtie nanoantenna. A very high Q/V ~ 107 (λ/n)−3 with a resonance transmission T = 29 % at λR = 1381.1 nm has been calculated by 3D finite element method, affording strong light–matter interaction and making the hybrid cavity suitable for optical trapping. A maximum optical force F = −4.4 pN, high values of stability S = 30 and optical stiffness k = 90 pN/nm W have been obtained with an input power Pin = 1 mW, for a polystyrene nanoparticle with a diameter of 40 nm. This performance confirms the high efficiency of the optical nanotweezer and its potential for trapping living matter at the nanoscale, such as viruses, proteins and small bacteria