Green Light-emitting Diodes Research Articles

In-line spectroscopy for iodine quantification in dynamic contrast-enhanced dedicated breast CT.

In 4D dynamic contrast-enhanced dedicated breast computed tomography (4D DCE-bCT), the functional properties of the breast will be characterized by monitoring the uptake and washout of iodine-based contrast agents over time. This information could be valuable in breast cancer treatment. However, prior to clinical implementation, it is crucial to validate the quantitative estimates of iodine concentrations at each time point during acquisition. To develop an in-line spectroscopy system capable of measuring iodine concentrations in a dynamic x-ray breast phantom in real-time. Potassium iodide served as the contrast agent. The system was set-up at both the entrance and exit of the phantom. It comprises a fiber-coupled green LED and collimator, which together ensure that a parallel beam passes through the sample holder. Transmitted light is captured by a collimator on the opposite side and directed through a fiber optic cable to a photodetector for intensity measurement. The relationship between 13 iodine concentrations (0-6mg I/mL) and light transmission was tested, and the system's repeatability and accuracy were determined. The system exhibited a strong correlation between iodine concentration and transmission values, achieving a root-mean-square error of 0.007. The repeated measurements had relative standard deviations of 0.04% and 0.1% for repeated water measurements at the phantom's entrance and exit, respectively. Furthermore, the accuracy measurements gave a mean error of fitting of 0.008(±0.07) mg I/mL. The in-line spectroscopy system can effectively monitor iodine concentrations in a dynamic breast phantom, providing a reliable method for quantitative validation of 4D DCE-bCT.

Proposal for Low-Cost Optical Sensor for Measuring Flow Velocities in Aquatic Environments

The ocean, with its intricate processes, plays a pivotal role in shaping marine life, habitats, and the Earth’s climate. This study addresses issues such as beach erosion, the survival of propagules from species like Posidonia oceanica, and nutrient distribution. To tackle these challenges, we propose an innovative sensor that quantifies hydrodynamic velocity by measuring the output voltage derived from detecting changes in light absorption and scattering using LEDs and LDRs. Our results not only demonstrate the effectiveness of the sensor but also the accuracy of the processing algorithm. Notably, the blue LED exhibited the lowest mean relative error of 7.59% in freshwater, while the yellow LED was most precise in chlorophyll-containing water, with a mean relative error of 6.80%. In a runoff simulation, we observed similar velocities with the blue, green, and white LEDs, 6.89 cm/s, 6.99 cm/s, and 7.05 cm/s, respectively, for nearly identical time intervals. It is important to highlight that our proposed sensor is not only effective but also highly cost-efficient, representing less than 0.43% of the cost of a Nortek Vector 6 MHz and 0.18% of the Teledyne Workhorse II 300 kHz Marine. This makes it a key tool for managing marine ecosystems sustainably.

Bottom Electrode Modification Enables Efficient and Bright Silicon-Based Top-Emission Perovskite Light-Emitting Diodes.

The integration of perovskites with mature silicon platform has emerged as a promising approach in the development of efficient on-chip light sources and high-brightness displays. However, the performance of Si-based green perovskite light-emitting diodes (PeLEDs) still falls significantly short compared to their red and near-infrared counterparts. In this study, it is revealed that the high work function Au, widely employed in Si-based top-emission PeLEDs as the reflective bottom electrode, exhibits considerably lower reflectivity in the green spectrum than in the longer wavelengths. Consequently, Ag electrode is introduced to replace Au to enhance the green light reflectivity, and the ultrathin MoO3 and self-assembled monolayers (SAMs) are sequentially deposited for surface modification. These results indicate that the MoO3 layer removes the energy barrier at Ag/polymer hole transport layer interface, enhancing the hole injection efficiency; while the SAMs firmly anchor onto the MoO3 layer, effectively preventing interfacial defect formation. Benefited from this organic/inorganic dual-layer modification strategy, Si-based green PeLEDs with an impressive peak external quantum efficiency of 18.2% and a maximum brightness of 81931 cd m-2 are successfully fabricated, on par with those of the red and near-infrared counterparts. This achievement marks an advancement in developing high-performance Si-based PeLEDs with full-spectrum output.

