Excitation Light Source Research Articles

Advances in luminescence-based technologies for drug discovery

ABSTRACT Introduction Luminescence-based technologies, specifically bioluminescence and chemiluminescence, are powerful tools with extensive use in drug discovery. Production of light during chemiluminescence and bioluminescence, unlike fluorescence, doesn’t require an excitation light source, resulting in high signal-to-noise ratio, less background interference, and no issues from phototoxicity and photobleaching. These characteristics of luminescence technologies offer unique advantages for experimental designs, allowing for greater flexibility to target a wide range of proteins and biological processes for drug discovery at different stages. Areas covered This review provides a basic overview of luciferase-based technologies and details recent advances and use cases of luciferase and luciferin variations and their applicability in the drug discovery toolset. The authors expand upon specific applications of luciferase technologies, including chemiluminescent and bioluminescent-based microscopy. Finally, the authors lay out forward-looking statements on the field of luminescence and how it may shape the translational scientists’ work moving forward. Expert opinion The demand for improved luciferase and luciferin pairs correlates strongly with efforts to improve the sensitivity and robustness of high-throughput assays. As luminescent reporter systems improve, so will the expansion of use cases for luminescence-based technologies in early-stage drug discovery. With the synthesis of novel, non-enzymatic chemiluminescence-based probes, which previously were restrained to only basic research applications, they may now be readily implemented in drug discovery campaigns.

Integrated solar-powered MEMS-based photoelectrochemical immunoassay for point-of-care testing of cTnI protein

Considering the fact that acute myocardial infarction has shown a trend towards younger age and has become a major health problem, it is necessary to develop rapid screening devices to meet the needs of community health care. Herein, we developed an artificial neural network-assisted solar-powered photoelectrochemical (SP-PEC) sensing platform for rapid screening of cardiac troponin I (cTnI) protein in the prognosis of patients with acute myocardial infarction (AMI) by integrating a self-powered photoelectric signal output system with low-cost screen-printed paper electrodes functionalized with ultrathin Bi2O2S (BOS) nanosheets. An integrated solar-powered PEC immunoassay with micro-electro-mechanical system (MEMS) was constructed without an excitation light source. The quantification of cTnI protein was obtained by the electrical signal changes caused by the electro-oxidation process of H2O2, generated by the classical split immune reaction, on the electrode surface. The test electrodes were developed as dual working electrodes, one for target cTnI testing and the other for evaluating light intensity, to reduce the temporal inconsistency of sunlight. The photoelectrodes were discovered to exhibit satisfactory negative response to target concentrations in the dynamic range of 2.0 pg mL−1-10 ng mL−1 since being regressed in an improved artificial neural network (ANN) model using the pooled dataset of target signals affected by the light source. The difference of hot electron and hole transfer behavior in different thickness of nano-materials was determined by finite element analysis (FEA), which provided a theoretical basis for the development of efficient PEC sensors. This work presents a unique perspective for the design of a revolutionary low-cost bioassay platform by inventively illuminating the PEC biosensor's component process without the use of light.

Paper-based photoelectrochemical immunoassay for ultrasensitive screening of carcinoembryonic antigen on hollow CdS/CdMoO4-functionalized photoanode

Lab-based testing systems utilizing photoelectrochemical (PEC) biosensing methodologies for the ultrasensitive carcinoembryonic antigen (CEA) have been developed, although the majority have shown complicated operating procedures and dependence on precise apparatus. Herein, a portable photoelectrochemical split diagnostic platform based on a hollow CdS/CdMoO4 (h-CdS@CdMoO4) shell-shell structured photoanode system was developed for ultrasensitive detection of CEA. Using a small LED flashlight as the excitation light source and a digital multimeter (DMM) as the signal readout device, real-time CEA on a paper-based printed screen electrode developed in-house was quickly detected. The composite h-CdS@CdMoO4 featured a special hollow shell-shell heterojunction structure that optimizes photon usage in the bulk phase on the one hand, and facilitates directed separation of the electrons and holes therein on the other. A split-sandwich immunoassay and detection antibodies for modified glucose oxidase were introduced into the paper-based photoanode test system, and the signals were displayed with a DMM to realize a point-of-care test for CEA. Under optimized conditions, the constructed portable PEC sensing system was sensitive to the target CEA from 0.02 to 50.0 ng mL−1 with a detection limit of 11.3 pg mL−1. Interferent experiments and stability test evaluations demonstrate the specificity and robustness of the constructed paper-based portable PEC sensor. The portable, paper-based PEC immunoassay system developed offers a fresh way of exploring affordable, approachable sensors to satisfy both the relevant community medical testing demands and hospital objectives for quick testing.

