Competitive immunoassay for recombinant hirudin using capillary electrophoresis with laser-induced fluorescence detection

Aptamer-thrombin loaded magnetic microspheres for bio-specific extraction and precise detection of hirudin

Hirudin, that is naturally occurring in leeches (Hirudo medicinalis) and known as the most potent natural inhibitor of thrombin, exerts double-edged effects in clinic application. It can be used as a therapeutic ingredient for cardiovascular disease, while it can be regarded as a toxic polypeptide with bleeding risk. Effective detection of hirudin in biological samples contributes greatly to reasonable therapy. In this study, we proposed a smart adsorbent based on affinity magnetic microspheres, where thrombin was immobilized for capturing hirudin in the animal serum. Aptamer was introduced as a ligand for linking the magnetic agarose microspheres and thrombin, thereby avoiding loss of biological activity of the enzyme to hirudin. Taken recombinant hirudin variant 2-Lys47 (rHV2) as a model, we established a rapid and bio-specific extraction method coupled with liquid chromatography and quadrupole-time-of-flight mass spectrometry (LC-QTOF/MS) for determination of hirudin in the serum. Owing to this strategy, a low limit of detection (LOD) of rHV2 (0.5 nM), a good linearity with correlation coefficient of 0.9975, an acceptable precision with relative standard deviation (RSD) below 3.6% (n = 6) and acceptable recoveries ranging from 85.7% to 90.2% were achieved. Moreover, the functionalized magnetic composite could be reused for at least nine cycles. Our work combined the merits of affinity separation and advanced instrument analysis for hirudin, providing a new vision to precise determination of hirudin in medical and pharmaceutical fields.

Capillary electrophoresis-based immunoassay and aptamer assay: A review

Over the last two decades, the group of techniques called affinity probe CE has been widely used for the detection and the determination of several types of biomolecules with high sensitivity. These techniques combine the low sample consumption and high separation power of CE with the selectivity of the probe to the target molecule. The assays can be defined according to the type of probe used: CE immunoassays, with an antibody as the probe, or aptamer-based CE, with an aptamer as the probe. Immunoassays are generally divided into homogeneous and heterogeneous groups, and homogeneous variant can be further performed in competitive or noncompetitive formats. Interacting partners are free in solution at homogeneous assay, as opposed to heterogeneous analyses, where one of them is immobilized onto a solid support. Highly sensitive fluorescence, chemiluminescence or electrochemical detections were typically used in this type of study. The use of the aptamers as probes has several advantages over antibodies such as shorter generation time, higher thermal stability, lower price, and lower variability. The aptamer-based CE technique was in practice utilized for the determination of proteins in biological fluids and environmentally or clinically important small molecules. Both techniques were also transferred to microchip. This review is focused on theoretical principles of these techniques and a summary of their applications in research.

Capillary electrophoresis-laser-induced fluorescence (CE-LIF)-based immunoassay for quantifying antibodies against cyclic citrullinated peptides

CE-LIF based immunoassay to quantify antibodies against cyclic citrullinated peptides in rheumatoid arthritis patients.

Clinical applications of capillary electrophoresis based immunoassays

Immunoassays have long been an important set of tools in clinical laboratories for the detection, diagnosis, and treatment of disease. Over the last two decades, there has been growing interest in utilizing CE as a means for conducting immunoassays with clinical samples. The resulting method is known as a CE immunoassay. This approach makes use of the selective and strong binding of antibodies for their targets, as is employed in a traditional immunoassay, and combines this with the speed, efficiency, and small sample requirements of CE. This review discusses the variety of ways in which CE immunoassays have been employed with clinical samples. An overview of the formats and detection modes that have been employed in these applications is first presented. A more detailed discussion is then given on the type of clinical targets and samples that have been measured or studied by using CE immunoassays. Particular attention is given to the use of this method in the fields of endocrinology, pharmaceutical measurements, protein and peptide analysis, immunology, infectious disease detection, and oncology. Representative applications in each of these areas are described, with these examples involving work with both traditional and microanalytical CE systems.