High‐performance triboelectric nanogenerators boosted by synergistically aligned piezoelectric/conductive composite nanofibers

AbstractTo address the need for efficient, flexible, and wearable power sources for portable electronics, a high performance triboelectric nanogenerator (TENG) was proposed by incorporating vertically‐aligned barium titanate (BaTiO3)/antimony tin oxide (ATO) nanofibers in polydimethylsiloxane (PDMS) negative triboelectric layer, where BaTiO3 served as piezoelectric material, and ATO served as conductive filler. Silver‐coated conductive fabric was used as electrode to ensure integrability and wearability. By strategically coupling the triboelectric effect of PDMS, the piezoelectric effect of BaTiO3 nanofibers, and the charge transfer effect of ATO nanofibers, the TENG exhibited the optimum output voltage and current of approximately 119 V and 28 μA, and power density of 11.74 μW/cm2, respectively. This device demonstrates its potential applications in energy supply by effectively illuminating 174 commercial green LEDs and charging capacitors for powering electronics. Additionally, the successful integration of the TENG into a smart fencing jacket highlights its utility in practical applications.Highlights TENGs with vertically‐aligned BaTiO3/ATO composite nanofibers was constructed. The output performance of TENGs were enhanced by coupling triboelectric and piezoelectric effects. Conductive ATO nanofibers were incorporated to enhance charge transfer for performance enhancement. A smart fencing jacket with scoring system was developed using the wearable TENG.

Riboflavin‐Catalyzed Photoinduced Atom Transfer Radical Polymerization

AbstractThe photoATRP of methyl acrylate (MA) is investigated using riboflavin (RF) and CuBr2/Me6TREN as a dual catalyst system under green LED irradiation (λ ≈ 525 nm). Both RF and CuBr2/Me6TREN enhanced oxygen tolerance, enabling effective ATRP in the presence of residual oxygen. High molar mass polymers (up to Mn ≈ 129 000 g·mol−1) with low dispersity (Đ ≤ 1.16) are prepared, and chain‐end fidelity is confirmed through successful chain extension. The molecular masses of the obtained polymer increased linearly with conversion and showed high initiation efficiency. Mechanistic studies by laser flash photolysis reveal that the predominant activator generation mechanism is reductive quenching of RF by Me6TREN (83%, under [CuBr2]/[Me6TREN] = 1/3 condition), supported by polymerization kinetics and thermodynamic calculations.

Polyaniline‐Doped Textile‐Based Triboelectric Nanogenerator: Self‐Powered Device for Wearable Electronics

ABSTRACTThe emergence of wearable electronics in contemporary lifestyles has spurred the need for smart fabrics capable of harnessing biomechanical energy. In the present study, a flexible polyaniline‐doped textile‐based triboelectric nanogenerator (PT‐TENG) is designed to harvest low‐frequency mechanical vibrations and convert them into electricity. For the device fabrication, five different textile fabrics are doped with conducting PANI, which is utilized as the tribopositive material, PVC thin film as the tribonegative material, and Al foil as electrodes. The PT‐TENG works in vertical‐contact separation mode, devised in arch structure for easy and complete contact between the working layers. Interestingly, the device featuring a PANI‐doped silk fabric generated the highest output voltage of 257.68 V and a current of 5.36 μA, respectively. Additionally, the PT‐TENG exhibits mechanical durability and electrical stability during continuous 7000 cyclic operations. Furthermore, the PT‐TENG showcases practical applications such as charging commercial capacitors, powering green LEDs and smartwatches, and as a self‐powered touch sensor. Thus, the PT‐TENG offers a facile fabrication process and robustness, highlighting its potential for sustainable energy harvesting in wearable electronics.

Enhancing optical output power efficiency in nitride‐based green micro light‐emitting diodes by sidewall ion implantation

AbstractThough micro‐LED (light‐emitting diode) displays are considered the emerging display technology, the micron‐scale LED chip size encounters severe efficiency degradation that may impact the power budget of the displays. This work proposes an ion implantation method to deliberately create a high‐resistivity sidewall in the InGaN/GaN green LED. Our study demonstrates that ion implantation suppresses reverse leakage current due to the mitigation of sidewall defects. For an LED mesa size of 10 × 10 μm2, optical output power density is improved by 36.2% compared to the device without implantation. Compared to a larger 100 × 100 μm2 device without implantation, we achieve only 21.3% degradation of output power density under 10 A/cm2 injection for a 10 × 10 μm2 LED with implantation. In addition, the ion implantation method can lower the wavelength shift by reducing light emission from the region near the sidewall (where the amount of Indium [In] clustering differs from the mesa region). The results show promise in addressing the efficiency challenges of micro‐LED displays by selective ion implantation.

ATRP with ppb Concentrations of Photocatalysts.

