LIF detection of peptides and proteins in CE

A comprehensive review on LED-induced fluorescence in diagnostic pathology

Sensitivity, specificity, mobility, and affordability are important criteria to consider for developing diagnostic instruments in common use. Fluorescence spectroscopy has been demonstrating substantial potential in the clinical diagnosis of diseases and evaluating the underlying causes of pathogenesis. A higher degree of device integration with appropriate sensitivity and reasonable cost would further boost the value of the fluorescence techniques in clinical diagnosis and aid in the reduction of healthcare expenses, which is a key economic concern in emerging markets. Light-emitting diodes (LEDs), which are inexpensive and smaller are attractive alternatives to conventional excitation sources in fluorescence spectroscopy, are gaining a lot of momentum in the development of affordable, compact analytical instruments of clinical relevance. The commercial availability of a broad range of LED wavelengths (255-4600 nm) has opened up new avenues for targeting a wide range of clinically significant molecules (both endogenous and exogenous), thereby diagnosing a range of clinical illnesses. As a result, we have specifically examined the uses of LED-induced fluorescence (LED-IF) in preclinical and clinical evaluations of pathological conditions, considering the present advancements in the field.

Automated fluorimetric sensor for hydrazine determination in water samples based on the concept of zone fluidics

In the present study, we report an automated fluorescence sensor for the determination of hydrazine in various water samples based on the concept of zone fluidics. Hydrazine and O-phthalaldehyde react through a unique mechanism in acidic medium (pH = 1.5) and without the presence of additional nucleophilic compounds. Another interesting feature of the proposed reaction is that it is not based on the Red/Ox properties of hydrazine, enhancing further the selectivity of the analytical procedure. The produced hydrazone exhibits high fluorescence at Ex = 318/Em = 376 nm. Using 120 s as a stopped flow step and temperature of 70 °C, we achieved satisfactory sensitivity for the determination of the analyte at a microgram per liter level with a limit of detection of 1.4 μg L^-1 and an analysis rate of 12 h^-1. The absence of matrix effect enabled the direct analysis of drinking (tap, mineral, table) and boiler feedwater samples with percent recoveries in the range of 91-111%.

Separation and determination of alpha-synuclein monomeric and oligomeric species using two electrophoretic approaches

Parkinson's disease (PD) is a frequent degenerative disorder that is diagnosed based on clinical symptoms. When the first symptoms appear, more than 70% of the dopaminergic cells are already lost. Therefore, it is of utmost importance to have reliable biomarkers to diagnose much earlier PD. In this context, alpha-synuclein (aSyn) is a protein of high interest because of its tendency to form oligomers and amyloid fibrils. The oligomeric forms seem to play a critical pathological role in PD. To date, most of studies aiming at detecting and quantifying aSyn oligomers were performed by immunoassays, mainly by ELISA using specific antibodies. In this study a capillary gel electrophoresis (CGE) coupled with fluorescence detection method was developed to detect and quantify the oligomeric forms of aSyn formed in vitro. All the results obtained were supported by SDS-PAGE analysis, a widely used and well-known technique but exhibiting a main drawback since it is not an automated technique. The repeatability and the intermediate precision of the method were evaluated, as well as the stability of the labeled and non-labeled aSyn samples. After careful screening and optimization of various labeling reagents, 4-fluoro-7-nitrobenzofurazan (NBD-F) was selected and used to establish a calibration curve with monomeric fluorescently-labeled aSyn. Finally, the method was used to study the effect of doxycycline on the oligomerization process. Altogether, our results show that CGE is a very promising automated technique to analyze aSyn monomers, as well as small oligomers.

Isoelectric Point Separations of Peptides and Proteins

The separation of ampholytic components according to isoelectric point has played an important role in isolating, reducing complexity and improving peptide and protein detection. This brief review outlines the basics of isoelectric focusing, including a summary of the historical achievements and considerations in experimental design. Derivative methodologies of isoelectric focusing are also discussed including common detection methods used. Applications in a variety of fields using isoelectric point based separations are provided as well as an outlook on the field for future studies.