Organic Light-Emitting Diode Based Fluorescence-Linked Immunosorbent Assay for SARS-CoV-2 Antibody Detection.

Immunodiagnostics have been widely used in the detection of disease biomarkers. The conventional immunological tests in central laboratories require expensive equipment and, for non-specialists, the tests are technically demanding and time-consuming, which has prevented their use by the public. Thus, point-of-care tests (POCT), such as lateral flow immunoassays, are being, or have been, developed as more convenient and low-cost methods for immunodiagnostics. However, the sensitivity of such tests is often a concern. Here, a fluorescence-linked immunosorbent assay (FLISA) using organic light-emitting diodes (OLEDs) as excitation light sources was investigated as a way forward for the development of compact and sensitive POCTs. Phycoerythrin (PE) was selected as the fluorescent dye, and OLEDs were designed with different emission spectra. The leakage light of different OLEDs for exciting PE was then investigated to reduce the background noise and improve the sensitivity of the system. Finally, as proof-of-principle that OLED-based technology can be successfully further developed for POCT, antibodies to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in human serum was detected by OLED-FLISA.

Photostability Enhancement of Dual-Luminophore Pressure-Sensitive Paint by Adding Antioxidants

Antioxidants were applied to a dual-luminophore pressure-sensitive paint (PSP), and the effects on photodegradation caused by exposure to excitation light were studied. Three types of antioxidants that are commonly used for the photostability enhancement of polymers were added to a dual-luminophore PSP, and degradation rates and pressure/temperature sensitivities were investigated by coupon-based tests. One-hour-long aging tests were performed in a pressure chamber with a continuous excitation light source under dry air and argon atmospheres at 100 kPa and 20 °C. As a result of the aging tests, a singlet oxygen quencher type antioxidant was found to reduce the degradation rate by 91% when compared with the dual-luminophore PSP without antioxidants. This implies that singlet oxygen has a dominant role in the photodegradation mechanism of the dual-luminophore PSP.

Symmetrical Coupling Multi-Cavity Bandpass Filter for CMOS Compatible Fluorescence Detection

Integration of functional components such as excitation light source, micro-fluidic chip, optical filters, and complementary metal–oxide–semiconductor (CMOS) sensors on a single photonics chip for fluorescence detection by advanced semiconductor process, is a future technology for rapid responding, high accuracy, and handheld point-of-care diagnosis protocol in field application of daily life. We designed a CMOS compatible bandpass filter on a glass substrate based on symmetrical coupling multi-cavity (SCMC) SiN/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> thin film stacker aimed at detection of 5-carboxylfluorescein (5-FAM), a commonly used fluorescence probe in biotechnology and medicine diagnosis. The calculation based on transfer matrix method (TMM) and 2D finite difference time domain (FDTD) algorithm, revealed that there was an optimized number of cavities in the SCMC stacker, for the transmittance in the pass band decreasing with the increment of the number of cavities while the optical density in the stop band improving with it. For a SCMC stacker with 10 resonant cavities, both the TMM and 2D FDTD calculation, figured out that the fluorescence emission and the remained excitation source should be directed to incident on the SCMC stacker with an angle less than 18° for a good passing of fluorescence emission centered at 520 nm and blocking of excitation light of a wavelength of 488 nm. It provided new insights for future design and fabrication of micro-lens array and micro-apertures array for the highly integrated photonics chip aimed at detection of fluorescence on a single chip.

