LED-induced Fluorescence Research Articles

A novel label-free capillary electrophoresis LED-induced fluorescence platform based on catalytic hairpin assembly for sensitive detection of multiple circulating tumor DNA.

Circulating tumor DNA (ctDNA) is a highly promising biomarker for the early diagnosis and treatment of gastric cancer (GC). However, there is still a lack of effective and practical ctDNA detection methods. In this work, a simple and economical capillary non-gel sieving electrophoresis-LED induced fluorescence detection (NGCE-LEDIF) platform coupled with catalytic hairpin assembly (CHA) as the signal amplification strategy is proposed for quantitative detection of PIK3CA E542K and TP53 (two types of ctDNA associated with GC). We have reasonably designed two pairs of programmable oligonucleotide hairpin probes for PIK3CA E542K and TP53. Using a one-pot reaction, the presence of ctDNA triggers the cyclic amplification of CHA, forming numerous thermodynamically stable H1/H2 double-strands. The H1/H2 double-stranded DNA catalyzed by PIK3CA E542K and TP53 can be easily separated by NGCE due to their different lengths, enabling simultaneous detection of both ctDNAs. Under optimal experimental conditions, the detection limits of this strategy for detecting GC-related biomarkers PIK3CA E542K and TP53 are 20.35 pM and 19.61 pM, respectively, and can achieve 730-fold signal amplification. This strategy has a good recovery in the serum matrix. The results of this study show that this strategy has significant advantages such as high selectivity, a simple process, no special instruments and equipment, no need for fluorescence modification of hairpin probes in advance, high automation, low cost, and minimal sample consumption. This provides a powerful method for the detection of trace cancer biomarkers in the serum matrix with good application prospects.

Predicting piperine content in javanese long pepper using fluorescence imaging and machine learning model

The conventional method for determining piperine content involves a series of labor-intensive steps, including drying the pepper samples, grinding them, and then extracting them using high-grade ethanol through a reflux method. While effective, this process is time-consuming and resource-intensive, posing limitations in terms of efficiency and the ability to address potential variations. Therefore, there is an urgent need to explore more efficient and rapid approaches for accurately measuring and predicting piperine content, with machine learning approach. This research aims to explore the potential of using fluorescence imaging methods and ANN models to increase the efficiency of measuring piperine content on Javanese long pepper. We propose a machine learning approach using UV-induced fluorescence imaging of Javanese long pepper. UV LEDs (365 nm) induced fluorescence, with color variation indicating piperine content. An artificial neural network (ANN) model, trained on color texture features from fluorescence images, predicted piperine content, achieving an R2 value of 0.88025 with ten selected features using the One-R attribute. The final ANN, configured with 'trainoss' learning, 'tansig' activation, 0.1 learning rate, and 10-40-10 nodes, demonstrated a testing R2 of 0.8943 and MSE of 0.0875. LED-induced fluorescence enhances machine learning's piperine content prediction. This research contributes to more efficient piperine content measurement methods.

Dual optical detection approach for capillary electrophoresis following two-step liquid-liquid extraction to determine ten phenols in water samples

In this research, the analytical method was developed and evaluated for determining phenol and its nine derivatives belong to the US EPA priority pollutant list in water samples by using dual-channeled capillary electrophoresis (CE) coupled with two types of optical detectors, namely LED-induced fluorescence (LEDIF) and ultraviolet (UV) detectors. The optimal background electrolytes for the first and second CE channels were 20 mM borate (pH 9.80) with 400 µM fluorescein and 55 mM borate (pH 11.75), respectively. The two-step liquid-liquid extraction (LLE) was used for sample preparation and enrichment, in which phenol and its derivatives were extracted from the aqueous phase using 10 mL of n-hexane/1-octanol (60/40, v/v) and then were back extracted into a 0.1 M NaOH as a final acceptor phase. Under the optimal CE and two-step LLE conditions, the enrichment factors of 10 phenols were 184 – 1120-fold, and the method detection limits were lowered to 0.02–0.60 µg/L. The obtained intra-day and inter-day precisions in terms of relative standard deviations (RSD) were between 4.0 and 7.3 % and 6.7 and 14 %, respectively. This approach was used to determine phenols in water samples, with recoveries ranging from 82.0 to 108.9 %. In combination with sample enrichment by two-step LLE extraction, this is the first CE study conducted to determine phenols in the EPA list using two detector approaches, specifically CE-LEDIF/CE-UV.