Analysis of proteins and peptides by electromigration methods in microchips

This review presents the developments and applications of microchip electromigration methods in the separation and analysis of peptides and proteins in the period 2011-mid-2016. The developments in sample preparation and preconcentration, microchannel material, and surface treatment are described. Separations by various microchip electromigration methods (zone electrophoresis in free and sieving media, affinity electrophoresis, isotachophoresis, isoelectric focusing, electrokinetic chromatography, and electrochromatography) are demonstrated. Advances in detection methods are reported and novel applications in the areas of proteomics and peptidomics, quality control of peptide and protein pharmaceuticals, analysis of proteins and peptides in biomatrices, and determination of physicochemical parameters are shown.

Capture efficiency of dynamic pH junction focusing in capillary electrophoresis

Dynamic pH junction is one of the techniques used to overcome the issue of poor concentration sensitivity in CE. By introducing a long sample plug in the capillary and focusing the target molecules at the pH boundary between the sample plug and background electrolyte, this focusing technique can achieve a detection limit that is one to two orders of magnitude better than conventional CE. For quantification purposes, the capturing efficiency of the injected molecules should be scrutinized. Focusing of all target molecules inside the sample plug is desired to ensure good linearity across the whole dynamic range. To test the theoretical prediction with a real experiment, nicotine is used as the test molecule for two types of dynamic pH junctions. The first one is with acidic background electrolyte, and can accommodate both optical detection methods and positive-ion mode mass spectrometric detection, while the other is suitable for optical detection only due to the use of basic separation background electrolyte. With a theoretical simulation study, it is demonstrated that, for either of these dynamic pH junctions, focusing of at least 95% of target molecule injected into the capillary was easily achievable. More importantly, a longer sample plug could generate a high percentage of molecules captured by dynamic pH junction focusing. Sharp, symmetrical peaks and good linearity for calibration curve can be obtained. Real samples with complex matrixes were also used to demonstrate that nicotine can be selectively focused and quantified using CE-MS.

Chemical and Instrumental Approaches for Capillary Electrophoresis (CE)-Fluorescence Analysis of Proteins

Capillary electrophoresis (CE) coupled to fluorescence detection is an invaluable technique for the quantitative analysis of proteins of interest in the field of clinical diagnosis and quality control of novel biotechnology products. The various chemical and instrumental approaches that have been reported to carry out such sensitive analysis are described in this paper. To illustrate the contribution of CE to the analysis of therapeutic proteins, a detailed protocol for impurities profiling of a recombinant antibody sample using CE-LEDIF is given.

Separation of Peptides by Capillary Electrophoresis

Peptides are an important class of analytes in chemistry, biochemistry, food chemistry, as well as medical and pharmaceutical sciences including biomarker analysis in peptidomics and proteomics. As a high-resolution technique, capillary electrophoresis (CE) is well suited for the analysis of polar compounds such as peptides. In addition, CE is orthogonal to high-performance liquid chromatography (HPLC) as both techniques are based on different physicochemical separation principles. For the successful development of peptide separations by CE, operational parameters including puffer pH, buffer concentration and buffer type, applied voltage, capillary dimensions, as well as background electrolyte additives such as detergents, ion-pairing reagents, cyclodextrins, (poly)amines, and soluble polymers have to be considered and optimized.

Capillary Electrophoresis Method for the Assessment of Erythropoiesis-Stimulating Agents in Final Formulations

Capillary electrophoresis (CE) comprises several separation modes that can be used to characterize proteins in terms of physico-chemical properties such as isoelectric point or molecular weight, or in terms of purity/heterogeneity for the presence of charge or size variants. In glycoproteins the heterogeneity occurring as a consequence of variable amounts of terminal sialic acid residues on glycan moieties can be detected by CE. As such, a capillary zone electrophoresis (CZE) method was found suitable for the detection of isoforms of several erythropoiesis-stimulating agents (Bietlot and Girard, J Chromatogr A 759:177-184, 1997; Boucher et al., J Pharm Biomed Anal 71:207-213, 2012). In particular, the method can be used to analyze finished products containing erythropoietin-α, erythropoietin-β, or darbepoetin-α regardless of the formulation and without the need for sample pretreatment. The major excipients encountered in the various formulations included polysorbate 80, polysorbate 20, or human serum albumin. The ability of the method to resolve isoforms of the active ingredient in finished product enables the comparison of the isoform profile with that of the corresponding drug substance, allowing the assessment of the structural integrity and content of the active ingredients in finished products.