Ratiometric optical thermometry based on upconversion luminescence with different multi-photon processes in CaWO4:Tm3+/Yb3+ phosphor.

Ratiometric optical thermometry based on upconversion (UC) luminescence with different multi-photon processes in CaWO4:Tm3+,Yb3+ phosphor was developed. A new fluorescence intensity ratio (FIR) thermometry, utilizing the ratio of the cube of 3F2,3 emission to the square of 1G4 emission of Tm3+ and retaining the feature of anti-interference of excitation light source fluctuations, is proposed. Under the hypotheses of the UC terms being neglected in the rate equations and the ratio of the cube of 3H4 emission to the square of 1G4 emission of Tm3+ being a constant in a relatively narrow temperature range, the new FIR thermometry is valid. The correctness of all hypotheses was confirmed by testing and analyzing the power-dependent emission spectra at different temperatures and the temperature-dependent emission spectra of CaWO4:Tm3+,Yb3+ phosphor. The results prove that the new ratiometric thermometry based on UC luminescence with different multi-photon processes is feasible through optical signal processing, and maximum relative sensitivity of the thermometry is 6.61% K-1 at 303 K. This study provides guidance in selecting UC luminescence with different multi-photon processes to construct ratiometric optical thermometers with anti-interference of excitation light source fluctuation.

Detection and analysis of microplastics in offshore sediment by microscopic differential Raman spectroscopy.

In view of the problems of low pre-screening efficiency, a weak Raman signal, and strong fluorescence interference in the detection of microplastics by traditional Raman spectroscopy, a set of rapid detection system and research methods for microplastics, including fluorescence imaging technology, differential Raman spectroscopy technology, and confocal microscopic Raman technology, are constructed in this paper. A 784/785nm dual-wavelength laser was used as the excitation light source in the rapid detection system for microplastics. The sediment in the coastal waters of Qingdao Shilaoren was taken as the research object. Polycarbonate and high-density polyethylene with a particle size of 40µm in the samples were accurately detected and analyzed. The research method for microplastics proposed in this study breaks through relevant key technologies, which we believe will help promote the development of microplastic monitoring technology in the global marine environment and provide strong technical support for the healthy development of the global marine ecological environment.

A sequential dual-lock strategy for generation of room-temperature phosphorescence of boron doped carbon dots for dynamic anti-counterfeiting

Stimuli-responsive materials with dynamically switched room-temperature phosphorescence (RTP) aroused great interest. However, the dynamic control of RTP with a color-tunable persistent afterglow by external stimuli is still challenging. Herein, an appealing strategy for constructing dynamic hydrogen-bond networks based on boron-doped carbon quantum dots (BCQDs) was proposed to generate sequence-dependent stimuli-responsive RTP. The BCQDs exhibited bright RTP in paper matrix after successive stimulation by water and heat, demonstrating a fascinating regulation based on an AND logic gate. The RTP generated experienced a reversible switching without attenuation fatigue when BCQDs were heated and exposed to air. The switching of hydrogen-bond network from that among BCQDs to that between BCQDs and paper could facilitate the population of triplet-state BCQDs. The RTP can last a long timie of 10 s after the ceasation of excitation light source. Furthermore, the AND logic gate stimuli-responsive RTP with different colors in papers were obtainded for the first time after blending with various non-RTP dyes. The BCQDs with controllable and on-demand afterglow were further applied for advanced multi-level information encryption and anti-counterfeiting materials. The finding provided assistance to understand the origin and mechanism of the stimuli-responsive RTP of smart materials and offered opportunities for developing multiple continuous stimuli-responsive intelligent RTP materials.

Spatiotemporal singular value decomposition for denoising in photoacoustic imaging with a low-energy excitation light source.

