A facile light-emitting-diode induced fluorescence detector coupled to an integrated microfluidic device for microchip electrophoresis

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.

Recent advances in microchip enantioseparation and analysis

This review summarizes recent developments (over the past decade) in the field of microfluidics-based solutions for enantiomeric separation and detection. The progress in various formats of microchip electrodriven separations, such as MCE, microchip electrochromatography, and multidimensional separation techniques, is discussed. Innovations covering chiral stationary phases, surface coatings, and modification strategies to improve resolution, as well as integration with detection systems, are reported. Finally, combinations with other microfluidic functional units are also presented and highlighted.

Microfluidics as a Novel Tool for Biological and Toxicological Assays in Drug Discovery Processes: Focus on Microchip Electrophoresis

The last decades of biological, toxicological, and pharmacological research have deeply changed the way researchers select the most appropriate 'pre-clinical model'. The absence of relevant animal models for many human diseases, as well as the inaccurate prognosis coming from 'conventional' pre-clinical models, are among the major reasons of the failures observed in clinical trials. This evidence has pushed several research groups to move more often from a classic cellular or animal modeling approach to an alternative and broader vision that includes the involvement of microfluidic-based technologies. The use of microfluidic devices offers several benefits including fast analysis times, high sensitivity and reproducibility, the ability to quantitate multiple chemical species, and the simulation of cellular response mimicking the closest human in vivo milieu. Therefore, they represent a useful way to study drug-organ interactions and related safety and toxicity, and to model organ development and various pathologies 'in a dish'. The present review will address the applicability of microfluidic-based technologies in different systems (2D and 3D). We will focus our attention on applications of microchip electrophoresis (ME) to biological and toxicological studies as well as in drug discovery and development processes. These include high-throughput single-cell gene expression profiling, simultaneous determination of antioxidants and reactive oxygen and nitrogen species, DNA analysis, and sensitive determination of neurotransmitters in biological fluids. We will discuss new data obtained by ME coupled to laser-induced fluorescence (ME-LIF) and electrochemical detection (ME-EC) regarding the production and degradation of nitric oxide, a fundamental signaling molecule regulating virtually every critical cellular function. Finally, the integration of microfluidics with recent innovative technologies-such as organoids, organ-on-chip, and 3D printing-for the design of new in vitro experimental devices will be presented with a specific attention to drug development applications. This 'composite' review highlights the potential impact of 2D and 3D microfluidic systems as a fast, inexpensive, and highly sensitive tool for high-throughput drug screening and preclinical toxicological studies.

A miniaturized and high sensitive dual channel fluorimeter based on compact collinear optical arrangement

A miniaturized and high sensitive dual channel fluorimeter was developed and evaluated. It employed collinear optical arrangement, a 365 nm and a 470 nm light emitting diodes (LEDs) as light sources, two photodiodes (PDs) integrated with pre-amplifiers as optoelectronic detectors, and a 12.5 mm × 12.5 mm × 45 mm (width × length × height) quartz cuvette as detection cell. The optical parameters such as spectrum compatibility of dual channel, reshaping lens, the common optical path length (COPL), the common focus lens (CFL), as well as working distance of the cuvette were optimized carefully. It was found that the use of shortened optical path and common focal lens could improve the sensitivity of the dual channel fluorimeter significantly. The limits of detection (LODs) for coumarin, aflatoxin B₁, fluorescein sodium, and vitamin B₂ were 0.002 μg L^-1, 0.006 μg L^-1, 0.008 μg L^-1, and 0.03 μg L^-1, respectively. The dual channel fluorimeter can be used for detection of several categories of substance, such as mycotoxins, polycyclic aromatic hydrocarbons, fluorescein, vitamins, and pathogenic microorganisms etc. As a key component, it can also find application in different disciplines such as fluorescent PCR instruments and 96-well plate fluorescence analyzer.