In atom transfer radical polymerization (ATRP), dormant alkyl halides are intermittently activated to form growing radicals in the presence of a CuI/L/X-CuII/L (activator/deactivator) catalytic system. Recently developed very active copper complexes could decrease the catalyst concentration to ppm level. However, unavoidable radical termination results in irreversible oxidation of the activator to the deactivator species, leading to limited monomer conversions. Therefore, successful ATRP at a low catalyst loading requires continuous regeneration of the activators. Such a regenerative ATRP can be performed with various reducing agents under milder reaction conditions and with catalyst concentrations diminished in comparison to conventional ATRP. Photoinduced ATRP (PhotoATRP) is one of the most efficient methods of activator regeneration. It initially employed UV irradiation to reduce the air-stable excited X-CuII/L deactivators to the activators in the presence of sacrificial electron donors. Photocatalysts (PCs) can be excited after absorbing light at longer wavelengths and, due to their favorable redox potentials, can reduce X-CuII/L to CuI/L. Herein, we present the application of three commercially available xanthene dyes as ATRP PCs: rose bengal (RB), rhodamine B (RD), and rhodamine 6G (RD-6G). Even at very low Cu catalyst concentrations (50 ppm), they successfully controlled PhotoATRP. Well-defined polymers with preserved livingness were prepared under green LED irradiation, with subppm concentrations ([PC] ≥ 10 ppb) of RB and RD-6G or 5 ppm of RD. Interestingly, these PCs efficiently controlled ATRP at wavelengths longer than their absorption maxima but required higher loadings. Polymerizations proceeded with high initiation efficiencies, yielding polymers with narrow molecular weight distributions and high chain-end fidelity. UV-vis, fluorescence, and laser flash photolysis studies helped to elucidate the mechanism of the processes involved in the dual-catalytic systems, comprising parts per million of Cu complexes and parts per billion of PCs.

Soft hydrogels obtained by photothermal curing of poly(vinylpyrrolidone)/gold nanoparticles dispersions showing anisotropic swelling and photo-activated antimicrobial properties

Poly(vinylpyrrolidone) (PVP) hydrogels were obtained by green light irradiation of aqueous PVP/ammonium persulfate solutions modified with gold nanoparticles (AuNPs). The increase in temperature produced through the activation of the photothermal effect of AuNPs triggers the decomposition of ammonium persulfate producing radicals that, by attacking the polymer main chain and generating macro-radicals, induce the crosslinking of the polymer via recombination paths. Irradiation from the top of the solutions in an open configuration produced water evaporation and a concomitant increase in temperature during curing, giving rise to dry materials with high aspect ratio and moderate swelling anisotropy. Pads that reversibly adhere to different substrates, including human skin, were produced by simple contact of the final materials with water. Impregnation of gauze wound dressings with PVP-Au-ammonium persulfate dispersions, followed by direct “in situ” photothermal crosslinking, enabled the fabrication of supported functional pads with potential applications as reversible adhesive skin wound dressings. Infusion of the hydrogels with Rose Bengal (RB) provides the materials with photosensitizing properties useful for the photodynamic inactivation of Staphylococcus aureus. A decrease in cell viability of 99.9% was attained after 30 min of irradiation with a low-power green LED source, which demonstrates the efficient singlet oxygen production by RB in the hydrogels and paves the way towards the design of new stimulus-activated bactericidal supplies for biomedical uses.

Reducing red light proportion in full-spectrum LEDs enhances runner plant propagation by promoting the growth and development of mother plants in strawberry.

Full-spectrum light-emitting diodes (LEDs) have gradually replaced narrow-spectrum LEDs and are widely used in plant factories with artificial lighting (PFALs). However, the specific effect of LED light quality on dry mass allocation in runner plant propagation remains unclear. Hence, we cultivated "Akihime" strawberries as mother plants for 115 days to conduct runner plant propagation experiment under white LEDs (W100), white and red LEDs (W84R16 and W55R45), red and blue LEDs (RB100), and red, blue and green LEDs (RB80G20) in PFALs, and determined key factors affecting dry mass accumulation and allocation among mother plants and runner plants based on growth component analysis. The results showed that the net photosynthetic rate and total leaf area in mother plants in W100 increased by 11% and 31%, respectively, compared with W55R45. In comparison to W84R16 and W55R45, W100 increased the dry mass (23%-30%) of runner plants mainly by increasing the total dry mass (TDM) (23%) of strawberry plants, without significantly affecting the fraction of dry mass partitioning to runner plants. However, the number of runners in W55R45 was 5.1 per plant, representing only 78% of that in W100. Compared with RB100, RB80G20 significantly increased the number of runner plants and runner numbers by 16% and 19% to 13.0 per plant and 5.8 per plant, respectively. The partial replacement of blue light with green light in RB80G20 induced a shade avoidance response in runner plants, resulting in a 55% increase in the total leaf area of runner plants compared with RB100. Data from growth component analysis showed that compared with red and blue LEDs, white LEDs increased the TDM of runner plants by 83% by increasing the plant TDM accumulation (44%) and the fraction of dry mass partitioning to runner plants (37%). Additionally, the dry mass (g) of runner plants per mol and per kilowatt-hour under in W100 were 0.11 and 0.75, respectively, significantly higher than other treatments. Therefore, reducing red light proportion in full-spectrum LEDs is beneficial for strawberry runner plant propagation in PFALs.

