Sensitive Chemiluminescence Immunoassay by Capillary Electrophoresis with Gold Nanoparticles

Simultaneous determination of four phenolic acids in traditional Chinese medicine by capillary electrophoresis-chemiluminescence

Chlorogenic, ferulic, vanillic, and caffeic acids are phenolic acids found in natural drugs. They possess the biological activities of scavenging free radicals and inhibiting thrombus formation. Phenolic acids can inhibit the oxidation of low-density lipoprotein, as well as have anti-inflammatory effects. This paper reports for the first time a capillary electrophoresis-chemiluminescence (CE-CL) method for the simultaneous determination of the four phenolic acids found in traditional and proprietary Chinese medicine, including Lycium chinense Miller, Shuanghuanglian oral liquid, and Taraxacum mongolicum granules. Capillary electrophoretic separation was performed on a self-assembled CE-CL device with an uncoated fused-silica capillary (66 cm effective length, 50 μm i.d.), and the background electrolyte was composed of 3.0 × 10-5 M Ag(iii) (pH = 12.01), 3.0 mM luminol (pH = 9.20), and 10 mM sodium tetraborate solution. The injection time was 12 s (under gravity) and the separation voltage was 22 kV. The combination of solid-phase extraction (SPE) and CE-CL improves the sensitivity. Under optimal conditions, calibration graphs displayed a linear range between 0.625 and 20.0, 1.000 and 30.0, 0.150 and 1.50, and 0.045 and 1.00 μg mL-1 for chlorogenic, ferulic, vanillic, and caffeic acid, respectively. The detection limit ranged from 0.014 to 0.300 μg mL-1. The practicality of using the proposed method to determine the four target analytes in traditional Chinese medicine was also validated, in which recoveries ranged from 90.9% to 119.8%. Taken together, these results indicate that the developed method is sensitive and reliable. Furthermore, the method was successfully applied to real traditional Chinese medicine samples.

Engineering WS2–Au–HRP-assisted multiple signal amplification strategy for chemiluminescence immunoassay of prostate specific antigen

Engineering of a WS₂–Au–HRP-assisted multiple signal amplification strategy for CL immunoassay of PSA.

Multivalent and synergistic chitosan oligosaccharide-Ag nanocomposites for therapy of bacterial infection

Chitosan oligosaccharide functionalized silver nanoparticles with synergistic bacterial activity were constructed as a multivalent inhibitor of bacteria. Placing the chitosan oligosaccharide on silver nanoparticles can dramatically enhance the adsorption to the bacterial membrane via multivalent binding. The multicomponent nanostructures can cooperate synergistically against gram-positive and gram-negative bacteria. The antibacterial activity was increased via orthogonal array design to optimize the synthesis condition. The synergistic bacterial activity was confirmed by fractional inhibitory concentration and zone of inhibition test. Through studies of antimicrobial action mechanism, it was found that the nanocomposites interacted with the bacteria by binding to Mg²⁺ ions of the bacterial surface. Then, the nanocomposites disrupted bacterial membrane by increasing the permeability of the outer membrane, resulting in leakage of cytoplasm. This strategy of chitosan oligosaccharide modification can increase the antibacterial activity of silver nanoparticles and accelerate wound healing at the same time. The nanomaterial without cytotoxicity has promising applications in bacteria-infected wound healing therapy.

Au nanoparticle preconcentration coupled with CE-electrochemiluminescence detection for sensitive analysis of fluoroquinolones in European eel (Anguilla anguilla)

In this work, a novel method based on gold nanoparticle preconcentration coupled with CE for electrochemiluminescence detection of ciprofloxacin, enrofloxacin, ofloxacin, and norfloxacin in European eels was developed. The addition of gold nanoparticles induced the rapid enrichment of fluoroquinolones, which was simpler than the conventional enrichment approaches such as solid phase extraction and solid-phase microextraction. More than 100 times enrichment was observed after gold nanoparticle aggregation-based preconcentration. The CE-electrochemiluminescence parameters that affected the separation and detection were optimized. Under the optimized conditions, the linear ranges for the four fluoroquinolones were 0.090-8.0 μmol L-1 with the detection limits between 0.020 and 0.050 μmol L-1. The proposed approach showed the advantages of high sensitivity, high selectivity, a wide linear range, and a low detection limit. It was used to analyze fluoroquinolones in European eel, and the results showed that the developed method can satisfy the detection requirements for fluoroquinolone determination in aquatic products set by China and the European Union.

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.

Expanding the scope of chemiluminescence in bioanalysis with functional nanomaterials

Nanomaterial-enabled chemiluminescence (CL) detection has become a growing area of interest in recent years. We review the development of nanomaterial-based CL detection strategies and their applications in bioanalysis. Much progress has been achieved in the past decade, but most attempts still remain in the proof-of-concept stage. This review highlights recent advances in nanomaterials in CL detection and organizes them into three groups based on their role in detection: as a sensing platform, as a signal probe, and applications in homogeneous systems. Furthermore, we have discussed the critical challenges we are facing and future prospects of this field.