High-speed measurement of thickness of a water film formed by a jet obliquely impinging onto a plate using an LED-induced fluorescence method

A transient thickness distribution measured with a high temporal resolution is elemental for exploring the flow characteristics and mechanism of a liquid film formed by an impinging jet. Therefore, this paper develops a high-speed Light-Emitting Diode-Induced Fluorescence (LEDIF) system based on the brightness measured directly above the liquid film. An Ultraviolet (UV) LED lamp is used to provide sufficient and continuous excitation light. Then, a system performance analysis proves that the system can continuously measure the global film thickness at a high acquisition frequency of 5000 Hz when the dye concentration is 200 mg/L. The influence of the irregularity of the excitation intensity, including the spatial non-uniformity, temporal instability, and long-term instability, on the measurement uncertainty is analyzed in detail. The analysis indicates that the system has an acceptable uncertainty of 10%. Compared with theoretical results, experimental results verify that the LEDIF system can accurately measure the global thickness of a liquid film formed by a water jet obliquely impinging onto a plate. An experimental investigation of the radial section of the raised zone demonstrates that the radial section changes from a sewing needle to an oval when the azimuth angle increases from 10° to 90°. Meanwhile, the dynamic contact angle exponentially decreases from 41.4° to 30.1°. A dynamic analysis of surface waves shows that the measured wave velocity decreases from 12 m/s to 1 m/s and the dominant frequency decreases from 1000 Hz to 10 Hz along the flow direction.

Toward commercial applications of LED and laser-induced fluorescence techniques for food identity, quality, and safety monitoring: A review.

The assessment of food safety and quality is a matter of paramount importance, especially considering the challenges posed by climate change. Convenient, eco-friendly, and non-destructive techniques have attracted extensive attention in the food industry because they can retain food safety and quality. Fluorescence radiation, the process by which fluorophore emits light upon the absorption of ultraviolet or visible light, offers the advantages of high sensitivity and selectivity. The use of excitation-emission matrix (EEM) has been extensively explored in the food industry, but on-site detection of EEMs remain a challenge. To address this limitation, laser-induced fluorescence (LIF) and light emitting diode-induced fluorescence (LED-IF) have been implemented in many cases to facilitate the transition of fluorescence measurements from the laboratory to commercial applications. This review provides an overview of the application of commercially available LIF/LED-IF devices for non-destructive food measurement and recent studies that focus on the development of LIF/LED-IF devices for commercial applications. These studies were categorized into two stages: the preliminary exploration stage, which emphasizes the selection of an appropriate excitation wavelength based on the combination of EEM and chemometrics, and the pre-application stage, where experiments were conducted on scouting with specific excitation wavelength. Although commercially available devices have emerged in many research fields, only a limited number have been reported for use in the food industry. Future studies should focus on enhancing the diversity of test samples and parameters that can be measured by a single device, exploring the application of LIF techniques for detecting low-concentration substances in food, investigating more quantitative approaches, and developing embedded computing devices.

Capillary Zone Electrophoresis with Light-Emitting Diode-Induced Fluorescence Detection for the Analysis of Monoclonal Antibodies: Detector Optimization through Design of Experiments and Comparison to UV Detection

Capillary zone electrophoresis (CZE) is an important technique for the analysis of monoclonal antibodies (mAbs). A recently released light-emitting diode (LED)-induced fluorescence (LEDIF) detector equipped with a 275 nm LED for the detection of proteins through their native fluorescence was used in this study and compared to results obtained using the predominant detection mode, the measurement of the absorption of ultraviolet light (UV detection). This was accomplished using an established CZE method for the analysis of three mAbs: NISTmAb, matuzumab, and Intact Mass Check Standard (Waters). For this purpose, the detector’s settings were first optimized using a design of experiments approach. Three factors, rise time, photomultiplier high voltage supply, and acquisition frequency, were optimized by means of a D-optimal design. The optimal settings were then used for the investigation of signal-to-noise ratios (S/Ns), linearity, and precision. LEDIF detection offered a similar separation quality, up to 12 times higher S/Ns, and lower limits of detection compared to UV detection. Repeatability was excellent, with relative standard deviations (RSDs) of approximately 1% for percentage areas. For intermediate precision, RSDs of <2% (n = 3 × 10) were typically achieved. Overall, LEDIF detection was found to be an excellent and easily optimizable alternative to UV detection.

