Light-emitting Diode Excitation Source Research Articles

Metal-enhanced fluorescence biosensor integrated in capillary flow-driven microfluidic cartridge for highly sensitive immunoassays

Point-of-care testing (POCT) for low-concentration protein biomarkers remains challenging due to limitations in biosensor sensitivity and platform integration. This study addresses this gap by presenting a novel approach that integrates a metal-enhanced fluorescence (MEF) biosensor within a capillary flow-driven microfluidic cartridge (CFMC) for the ultrasensitive detection of the Parkinson's disease biomarker, aminoacyl-tRNA synthetase complex interacting multi-functional protein 2 (AIMP-2). Crucial point to this approach is the orientation-controlled immobilization of capture antibody on a nanodimple-structured MEF substrate within the CFMC. This strategy significantly enhances fluorescence signals without quenching, enabling accurate quantification of low-concentration AIMP-2 using a simple digital fluorescence microscope with a light-emitting diode excitation source and a digital camera. The resulting platform exhibits exceptional sensitivity, achieving a limit of detection in the pg/mL range for AIMP-2 in human serum. Additionally, the CFMC design incorporates a capillary-driven passive sample transport mechanism, eliminating the need for external pumps and further simplifying the detection process. Overall, this work demonstrates the successful integration of MEF biosensing with capillary microfluidics for point-of-care applications.

Luminescence and Scintillation Characterization of Sodium-Based Tungstate (Na2W2O7) Crystal for Dark Matter Search

A Na <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> single crystal was grown with a conventional Czochralski technique in a platinum crucible. A solid-state reaction method was used for the preparation of the polycrystalline compound. Temperature-dependent luminescence and scintillation properties of the crystal were studied under the excitation with a 280 nm UV light-emitting diode (LED) source, an X-ray source, and a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">90</sup> Sr (beta) source. At different temperatures (from 300 to 10 K), an as-grown crystal’s luminescence and scintillation light output was compared with a CaMoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystal. Although the light output of Na <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> crystal at room temperature is lower than CaMoO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> crystal, at 10 K, it is almost comparable. Compared to room temperature, the crystal’s luminescence and scintillation light output at 10 K were increased by ~17 and ~14 fold, respectively. The decay time of the crystal was studied between 300 to 10 K using a 280 nm LED excitation source, and it varies from 3 (300 K) to ~94 μs (10 K). A thermoluminescence (TL) study was carried out between 10 to 550 K. The kinetic parameters of the TL peaks are calculated with various standard methods. The current result suggests that the studied crystal has good potential as a cryogenic detector for dark matter search experiments in the near future.

Low-cost photoacoustic imaging systems based on laser diode and light-emitting diode excitation

Photoacoustic imaging, an emerging biomedical imaging modality, holds great promise for preclinical and clinical researches. It combines the high optical contrast and high ultrasound resolution by converting laser excitation into ultrasonic emission. In order to generate photoacoustic signal efficiently, bulky Q-switched solid-state laser systems are most commonly used as excitation sources and hence limit its commercialization. As an alternative, the miniaturized semiconductor laser system has the advantages of being inexpensive, compact, and robust, which makes a significant effect on production-forming design. It is also desirable to obtain a wavelength in a wide range from visible to near-infrared spectrum for multispectral applications. Focussing on practical aspect, this paper reviews the state-of-the-art developments of low-cost photoacoustic system with laser diode and light-emitting diode excitation source and highlights a few representative installations in the past decade.

Characterization and Energy Absorption Efficiency Determination of LED as an Effective Photothermal Excitation Source in Lock-In Thermography

This paper studies the use of light-emitting diode (LED) as an excitation source for photothermal lock-in experiments, and investigates the energy absorption efficiency and signal-to-noise ratio of the established setup. Existing lock-in excitation sources usually use high power (in the range of kilowatt) halogen lamps. The present LED excitation source has an advantage of low power consumption making the setup much more energy efficient. Another advantage of LED in this paper is their low infrared (IR) content, in contrast to halogen lamps, the IR content gets reflected into the IR camera, and leads to an unpredicted change in phase image in lock-in thermography.

Direct Fluorescent Decay Measurements Using High Speed Electronics

High speed data acquisition architecture is implemented as part of a time-resolved fluorescence detection instrument to directly measure the time course of fluorescent decay. The architecture is implemented using a very fast dynode chain photomultiplier tube and associated gating circuitry, a broad spectrum light emitting diode excitation source, very wide band electronics for amplification and filtering, and a high speed digital oscilloscope. The fluorescence decay of tris (2,2´-bipyridyl) ruthenium (II) is measured and the lifetime measurement is compared with that using other reported methods. The system’s architecture is thereby validated for data acquisition of broadband signals including transient fluorescent recording.

Low-cost gated system for monitoring phosphorescence lifetimes

A low-cost, gated system for measurements of phosphorescence lifetimes is presented. An extensive description of the system operating principles and metrological characteristics is given. Remarkably, the system operates without optical filtering of the light emitting diode excitation source. A description of a practical system is also given and its performance is discussed. Because the device effectively suppresses high-level background fluorescence and scattered light, it is expected to find widespread application in bioprocess, environmental, and biomedical fields.

Low cost phase-modulation measurements of nanosecond fluorescence lifetimes using a lock-in amplifier

The use of a 200 MHz lock-in amplifier was demonstrated as a low cost instrument for frequency domain measurements of nanosecond fluorescence lifetimes. The lock-in directly provided both the dc bias and the ac signal used to modulate the intensity of a blue light emitting diode excitation source. The emission was measured by a photomultiplier tube and the resulting signal was sent back through a dc block to the lock-in with no external signal processing or heterodyning required. The system was highly accurate at measuring phase and modulation up to 80 MHz and moderately so up to 100 MHz. The fluorescence lifetimes of several standard fluorophores (Fluorescein, Rhodamine B, and [Ru(bpy)3]2+) were measured by the lock-in, and the results agreed closely with those made on a research grade fluorometer. The entire lock-in based system costs less than US $10,000 to build and can be controlled by any standard computer through a GPIB or serial connection. The system is also portable, consumes little power, and can easily be configured for use with fiber optics, making it ideal for use with fluorescence lifetime based sensors.

Anisotropy-Based Sensing with Reference Fluorophores

We describe a new approach to fluorescence sensing based on measurements of steady-state anisotropies in the presence of reference fluorophores with known anisotropies. The basic concept is that the anisotropy of a mixture reflects a weighted average of the anisotropies of the emitting species. By use of reference fluorophores the starting anisotropy can be near zero, or near 0.9 for oriented films which contain the reference fluorophore. Changing intensities of the analyte result in changes in anisotropy. A wide dynamic range of anisotropies is available because of the freedom to select high or low starting values. Anisotropy-based sensing was demonstrated for pH using 6-carboxyfluorescein and for protein affinity or immunoassay using an oriented film with high anisotropy and a protein labeled with a metal–ligand complex. The latter measurements were performed with a simple light-emitting diode excitation source without an excitation polarizer. The sensitive range of the assay can be adjusted by changing the intensity of the reference fluorophore. Anisotropy-based sensing can have numerous applications in clinical and analytical chemistry.