Capillary electrophoresis-based immunoassays: principles and quantitative applications

The use of CE as a tool to conduct immunoassays has been an area of increasing interest over the last decade. This approach combines the efficiency, small sample requirements, and relatively high speed of CE with the selectivity of antibodies as binding agents. This review examines the various assay formats and detection modes that have been reported for these assays, along with some representative applications. Most CE immunoassays in the past have employed homogeneous methods in which the sample and reagents are allowed to react in solution. These homogeneous methods have been conducted as both competitive binding immunoassays and as noncompetitive binding immunoassays. Fluorescent labels are most commonly used for detection in these assays, but enzyme labels have also been utilized for such work. Some additional work has been performed in CE immunoassays with heterogeneous methods in which either antibodies or an analog of the analyte is immobilized to a solid support. These heterogeneous methods can be used for the selective isolation of analytes prior to their separation by CE or to remove a given species from a sample/reagent mixture prior to analysis by CE. These CE immunoassays can be used with a variety of detection modes, such as fluorescence, UV/Vis absorbance, chemiluminescence, electrochemical measurements, MS, and surface plasmon resonance.

Development of a capillary electrophoresis-based immunoassay with laser-induced fluorescence for the detection of carbaryl in rice samples

A capillary electrophoresis-based competitive immunoassay (CEIA) with a laser-induced fluorescence (LIF) detector for the determination of carbaryl was developed. The method was based on the competitive reactions between fluorescently labeled carbaryl tracer (Ag*) and free carbaryl (Ag) with a limited amount of anticarbaryl antibody (Ab), and the relative amounts of each were separated and determined by capillary electrophoresis (CE) with an LIF detector. Using CEIA, equilibrium was reached in 30 min, and the analytical results were obtained within a further 8 min. The linear range and the detection limit for carbaryl were 0.16-50 ng/mL and 0.05 ng/mL, respectively. The sensitivity of this CEIA with an LIF detector was almost 14 times greater than that of ELISA, which used the same immuno-reagents. The method was also applied to the analysis of carbaryl in rice with rapid and simple sample pretreatment. The method is thus proposed as a fast and sensitive assay for the detection of carbaryl.

Competitive immunoassay for clenbuterol using capillary electrophoresis with laser-induced fluorescence detection

A competitive immunoassay for detecting clenbuterol in urine was established by capillary electrophoresis (CE) with laser-induced fluorescence (LIF). The clenbuterol was conjugated with bovine serum albumin (BSA), and then the derivative was labeled with fluorescein isothiocyanate (FITC) and competes for antibody with free clenbuterol in the sample. Under the optimal conditions, Free and bound FITC labeled clenbuterol was separated within 8 min with the relative standard deviation (R.S.D.) 0.72% for migration time and 2.8% for peak area. The detection limit reached 0.7 ng/ml.

Capillary electrophoretic competitive immunoassay with laser-induced fluorescence detection for methionine-enkephalin

Immunoassays are commonly used in bioresearch for the detection and quantification of small proteins and macromolecules in biological fluids and other complex matrices. In this report, a competitive immunoassay using capillary electrophoresis (CE) with laser-induced fluorescence was developed for methionine-enkephalin (ME). The method is based on the competitive reaction between the ME and fluorescein conjugated ME (ME-F) with anti-ME antibody, capillary electrophoresis separation of the ME-antibody bound and free ME-F, followed by the laser-induced fluorescence detection of the fluorescent species. With the optimized separation conditions, it was possible to separate the antibody bound and free fluorescien conjugated ME by a capillary electrophoresis-laser-induced fluorescence (CE-LIF) analysis using an uncoated fused-silica capillaries. The results concluded that the assay specificity, selectivity and accuracy were excellent.

Using capillary electrophoresis with laser-induced fluorescence to study the interaction of green fluorescent protein-labeled calmodulin with Ca2+- and calmodulin-binding protein

A separation using capillary electrophoresis with laser-induced fluorescence (CE-LIF) was applied to the study of green fluorescent protein tagged calmoldulin (GFP-CaM) that was expressed from Escherichia coli and purified with Ni(2+)-nitrilotriacetate (Ni-NTA) resin column. It was found that GFP-CaM not only has good fluorescence properties under various conditions similar to GFP, but also retains its calcium-binding ability as the native CaM. GFP-CaM was separated and detected by CE-LIF within 10 min with a limit-of-detection (LOD) of 2 x 10(-10) M for an injection volume of 3 nl, higher than that of common chemical fluorescent-tagged protein method. The results indicated that, as a fluorescence probe, GFP could overcome the drawback of inefficient derivatization of chemical fluorescence probes. The interaction between the GFP-CaM and Ca(2+) was studied in detail using affinity capillary electrophoresis with laser-induced fluorescence and the dissociation constant (K(d)) between GFP-CaM and Ca(2+) was determined to be 1.2 x 10(-5), which is in good agreement with the literature values of untagged CaM (10(-6) to 10(-5)M) obtained by conventional method. As a preliminary application, the interaction between GFP-CaM and OsCBK was also investigated. The method makes it possible to screen the trace amounts of target proteins in crude extracts interacting with CaM under physiological conditions.