A simple and highly sensitive masking fluorescence detection system for capillary array electrophoresis and its application to food and medicine analysis

A high sampling rate, good stability, high throughput masking fluorescence detection system with easy positioning of each channel for capillary array electrophoresis was prepared and studied. A special mask combined with convex lenses was designed to modulate signals, without using any extra device to position each channel. The signal of each channel was detected by a photomultiplier tube, classified and saved by software. The design was used to evidently reduce the rotational vibration of optical components and to stabilize the system, so a high sampling rate was obtained by increasing the DC motor speed. To improve the optical system, optical fibers instead of conventional bulky optical components were used to transmit optical signal and to collect fluorescences in multiple directions, which greatly raised the sensitivity. Other important parameters including sampling rate, rotating speed and driven voltage laser diode (LDs) have also been investigated. Under optimal conditions, the performance of the detection system was evaluated. This novel system had a well-designed structure, and allowed independent multiple capillary operations and easy microanalysis. Its limit of detection for rhodamine 6G was 2.0 × 10^-2 µg/mL.

Application of Capillary Electrophoresis with Laser-Induced Fluorescence to Immunoassays and Enzyme Assays

Capillary electrophoresis using laser-induced fluorescence detection (CE-LIF) is one of the most sensitive separation tools among electrical separation methods. The use of CE-LIF in immunoassays and enzyme assays has gained a reputation in recent years for its high detection sensitivity, short analysis time, and accurate quantification. Immunoassays are bioassay platforms that rely on binding reactions between an antigen (analyte) and a specific antibody. Enzyme assays measure enzymatic activity through quantitative analysis of substrates and products by the reaction of enzymes in purified enzyme or cell systems. These two category analyses play an important role in the context of biopharmaceutical analysis, clinical therapy, drug discovery, and diagnosis analysis. This review discusses the expanding portfolio of immune and enzyme assays using CE-LIF and focuses on the advantages and disadvantages of these methods over the ten years of existing technology since 2008.

In-Situ Measurements in Microscale Gas Flows-Conventional Sensors or Something Else?

Within the last few decades miniaturization has a driving force in almost all areas of technology, leading to a tremendous intensification of systems and processes. Information technology provides now data density several orders of magnitude higher than a few years ago, and the smartphone technology includes, as well the simple ability to communicate with others, features like internet, video and music streaming, but also implementation of the global positioning system, environment sensors or measurement systems for individual health. So-called wearables are everywhere, from the physio-parameter sensing wrist smart watch up to the measurement of heart rates by underwear. This trend holds also for gas flow applications, where complex flow arrangements and measurement systems formerly designed for a macro scale have been transferred into miniaturized versions. Thus, those systems took advantage of the increased surface to volume ratio as well as of the improved heat and mass transfer behavior of miniaturized equipment. In accordance, disadvantages like gas flow mal-distribution on parallelized mini- or micro tubes or channels as well as increased pressure losses due to the minimized hydraulic diameters and an increased roughness-to-dimension ratio have to be taken into account. Furthermore, major problems are arising for measurement and control to be implemented for in-situ and/or in-operando measurements. Currently, correlated measurements are widely discussed to obtain a more comprehensive view to a process by using a broad variety of measurement techniques complementing each other. Techniques for correlated measurements may include commonly used techniques like thermocouples or pressure sensors as well as more complex systems like gas chromatography, mass spectrometry, infrared or ultraviolet spectroscopy and many others. Some of these techniques can be miniaturized, some of them cannot yet. Those should, nevertheless, be able to conduct measurements at the same location and the same time, preferably in-situ and in-operando. Therefore, combinations of measurement instruments might be necessary, which will provide complementary techniques for accessing local process information. A recently more intensively discussed additional possibility is the application of nuclear magnetic resonance (NMR) systems, which might be useful in combination with other, more conventional measurement techniques. NMR is currently undergoing a tremendous change from large-scale to benchtop measurement systems, and it will most likely be further miniaturized. NMR allows a multitude of different measurements, which are normally covered by several instruments. Additionally, NMR can be combined very well with other measurement equipment to perform correlative in-situ and in-operando measurements. Such combinations of several instruments would allow us to retrieve an "information cloud" of a process. This paper will present a view of some common measurement techniques and the difficulties of applying them on one hand in a miniaturized scale, and on the other hand in a correlative mode. Basic suggestions to achieve the above-mentioned objective by a combination of different methods including NMR will be given.