Clinical and pharmaceutical applications of affinity ligands in capillary electrophoresis: A review

Affinity capillary electrophoresis (ACE) is a separation technique that combines a biologically-related binding agent with the separating power and efficiency of capillary electrophoresis. This review will examine several classes of binding agents that have been used in ACE and applications that have been described for the resulting methods in clinical or pharmaceutical analysis. Binding agents that will be considered are antibodies, aptamers, lectins, serum proteins, carbohydrates, and enzymes. This review will also describe the various formats in which each type of binding agent has been used in CE, including both homogeneous and heterogeneous methods. Specific areas of applications that will be considered are CE-based immunoassays, glycoprotein/glycan separations, chiral separations, and biointeraction studies. The general principles and formats of ACE for each of these applications will be examined, along with the potential advantages or limitations of these methods.

Electrochemiluminescent biosensor with DNA link for selective detection of human IgG based on steric hindrance

A highly selective DNA-based electrochemiluminescence (ECL) based biosensor is described for the detection of human IgG. It is exploiting the effect of steric hindrance that affects the strength of the ECL signal in the presence of IgG. Digoxin-linked signaling DNA was specifically bound to IgG, and this causes steric hindrance which limits the ability of DNA to hybridize with capturing DNA attached to a gold electrode. Europium (II) doped CdSe quantum dots were covalently linked to the DNA in order to generate the ECL signal. Using this steric hindrance hybridization method, the ECL signal of the biosensor were proportional to the concentration of IgG with a wide linear range and a 14 pM detection limit. Conceivably, the method can be expanded to the detection of a wide range of proteins for which homologous recognition elements are available.

Efficient label-free chemiluminescent immunosensor based on dual functional cupric oxide nanorods as peroxidase mimics

Dual-functional cupric oxide nanorods (CuONRs) as peroxidase mimics are proposed for the development of a flow-through, label-free chemiluminescent (CL) immunosensor. Forming the basis of this cost-efficient, label-free immunoassay, CuONRs, synthesized using a simple hydrothermal method, were deposited onto epoxy-activated standard glass slides, followed by immobilization of biotinylated capture antibodies through a streptavidin bridge. The CuONRs possess excellent catalytic activity, along with high stability as a solid support. Antigens could then be introduced to the sensing system, forming large immunocomplexes that prevent CL substrate access to the surface, thereby reducing the CL signal in a concentration dependent fashion. Using carcinoembryonic antigen (CEA) as a model analyte, the proposed label-free immunosensor was able to rapidly determine CEA with a wide linear range of 0.1-60ngmL^-1 and a low detection limit of 0.05ngmL^-1. This nanozyme-based immunosensor is simple, sensitive, cost-efficient, and has the potential to be a very promising platform for fast and efficient biosensing applications.

Applications of capillary electrophoresis with chemiluminescence detection in clinical, environmental and food analysis. A review

This paper reviews the latest developments and analytical applications of chemiluminescence detection coupled to capillary electrophoresis (CE-CL). Different sections considering the most common CL systems have been included, such as the tris(2,2'-bipyridine)ruthenium(II) system, the luminol and acridinium derivative reactions, the peroxyoxalate CL or direct oxidations. Improvements in instrumental designs, new strategies for improving both resolution and sensitivity, and applications in different fields such as clinical, pharmaceutical, environmental and food analysis have been included. This review covers the literature from 2010 to 2015.

Sensitive CE-ECL method with AuNPs-enhanced signal for the detection of β-blockers and the study of drug–protein interactions

A sensitive capillary electrophoresis (CE) system coupled with electrochemiluminescence (ECL) of tris(2,2′-bipyridyl) ruthenium (ii) is described for the detection of propranolol (Pro) and acebutolol (Ace).

A highly sensitive colorimetric metalloimmunoassay based on copper-mediated etching of gold nanorods

A highly sensitive colorimetric metalloimmunoassay based on copper-mediated etching of gold nanorods was developed.