Capillary electrophoresis-based immunoassay

Capillary electrophoresis-based immunoassay (CEIA) is a developing analytical technique with a number of advantages over conventional immunoassay, such as reduced sample consumption, simpler procedure, easy simultaneous determination of multiple analytes, and short analysis time. However, there are still a number of technical issues that researchers on CEIA have to solve before the assay can be more widely used. These issues include method to improve the concentration sensitivity of the assay, requirement for robust separation strategy for different analytes, and method to increase the throughput of the assay. The approaches to solve these issues are reviewed. Several studies have been devoted to develop general separation strategies for CEIA, and to enhance the sensitivity of detection. The recent development of microchip-based CEIA is encouraging and is likely to address more drawbacks of CEIA, particularly on the throughput issue.

Analysis of secretory immunoglobulin A in human saliva by laser-induced fluorescence capillary electrophoresis

The utility of capillary electrophoresis (CE) has been demonstrated for the analysis of secretory immunoglobulin A (sIgA) in human saliva. The amount of sIgA in saliva correlates with immune status. For detecting salivary sIgA, laser-induced fluorescence was conducted in this report for signal amplification. sIgA and anti-sIgA antibody were labeled with cyanine fluorescence (Cy5) for competitive immunoassay and non-competitive analysis, respectively. Cy5 was excited by He-Ne laser with a wavelength of 635 nm, with maximum emission at 670 nm. Migration time during electrophoresis depended on whether sIgA-Cy5 was mixed with antibody or anti-sIgA-Cy5 mixed with sIgA to form Ag-Ab complex. The results indicated that CE competitive immunoassay was effective for analyzing serum sIgA, but not for salivary sIgA. However, salivary sIgA can be analyzed by complex formation assay. The peak area of the complex was proportional to the amount of sIgA added. A standard linear regression curve was generated using purified sIgA. From this standard curve, the amount of sIgA from saliva of either normal or immunocompromised patients can be calculated from the Ag-Ab complex peak area.

Direct monitoring of the expression of the green fluorescent protein-extracellular signal-regulated kinase 2 fusion protein in transfected cells using capillary electrophoresis with laser-induced fluorescence detection

Proper subcellular localization of the extracellular signal-regulated kinases (ERKs) is important in regulating physiological functions such as proliferation and differentiation in the pheochromocytoma cell line (PC12 cells). Thus, a direct visualization method is necessary to observe ERK localization within the cell or in crude cellular extracts. In this paper, a determination method was established for the detection of ERK2 localization in PC12 cells using green fluorescent protein (GFP) and capillary electrophoresis with laser-induced fluorescence (LIF). GFP as a reporter or labeling tag for gene expression in biochemistry and cell biology was used for the detection of ERK2 localization in PC12 cells. PC12 cells were transfected with GFP-ERK2 plasmid construct that was inserted into a variant GFP gene (enhanced green fluorescent protein), and successfully expressed GFP-ERK2 fusion proteins. GFP-ERK2 fusion proteins were detected within 5 min by CE analysis using an uncoated fused-silica capillary with LIF. Optimum conditions for GFP-ERK2 fusion proteins detection were 100 mM 3-(cyclohexylamino)-1-propanesulfonic acid buffer containing 100 mM sodium dodecylsulfate, pH 11, running at 20 degrees C. This result offers new opportunity in screening for the determination of localization of intracellular components, protein-protein interactions and kinase activity within the cells.

Non-competitive immunoassay for alpha-fetoprotein using micellar electrokinetic capillary chromatography and laser-induced fluorescence detection

A non-competitive immunoassay based on micellar electrokinetic capillary chromatography (MECC) with laser-induced fluorescence (LIF) detection has been developed for the determination of alpha-fetoprotein (AFP). The anti-AFP antibody was labeled with fluorescein isothiocyanate (FITC) and the product was used as a fluorescent tracer, then AFP was mixed with the labeled antibody. After incubation, the immune AFP-antibody complex was separated from labeled free antibody by MECC. The parameters affecting separation such as the concentration of sodium dodecyl sulfate (SDS), the buffer pH and separation voltage were investigated and the following conditions were selected: 20 mM tetraborate containing 100 mM SDS at pH 9.50, and 20 kV separation voltage. The detection limit of this assay was 0.1 ng/ml with a linear range spanning two orders of magnitude. This method was applied to determine AFP in human serum.