Extensible LED-Induced Integrated Fluorescence Detection Module for Quantitative Analysis of Lucigenin Concentration

We developed an extensible LED-induced fluorescence detection module with a highly integrated and ultra-compact structure. A target-oriented design methodology was used to demonstrate the module’s optimal design. Lucigenin solution was used as a test sample in evaluation trials to demonstrate the module’s quantitative fluorescence detection capability. Results showed that the integrated module has an outstanding linear response in the range of 0–1 μmol·L−1, with sensitivity and limit of detection (LOD) of 0.1692 V/μmol·L−1 and 0.03 μmol·L−1, respectively. Statistical analyses showed that our integrated module has extremely high repeatability and accuracy, i.e., the values of Pearson’s correlation coefficient and root-mean-square error exceeded 0.9995 and 1.8‰, respectively. More importantly, the integrated module possesses favorable extensibility and can realize on-demand rapid fluorescence-signal detection of other targets using appropriate parameter combinations. This module offers new opportunities for reliable, cost-effective and easy-to-use fluorescence-signal detection, especially in resource-constrained fluorescence detection applications.

Analysis of Sugars in Honey Samples by Capillary Zone Electrophoresis Using Fluorescence Detection

The applicability of capillary electrophoresis (CE) with light-emitting diode-induced fluorescence detection (LEDIF) for the separation of sugars in honey samples was studied. An amount of 25 mM ammonium acetate (pH 4.5) with 0.3% polyethylene oxide (PEO) was found to be optimal for the efficient separation of carbohydrates. 8-aminopyrene-1,3,6-trisulfonic acid (APTS) was used for the labeling of the carbohydrate standards and honey sugars for fluorescence detection. The optimized method was applied in the quantitative analysis of fructose and glucose by direct injection of honey samples. Apart from the labeling reaction, no other sample preparation was performed. The mean values of the fructose/glucose ratio for phacelia honey, acacia honey and honeydew honey were 0.86, 1.61 and 1.42, respectively. The proposed method provides high separation efficiency and sensitive detection within a short analysis time. Apart from the labeling reaction, it enables the injection of honeys without sample pretreatment. This is the first time that fluorescence detection has been applied for the CE analysis of sugars in honeys.

Protein profile analysis of tear fluid with hyphenated HPLC-UV LED-induced fluorescence detection for the diagnosis of dry eye syndrome.

Tear fluid contains organic and inorganic constituents, variations in their relative concentrations could provide valuable information and can be useful for the detection of several ophthalmological diseases. This report describes the application of the lab-assembled light-emitting diode (LED)-based high-performance liquid chromatography system for protein profiling of tear fluids to diagnose dry eye disease. Principal Component Analysis (PCA), match/no-match, and Artificial Neural Network (ANN) based binary classification of protein profile data were performed for disease diagnosis. Results from the match/no-match test of the protein profile data showed 94.4% sensitivity and 87.8% specificity. ANN with the leaving one out procedure has given 91.6% sensitivity and 93.9% specificity.

Development of a methodology for the characterisation and assessment of biodeteriogens on archaeological surfaces by use of a portable LED-induced fluorescence instrument

The present study focuses on the development of a fast, non-invasive methodology, appropriate for the detection and characterization of biodeterioration present on the surface of archaeological/historical stone objects and monuments, by exploiting the characteristic fluorescence emission of biological deposits. Fluorescence spectra were collected by use of a portable LED (Light Emitting Diode)-Induced Fluorescence (LED-IF) instrument. Three limestone fragments and one mortar fragment, from different monuments in Greece, presenting various types of biodeterioration on their surface, have been investigated in the laboratory. First, fluorescence emission spectra were acquired with a benchtop laboratory spectrofluorometer in order to select the optimum excitation wavelengths for the fluorophores present in the biological crust. An evaluation of the portable LED-IF instrument was conducted by assessing the performance of its optical components and different LED excitation sources, while an investigation of several experimental parameters on the fluorescence signal was also performed. Furthermore, issues related to the efficiency of detection and identification of biological growth have been studied, such as the effect of sample surface wetting on the fluorescence signal. The results of the present study demonstrate that the LED-IF instrument can be used for a fast and reliable assessment of the presence of biodeterioration on monuments.