A decade of microchip electrophoresis for clinical diagnostics - A review of 2008-2017

A core element in clinical diagnostics is the data interpretation obtained through the analysis of patient samples. To obtain relevant and reliable information, a methodological approach of sample preparation, separation, and detection is required. Traditionally, these steps are performed independently and stepwise. Microchip capillary electrophoresis (MCE) can provide rapid and high-resolution separation with the capability to integrate a streamlined and complete diagnostic workflow suitable for the point-of-care setting. Whilst standard clinical diagnostics methods normally require hours to days to retrieve specific patient data, MCE can reduce the time to minutes, hastening the delivery of treatment options for the patients. This review covers the advances in MCE for disease detection from 2008 to 2017. Miniaturised diagnostic approaches that required an electrophoretic separation step prior to the detection of the biological samples are reviewed. In the two main sections, the discussion is focused on the technical set-up used to suit MCE for disease detection and on the strategies that have been applied to study various diseases. Throughout these discussions MCE is compared to other techniques to create context of the potential and challenges of MCE. A comprehensive table categorised based on the studied disease using MCE is provided. We also comment on future challenges that remain to be addressed.

A novel HPLC flow cell integrated UV light emitting diode induced fluorescence detector as alternative for sensitive determination of aflatoxins

A novel UV light emitting diode induced fluorescence detector (LED-IF) with HPLC flow cell was designed and evaluated for determination of aflatoxins. Ray tracing method was employed to optimize the design of the optical components (such as reshaping thin lens for light source and fluorescence collection), and optical structure, and the geometry of flow cell. An ordinary UV LED with wavelength of 370 nm and radiant power of 5 mW was used as excitation light source. A photoelectric amplifier AccuOpt2000 with light sensitivity of 10^-5∼10^-4lx was utilized for fluorescence detection, instead of a photo multiplier tube (PMT). The lowest detection limit (LOD) of the LED-IF was 0.077 ppb for aflatoxin B₁ by HPLC method without derivatization. The LED-IF was then coupled with a homemade iodine derivatization device, which was connected to the HPLC column outlet for determination of aflatoxins in edible oil and peanut samples. It was found that the edible oil sample contained aflatoxin B₁ and B₂ at average level of 7.14 (n = 3) and 0.30 ng/g (n = 3), respectively; while the peanut sample contained aflatoxin B₁ and B₂ at average level of 9.22 (n = 3) and 1.36 ng/g (n = 3), respectively. The overall power consumption of the LED-IF was 1 W/12 V. The sensitivity of the LED-IF was similar to commercial fluorescence detectors, which utilized a pulse Xe lamp as excitation light source and a PMT for detection, with power consumption of 150 W.

Light emitting diode, photodiode-based fluorescence detection system for DNA analysis with microchip electrophoresis

Electrophoretic separation of fluorescently end-labeled DNA after a PCR serves as a gold standard in genetic diagnostics. Because of their size and cost, instruments for this type of analysis have had limited market uptake, particularly for point-of-care applications. This might be changed through a higher level of system integration and lower instrument costs that can be realized through the use of LEDs for excitation and photodiodes for detection--if they provide sufficient sensitivity. Here, we demonstrate an optimized microchip electrophoresis instrument using polymeric fluidic chips with fluorescence detection of end-labeled DNA with a LOD of 0.15 nM of Alexa Fluor 532. This represents orders of magnitude improvement over previously reported instruments of this type. We demonstrate the system with an electrophoretic separation of two PCR products and their respective primers. We believe that this is the first LED-induced fluorescence microchip electrophoresis system with photodiode-based detection that could be used for standard applications of PCR and electrophoresis.

A simple and compact fluorescence detection system for capillary electrophoresis and its application to food analysis

A novel fluorescence detection system for CE was described and evaluated. Two miniature laser pointers were used as the excitation source. A Y-style optical fiber was used to transmit the excitation light and a four-branch optical fiber was used to collect the fluorescence. The optical fiber and optical filter were imported into a photomultiplier tube without any extra fixing device. A simplified PDMS detection cell was designed with guide channels through which the optical fibers were easily aligned to the detection window of separation capillary. According to different requirements, laser pointers and different filters were selected by simple switching and replacement. The fluorescence from four different directions was collected at the same detecting point. Thus, the sensitivity was enhanced without peak broadening. The fluorescence detection system was simple, compact, low-cost, and highly sensitive, with its functionality demonstrated by the separation and determination of red dyes and fluorescent whitening agents. The detection limit of rhodamine 6G was 7.7 nM (S/N = 3). The system was further applied to determine illegal food dyes. The CE system is potentially eligible for food safety analysis.