Photoacoustic (PA) imaging is an emerging hybrid imaging modality that combines rich optical spectroscopic contrast and high ultrasonic resolution, and thus holds tremendous promise for a wide range of pre-clinical and clinical applications. Compact and affordable light sources such as light-emitting diodes (LEDs) and laser diodes (LDs) are promising alternatives to bulky and expensive solid-state laser systems that are commonly used as PA light sources. These could accelerate the clinical translation of PA technology. However, PA signals generated with these light sources are readily degraded by noise due to the low optical fluence, leading to decreased signal-to-noise ratio (SNR) in PA images. In this work, a spatiotemporal singular value decomposition (SVD) based PA denoising method was investigated for these light sources that usually have low fluence and high repetition rates. The proposed method leverages both spatial and temporal correlations between radiofrequency (RF) data frames. Validation was performed on simulations and in vivo PA data acquired from human fingers (2D) and forearm (3D) using a LED-based system. Spatiotemporal SVD greatly enhanced the PA signals of blood vessels corrupted by noise while preserving a high temporal resolution to slow motions, improving the SNR of in vivo PA images by 90.3%, 56.0%, and 187.4% compared to single frame-based wavelet denoising, averaging across 200 frames, and single frame without denoising, respectively. With a fast processing time of SVD (∼50 µs per frame), the proposed method is well suited to PA imaging systems with low-energy excitation light sources for real-time in vivo applications.

A photochromic material-based platform for high-precision UV light detection and erasable optical information storage

The ultraviolet (UV) light detection has important applications in photochemistry, material aging, plant cultivation, and integrated circuit lithography. And photochromic materials have attracted more and more attention in technological applications due to their different physical and chemical properties before and after irradiation with a specific excitation light source. Therefore, it is a very interesting work to realize the detection of ultraviolet light intensity based on photochromic materials with good response to ultraviolet light. Here, we design a dual excitation detection mode based on the inorganic photochromic material SrHfO3: Ho3+, and propose a simple and high-precision UV intensity detection method. The doping of Ho3+ ions optimizes the photochromic effect of the SrHfO3 host material and also enables the material to integrate the up-conversion and the downshifting luminescence modes. Different luminescence quenching degrees appear in response to photochromic effect between up-conversion and the downshifting luminescence modes, thereby constructing a dual excitation mode for high-precision UV light intensity detection. In addition, flexible films and 3D micro-rod arrays using the as-obtained photochromic material were designed and fabricated a photochromism platform toward the implementation of optical information storage. This work not only provides a photochromic platform for optical data storage, but also opens a way for simplification of UV intensity detection with high accuracy.

Charging storage phosphors using a white flashlight via the upconversion approach

As an emerging approach to charge storage phosphors, upconversion charging (UCC) is attracting increased attention owing to its fundamental and practical perspectives. Despite the potential, further development of the UCC technology is restricted by the limited types of excitation light sources. Here, we use a white flashlight as excitation to investigate the UCC performance of storage phosphors. We demonstrate, as an example, that a Y3Al2Ga3O12:Pr3+ phosphor exhibits long-lasting emissions in the ultraviolet and visible regions after intense illumination from the flashlight. Thermoluminescence investigations reveal that both excited-state absorption and energy-transfer upconversion are involved in the UCC process. Based on the luminescence performance of the white-light charged phosphor, a conceptual thermometry approach is introduced, which can remotely sense the local temperature by monitoring the afterglow intensity ratio. Considering the wide use of flashlight, such a white-light excitability and the associated glow emission may potentially revolutionize the way to utilize storage phosphors.

Reversible photochromic effect in natural gemstone sapphires.

Photochromic sapphires show an optically controllable orange coloration under ambient temperatures, which strongly affects the color appearance and market value of gemstone sapphires. An in situ absorption spectroscopy technique using a tunable excitation light source has been developed to investigate the wavelength- and time-dependence of sapphire's photochromism. Excitations of ≤370 nm and ≥410 nm introduce and remove orange coloration, respectively, whereas there is a stable absorption band at 470 nm. Both the color enhancement and diminishing rates are proportional to the excitation intensity; hence, strong illumination can significantly accelerate the photochromic effect. Finally, the origin of the color center can be explained by a combination of the differential absorption and the opposite trends between the orange coloration and Cr3+ emission, indicating that the origin of this photochromic effect is related to a magnesium-induced trapped hole and chromium. The results can be used to minimize the photochromic effect and improve the reliability of color evaluation for valuable gemstones.