Taylor dispersion analysis discloses the impairment of Aβ peptide aggregation by the presence of a fluorescent tag.

The use of fluorescently tagged amyloid peptides, implicated in Alzheimer's disease, to study their aggregation at low concentrations is a common method; however, the fluorescent tag should not introduce a bias in the aggregation process. In this work, native amyloid peptides Aβ(1-40) and Aβ(1-42) and fluorescein-5-isothiocyanate (FITC), tagged ones, were studied using Taylor dispersion analysis coupled with a simultaneous UV and light-emitting diode-induced fluorescence detection, to unravel the effect of FITC on the aggregation process. For that, a total concentration of 100µM of peptides consisting of a mixture of native and tagged ones (up to 10% in moles) was applied. Results demonstrated that FITC had a strong inhibition effect upon the aggregation behaviour of Aβ(1-42), whereas for Aβ(1-40), only a retardation in kinetics was observed. It was also shown that when mixed solutions of Aβ(1-40) and Aβ(1-42) are used, the Aβ(1-42) alloform was the leading peptide in the aggregation process, and when the latter was tagged, the aggregation kinetics decreased but the lifetime of potentially toxic oligomers was drastically increased. These results confirmed that the hydrophilicity of the N-terminus part of the peptide plays a major role in the aggregation process.

Predicting ASTA color values of peppers via LED-induced fluorescence

American Spice Trade Association (ASTA) color value is a key factor for determining the commercial value of red pepper. This study investigates the potential of predicting ASTA color values of red pepper using LED-induced fluorescence. Excitation emission matrixes (EEMs) were first obtained in a front-face configuration. To determine the excitation wavelengths for LED-induced fluorescence measurement, parallel factor analysis (PARAFAC) combined with EEMs were used. According to PARAFAC, 375 nm was selected be the peak wavelength of the excitation light source of the LED-induced fluorescence system. The spectra obtained from the system were used to predict ASTA color values using partial least squares regression (PLSR) and support vector machine (SVM). With optimal preprocessing method, the highest correlation coefficients of prediction ( R p ) could reach 0.971 with RMSEP of 3.672, RPD of 3.563 and REP of 6.170. Results revealed that LED-induced fluorescence has the potential for rapid prediction of ASTA color values of red peppers. • LED-induced fluorescence was used for the first time to predict ASTA color values. • PARAFAC model was established to retrieve pure fluorophores in EEMs. • Excitation light source wavelength was selected based on the result of PARAFAC. • PLSR and SVM models were built using the LED-induced fluorescence spectra. • Models exhibited good predictive performance on the ASTA color values.

Classification of Tea Leaves Based on Fluorescence Imaging and Convolutional Neural Networks.

The development of the smartphone and computer vision technique provides customers with a convenient approach to identify tea species, as well as qualities. However, the prediction model may not behave robustly due to changes in illumination conditions. Fluorescence imaging can induce the fluorescence signal from typical components, and thus may improve the prediction accuracy. In this paper, a tea classification method based on fluorescence imaging and convolutional neural networks (CNN) is proposed. Ultra-violet (UV) LEDs with a central wavelength of 370 nm were utilized to induce the fluorescence of tea samples so that the fluorescence images could be captured. Five kinds of tea were included and pre-processed. Two CNN-based classification models, e.g., the VGG16 and ResNet-34, were utilized for model training. Images captured under the conventional fluorescent lamp were also tested for comparison. The results show that the accuracy of the classification model based on fluorescence images is better than those based on the white-light illumination images, and the performance of the VGG16 model is better than the ResNet-34 model in our case. The classification accuracy of fluorescence images reached 97.5%, which proves that the LED-induced fluorescence imaging technique is promising to use in our daily life.