High-performance liquid chromatography combined with intrinsic fluorescence detection to analyse melittin in individual honeybee (Apis mellifera) venom sac

Melittin is the major toxin peptide in bee venom, which has diverse biological effects. In the present study, melittin was separated by reverse-phase high-performance liquid chromatography, and was then detected using intrinsic fluorescence signal of tryptophan residue. The accuracy, linearity, limit of quantitation (LOQ), intra-day and inter-day precision of the method were carefully validated in this study. Results indicate that the intrinsic fluorescence signal of melittin has linear range from 0.04μg/mL to 20μg/mL with LOQ of 0.04μg/mL. The recovery range of spiked samples is between 81.93% and 105.25%. The precision results are expressed as relative standard deviation (RSD), which is in the range of 2.1-7.4% for intra-day precision and 6.2-10.8% for inter-day precision. Because of the large linear dynamic range and the high sensitivity, intrinsic fluorescence detection (IFD) can be used for analyzing melittin contents in individual venom sac of honeybee (Apis mellifera). The detected contents of melittin in individual bee venom sac are 0.18±0.25μg for one-day old honeybees (n=30), and 114.98±43.51μg for 25-day old (n=30) honeybees, respectively. Results indicate that there is large bee-to-bee difference in melittin contents. The developed method can be useful for discovering the melittin related honeybee biology information, which might be covered in the complex samples.

Evaluation of fritless solid-phase extraction coupled on-line with capillary electrophoresis-mass spectrometry for the analysis of opioid peptides in cerebrospinal fluid

Fritless SPE on-line coupled to CE with UV and MS detection (SPE-CE-UV and SPE-CE-MS) was evaluated for the analysis of opioid peptides. A microcartridge of 150 μm id was packed with a C18 sorbent (particle size > 50 μm), which was retained between a short inlet capillary and a separation capillary (50 μm id). Several experimental parameters were optimized by SPE-CE-UV using solutions of dynorphin A (DynA), endomorphin 1 (End1), and methionine-enkephaline (Met). A microcartridge length of 4 mm was selected, sample was loaded for 10 min at 930 mbar and the retained peptides were eluted with 67 nL of an acidic hydro-organic solution. Using SPE-CE-MS, peak area and migration time repeatabilities for the three opioid peptides were 12-27% and 4-5%, respectively. SPE recovery was lower for the less hydrophobic DynA (22%) than for End1 (66%) and Met (78%) and linearity was satisfactory in all cases between 5 and 60 ng/mL. The LODs varied between 0.5 and 1.0 ng/mL which represent an enhancement of two orders of magnitude when compared with CE-MS. Cerebrospinal fluid (CSF) samples spiked with the opioid peptides were analyzed to demonstrate the applicability to biological samples. Peak area and migration time repeatabilities were similar to the standard solutions and the opioid peptides could be detected down to 1.0 ng/mL.

Label-free microfluidic free-flow isoelectric focusing, pH gradient sensing and near real-time isoelectric point determination of biomolecules and blood plasma fractions

Continuous biomolecular separation and pH gradient observation using UV and NIR fluorescence.

