Analysis of biological samples by capillary electrophoresis with laser induced fluorescence detection

Nucleic acid degradation as barrier to gene delivery: a guide to understand and overcome nuclease activity

Gene therapy is on its way to revolutionize the treatment of both inherited and acquired diseases, by transferring nucleic acids to correct a disease-causing gene in the target cells of patients. In the fight against infectious diseases, mRNA-based therapeutics have proven to be a viable strategy in the recent Covid-19 pandemic. Although a growing number of gene therapies have been approved, the success rate is limited when compared to the large number of preclinical and clinical trials that have been/are being performed. In this review, we highlight some of the hurdles which gene therapies encounter after administration into the human body, with a focus on nucleic acid degradation by nucleases that are extremely abundant in mammalian organs, biological fluids as well as in subcellular compartments. We overview the available strategies to reduce the biodegradation of gene therapeutics after administration, including chemical modifications of the nucleic acids, encapsulation into vectors and co-administration with nuclease inhibitors and discuss which strategies are applied for clinically approved nucleic acid therapeutics. In the final part, we discuss the currently available methods and techniques to qualify and quantify the integrity of nucleic acids, with their own strengths and limitations.

Open flow cytometer with the combination of 3D hydrodynamic single cell focusing and confocal laser-induced fluorescence detection

Flow cytometry is among the most powerful tools for single-cell analysis, while the high cost and mechanical complexity of the commercial instrumentation limit the applications in personalized single-cell analysis. For this issue, we hereby construct an open and low-cost flow cytometer. It is highly compact to integrate the functions of (1) single cell aligning by a lab-made modularized 3D hydrodynamic focusing device, and (2) fluorescence detection of the single cells by a confocal laser-induced fluorescence (LIF) detector. The ceiling cost of the entire hardware for the LIF detection unit and 3D focusing device is $ 3200 and $ 400 respectively. A sheath flow velocity of 150 μL/min produces a focused sample stream of 17.6 μm × 14.6 μm at sample flow of 2 μL/min, based on the LIF response frequency and the laser beam spot diameter. The assay performance of the flow cytometer was evaluated by characterizing fluorescent microparticles and acridine orange (AO) stained HepG2 cells, producing throughputs of 40.5/s and 6.2/s respectively. Favorable assay precision and accuracy were demonstrated by the agreement of frequency histogram with imaging analysis, and good Gaussian-like distributions of fluorescent microparticles and AO-stained HepG2 cells. Practically, the flow cytometer was successfully applied for the evaluation of ROS generation in single HepG2 cells.

Solvent effect on the Spectra of Methylene Green and Methylene Blue

This investigation focuses on dyes that differ only in the nitro substituent. The NO₂ group leads to a strong hardening of the fluorescence at 298 K. In methylene green (MG) the excitation energy migrates to the system of triplet states. This non-radiative process causes the MG fuorescence absent or too low compared to methylene blue (MB). Moreover, laser-induced fluorescence is completely absent for MG in the investigated solvents. However, at liquid nitrogen temperature, we recorded fluorescence for MG in ethanol 250 times higher than at room temperature and phosphorescence too. The intensity of the MB fluorescence band in ethanol at 77 K is 6 times higher than at room temperature. According to the results of this study, the lifetime in the excited state decreases in the following order: isopropanol > acetonitrile≈ethanol≈dimethyl sulfoxide >  > water for MG and chloroform > acetonitrile≈ethanol≈dimethyl sulfoxide >  > water≈isopropanol for MB. In addition, MG has phosphorescence in ethanol at 780 nm (12,800 cm^-1) and in chloroform at 810 nm (12,300 cm^-1).