Aptamer-based detection and quantitative analysis of human immunoglobulin E in capillary electrophoresis with chemiluminescence detection

A novel aptamer-based CE with chemiluminescence (CL) assay was developed for highly sensitive detection of human immunoglobulin E (IgE). The IgE aptamer was conjugated with gold nanoparticles (AuNPs) to form AuNPs-aptamer that could specifically recognize the IgE to produce an AuNPs-aptamer-IgE complex. The mixture of the AuNPs-aptamer-IgE complex and the unbounded AuNPs-aptamer could be effectively separated by CE and sensitively detected with luminol-H2 O2 CL system. By taking the advantage of the excellent catalytic behavior of AuNPs on luminol-H2 O2 CL system, the ultrasensitive detection of IgE was achieved. The detection limit of IgE is 7.6 fM (S/N = 3) with a linear range from 0.025 to 250 pM. Successful detection of IgE in human serum samples was demonstrated and the recoveries of 94.9-103.2% were obtained. The excellent assay features of the developed approach are its specificity, sensitivity, adaptability, and very small sample consumption. Our design provides a methodology model for determination of rare proteins in biological samples.

Highly sensitive colorimetric determination of amoxicillin in pharmaceutical formulations based on induced aggregation of gold nanoparticles

A novel, simple and highly sensitive colorimetric method is developed for determination of Amoxicillin (AMX). The system is based on aggregation of citrate-capped gold nanoparticles (AuNP) in acetate buffer (pH=4.5) in the presence of the degradation product of Amoxicillin (DPAMX). It was found that the color of gold nanoparticles changed from red to purple and the intensity of surface plasmon resonance (SPR) peak of AuNPs decreased. A new absorption band was appeared in the wavelength range of 600-700nm upon addition of DPAMX. The absorbance ratio at the wavelength of 660 and 525nm (A660/A525) was chosen as the analytical signal indirectly related to AMX concentration. The linearity of the calibration graph was found over the concentration range of 0.3-4.5μM AMX with a correlation coefficient of 0.9967. Under the optimum experimental conditions, the detection limit was found to be 0.15μM. The applicability of the method was successfully demonstrated by analysis of AMX in pharmaceutical formulations including capsules and oral suspensions.

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.

Chemiluminescence detection of protein in capillary electrophoresis using aptamer-functionalized gold nanoparticles as biosensing platform

Highly sensitive and selective detection of disease-related proteins play critical roles in clinical practice and diagnostic assays. Herein, we proposed a highly selective and ultrasensitive chemiluminescence (CL) method for protein detection in capillary electrophoresis (CE) using aptamer-functionalized gold nanoparticles (AuNPs) as biosensing platform. In this protocol, AuNPs were synthesized and conjugated with aptamer to form AuNPs-aptamer. Using thrombin and thrombin binding aptamer as an initial proof-of-concept recognization pair, AuNPs-aptamer was linked to thrombin to produce an AuNPs-aptamer-thrombin complex. The resulted complex and unbound AuNPs-aptamer were separated in CE and detected with luminol-H2O2 CL system. The developed strategy produced an ultrasensitive detection of thrombin down to 13.5 fmol/L (S/N=3) with a linear range from 0.033 to 66.0 pmol/L. The application of the present protocol was demonstrated by analyzing thrombin in human plasma samples with the recoveries of 87.6-116.8%. This novel strategy has many outstanding merits including high specificity of aptamer, excellent catalysis behavior of AuNPs, high sensitivity of CL detection, and high separation efficiency of CE.

Synthesis and biomedical applications of copper sulfide nanoparticles: from sensors to theranostics

Copper sulfide (CuS) nanoparticles have attracted increasing attention from biomedical researchers across the globe, because of their intriguing properties which have been mainly explored for energy- and catalysis-related applications to date. This focused review article aims to summarize the recent progress made in the synthesis and biomedical applications of various CuS nanoparticles. After a brief introduction to CuS nanoparticles in the first section, we will provide a concise outline of the various synthetic routes to obtain different morphologies of CuS nanoparticles, which can influence their properties and potential applications. CuS nanoparticles have found broad applications in vitro, especially in the detection of biomolecules, chemicals, and pathogens which will be illustrated in detail. The in vivo uses of CuS nanoparticles have also been investigated in preclinical studies, including molecular imaging with various techniques, cancer therapy based on the photothermal properties of CuS, as well as drug delivery and theranostic applications. Research on CuS nanoparticles will continue to thrive over the next decade, and tremendous opportunities lie ahead for potential biomedical/clinical applications of CuS nanoparticles.

Highly sensitive analysis of four hemeproteins by dynamically-coated capillary electrophoresis with chemiluminescence detector using an off-column coaxial flow interface