Determination of neurotransmitter amino acids in mouse central nervous system by CE-LIF

An MEKC method with LIF detection has been developed for the determination of seven neurotransmitter amino acids (NAAs) using 1,3,5,7-tetramethyl-8-(N-hydroxysuccinimidyl butyric ester)difluoroboradiaza-S-indacene as the labeling reagent. After derivatization at room temperature for 30 min, the seven target NAAs including glycine, alanine, γ-aminobutyric acid, taurine, glutamine, glutamic acid, and aspartic acid were separated in running buffer, which consisted of 70 mM pH 4.00 H3 PO4 /Na3 PO4 buffer, 5.5 mM cetyltrimethyl ammonium bromide and 20% v/v acetonitrile within 17 min. The LODs were 2 ~ 14 × 10(-10) M without interference from other coexisting amino acids. The proposed method has been applied to the analysis of NAAs in the central nervous systems of healthy mice and those with Alzheimer's disease with recoveries of 92-104%.

Large-volume sample stacking for in vivo monitoring of trace levels of γ-aminobutyric acid, glycine and glutamate in microdialysates of periaqueductal gray matter by capillary electrophoresis with contactless conductivity detection

A new variant of large-volume sample stacking injection (LVSS) was used in the capillary electrophoresis with capacitively coupled contactless conductivity detection (CE/C(4)D) determination of the neurotransmitters γ-aminobutyric acid (GABA), glycine (Gly) and glutamate (Glu) in microdialysates of periaqueductal gray matter (PAG). The separation capillary was filled to 98% from the injection side with a sample of microdialysate in acetonitrile. Simultaneously with turning on the separation voltage, the sample zone was forced out by the background electrolyte by increasing the pressure in the terminal capillary outlet vessel. As a consequence of the stacking effect, the analyte was concentrated from the large sample volume into a narrow zone at the sample/background electrolyte boundary close to the injection end of the capillary. Under these conditions, LOD values of 9, 10 and 15nM were determined in the model samples for GABA, Gly and Glu, respectively; RSD equalled 0.5% for the migration times and 1.0-1.9% for the peak areas, respectively. In analysis of microdialysates of PAG, LOD values of 29, 29 and 37nM were determined for GABA, Gly and Glu, respectively; RSD equalled 0.5-0.7% for the migration times and 2.6-8.2% for the peak areas, respectively. The determined basal levels of the neurotransmitters in PAG microdialysates are 0.08, 4.7 and 0.8μM for GABA, Gly and Glu, respectively. Carrageenan-induced hyperalgesia increases the Gly and Glu levels and reduces GABA in PAG microdialysate. Peroral administration of paracetamol in hyperalgesia effectively reduces the Gly value and has no effect on Glu and GABA.

Bleomycin DNA damage: Anomalous mobility of 3'-phosphoglycolate termini in an automated capillary DNA sequencer

An automated capillary DNA sequencer with laser-induced fluorescence detection can be utilised for DNA fragment analysis. The precise mobilities of DNA fragments with different chemical termini are especially important in the determination of the sequence specificity of DNA damaging agents. The aim of this study was to examine the electrophoretic mobility profile of DNA fragments with different 3'-termini. The nature of the 3'-teminal residue was found to have a major effect on the electrophoretic mobility of the DNA fragment, especially for 3'-phosphoglycolate termini that migrated anomalously by 3-6 nucleotides. Using the automated capillary sequencer, the electrophoretic mobilities of DNA fragments with different 3'-termini including 3'-hydrogen, 3'-hydroxyl, 3'-phosphate, and 3'-phosphoglycolate were extensively quantified and compared relative to each other. The 3'-hydrogen termini were generated by dideoxy sequencing; 3'-hydroxyl ends by minus sequencing; 3'-phosphate by Maxam-Gilbert chemical sequencing; and 3'-phosphoglycolate by bleomycin cleavage. The mobilities of these DNA fragments with different 3'-termini were found to be: (slowest) 3'-hydroxyl<3'-hydrogen<3'-phosphate<3'-phosphoglycolate (fastest); with average relative mobilities of 0.00<0.12<0.63<4.42 nucleotides, respectively. The possible causes of the unusual electrophoretic mobility of the 3'-phosphoglycolate termini were discussed.