Initial Deployment of a Mobile Sensing System for Water Quality in Urban Canals

Although water quality has extensively improved over the last decade, recreational uses of the canal network in Amsterdam are limited by variations in water quality associated with stormwater runoff and episodic harmful algal blooms. The current systems for monitoring water quality are based on a stationary network of sampling points, offline testing methods, and online measurements of conventional water quality parameters on board a boat that continuously navigates the urban canal network. Here we describe the development and deployment of online algal sensors on board the boat, including a prototype LED-induced fluorescence instrument for algal identification and quantification. We demonstrate that by using only a single patrol vessel, we are able to achieve enough sampling coverage to observe spatiotemporal heterogeneity of algal and chemical water quality within the canal network. The data provide encouraging evidence that opportunistic measurements from a small number of mobile platforms can enable high-resolution mapping and can be used to improve the monitoring of water quality across the city compared to the current network of fixed sampling locations. We also discuss the challenges of operating water quality sensors for long-term autonomous monitoring.

Assessment of bioaccumulation of glyphosate and aminomethylphosphonic acid in marine mussels using capillary electrophoresis with light‐emitting diode‐induced fluorescence detection

Glyphosate or N-(phosphonomethyl)glycine, widely used as herbicide in agriculture to control weeds and to facilitate harvesting, has been included in Group 2A pollutants (probably carcinogenic to humans) by the International Agency for Research on Cancer (IARC). In intensive agricultural areas, runoff and soil leaching are likely to drive glyphosate to surface waters, where the compound is often detected together with its main microbial metabolite, aminomethylphosphonic acid (AMPA).In the present study a method based on capillary electrophoresis coupled with light-emitting diode-induced fluorescence detection has been developed and validated for the determination of the two compounds in whole soft mass of marine mussels (Mytilus galloprovincialis). The method is based on the acidic hydrolysis of lyophilized tissue using 6 M HCl (oven at 110 °C for 22 h) to release the target analytes; their subsequent derivatization using 4-fluoro-7-nitro-2,1,3-benzoxadiazole, was found to be suitable for the sensitive fluorescence detection. To achieve optimum separation of the analytes from the matrix and degradation reagent interferences, the background electrolyte constituted by borate buffer (pH 9.2, 30 mM) was supplemented with 10 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin. The method was validated for linearity, precision, accuracy, robustness and sensitivity showing LOQ of 0.2 and 1.0 µg/g in fresh tissues, for AMPA and glyphosate, respectively; the recovery values ranged within 88.5 – 94.6% for glyphosate and 70.4 – 76.6% for AMPA. Experimental samples of Mediterranean mussels M. galloprovincialis treated with 100 µg/L or 500 µg/L of both glyphosate and AMPA, showed a dose dependent bioaccumulation of the compounds reaching maximum level of 77.0 µg/g and 11.3 µg/g of AMPA and glyphosate, respectively. The study demonstrates for the first time M. galloprovincialis as potential sentinel organisms for the environmental occurrence of these small amphoteric pollutants.

Quantitative Detection of Extra Virgin Olive Oil Adulteration, as Opposed to Peanut and Soybean Oil, Employing LED-Induced Fluorescence Spectroscopy.

As it is high in value, extra virgin olive oil (EVOO) is frequently blended with inferior vegetable oils. This study presents an optical method for determining the adulteration level of EVOO with soybean oil as well as peanut oil using LED-induced fluorescence spectroscopy. Eight LEDs with central wavelengths from ultra-violet (UV) to blue are tested to induce the fluorescence spectra of EVOO, peanut oil, and soybean oil, and the UV LED of 372 nm is selected for further detection. Samples are prepared by mixing olive oil with different volume fractions of peanut or soybean oil, and their fluorescence spectra are collected. Different pre-processing and regression methods are utilized to build the prediction model, and good linearity is obtained between the predicted and actual adulteration concentration. This result, accompanied by the non-destruction and no pre-treatment characteristics, proves that it is feasible to use LED-induced fluorescence spectroscopy as a way to investigate the EVOO adulteration level, and paves the way for building a hand-hold device that can be applied to real market conditions in the future.