Sensitive analysis of doxorubicin and curcumin by micellar electromagnetic chromatography with a double wavelength excitation source

Doxorubicin has been extensively used to treat cancers, and there are recent findings that the anticancer activities can be enhanced by curcumin. Although the two compounds have native fluorescence, they can hardly be quantified directly simultaneously using the laser-induced fluorescence (LIF) detection method. To avoid complex fluorescence derivatization and introduction of interfering components, a highly sensitive double wavelength excitation source LIF (D-W-Ex-LIF) detector composed of a 445-nm and 488-nm commercial laser diode was constructed to detect them simultaneously. Rhodamine 6G was selected as an internal standard, because its fluorescence can be excited at 445 nm and 488 nm. The native fluorescence of doxorubicin and curcumin and their resolution were enhanced by introducing mixed micelles. The optimal electrophoretic separation buffer was 10 mM borate buffer containing 20 mM Triton X-100, 5 mM sodium dodecyl sulfate, and 30% (v/v) methanol at pH 9.00. Therefore, the developed method was specific, accurate, and easily operable. Its limits of detection for doxorubicin and curcumin in human urine samples were 4.00 × 10^-3 and 1.00 × 10^-2 μg/mL, respectively, and the limits of quantification were 1.00 × 10^-2 and 3.00 × 10^-2 μg/mL, respectively. The recoveries were 94.9-109.1%. Graphical abstract.

Dual aptamer assay for detection of Acinetobacter baumannii on an electromagnetically-driven microfluidic platform

Rapid detection of Acinetobacter baumannii (AB) is critical for limiting healthcare-associated infections and providing the best treatment for infected individuals. Herein an integrated microfluidic device for AB diagnosis utilizing a new dual aptamer assay was developed for point-of-care (POC) applications; magnetic beads coated with AB-specific aptamers were used to capture bacteria, and quantum dots (QD) bound to a second aptamer were utilized to quantify the amount of bacteria with a light-emitting diode (LED)-induced fluorescence module integrated into the device. Within a rapid detection of 30 min, a limit of detection of only 100 colony-forming units (CFU)/reaction was obtained, and all necessary microfluidic devices were actuated by a combination of permanent magnets and electromagnets. The pumping rate of the micropump was 270 μL/min at only 10 V, which is amenable for POC applications with lower power consumption, and only 10 μL of sample and reagents were required. Given these attributes, an automatic POC device was demonstrated which could perform a dual aptamer assay to diagnose AB by using electromagnetically-driven microfluidic system. This system provides a rapid, sensitive, low power and reagents consumption and fully automated for AB detection by using a dual aptamer assay. It will allow rapid clinical diagnosis of AB in the near future.

Polypyrrole-Modified Nylon 6 Nanofibers as Adsorbent for the Extraction of Two β-Lactam Antibiotics in Water Followed by Determination with Capillary Electrophoresis

A solid phase membrane adsorbent—a nylon 6 nanofibers membrane coated by polypyrrole (PPy-PA6-NFsM)—was firstly synthesized and used for extraction of two β-lactam antibiotics (oxacillin and cloxacillin) in urban river water. Then the analytes were detected by capillary electrophoresis with a diode array detector (CE-DAD). The synthesized nanofibers membrane was characterized by scanning electron microscopy and a Fourier transform infrared spectrometer. The experimental conditions were optimized, including the amount used of PPy-PA6-NFsM, pH of the sample solutions, adsorption volume, and desorption conditions. Under the optimal extraction and separation conditions, the detection limits were found to be 2.0 ng/mL for both oxacillin and cloxacillin. The proposed method was applied to the determination of the two β-lactams in water samples of an urban river. The recoveries of these two β-lactams were found to be in the range 84.2–96.4%, demonstrating that PPy-PA6-NFsM has a high extraction capability for these two antibiotics. The relative standard deviations, ranging from 2.26% to 5.29% for intraday measurements and from 2.38% to 7.02% for inter-day determinations, were derived respectively.

Measuring Kinase Activity-A Global Challenge

The kinase enzymes within a cell, known collectively as the kinome, play crucial roles in many signaling pathways, including survival, motility, differentiation, stress response, and many more. Aberrant signaling through kinase pathways is often linked to cancer, among other diseases. A major area of scientific research involves understanding the relationships between kinases, their targets, and how the kinome adapts to perturbations of the cellular system. This review will discuss many of the current and developing methods for studying kinase activity, and evaluate their applications, advantages, and disadvantages. J. Cell. Biochem. 118: 3595-3606, 2017. © 2017 Wiley Periodicals, Inc.