The electrophoretic mobility of DNA fragments differing by a single 3'-terminal nucleotide in an automated capillary DNA sequencer

The electrophoretic mobility of DNA fragments that differ by a single 3'-terminal nucleotide was assessed by capillary electrophoresis. This was accomplished using dideoxy sequencing with a 5'-fluorescently labelled primer to generate DNA fragments with 3'-hydrogen ends. The resulting DNA fragments were electrophoresed on the ABI 3730 automated capillary sequencer, and the data were analysed with the GeneMapper software to determine the electrophoretic mobility differences on addition of a 3'-terminal nucleotide. It was found that the 3'-terminal nucleotide gave rise to different electrophoretic mobility profiles depending on the identity of the terminal nucleotide. The apparent electrophoretic mobility was (faster) -C > -A > -T > -G (slower). The C-terminated fragments were the fastest and the G-terminated fragments the slowest, relative to other nucleotides. It was proposed that the terminal nucleotide effect was due to changes in partial net charges on the nucleotides that resulted in alterations in the electrophoretic mobility of the DNA fragments in the automated capillary DNA sequencer. Other alternative explanations are also discussed.

Parkinson disease drug screening based on the interaction between D(2) dopamine receptor and beta-arrestin 2 detected by capillary zone electrophoresis

Parkinson’s disease is the second most common neurodegenerative disease in the world. Beta-arrestin-2 has been reported to be an important protein involved in D₂ dopamine receptor desensitization, which is essential to Parkinson’s disease. Moreover, the potential value of pharmacological inactivation of G protein-coupled receptor kinase or arrestin in the treatment of patients with Parkinson’s disease has recently been shown. We studied the interaction between D₂ dopamine receptor and beta-arrestin-2 and the pharmacological regulation of chemical compounds on such interaction using capillary zone electrophoresis. The results from screening more than 40 compounds revealed three compounds that remarkably inhibit the beta-arrestin-2/D₂ dopamine receptor interaction among them. These compounds are promising therapies for Parkinson’s disease, and the method used in this study has great potential for application in large-scale drug screening and evaluation.

Peptide mapping using capillary electrophoresis offline coupled to matrix-assisted laser desorption ionization time of flight mass spectrometry

This article reports the results of a study carried out to evaluate the offline hyphenation of capillary zone electrophoresis with matrix-assisted lased desorption ionization time of flight mass spectrometry (MALDI-TOF-MS) for the analysis of low-abundant complex samples, represented by the tryptic phosphorylated peptides of phosphoproteins, such as α-casein, β-casein, and fetuin. The proposed method employs a latex-coated capillary and consists in the online preconcentration of the tryptic peptides by a pH-mediated stacking method, their separation by capillary zone electrophoresis, and subsequent deposition of the separated analytes onto a MALDI target for their MS analysis. The online preconcentration method allows loading a large sample volume (∼150 nL), which is introduced into the capillary after the hydrodynamic injection of a short plug of 1.0 M ammonium hydroxide solution and is sandwiched between two plugs of the acidic background electrolyte solution (BGE) filling the capillary. The sample spotting of the separated analytes onto the MALDI target is performed either during or postseparation using an automatic spotting device connected to the exit of the separation capillary. The proposed method allows the separation and identification of multiphosphorylated peptides from other peptides and enables their identification at femtomole level with improved efficiency compared with LC approaches hyphenated to MS.

Fast analysis of amino acids in wine by capillary electrophoresis with laser-induced fluorescence detection

A fast analytical method has been developed for the determination of nine amino acids, together with serotonin, in wine samples of different origin and vintage. The method is based on capillary electrophoresis coupled to laser-induced fluorescence detection. Separation was obtained by using a fused-silica capillary (75 μm id, 74.0 cm total length, 60.0 cm length to detector) and a background electrolyte composed of carbonate buffer (20 mM, pH 9.2), applying a 20 kV voltage. Direct hydrodynamic injection of wine samples was made after an original microwave-assisted derivatisation step with 5-(4,6-dichlorotriazinyl)aminofluorescein. Fluorescence was induced by an Ar-Ion laser, exciting at 488 nm. Good linearity (r(2) >0.9990) was obtained for all considered analytes and sensitivity was also good, with limits of detection in the 7-50 ng/mL range. The method was successfully applied for the analysis of commercial Italian wines and thus seems to be suitable for the determination of the relevant amino acids and serotonin, providing good results in terms of accuracy and precision, together with the advantage of a very fast, microwave-assisted derivatisation procedure. Future applications of the method are planned to check for wine adulterations and commercial frauds.

