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Investigation of Electrochemical Methods and Construction of Immunosensors in Microfluidic Chip

Author: ZhouFang
Tutor: ZhuJunJie
School: Nanjing University
Course: Analytical Chemistry
Keywords: Microfluidic chip Tilting microchip Low Electroosmotic flowmeasurement Polyelectrolyte Layer-by-layer assembly Microfluidic system End-channel amperometry Electrochemical detection Polydimethylsiloxane (PDMS) Gold nanoparticles Quantum Dots Cardiac markers Dual protein simultaneousdetection Cilinica analysis
CLC: O657.1
Type: PhD thesis
Year: 2010
Downloads: 22
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Abstract

The area of micro total analysis systems (μTAS), also called "lab on a chip", miniaturized or microfluidic analysis systems, is a rapidly developing field. During the last several years, we have witnessed a steady expansion in the number of publications made associated with this research field. Simultaneously, there is an obvious increase in the overall quality of the study performances, as numerous obstacles have been overcome and microfluidic devices are, nowadays, considered as a common aid to various applications in natural and life sciences. My purpose in this research was to well know the studies on electrochemical methods and designs of immunosensors in microfluidic chip.1. Low electroosmotic flow measurement by tilting microchip A novel method for low electroosmotic flow (EOF) rates measurement by tilting microchip which based upon the hydrostatic pressure conception and sampling zone method is described. Sampling zone could be detected in the tilting microchip but not in non-tilting one due to the hydrostatic pressure driven. The method is fulfilled to calculate low EOF rates by detecting the liquid flow velocity driven by hydrostatic pressure, and difference between the apparent mobility of the migrating analyte in two modes is caused by the effect of hydrostatic pressure. And then the EOF rates in unknown low EOF microchip can be calculated. Different microchannels modified with bovine serum albumin (BSA), myoglobin (MB) and polyvinyl alcohol (PVA) were used to verify the method, the EOF rate value was1.73±0.03,1.21±0.05,0.34±0.04×10-4cm2V-1s-1, respectively. The results obtained by the proposed method were agreed well with conventional methods.2. PDMS microchannel assembled layer-by-layer with polyelectrolye PDMS microchannel was assembled layer-by-layer with polyelectrolye. Microchip enzyme biosensor was designed to detecte H2O2by changing the position of the electrode on the same microchip. Poly(allylamine hydrochloride)(PAH) was firstly coated on the surface of PDMS microchannel to form polymer film. And then Poly(styrensulfonate)(PSS) was coated on the PAH polymer film. After that, PAH and PSS was coated exchanged to form [PAH/PSS]n polymer films. Immunoassay was performed on the polymer films. Microchannel coated with polyelectrolyes has the advantages of excellent stability and repeatability.3. MicroChannel flow injection square wave anodic stripping voltammetry for heavy metal ions with Carbon fiber electrode electrochemical analysis on microfluidic chipA novel method for fast detection for heavy metal ions on microfluidic chips is established in this article. In this experiment, carbon fiber electrode and bismuth-coated fiber electrode, placed at the end of the micro-channel, are used as working electrode respectively. Heavy metal ions are driven by flow injection mode, enriched on the working electrode and then oxidized back to ions in the stripping mode, which generates current peaks, proportional to the concentration of each ion. Bismuth-coated electrode is produced by adding Bi3+into the buffer solution, and Bi3+is reduced and enriched on the electrode, as the target ions. Bismuth-coated electrode produces lower detection limit and higher sensitivity. This method has both advantages of microchips and stripping voltammetry, such as fast detection and little reagent consumption on the microchip, high sensitivity and signal-to-noise ratio of the stripping voltammetry method. The optimized condition is as followed:separation voltage at1200V, deposition potential at-1.2V, deposition time at120s, and in this condition, the detection limits are8.6ng/mL and7.6ng/mL for Cd2+and Zn2+, respectively.4. A novel Electrochemical Immunosensor for Simultaneous Detection of Dual Cardiac Markers Based on PDMS-Gold Nanoparticles Composite Microfluidic ChipAn effective and convenient electrochemical immunoassay for simultaneous detection of dual biomarkers cTnI and CRP in microchannel via flow injection mode was introduced. The quantitative methodology was based on ELISA in poly(dimethylsiloxane)-gold nanoparticles composite microreactors. CdTe and ZnSe quantum dots were bioconjugated with antibodies for sandwich immunoassay. After CdTe and ZnSe QDs were dissolved, Cd2+and Zn2+were detected by square wave anodic stripping voltammetry (SWASV) that the biomarkers could be quantified. This immunosensor allowed simultaneous detection of cTnl and CRP in clinical serum samples. The linear range of this assay was between0.01～50ng/mL and0.5-200ng/mL, and with the detection limits of～5amol and～307amol in30μL samples corresponding to cTnI and CRP, respectively.20clinical human serum samples were detected using the proposed method. The results indicated acceptable accuracy of this proposed method and no significant difference was observed among the results given by the proposed method and traditional methods. The sensor was successful applied in clinical serum samples for point-of-care monitoring of dual cardiac markers. The method has the advantage of good precision, high sensitivity, acceptable stability, and with the amol detection limits. This strategy demonstrated the successful integration of microfluidics with electrochemistry. The method can provide an interesting alternative tool for protein detection in clinical laboratory.

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