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.

An update of the classical and novel methods used for measuring fast neurotransmitters during normal and brain altered function

To understand better the cerebral functions, several methods have been developed to study the brain activity, they could be related with morphological, electrophysiological, molecular and neurochemical techniques. Monitoring neurotransmitter concentration is a key role to know better how the brain works during normal or pathological conditions, as well as for studying the changes in neurotransmitter concentration with the use of several drugs that could affect or reestablish the normal brain activity. Immediate response of the brain to environmental conditions is related with the release of the fast acting neurotransmission by glutamate (Glu), γ-aminobutyric acid (GABA) and acetylcholine (ACh) through the opening of ligand-operated ion channels. Neurotransmitter release is mainly determined by the classical microdialysis technique, this is generally coupled to high performance liquid chromatography (HPLC). Detection of neurotransmitters can be done by fluorescence, optical density, electrochemistry or other detection systems more sophisticated. Although the microdialysis method is the golden technique to monitor the brain neurotransmitters, it has a poor temporal resolution. Recently, with the use of biosensor the drawback of temporal resolution has been improved considerably, however other inconveniences have merged, such as stability, reproducibility and the lack of reliable biosensors mainly for GABA. The aim of this review is to show the important advances in the different ways to measure neurotransmitter concentrations; both with the use of classic techniques as well as with the novel methods and alternant approaches to improve the temporal resolution.

Synthesis and Anticancer Properties of Silver(I) Complexes Containing 2,6-Bis(substituted)pyridine Derivatives

Several new 2,6-bis(substituted)pyridine ligands and 2,6-bis(substituted)pyridine Ag(I) nitrate complexes were synthesized and characterized spectroscopically. The newly synthesized ligands include pyridine-2,6-bis(3-oxopropanenitrile) (1), pyridine-2,6-bis(2-cyano-N-phenyl-3-oxopropanethioamide) (2), and pyridine-2,6-bis((E)-2-(2-phenylhydrazono)-3-oxopropanenitrile) (3). The newly synthesized ligands and silver(I) complexes were evaluated for their in vitro anticancer activity against four human cancer cell lines including hepatocellular carcinoma (HePG2), lung adenocarcinoma (A549), colon carcinoma (HT29), and breast adenocarcinoma (MCF7). Most of the newly synthesized silver(I) complexes exhibited better activity than the ligands, and the results have been compared with doxorubicin as a reference drug.

Chiral analysis of amino acid neurotransmitters and neuromodulators in mouse brain by CE-LIF

Chiral CE method has been developed for quantitative determination of d-amino acid modulators of NMDA glutamate receptor; d-serine and d-aspartate along with l-glutamate and l-aspartate in biological samples. These ligands are suggested to be involved in regulation of NMDA receptor related brain functions, such as neurogenesis, neuronal plasticity, and memory formation. For sensitive determination of the amino acids LIF detection was chosen, and a fluorogenic reagent, 7-fluoro-4-nitro-2,1,3-benzoxadiazole was used for derivatization. An amino-modified β-CD, 6-monodeoxy-6-mono(3-hydroxy)propylamino-β-CD (HPA-β-CD) was applied as chiral selector. Determinations were accomplished in a polyacrylamide coated capillary and reverse polarity was used for the analysis of the negatively charged analytes. The method was optimized and validated; 6 mM HPA-β-CD in 50 mM HEPES buffer, pH 7 was appropriate to achieve baseline separation of the analytes. The limit of quantification with acceptable accuracy is 0.05 μM for both d-amino acids. The method was used for the determination of d-aspartate and d-serine content in various brain regions of adult mice.

The application of capillary electrophoresis techniques in toxicological analysis

Capillary electrophoresis (CE) comprises a group of techniques used to separate chemical mixtures. Analytical separation is based on different electrophoretic mobilities, thereby allowing qualitative and quantitative evaluations to be made. The application of CE in medical science, especially in toxicological studies, is developing rapidly because of the short time required for analysis and its high sensitivity, selectivity and ability to determine substances of an acidic, alkaline and neutral character. This review focuses on the possibility of applying CE in toxicological analysis. Advances in different CE analyses and detection techniques connected with this method are described.