Parallel detection of intrinsic fluorescence from peptides and proteins for quantification during mass spectrometric analysis

Direct mass spectrometric quantification of peptides and proteins is compromised by the wide variabilities in ionization efficiency which are hallmarks of both the MALDI and ESI ionization techniques. We describe here the implementation of a fluorescence detection system for measurement of the UV-excited intrinsic fluorescence (UV-IF) from peptides and proteins just prior to their exit and electrospray ionization from an ESI capillary. The fluorescence signal provides a quantifiable measure of the amount of protein or peptide present, while direct or tandem mass spectrometric analysis (MS/MS) on the ESI-generated ions provides information on identity. We fabricated an inexpensive, modular fluorescence excitation and detection device utilizing an ultraviolet light-emitting diode for excitation in a ∼300 nL fluorescence detection cell integrated into the fused-silica separation column. The fluorescence signal is linear over 3 orders of magnitude with on-column limits of detection in the low femtomole range. Chromatographically separated intact proteins analyzed using UV-IF prior to top-down mass spectrometry demonstrated sensitive detection of proteins as large as 77 kDa.

Evaluation of an on-capillary copper complexation methodology for the investigation of in vitro metabolism of dynorphin A 1-17

Dynorphin A 1-17 is an endogenous neuropeptide implicated in a variety of neurological disorders including Alzheimer's and Parkinson's diseases and neuropathic pain. Metabolites of this peptide can exhibit their own unique effects in vivo, and it is possible that one of these metabolites is responsible for the neurotoxicity. In this article, the use of CE for the separation of dynorphin A 1-17 from four of its metabolites is described. Buffer additives were investigated to eliminate peptide adsorption to the capillary wall and to improve resolution between closely related metabolites. On-capillary copper complexation was employed and was shown to improve separation efficiency as compared with the separation of native peptides. The method was then applied to in vitro dynorphin metabolism in human plasma as well as rat brain and rat spinal cord slices.

Optimization of native fluorescence detection of proteins using a pulsed nanolaser excitation source

We present a mathematical description of the signal-to-noise ratio (S/N) in a fluorescence-based protein detector for capillary electrophoresis that uses a pulsed ultraviolet (UV) laser at 266 nm as an excitation source. The model accounts for photobleaching, detector volume, laser repetition rate, and analyte flow rate. We have experimentally characterized such a system, and we present a comparison of the experimental data with the predictions of the model. Using the model, the system was optimized for test analytes tryptophan, tyrosine, bovine serum albumin (BSA), and conalbumin, producing detection limits (3σ) of 0.67 nM, 5.7 nM, 0.9 nM, and 1.5 nM, respectively. Based on the photobleaching data, a photobleaching cross-section of 1.4 × 10(-18)cm(2) at 266 nm was calculated for tryptophan.

Bioanalytical applications of capillary electrophoresis with laser-induced native fluorescence detection

In this article we describe recent developments and applications of capillary electrophoresis (CE) coupled with laser-induced native fluorescence (LINF) detection in the analysis of biological, pharmaceutical and environmental samples. Compared with traditional UV absorbance detection used in CE, the LINF technique can greatly improve the concentration sensitivity of CE without the need for derivatization; the only requirement being that the analyte must have native fluorescence. Instrumentation and laser sources used in CE–LINF are summarized and specific applications of CE–LINF to small-biomolecule analysis, profiling of human biofluids, detection of native fluorescent peptides and proteins, single-cell analysis and the use of online sample preconcentration methods are also reviewed in detail.