Use of Isoproturon Imprinted Polymer Membranes as a Selective Recognition Platform in a Resistance Based Electrochemical Sensor

Methacrylic acid with isoproturon has been utilized to prepare molecularly imprinted polymeric (MIP) membrane on Whatman filter paper no. 5 for selective electrochemical estimation of isoproturon pesticide. MIP membrane was prepared by radical polymerization and characterized using Ultra Violet spectrophotometer, Fourier Transform Infra Red (FTIR) spectroscopy and Scanning Electron Microscopy (SEM). Contact angle study was used to determine the surface energy of the MIP membrane and electrical conductivity measurements were performed by applying a small-amplitude alternating voltage (20 mV) with frequencies varying from 20 Hz to 80 kHz generated by a low-frequency wave form generator. Different isoproturon concentrations in samples were tested and analyzed. Results indicate linear increase in membrane resistance with increasing isoproturon in 10-3 to 10-6 M range. The selectivity of the electrochemical sensor was confirmed by testing isoproturon in presence of the structurally related compounds monouran and diuran. Results reveal highly selective and sensitive sensor, which can be employed for regular estimation of isoproturon in fields.

Development of Non-Labeled QCM Biosensor for the Detection of <i>β</i>-Galactosidase: A Comparative Study of Gold and Polystyrene Nanoparticles

The performance of gold and polystyrene nanoparticles was investigated using quartz crystal microbalance (QCM) as sensor platform;β-Galactosidase antibody with corresponding antigen was utilized for the immunoreaction. The development of the immunosensor included: 1) formation of self assembled monolayers on quartz crystals;2a) immobilization of p-aminothiophenol functionalized gold nanoparticles on carboxyl-terminated self assembled monolayer, or 2b) immobilization of polystyrene nanoparticles on crystals modified with p-aminothiophenol self assembled monolayer;3) attachment of monoclonal anti β-Gal on nanoparticles;and 4) detection of target analyte. The nanoparticles used were synthesized in house and characterized by transmission electron microscopy and infrared spectroscopy. The results revealed that antibodies were strongly attached to functionalized gold nanoparticles;the weaker immobilization of antibodies to polystyrene nanoparticles provoked their detachment during antigen detection. When cross reactivity of polystyrene nanoparticles was checked using a different antigen (Brucella), displacement of antibody was not recorded, demonstrating specificity of the reaction. To the best of our knowledge this is the first direct comparison between behaviors of biosensors developed with two commonly used nanoparticles. The results showed that both nanoparticles produced biosensors capable to detect β-Gal. Nevertheless biosensors developed using polystyrene nanoparticles are simpler, cheaper and more eco-friendly than those developed using gold nanoparticles.

Hydrodynamic function and spring constant calibration of FluidFM micropipette cantilevers

Fluidic force microscopy(FluidFM)fuses the force sensitivity of atomic force microscopy with the manipulation capabilities of microfluidics by using microfabricated cantilevers with embedded fluidic channels.This innovation initiated new research and development directions in biology,biophysics,and material science.To acquire reliable and reproducible data,the calibration of the force sensor is crucial.Importantly,the hollow FluidFM cantilevers contain a row of parallel pillars inside a rectangular beam.The precise spring constant calibration of the internally structured cantilever is far from trivial,and existing methods generally assume simplifications that are not applicable to these special types of cantilevers.In addition,the Sader method,which is currently implemented by the FluidFM community,relies on the precise measurement of the quality factor,which renders the calibration of the spring constant sensitive to noise.In this study,the hydrodynamic function of these special types of hollow cantilevers was experimentally determined with different instruments.Based on the hydrodynamic function,a novel spring constant calibration method was adapted,which relied only on the two resonance frequencies of the cantilever,measured in air and in a liquid.Based on these results,our proposed method can be successfully used for the reliable,noise-free calibration of hollow FluidFM cantilevers.

Microfluidic Electrochemical Devices for Biosensing

The integration of the electrochemical detection system together with microfluidic technology is an attractive choice for the construction of miniaturized components in a single platform.Microchannel networks fabricated on conductive substrates prevent environmental contaminants and require only a tiny(μL or nL)sample for electroanalysis.Microfluidics coupled electrochemical detection system is particularly advantageous compared to traditional electrochemical sensing systems due to its flexibility,rapid analysis,low fabrication costs,ease of implementation and disposability.With these electrochemical sensing platforms,biochemical assays that require complex pre-processing of biological samples can be conducted on a chip.In this review,a comprehensive overview of the basic concepts of microfluidics and its recent applications in the design of miniaturized electrochemical sensors for biosensing applications are presented.