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.

Graphene oxide enhanced phase change tolerance of Ge2Sb2Se4Te1 for all-optical multilevel non-volatile photonics memory

The low optical loss of G e 2 S b 2 S e 4 T e 1 (GSST) makes it a potential functional material for all-optical multilevel photonics memory devices that can operate in the optical telecommunication wavelength band. However, the same characteristic also restricted the tolerance of GSST phase change conditions using 1550 nm as an excitation light source. This work reports on the enhancement of GSST phase change condition tolerance using a graphene oxide (GO) intermediate layer on a polymer waveguide platform. The hybrid waveguide exhibits an insertion loss of around 1 dB and a maximum readout contrast of 25% between amorphous and crystalline states, with a step increase in readout contrast of around 5% per step. This work serves as a proof of concept for the implementation of a GSST–GO hybrid structure as an optical functional material in all-optical photonics memory applications.

Photon Upconversion with a Low Threshold Excitation Intensity in Plain Water.

A triplet-triplet annihilation-based photon upconversion (TTA-UC) system with a low threshold excitation intensity (Ith) in plain water was developed. Water-soluble anionic porphyrin (PdTPPS4-) and diphenylanthracene (DCDPA2-) derivatives were used as light absorbers and emitter molecules, respectively, and no additives such as surfactants were required. The phosphorescence emission from PdTPPS4- under an excitation wavelength of 528 nm was quenched by DCDPA2-, resulting in triplet energy transfer, whereas fluorescence from DCDPA2- was observed in a short wavelength region (400-500 nm). Three independent emission studies utilizing different excitation light sources validated the TTA-UC process in a simple aqueous solution. TTA occurred after the triplet energy transfer, according to the time profiles of phosphorescence and fluorescence detected following pulse laser excitation. The Ith for TTA-UC was estimated to be lower than 6 mW cm-2, although it could not be exactly determined due to the sensitivity limit of the experimental setup. The upper limit of Ith for the aqueous solution of DCDPA2- and PdTPPS4- is the smallest value obtained to date for aqueous systems and comparable to that of high-performance TTA-UC systems in organic solutions.

Enhanced X-ray-induced luminescence and persistent luminescence of NaLuF4:Tb3+ nanoparticles with Li+ and Gd3+ co-doped

X-ray excitation photodynamic therapy is a new photodynamic therapy mode that induces tumor cell apoptosis by indirectly stimulating photosensitizer on nanoparticles with X-ray as excitation light source and generating singlet oxygen. It solves the problem of light penetration in traditional photodynamic therapy and realizes the treatment of deep tumors. At present, the weak X-ray-induced luminescence restricts further development of X-ray photodynamic therapy. NaLuF4:Li+/Gd3+/Tb3+ rare-earth nanoparticles with uniform size and regular morphology were synthesized by solvothermal method. The X-ray-induced luminescence intensity of NaLuF4:Li+/Gd3+/Tb3+ NPs was improved by Li+ and Gd3+ ions co-doping. The light yield of NaLuF4:Li+/Gd3+/Tb3+ NPs with 5% Li+ ions doping was 1.4 times than that of reference sample due to the change of crystal field symmetry. Furthermore, the effective lifetime of persistent luminescence increased from 221.5 s to 251.9 s after 15% Li+ ions doping. The thermoluminescence curves confirmed that the trap concentration was increased after Li+ ions doping, which was responsible for enhancing persistent luminescence lifetime. Long persistent luminescence emission laid a foundation for further application in photodynamic therapy.

Detection of Hydrogen Sulfide in Sewer Using an Erbium-Doped Fiber Amplified Diode Laser and a Gold-Plated Photoacoustic Cell.