Present state of microchip electrophoresis: state of the art and routine applications

Microchip electrophoresis (MCE) was one of the earliest applications of the micro-total analysis system (μ-TAS) concept, whose aim is to reduce analysis time and reagent and sample consumption while increasing throughput and portability by miniaturizing analytical laboratory procedures onto a microfluidic chip. More than two decades on, electrophoresis remains the most common separation technique used in microfluidic applications. MCE-based instruments have had some commercial success and have found application in many disciplines. This review will consider the present state of MCE including recent advances in technology and both novel and routine applications in the laboratory. We will also attempt to assess the impact of MCE in the scientific community and its prospects for the future.

Fluorescence detector for capillary separations fabricated by 3D printing

A simple inexpensive light-emitting diode (LED)-based fluorescence detector for detection in capillary separations is described. The modular design includes a separate high power LED source, detector head, designed in the epifluorescence arrangement, and capillary detection cells. The detector head and detection cells were printed using a 3D printer and assembled with commercially available optical components. Optical fibers were used for connecting the detector head to the LED excitation source and the photodetector module. Microscope objective or high numerical aperture optical fiber were used for collection of the fluorescence emission from the fused silica separation capillary. As an example, mixture of oligosaccharides labeled by 8-aminopyrene-1,3,6-trisulfonate (APTS) was separated by capillary zone electrophoresis and detected by the described detector. The performance of the detector was compared with both a semiconductor photodiode and photomultiplier as light sensing elements. The main advantages of the 3D printed parts, compared to the more expensive alternatives from the optic component suppliers, include not only cost reduction, but also easy customization of the spatial arrangement, modularity, miniaturization, and sharing of information between laboratories for easy replication or further modifications of the detector. All information and files necessary for printing the presented detector are enclosed in the Supporting Information.

Photometric flow injection determination of phosphate on a PDMS microchip using an optical detection system assembled with an organic light emitting diode and an organic photodiode

A compact photometric detector was constructed from an organic light emitting diode (OLED) based on a europium complex, europium(diben-zoylmethanato)3(bathophenanthroline) (Eu(DBM)3bath), as the light source and an organic photodiode (OPD) fabricated from a hetero-junction of two layers of copper phthalocyanine (CuPc)/fullerene (C60) as the photo-detector on a microchip prepared from poly(dimethylsiloxan) (PDMS) and was applied to the determination of phosphate. The OLED and the OPD were fabricated by a vapor deposition method on an indium tin oxide (ITO) coated glass substrate with the following layered structure; Glass (0.7 mm)/ITO (110 nm)/4,4'-bis[N-(1-naphthyl)-N-phenyl amino]-biphenyl (α-NPD) (30 nm)/4,4'-di(N-carbazolyl)biphenyl (CBP): Eu(3+) (8 wt%, 30 nm)/bathocuproine (BCP) (30 nm)/aluminum tris(8-hydroxyquinoline) (Alq3) (25 nm)/magnesium and silver (MgAg) (100 nm)/Ag (10nm) and Glass (0.7 mm)/ITO (110 nm)/CuPc (35 nm)/C60 (50 nm)/BCP (10 nm)/Ag (50 nm), respectively. The OLED based on the europium complex emitted a sharp light at the wavelength of 612 nm with a full width at half maximum (FWHM) of 8 nm. The performance of the photometric detector assembled was evaluated based on measurements of the absorbance of different concentrations of malachite green (MG) solutions for a batch system with 1cm long path length. The molar absorptive coefficient of the MG solution, calculated from the photocurrent of the OPD, was in good agreement with the value reported in the literature. A microchip with two inlets and one outlet U-shaped channel was prepared by a conventional photolithograph method. The OLED and the OPD were configured so as to face each other through the PDMS microchip in parallel in order to align the light axis of the OLED and the OPD with the flow cell (optical path length of 5mm), which was located at the end of outlet. For the determination of phosphate, an ion-association reaction between MG and a molybdenum-phosphate complex was utilized and a good linear relationship between the concentration and absorbance was observed in the concentration range 0-0.2 ppm, with a detection limit (S/N=3) of 0.02 ppm. The assembled photometric detector was also applied to the determination of phosphate by the flow injection of river water samples using the reagent solution containing MG and molybdenum ammonium in sulfuric acid. A good recovery (97-99%) for the river water samples, which had been spiked with the standard 0.08 ppm, with an RSD of ca 5% (n=5) was obtained using the constructed system.

