Anahita Karimi

Platinum-Doped Ceria Based Biosensor for in Vitro and in Vivo Monitoring of Lactate during Hypoxia

Measurements of lactate concentrations in blood and tissues are an important indication of the adequacy of tissue oxygenation and could be useful for monitoring the state and progress of a variety of diseases. This paper describes the fabrication, analytical characterization, and physiological application of an amperometric microbiosensor based on lactate oxidase and oxygen-rich platinum doped ceria (Pt-ceria) nanoparticles for monitoring lactate levels during hypoxic conditions. The Pt-ceria nanoparticles provided electrocatalytic amplification for the detection of the enzymatically produced hydrogen peroxide and acted as an internal oxygen source for the enzyme, enabling lactate monitoring in an oxygen depleted tissue. In vitro evaluation of the biosensor demonstrated high selectivity against physiological levels of ascorbic acid, a storage stability of 3 weeks, a fast response time of 6 s, and good, linear sensitivity over a wide concentration range. In vivo experiments performed by placing the biosensor in the hippocampus of anesthetized rats demonstrated the feasibility of continuous lactate monitoring over 2 h ischemia and reperfusion. The results demonstrate that Pt-ceria is a versatile material for use in implantable enzyme bioelectrodes, which may be used to assess the pathophysiology of tissue hypoxia. In addition to measurements in hypoxic conditions, the detection limit of this biosensor was low, 100 pM, and the materials used to fabricate this biosensor can be particularly useful in ultrasensitive devices for monitoring lactate levels in a variety of conditions.

Functional nanostructures for enzyme based biosensors: properties, fabrication and applications

With the increased use of nanobiotechnology-enabled solutions for diagnostics, therapeutics, bioelectronics, environmental, and energy-related applications, there exists a great demand for developing manufacturing processes that can reliably and reproducibly generate functional nanostructures with bioactive properties at low cost and in large quantities for implementation in practical devices. Interest in the development of field portable monitoring devices has increased throughout the past decade. Herein we describe fabrication, characterization and performance of portable and printable enzyme biosensors based on functional enzyme-nanoparticle conjugates. We review specific physicochemical and surface properties of nanoparticles used as carriers and sensing components for the design of portable biosensors and describe the role of these parameters in enhancing the performance, stability and field operability of these devices. Assembly of enzyme-nanoparticle conjugates is also discussed with an overview of current and emerging techniques enabling large scale roll-to-roll fabrication and miniaturization, including screen-printing, inkjet and 3D printing methods and their integration in flexible, wearable and inexpensive point-of-use devices. Current status and implementation challenges are provided with examples of applications in the clinical, environmental, public safety and food monitoring fields.

Surface and Subsurface Deformation of Wear-Resistant Steels Exposed to Impact Wear

The impact wear resistance of four different wear-resistant steel grades was investigated using different impact bodies. Post-test evaluation of the impact tested samples was performed by different techniques including 3D surface profilometry, microhardness indentation, optical and scanning electron microscopy, and energy dispersive x-ray spectroscopy. The tribological response of the steel plates during the impact is strongly dependent on the properties of the impacting body. The subsurface deformation was found to increase with increasing impact energy and/or impact velocity and decreasing steel hardness. On a microscopic scale, a number of interesting mechanisms were revealed within the deformed impact sites. Besides an overall plastic deformation, localized deformation resulting in narrow adiabatic shear bands with an ultra-fine microstructure was observed. Within these shear bands, showing intense shearing strain, nucleation of microvoids was frequently observed. Growth and linkage of these voids lead in crack formation along the shear bands and eventually flake-like wear fragments are detached when these cracks reach the surface.

Portable Enzyme-Paper Biosensors Based on Redox-Active CeO2 Nanoparticles.

Portable, nanoparticle (NP)-enhanced enzyme sensors have emerged as powerful devices for qualitative and quantitative analysis of a variety of analytes for biomedicine, environmental applications, and pharmaceutical fields. This chapter describes a method for the fabrication of a portable, paper-based, inexpensive, robust enzyme biosensor for the detection of substrates of oxidase enzymes. The method utilizes redox-active NPs of cerium oxide (CeO2) as a sensing platform which produces color in response to H2O2 generated by the action of oxidase enzymes on their corresponding substrates. This avoids the use of peroxidases which are routinely used in conjunction with glucose oxidase. The CeO2 particles serve dual roles, as high surface area supports to anchor high loadings of the enzyme as well as a color generation reagent, and the particles are recycled multiple times for the reuse of the biosensor. These sensors are small, light, disposable, inexpensive, and they can be mass produced by standard, low-cost printing methods. All reagents needed for the analysis are embedded within the paper matrix, and sensors stored over extended periods of time without performance loss. This novel sensor is a general platform for the in-field detection of analytes that are substrates for oxidase enzymes in clinical, food, and environmental samples.