Interaction of water soluble cationic gallium(III) phthalocyanines with different G-quadruplex DNAs

Small molecule-G-quadruplex DNA interaction has been gained considerable interest due to existence of G-quadruplex structures in telomeres and promotor regions of proto-oncogenes. In the present study, the interaction of 2(3), 9(10), 16(17), 23(24)-tetrakis-[(N-methyl-3-pyridyloxy)phthalocyaninato]chloro gallium (III) sulphate (TGaPc) and 2, 3, 9, 10, 16, 17, 23, 24-octakis-[(N-methyl-3-pyridyloxy) phthalocyaninato]chloro gallium (III) sulphate (OGaPc) with different DNA forms (ctDNA and G-quadruplex DNAs) was investigated. The interactions of compounds with DNA was extensively investigated by different methods, such as capillary gel electrophoresis (CGE) integrated with a high sensitivity LED-induced fluorescence detector, UV–Vis and circular dichroism spectroscopy, competitive dialysis experiments. UV–Vis. titrations and CGE studies showed that the two phthalocyanine compounds interacted with the G-quadruplex and ctDNA, but the binding affinity of TGaPc was high for AS1411. Dialysis experiments also supported the higher affinity of TGaPc to AS1411. CD studies showed that both TGaPc and OGaPc caused destabilization of Tel21 structure even at low concentrations. This was more or less observed in other G-quadruplex DNAs other than AS1411. The structure of AS1411 remained intact at binding stoichiometric ratios. The viscosimetric studies and gel electrophoresis studies have been used to explore the interaction of TGaPc and OGaPc with ctDNA. The viscosity experiments along with gel electrophoresis confirmed the intercalation binding for ctDNA with OGaPc and groove binding for TGaPc. All results show that these molecules interact with different DNA types at different strengths and different mechanisms and the binding affinity of TGaPc was high for AS1411. Therefore, these compounds have the potential for cancer treatment.

Investigation of Binding behaviour of a water-soluble gallium (III) phthalocyanine with double-stranded and G-quadruplex DNA via experimental and computational methods

DNA is an important target for the development of chemotherapeutic drug design due to increased and uncontrolled cell proliferation of cancer cells. In the present study, the affinity of water-soluble gallium(III) phthalocyanine chloride (GaPc) non-peripherally substituted with 2-mercapto-N-methylpyridinium groups to different types of DNA (double-stranded ctDNA and G-quadruplex DNA) was investigated. The interaction mechanisms were evaluated by UV-Vis, fluorescence and circular dichroism spectroscopic techniques, competitive dialysis assay, and capillary gel electrophoresis (CGE) system integrated with a high sensitivity LED-induced fluorescence (LIF) detector. Binding mode studies were carried out by molecular docking and molecular dynamic simulations. The experimental binding constants were determined as 1.9 × 106 M−1, 1.1 × 106 M−1, 8.5 × 105 M−1, 2.9 × 104 M−1 for c-MYC, AS1411, Tel21, and ctDNA, respectively. Competitive binding assay confirmed the higher affinity towards G-quadruplex structure rather than ctDNA. The GaPc-G-quadruplex DNA conjugates showed higher Kb constants and a strong absorption band closer to NIR window which is a desired feature for the photodynamic therapy applications. Besides, experimental data show that the formation of GaPc-G-quadruplex DNA conjugates reduced the aggregation of GaPc. Reduction of aggregation of phthalocyanine is important. Because aggregation decreases the photoactivity of most photosensitizers. The experimental results suggested that both intercalative and non‑intercalative binding contributions occurred in the case of double-stranded ctDNA. Confirming experiments, molecular docking studies showed that the GaPc can bind from two different major groove regions in double-stranded DNA while only one binding mode was observed in the G-quadruplex DNA. Both experimental and computational studies suggested that the conformational change and unfolding mechanism in G-quadruplex DNA structure were determined upon interaction with GaPc.

