Delayed voltammetric with respect to amperometric electrochemical detection of concentration changes in microchannels

The time response of an electrode incorporated into a fluidic channel to variations in analyte concentration of the outer-sphere redox probe ferrocenemethanol was investigated both for amperometry (AMP) and cyclic voltammetry (CV). The experimental data show that the temporal resolution of CV is not as good as that of AMP, as CV cannot properly detect fast concentration transients. The delayed response of CV was previously reported, for neurotransmitters, and mostly attributed to the adsorption of the analyte on the electrode surface. By using an outer-sphere redox couple, we show that mass transport also significantly delays the response of CV. The experimental delay time in CV was understood from mass transfer limitations due to the relaxation of the diffusion layer during repeated potential scanning. Furthermore, a robust protocol for the analysis of fast concentration transients was established, using the impulse and modulation transfer functions of the system. This method was found to be more precise than the mere analysis of undifferentiated traces in the time domain. As a proof of concept, the effect of increased viscosity was investigated, showing that AMP was more sensitive than CV to these variations. Overall, this analysis underlines further the enhanced temporal sensitivity of AMP over CV, at the expense of decreased chemical resolution, potentially having implications for in situ electrochemical detection of biologically relevant molecules

Interplay between the potential waveform and diffusion layer dynamics determines the time-response of voltammetric detection in microchannels

The diffusion layer is a critical factor affecting the temporal response of electrochemical devices. In this article, we have investigated the effect of the relaxation of the diffusion layer during the potentiodynamic sensing of ferrocenemethanol (FcMeOH) in microchannels and compared these results to amperometry. First, the effect of the relaxation of the diffusion layer is described, both theoretically and experimentally. Then, chronoamperometric and voltammetric measurements were considered, and the rate of current increase as a plug of FcMeOH is injected into the device was studied for both cases. It was found that, for the oxidation of FcMeOH, the waveform maximising the duration of the anodic phase provided an improved response for potentiodynamic methods, even though amperometry was always found to show the best results. This was further established by extracting the impulse response and modulation transfer functions, which characterize the time and frequency responses, respectively, of the fluidic/electrochemical system. These findings can help designing potential waveforms improving the time response of the device, in systems where high temporal resolution is needed. This is particularly appropriate to bioelectrochemical analyses, where release and uptake phenomena can occur on the millisecond timescale. (C) 2015 Elsevier Ltd. All rights reserved

Optical microscopy using a glass microsphere for metrology of sub-wavelength nanostructures

A technique that allows direct optical imaging of nanostructures and determines quantitatively geometric nanofeatures beyond the classical diffraction limit by using high-refractive index glass microspheres is introduced. The glass microsphere is put on a nanostructure that is immersed in oil and collects the sample's near-field evanescent wave and transforms it into a propagating one, thereby generating a magnified image in the far-field which is recorded by a conventional oil-immersion microscope objective. Experimental results on nanostructures demonstrates a resolution of similar to lambda/4-lambda/7, where lambda is the illumination wavelength, by using a 60 mu m glass microsphere and a normal wideband halogen lamp as illumination source. A two-dimensional numerical study of the light propagation through a glass microsphere using finite element method (FEM) is performed, providing key insight into the microsphere's superior imaging capability. (C) 2015 Elsevier B.V. All rights reserved

Microfluidic applications of functionalized magnetic particles for environmental analysis: focus on waterborne pathogen detection

The continuous surveillance of drinking water is extremely important to provide early warning of contamination and to ensure continuous supplies of healthy drinking water. Isolation and detection of a particular type of pathogen present at low concentration in a large volume of water, concentrating the analyte in a small detection volume, and removing detection inhibiting factors from the concentrated sample, present the three most important challenges for water quality monitoring laboratories. Combining advanced biological detection methods (e.g., nucleic acid-based or immunology-based protocols) with microfluidics and immunomagnetic separation techniques that exploit functionalized magnetic particles has tremendous potential for realization of an integrated system for pathogen detection, in particular, of waterborne pathogens. Taking advantage of the unique properties of magnetic particles, faster, more sensitive, and more economical diagnostic assays can be developed that can assist in the battle against microbial pathogenesis. In this review, we highlight current technologies and methods used for realization of magnetic particle-based microfluidic integrated waterborne pathogen isolation and detection systems, which have the potential to comply in future with regulatory water quality monitoring requirements

Simultaneous magnetic particles washing and concentration in a microfluidic channel

Purification of magnetic microparticles was demonstrated, with a purification efficiency of (72±14) % at a flow rate of 3 μl/min, in a microfluidic chip using a rotational magnetic system under continuous flow conditions. The rotation of a periodically arranged magnetic assembly close to a fluidic channel carrying magnetic particles suspension allows the trapping and releasing of particles in periodical manner, leaving other particles to be discarded in the waste. Each trapping and releasing event resembles one washing cycle in a conventional biological assay

Light focusing and additive manufacturing through highly scattering media using upconversion nanoparticles