Dynamic coating of the surface in capillary electrophoresis with chemiluminescence detection (CE-CL) using an off-column coaxial flow interface for the determination of four hemeproteins was developed. This method is based on the luminol-hydrogen peroxide reaction catalyzed by metalloproteins in alkaline medium. The experimental setup of the CE-CL system with the proposed off-column coaxial interface was evaluated by separation and detection of dopamine and catechol based on inhibition of the luminol-potassium ferricyanide reaction. Highly efficient separation of the two model compounds with symmetrical peak shape and satisfactory reproducibility was achieved by using this interface. In addition, in order to obtain a good resolution for hemeproteins, polyvinylpyrrolidone (PVP) combined with sodium dodecyl sulfate (SDS) were introduced as dynamic modifiers to reduce the unwanted adsorption of non-specific protein. Several parameters affecting the CE separation and CL detection were investigated in detail. Under the optimized conditions, a mixture of the four hemeproteins (horseradish peroxidase (HRP), catalase (Cat), myoglobin (Mb) and cytochrome C (Cyt C)) could be well separated within 20 min. The linear ranges of the four proteins were 5.7 × 10(-8) to 1.1 × 10(-6) mol L(-1) for HRP, 4.0 × 10(-8) to 2.0 × 10(-6) mol L(-1) for Cat, 1.1 × 10(-10) to 5.6 × 10(-8) mol L(-1) for Mb, and 3.8 × 10(-7) to 7.7 × 10(-6) mol L(-1) for Cyt C. The limits of detection (LODs) (S/N = 3) for HRP, Cat, Mb and Cyt C were 2.2 × 10(-8) mol L(-1) (104.5 amol), 1.6 × 10(-8) mol L(-1) (74 amol), 5.6 × 10(-11) mol L(-1) (0.26 amol), and 1.95 × 10(-7) mol L(-1) (0.89 fmol), respectively. The proposed method has been successfully applied to the analysis of low-level Mb in a spiked human urine sample and the recoveries were above 97%. Our primary result demonstrated that the proposed CE-CL method has great potential for Mb determination in clinical diagnosis.

Multivalent polymer–Au nanocomposites with cationic surfaces displaying enhanced antimicrobial activity

Pathogenic bacteria pose a catastrophic threat to human health worldwide.

Plasmonic luminescent core-shell nanocomposites-enhanced chemiluminescence arising from the decomposition of peroxomonosulfite

A core-shell structure of plasmonic luminescent nanocomposite, Ni@SiO2@FITC@SiO2 (NSFS) combining the stable luminescence of fluorophore with the excellent plasmonic property of metal nanomaterials, has been synthesized through layer-by-layer assembly. The effect of NSFS on the ultraweak chemiluminescence (CL) reaction of hydrogen peroxide (H2O2) and sodium bisulfite (NaHSO3) was explored for the first time. It was found that the CL intensity from the decomposition of peroxomonosulfite was significantly enhanced by NSFS. The mechanism of the nanocomposite-enhanced CL was revealed as the coupling of chemically induced excited states of fluorescein isothiocyanate (FITC) with surface plasmons of Ni nanoparticles based on studies of CL emission spectra, electron spin resonance spectra, extinction spectra and fluorescence spectra. The work sheds new light on the characteristics of the versatile materials and gives us new insight into the optical properties of fluorophores.

Chemiluminescent cholesterol sensor based on peroxidase-like activity of cupric oxide nanoparticles

A chemiluminescent cholesterol sensor with good selectivity and enhanced sensitivity was constructed based upon the peroxidase-like activity of cupric oxide nanoparticles. Cupric oxide nanoparticles can catalyze the oxidation of luminol by H2O2, which was produced by the reaction of cholesterol and oxygen that was catalyzed by cholesterol oxidase. Therefore, the oxidation of cholesterol could be transduced into the chemiluminescence of luminol by combining these two reactions. Under the optimum conditions, the CL intensity was proportional to the concentration of cholesterol over the range of 0.625-12.5μM and a detection limit was 0.17μM. The applicability of proposed method has been validated by determination of cholesterol in milk powder and human serum samples with satisfactory results.

Sensitive and selective capillary electrophoretic analysis of proteins by zirconia nanoparticle-enhanced copper (II)-catalyzed luminol-hydrogen peroxide chemiluminescence

We report herein a sensitive, selective, convenient CE determination of heme proteins in complex matrices by a sodium-dodecyl-sulfate-assisted, zirconia nanoparticle-enhanced copper (II)-catalyzed luminol-hydrogen peroxide chemiluminescence (CCLHPCL). Introducing a segment of sodium dodecyl sulfate to the capillary after sample injection not only rendered selective detection by quenching the luminescence signals from the non-heme proteins but also owning to the suppressed protein adsorption, led to significant improvement in separation efficiency and detection sensitivity. The signals were further improved by addition of ZrO(2) nanoparticles to the chemiluminescence solution. Compared with the conventional CCLHPCL, the detection limits (S/N=3) were improved by 10.2-22.0 folds, with 7.8×10(-9), 3.3×10(-9) and 1.5×10(-9) M for three model proteins, viz, myoglobin, hemoglobin and cytochrome C, respectively. Because the method did not require sophisticated pretreatment, it was convenient to analyze heme proteins in complex matrices, as demonstrated, hemoglobin in human blood and spiked human urine samples.