Sensitivity improvement in fluorescence-based particle detection

Microfluidic flow cytometers are highly interesting candidates for biomedical point-of-care applications. However, the sensitivity, reliability, and throughput of these systems must be improved to provide the full functionality of established flow cytometric systems. One proposed method to improve fluorescence detection systems is to use spatial modulation techniques. We derive the noise-related statistics and calculate the coefficient of variation for a detection system with and without spatial modulation. We measure the noise properties of a nonmodulated microfluidic fluorescence particle detection system and analyze the possible performance gains using spatial modulation.

Light-emitting diodes for analytical chemistry

Light-emitting diodes (LEDs) are playing increasingly important roles in analytical chemistry, from the final analysis stage to photoreactors for analyte conversion to actual fabrication of and incorporation in microdevices for analytical use. The extremely fast turn-on/off rates of LEDs have made possible simple approaches to fluorescence lifetime measurement. Although they are increasingly being used as detectors, their wavelength selectivity as detectors has rarely been exploited. From their first proposed use for absorbance measurement in 1970, LEDs have been used in analytical chemistry in too many ways to make a comprehensive review possible. Hence, we critically review here the more recent literature on their use in optical detection and measurement systems. Cloudy as our crystal ball may be, we express our views on the future applications of LEDs in analytical chemistry: The horizon will certainly become wider as LEDs in the deep UV with sufficient intensity become available.

Flexible planar microfluidic chip employing a light emitting diode and a PIN-photodiode for portable flow cytometers

Detection of fluorescence particles is a key method of flow cytometry. We evaluate the performance of a design for a microfluidic fluorescence particle detection device. Due to the planar design with low layer thicknesses, we avoid optical components such as lenses or dichroic mirrors and substitute them with a shadow mask and colored film filters. A commercially available LED is used as the light source and a PIN-photodiode as detector. This design approach reduces component cost and power consumption and enables supplying the device with power from a standard USB port. From evaluation of this design, we obtain a maximum particle detection frequency of up to 600 particles per second at a sensitivity of better than 4.7 × 10(5) MESF (molecules of equivalent soluble fluorochrome) measured with particles for FITC sensitivity calibration. Lowering the flow rate increases the instrument sensitivity by an order of magnitude enabling the detection of particles with 4.5 × 10(4) MESF.

An integrated enzyme-linked immunosorbent assay system with an organic light-emitting diode and a charge-coupled device for fluorescence detection

A fluorescence detection system for a microfluidic device using an organic light-emitting diode (OLED) as the excitation light source and a charge-coupled device (CCD) as the photo detector was developed. The OLED was fabricated on a glass plate by photolithography and a vacuum deposition technique. The OLED produced a green luminescence with a peak emission at 512 nm and a half bandwidth of 55 nm. The maximum external quantum efficiency of the OLED was 7.2%. The emission intensity of the OLED at 10 mA/cm(2) was 13 μW (1.7 mW/cm(2)). The fluorescence detection system consisted of the OLED device, two band-pass filters, a five microchannel poly(dimethylsiloxane) (PDMS) microfluidic device and a linear CCD. The fluorescence detection system was successfully used in a flow-based enzyme-linked immunosorbent assay on a PDMS microfluidic device for the rapid determination of immunoglobulin A (IgA), a marker for human stress. The detection limit (S/N=3) for IgA was 16.5 ng/mL, and the sensitivity was sufficient for evaluating stress. Compared with the conventional 96-well microtiter plate assay, the analysis time and the amounts of reagent and sample solutions could all be reduced.