Quantification of serotonin O-sulphate by LC-MS method in plasma of healthy volunteers

The objective of this study was to test the hypothesis that serotonin O-sulphate (5-HT-SO4) could be quantified in human plasma using modern liquid chromatography–mass spectrometry (LC-MS) method as well as develop and validate that method. First, a suitable LC-MS method for detection of 5-HT-SO4 in human plasma samples was developed and validated. Second, a Pilot phase involving four healthy volunteers was executed, where a basal plasma level of 5-HT-SO4 was measured for all subjects and for one after the intake of 100 mg of a 5-hydroxytryptophan (5-HTP) -containing food supplement used to promote serotonergic stimulation of the central nervous system. The basal level of 0.9–2.8 ng/mL of 5-HT-SO4 was observed. The changes of plasma 5HT-O-SO4 showed 1.2 ng/mL before and 22.6 ng/mL 1 h after stimulation. Finally, nine healthy volunteers were selected for the Study phase, where a basal plasma level of 5-HT-SO4 was measured before and after the intake of 5-HTP. One hour after stimulation, six study subjects showed a decrease in 5-HT-SO4 levels while three subjects showed an increase. The changes of plasma 5HT-O-SO4 from the Study phase showed an average 5-HT-SO4 level of 19.2 ng/mL before and 15.7 ng/mL 1 h after stimulation indicating ability of method to emphasize quantitative changes. This was the first study in which naturally occurring 5-HT-SO4 was detected in the samples of human plasma obtained from healthy volunteers. The method developed herein is specific to the measurement of 5-HT-SO4, sensitive enough to quantify intra-individual changes in the samples of plasma and opens up new possibilities to evaluate pathways of serotonin metabolism by minimally invasive methods. The discovery of novel biomarkers using such approaches is increasingly required to expedite development of mechanism-based therapeutics and patient stratification.

Small-volume analysis of cell-cell signaling molecules in the brain

Modern science is characterized by integration and synergy between research fields. Accordingly, as technological advances allow new and more ambitious quests in scientific inquiry, numerous analytical and engineering techniques have become useful tools in biological research. The focus of this review is on cutting edge technologies that aid direct measurement of bioactive compounds in the nervous system to facilitate fundamental research, diagnostics, and drug discovery. We discuss challenges associated with measurement of cell-to-cell signaling molecules in the nervous system, and advocate for a decrease of sample volumes to the nanoliter volume regimen for improved analysis outcomes. We highlight effective approaches for the collection, separation, and detection of such small-volume samples, present strategies for targeted and discovery-oriented research, and describe the required technology advances that will empower future translational science.

Simultaneous determination of polyamines and acetylpolyamines in human urine by capillary electrophoresis with fluorescence detection

There has been evidence linking elevated polyamines (PAs) and acetylpolamines (AcPAs) level and cancer. So the simultaneous analysis of these compounds has become important task for cancer diagnosis and antitumor drug monitoring. A simple, fast and inexpensive CZE-LIF method has been developed for the determination of cadaverine (CAD), putrescine (PUT), spermine (SPM), spermidine (SPD), acetylspermine (ASPM), and acetylspermidine (ASPD) in human urine using 4-chloro-7-nitro-2,1,3-benzooxadiazole as a fluorescent reagent. Labeling reaction conditions were systematically investigated and were found to be 20 mM borate buffer at pH 7.4, labeling reaction time, and temperature were 10 min and 70°C, respectively. Under these optimized conditions the four PAs, two AcPAs and the internal standard were separated in 6 min. An Exactive-MS with an ESI source was used for identification of the bis-derivative of the ASPM. The method was validated in term of linearity, LODs, repeatability, intra- and interday assays, recovery, and selectivity. The LODs for CAD, PUT, SPM, SPD, ASPM, and ASPD were found to be 7.6, 10.0, 9.0, 8.8,7.8, and 3.3 nM, respectively. The method was successfully applied for the analysis of PAs and AcPAs in healthy human urine samples.