Light-based additive manufacturing holds great potential in the field of bioprinting due to its exceptional spatial resolution, enabling the reconstruction of intricate tissue structures. However, printing through biological tissues is severely limited due to the strong optical scattering within the tissues. The propagation of light is scrambled to form random speckle patterns, making it impossible to print features at the diffraction-limited size with conventional printing approaches. The poor tissue penetration depth of ultra-violet or blue light, which is commonly used to trigger photopolymerization, further limits the fabrication of high cell-density tissue constructs. Recently, several strategies based on wavefront shaping have been developed to manipulate the light and refocus it inside scattering media to a diffraction-limited spot. In this study, we present a high-resolution additive manufacturing technique using upconversion nanoparticles and a wavefront shaping method that does not require measurement from an invasive detector, i.e., it is a non-invasive technique. Upconversion nanoparticles convert near-infrared light to ultraviolet and visible light. The ultraviolet light serves as a light source for photopolymerization and the visible light as a guide star for digital light shaping. The incident light pattern is manipulated using the feedback information of the guide star to focus light through the tissue. In this way, we experimentally demonstrate that near-infrared light can be non-invasively focused through a strongly scattering medium. By exploiting the optical memory effect, we further demonstrate micro-meter resolution additive manufacturing through highly scattering media such as a 300-{\mu}m-thick chicken breast. This study provides a proof of concept of high-resolution additive manufacturing through turbid media with potential application in tissue engineering

Multi-photon polymerization using upconversion nanoparticles for tunable feature-size printing

The recent development of light-based 3D printing technologies has marked a turning point in additive manufacturing. Through photopolymerization, liquid resins can be solidified into complex objects. Usually, the polymerization is triggered by exciting a photoinitiator with ultraviolet (UV) or blue light. In two-photon printing (TPP), the excitation is done through the non-linear absorption of two photons; it enables printing 100-nm voxels but requires expensive femtosecond lasers which strongly limits their broad dissemination. Upconversion nanoparticles (UCNPs) have recently been proposed as an alternative to TPP for photopolymerization but using continuous-wave lasers. UCNPs convert near-infrared (NIR) into visible/UV light to initiate the polymerization locally as in TPP. Here we provide a study of this multi-photon mechanism and demonstrate how the non-linearity impacts the printing process. In particular, we report on the possibility of fine-tuning the size of the printed voxel by adjusting the NIR excitation intensity. Using gelatin-based hydrogel, we are able to vary the transverse voxel size from 1.3 to 2.8 {\mu}m and the axial size from 7.7 to 59 {\mu}m by adjusting the NIR power without changing the degree of polymerization. This work opens up new opportunities for speeding up the fabrication while preserving the minimum feature size with cheap light sources

Photonic Nanojet Array for Fast Detection of Single Nanoparticles in a Flow

We detect by optical microscopy Au and fluorescent nanopartides (NPs) during their motion in water based medium, using an array of dielectric microspheres that are patterned in a microwell array template. The Microspheres act as lenses focusing the light originating from a microscope objective into so-called photonic nanojets that expose the medium Within a microfluidic channel When a NP is randomly transported through a nanojet, its backscattered light (for a bare Au NP) or its fluorescent emission is instantaneously detected by video microscopy. Au NPs down to 50 nit in size, as well as fluorescent NPs down to 20 rim in size, are observed by using a low magnification/low numerical aperture microscope objective in bright field or fluorescence mode, respectively. Compared to the NPs present outside of the photonic nanojets, the light scattering or fluorescence intensity of the NPs in the nanojets is typically enhanced by tip to a factor of The experimental intensity is found to be proportional to the area Occupied by the NP in the nanojet. The technique is also used for immunodectection of biomolecules immobilized on At NPs in buffer and; in future, it may develop into a versatile tool to detect nanometric objects of environmental or biological importance, such as NPs, viruses, or other biological agents

Modal analysis and modeling of a frictionless electrostatic rotary stepper micromotor

We present the design, modeling and characterization of a 3-phase electrostatic rotary stepper micromotor. The proposed motor is a monolithic device fabricated using silicon-on-insulator (SOI) technology. The rotor is suspended with a frictionless flexural pivot bearing and reaches an unprecedented rotational range of 30° (+/- 15°) at 65 V. We have established a mechanical model of the deformation structure and performed finite element analysis (FEA) simulations of the dynamic properties. These studies are consistent with the extensive experimental characterization performed in the quasi-static, transient, and dynamic regimes

Automated longitudinal monitoring of in vivo protein aggregation in neurodegenerative disease C. elegans models

Background: While many biological studies can be performed on cell-based systems, the investigation of molecular pathways related to complex human dysfunctions - e.g. neurodegenerative diseases - often requires long-term studies in animal models. The nematode Caenorhabditis elegans represents one of the best model organisms for many of these tests and, therefore, versatile and automated systems for accurate time-resolved analyses on C. elegans are becoming highly desirable tools in the field. Results: We describe a new multi-functional platform for C. elegans analytical research, enabling automated worm isolation and culture, reversible worm immobilization and long-term high-resolution imaging, and this under active control of the main culture parameters, including temperature. We employ our platform for in vivo observation of biomolecules and automated analysis of protein aggregation in a C. elegans model for amyotrophic lateral sclerosis (ALS). Our device allows monitoring the growth rate and development of each worm, at single animal resolution, within a matrix of microfluidic chambers. We demonstrate the progression of individual protein aggregates, i.e. mutated human superoxide dismutase 1 - Yellow Fluorescent Protein (SOD1-YFP) fusion proteins in the body wall muscles, for each worm and over several days. Moreover, by combining reversible worm immobilization and on-chip high-resolution imaging, our method allows precisely localizing the expression of biomolecules within the worms' tissues, as well as monitoring the evolution of single aggregates over consecutive days at the sub-cellular level. We also show the suitability of our system for protein aggregation monitoring in a C. elegans Huntington disease (HD) model, and demonstrate the system's ability to study long-term doxycycline treatment-linked modification of protein aggregation profiles in the ALS model. Conclusion: Our microfluidic-based method allows analyzing in vivo the long-term dynamics of protein aggregation phenomena in C. elegans at unprecedented resolution. Pharmacological screenings on neurodegenerative disease C. elegans models may strongly benefit from this method in the near future, because of its full automation and high-throughput potential