A photoacoustic detection module based on a gold-plated photoacoustic cell was reported in this manuscript to measure hydrogen sulfide (H2S) gas in sewers. A 1582 nm distributed feedback (DFB) diode laser was employed as the excitation light source of the photoacoustic sensor. Operating pressure within the photoacoustic cell and laser modulation depth were optimized at room temperature, and the long-term stability of the photoacoustic sensor system was analyzed by an Allan-Werle deviation analysis. Experimental results showed that under atmospheric pressure and room temperature conditions, the photoacoustic detection module exhibits a sensitivity of 11.39 μV/ppm of H2S and can reach a minimum detection limit (1σ) of 140 ppb of H2S with an integration time of 1 s. The sensor was tested for in-field measurements by sampling gas in the sewer near the Shanxi University canteen: levels of H2S of 81.5 ppm were measured, below the 100 ppm limit reported by the Chinese sewer bidding document.

Site selective and enhanced blue emitting of Eu2+ activated fluorapatite-type phosphors with high color purity for NUV excited pc-wLEDs

As blue emitting component in phosphor-converted white-light-emitting-diodes (pc-wLEDs) encapsulated with near-ultraviolet (NUV) chips, Eu2+ activated fluorapatite structure phosphors play key roles because of strong structural stability and excellent photoluminescent properties. A series of M5(PO4)3F: Eu2+ (M = Ca, Sr) samples have been newly prepared by deposition-precipitation process (DP) and exhibited a 6.7-fold enhancement of photoluminescent (PL) intensity due to the highly dispersed Eu2+ luminescence centers when compared with the reference samples synthesized via traditional solid-state reaction method (SSR). Detailed analysis of crystal field around Eu2+ and the nonlinear fitting of PL spectra concludes that Eu2+ activators with the 4f6 → 4f75d transition preferentially replace Ca1 in 4f symmetry sites leading to a fitted peak at 446 nm and the other sites of 6h are contributed to the 479 nm emitting of Eu2+ ions. Remarkably, tunable chromaticity of DP-M5(PO4)3F: Eu2+ with high color purity (97.79%) retains steady photoelectric converting and full width at half maxima (FWHM) of 46 nm in the device of DP-FAp: 0.03Eu2+@365 nm LED under diverse driving currents, which perfectly satisfies the requirements of excitation light source for oral photocuring materials. Further, the 123.4% color gamut of National Television System Committee (NTSC) standard is efficiently obtained by matching Sr5(PO4)3F: Eu2+, CsPbBr3 and Lu3Al5O12: Mn4+ phosphors with a 365 nm chip (1 W) to achieve high-quality white light (CRI value reaches to 86, CCT is 7107 K and CIE chromaticity coordinate arrives at (0.292, 0.376), indicating a potential candidate for dentistry curing light and high-quality NUV excited pc-wLEDs.

Pulse fluorescence LIDAR system for identification and low concentration measurements of Phaeocystis globosa cells and colonies

A pulse fluorescent LIDAR system (pfLIDAR) for early-warning of Phaeocystis globosa cells and colonies outbreak is developed and demonstrated, which can realize species identification and low concentration measurement of Phaeocystis globosa in water areas. The system utilizes a high-power 532 nm nanosecond pulsed laser as excitation light source and a photomultiplier tube combined with a liquid crystal tunable filter as the detection setup. Measurement of Phaeocystis globosa solitary cells and colonies were performed in a water tank, simulating microalgae distributions and concentrations prior to blooms in real water areas. The concentration of Phaeocystis globosa cells or colonies can be accurately measured based on the received fluorescent echo signals. Obtained echo signals combined with spectral information can be used for species identification of high accuracy using a PCA-SVM method. The system works in staring scanning mode, and a gating technique is used to filter out scattering and background fluorescence noise in water path, which improves the SNR of detected fluorescent echo signals. Experimental demonstration results demonstrate the capability of the system for Phaeocystis globosa identification and biomass assessment, indicating a significant potential of the system for detailed monitoring in aquatic ecosystems.