Simultaneous determination of amino acids in tea leaves by micellar electrokinetic chromatography with laser-induced fluorescence detection

A rapid and effective method of micellar electrokinetic chromatography with laser-induced fluorescence detection was developed for the simultaneous determination of amino acids in tea leaves. Pre-column derivatization of the analytes used 4-chloro-7-nitrobenzofurazan (NDB-Cl). Optimal separation was achieved at +20kV using an uncoated fused silica capillary (40.0cm effective length, 50.2cm total length, 75μm internal diameter), as well as 20mM sodium borate (pH 8.5), 20mM Brij 35, and acetonitrile 10% (v/v) as running buffers. Within 11min, 15 amino acids were separated completely. The optimized method demonstrated good linearity (r(2)⩾0.9990), precision (⩽6.65%), accuracy (85.50-112.74%), and sensitivity (0.1ng/mL-100ng/mL). The method successfully determined the quantity of amino acids in five different tea leaves; furthermore, theanine was identified as the most abundant amino acid in teas. The proposed method showed great potential in further investigations on the biofunctions of different tea samples.

Optimization and validation of a capillary electrophoresis laser-induced fluorescence method for amino acids determination in human plasma: application to bipolar disorder study

Quantitative and qualitative analysis of amino acids in biofluids offers relevant information in diagnosis of diseases, evaluation of nutritional state, and in elucidating metabolic influences on physiology. A simple, rapid, and robust procedure in terms of sample treatment, separation, and quantitation based on CE-LIF has been optimized for use in human plasma samples. Time required for derivatization was 15 min and analysis time was 35 min. 4-Fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) was the labeling agent used for obtaining fluorescent derivatives. Electrophoretic conditions were: 175 mM borate buffer at pH 10.25 prepared with 12.5 mM β-cyclodextrin. The voltage applied was +21 kV. Fourteen amino acids could be quantified: L-proline, L-phenylalanine, L-leucine, L-isoleucine, L-ornithine, D-ornithine, L-glutamine, L-alanine, L-threonine, glycine, L-serine, D-serine, taurine and L-glutamate. With this chiral CE-LIF method, L- and D-amino acids are adequately separated. The method was validated for a representative group of amino acids in human plasma: L-proline, L-isoleucine, L-ornithine, L-glutamine, L-alanine L-threonine, glycine, L-serine, D-serine, and glutamate. The method has been successfully applied to human plasma from patients with bipolar disorder, all of whom were taking lithium as a mood stabilizer. Eleven amino acids were quantified in plasma from nine patients, aged 24-55 years. The results were in accordance to published values for the bipolar patients. The method is useful particularly in studies where plasma amino acid levels can be used as biomarkers for diagnosis of diseases, evaluating the disease progression, and monitoring response to drug therapy.

Contribution of CE to the analysis of protein or peptide biomarkers

Biomarker analysis is pivotal for disease diagnosis and one important class of biomarkers is constituted by proteins and peptides. This review focuses on protein and peptide analyses from biological fluids performed by capillary electrophoresis. The various strategies that have been reported to prevent difficulties due to the handling of real samples are described. Innovative techniques to overcome the complexity of the sample, to prevent the adsorption of the analytes on the inner capillary wall, and to increase the sensibility of the analysis are summarized and illustrated by different applications. To fully illustrate the contribution of CE to the analysis of biomarkers from human sample, two detailed protocols are given: the analysis from CSF of five amyloid peptide, biomarkers of the Alzheimer disease, and the analysis of sialoforms of transferrin from human serum.

Screening of matrix metalloproteinase inhibitors by microanalysis with fluorescence detection

Capillary electrophoresis has emerged as a small-scale analytical tool for enzyme assays. It is not only used to analyze and follow-up enzymatic reactions in an offline mode, but the reaction can also be performed online, inside the capillary, where the reaction products are formed and analyzed. In this way, an integrated setup is obtained which allows a higher degree of automation and miniaturization in analytical systems. This chapter presents an electrophoretically mediated microanalysis for in vitro characterization and screening of matrix metalloproteinase inhibitors.

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.