Electroosmotic flow modulation for improved electrokinetic preconcentration: Application to capillary electrophoresis of fluorescent magnetic nanoparticles

It is reported in this study a new approach for modulation and even suppression of the electroosmotic flow (EOF) to achieve better electrokinetic preconcentration in capillary electrophoresis. This is based on the augmentation of the buffer’s concentrations to very high levels (more than a thousand of mM) without recourse to any dynamic/permanent coating nor viscous gel. The use of large weakly charged molecules as background electrolyte’s constituents allows working at extreme concentration ranges without penalty of high electric currents and Joule heating. By this way, the electroosmotic mobility could be modulated over a wide range (2–60 × 10−5 cm2 V−1 s−1 under alkaline conditions), and suppressed to levels equivalent to those obtained with several neutral coatings. The highest buffer concentrations, and the lowest EOF magnitudes, accordingly, were achieved with diethanolamine/3-(Cyclohexylamino)-1-propanesulfonic acid (ionic strength (IS) of 250 mM, pH 9.5), Tris(hydroxymethyl)aminomethane (Tris)/2-(Cyclohexylamino)ethanesulfonic acid (CHES) (IS of 280 mM, pH 8.7) and triethanolamine/2-(Cyclohexylamino)ethanesulfonic acid (IS of 250 mM, pH 8.5). For demonstration, this new approach was applied for sensitive determination of core-shell magnetic nanoparticles (CSMNPs) having high potential for healthcare applications such as imaging agents for diagnostics and controllable cargos for nanomedicine. Different profiles were achieved for purpose-made and commercial magnetic nanoparticles using CE coupled with light-emitting-diode induced fluorescence (LEDIF) detection. The best performance for EOF-assisted preconcentration and CE-LEDIF of CSMNPs was achieved with these nanoparticles prepared in TRIS/CHES (IS 10 mM, pH 8.4) for preconcentration, and separation under BGE of TRIS/CHES (IS 100 mM, pH 8.4). Compared to the conventional capillary electrophoresis (CE-UV) method for characterization of magnetic nanoparticles, our proposed approach with fluorescent detection and EOF-assisted preconcentration offers almost 350-fold sensitivity improvement. Furthermore, our scheme can be used for monitoring the interaction between CSMNPs and target pharmaceutical molecules, serving for drug delivery development. A preliminary study with two antibiotics using this approach revealed that kanamycin interacts better with the target nanoparticles than amikacin.

3-(4-Carboxybenzoyl)quinoline-2-carboxaldehyde labeling for direct analysis of amino acids in plasma is not suitable for simultaneous quantification of tryptophan, tyrosine, valine, and isoleucine by CE/fluorescence.

Capillary electrophoresis coupled to LED-induced fluorescence detection is a robust and sensitive technique used for amino acids (AA) analysis in biological media, after labeling with 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA). We wanted to quantitate in plasma tryptophan (Trp), tyrosine (Tyr), valine (Val), and isoleucine (Ile). Among the different labeled AA-CBQCA, Trp has the lowest fluorescence yield, which makes its detection and quantification very difficult in biological samples such as plasma. We tried to improve Trp analysis by CE/LED-induced fluorescence detection to its maximal sensitivity by using large volume sample stacking as a preconcentration step in our analytical protocol. At pH 9.5, this step caused a drop in resolution during the separation of the four AAs and it was therefore necessary to work at pH 10. We have found that Tyr, Val, Ile, and Trp are detected and well separated from the other AAs, but Trp cannot be quantified in plasma samples, mainly because of the low fluorescence yield of the Trp-CBQCA derivative. The recorded LOD is 0.18μM for Trp-CBQCA in standard solution with a resolution between Trp and Tyr of 1.2, while the LOD is 6μM in plasma with the same resolution. Trp, Tyr, Val, and Ile are, however, efficiently quantified when using a 3 M acetic acid electrolyte and CE associated with capacitively coupled contactless conductivity detection, which also has the advantage of not requiring derivatization or large volume sample stacking. This article demonstrates, for the CE user, that quantitative analysis of these four AA in mouse plasma can be performed by CE-fluorescence after CBQCA labeling, with the exception of Trp. It can be advantageously replaced by CE/capacitively coupled contactless conductivity detection, the only efficient one for Trp, Tyr, Val, and Ile quantification. In this case, the LOD for Trp is 2μM. The four AAs are separated with resolution with neighbors above 1.5.