Chiral separation and determination of excitatory amino acids in brain samples by CE-LIF using dual cyclodextrin system

Chiral capillary electrophoresis method has been developed to separate aspartate and glutamate enantiomers to investigate the putative neuromodulator function of D-Asp in the central nervous system. To achieve appropriate detection sensitivity fluorescent derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiazole and laser-induced fluorescence detection was applied. Although, simultaneous baseline separation of the two enantiomer pairs could be achieved by using 3 mM 6-monodeoxy-6-mono(3-hydroxy)propylamino-β-cyclodextrin (HPA-β-CD), further improvement of the chemical selectivity was required because of the high excess of L-enantiomers in real samples to be analyzed. The system selectivity was fine-tuned by combination of 8 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin and 5 mM HPA-β-CD in order to increase the resolution between aspartate and glutamate enantiomers. The method was validated for biological application. The limits of detection for D-Asp and D-Glu were 17 and 9 nM, respectively, while the limit of quantification for both analytes was 50 nM. This is the lowest quantification limit reported so far for NBD-tagged D-Asp and D-Glu obtained by validated capillary electrophoresis laser-induced fluorescence method. The applicability of the method was demonstrated by analyzing brain samples of 1-day-old chickens. In all the studied brain areas, the D-enantiomer contributed 1-2 % of the total aspartate content, corresponding to 17-45 nmol/g wet tissue.

High-throughput flow injection analysis of labeled peptides in cellular samples - ICP-MS analysis versus fluorescence based detection

A high throughput method based on flow injection analysis was developed and validated for the quantification of the peptide Bβ(15-42) in cellular samples comparing different labeling strategies and detection methods. The used labels were 1,4,7,10-tetraazacyclododecane-N, N', N'', N'''-tetraaceticacid (In-DOTA) and 2-(4-isothiocyanatobenzyl) - 1,4,7,10-tetraazacyclododecane-N, N', N'', N'''-tetraacetic acid (In-DOTA-Bn) for elemental labeling. 6-Hydroxy-9-(2-carboxyphenyl)- (3H)-xanthen-3-on (fluorescein) was employed as fluorescence label. The explored peptide (mass = 3 kD) is a novel candidate drug, which shows an anti-inflammatory effect after an event of myocardial infarction. The analysed samples were fractioned cell compartments of human umbilical cord vein endothelial cells (HUVEC) maintained via lysis with Triton X buffer. In order to enhance sensitivity and selectivity of peptide quantification via flow injection the peptide was labeled prior to incubation using elemental and fluorescence labels. Quantification of the elemental and fluorescence labeled peptide was performed via flow injection analysis combined with inductive coupled plasma sector field mass spectrometry (FIA-ICP-SFMS) or fluorescence detection (FIA-FLD), respectively. The employed quantification strategies were external calibration in the case of fluorescence detection and external calibration with and without internal standardization and on-line IDMS in the case of ICP-MS detectionThe limit of detection (LOD) for FIA-ICP-MS was 9 pM In-DOTA-Bβ(15-42) (0.05 fmol absolute) whereas FIA-FLD showed a LOD of 100 pM (3 fmol absolute) for the fluorescein labeled peptide. Short term precision of FIA-ICP-MS was superior for all ICP-MS based quantification strategies compared to FIA-FLD (FIA-ICP-SFMS: 0.3-3.3%; FIA-FLD: 6.5%). Concerning long term precision FIA-ICP-SFMS with on-line IDMS and internal standardization showed the best results (3.1 and 4.6%, respectively) whereas the external calibration of both applied methodological approaches was only in the range of 10 %.The concentrations in the Triton X soluble fraction relative to the applied amount of Indium in the cell culture were in the range of 0.75-1.8% for In-DOTA or 0.30-0.79% for the 2-(4-isothiocyanatobenzyl) - 1,4,7,10-tetraazacyclododecane-N, N', N'', N'''-tetraacetic acid (In-DOTA-Bn) labeled peptide Bβ(15-42). In the Triton X insoluble fraction the relative concentrations of Indium were 0.03-0.18% for the In-DOTA labeled peptide and 0.03-0.13% for Bβ(15-42)-In-DOTA-Bn.