Light emitting diodes for the improvement of postharvest quality of wild rocket in soilless and soil-bound cultivation systems

Wild rocket (Diplotaxis tenuifolia (L.) DC cv. Dallas) is a leafy green vegetable appreciated for its pungent taste and healthy properties, often consumed as a ready-to-eat product. The cultivation system is crucial in determining the overall quality, while postharvest storage is fundamental for preserving nutritional quality, phytochemicals, and vitamins. This study aimed to investigate the phytochemical content and microbiological quality of soilless (SS) and soil-bound (SB) wild rocket during cold postharvest storage under blue, red, and green Light Emitting Diode (LED). Blue LED increased chlorophylls and carotenoids in SB after two days of storage, and chlorophyll a in SS after seven days. Furthermore, it reduced H2O2 levels after two days (SS and SB) and lipid peroxidation in SB. Red LED increased phenols in both SS and SB but was detrimental to chlorophyll, carotenoids, and oxidative markers. Green LED had less significant effects. Microbiological growth varied with LED treatment: green light increased mesophilic bacteria in SB, and red light did so in SS by day four, while blue light reduced bacterial growth at the end of storage. Overall, Blue LED was the most effective LED in preserving postharvest quality. Soilless cultivation was particularly beneficial in reducing lipid peroxidation and maintaining cell membrane integrity during long-term storage, and it might also be more effective in preserving ascorbic acid. Conversely, soil-bound cultivation methods could enhance initial polyphenol content or better preserve it during early storage. This study highlights the complex interplay of pre-harvest conditions, postharvest quality, and shelf-life performance.

Crystallization and luminescence properties of stable CsPbBr3 Nanocrystals in Li2B4O7 glass

All-inorganic CsPbX3 (X = Cl, Br, and I) perovskite nanocrystals (NCs), have achieved unprecedented advances in opto-electronic applications. However, issues such as poor stability and the volatility of halides in the preparation process continue to hinder their practical applications. Here, lithium tetraborate (Li2B4O7) was chosen as the glass matrix to prepare CsPbBr3 NCs glasses through traditional melting-quenching and heat treatment processes, effectively reducing the glass synthesis temperature to 940 °C. The heat treatment temperature and duration are examined. The Li2B4O7 glass matrix exhibits a uniform structure and high transmittance and CsPbBr3 NCs precipitated uniformly after heat treatment. Among these glasses, the sample heat-treated at 510 °C for 5 h exhibited an optimal photoluminescence quantum yield of 76.1 % and the narrowest full width at half maximum values of 24 nm. Its photoluminescence intensity maintained 96.6 % of its original value after multiple thermal cycles and thermal shocks, demonstrating the sample's robust thermal stability. Finally, by integrating the CsPbBr3 NCs glass sample with a blue chip in simple device packaging, a green light-emitting diode was successfully fabricated, featuring excellent luminescence stability and a color purity of up to 96.4 %, promising for applications in solid-state lighting and display technologies.

Drosophila require both green and UV wavelengths for sun orientation but lack a time-compensated sun compass.

Celestial orientation and navigation are performed by many organisms in contexts as diverse as migration, nest finding and straight-line orientation. The vinegar fly, Drosophila melanogaster, performs menotaxis in response to celestial cues during tethered flight and can disperse more than 10 km under field conditions. However, we still do not understand how spectral components of celestial cues and pauses in flight impact heading direction in flies. To assess individual heading, we began by testing flies in a rotating tether arena using a single green LED as a stimulus. We found that flies robustly perform menotaxis and fly straight for at least 20 min. Flies maintain their preferred heading directions after experiencing a period of darkness or stopping flight, even up to 2 h, but reset their heading when the LED changes position, suggesting that flies do not treat this stimulus as the sun. Next, we assessed the flies' responses to a UV spot alone or a paired UV-green stimulus - two dots situated 180deg apart to simulate the solar and antisolar hemispheres. We found that flies respond to UV much as they do to green light; however, when the stimuli are paired, flies adjust for sudden 90deg movements, performing sun orientation. Lastly, we found no evidence of a time-compensated sun compass when we moved the paired stimuli at 15degh-1 for 6 h. This study demonstrates that wavelength influences how flies respond to visual cues during flight, shaping the interpretation of visual information to execute an appropriate behavioral response.

Real-time Monitoring of Carbon Dioxide with IoT ThingSpeak using TiO2 Thick Film Gas Sensor

Carbon dioxide is a colorless, odorless, and non-flammable gas and is claimed to be the fourth most abundant in the earth's atmosphere. Carbon dioxide emission is mainly generated by human and animal exhalation, decomposition of organic matter, and forest fires. Moreover, human activities in the industrial sector emit high levels of carbon dioxide gas, such as through fossil fuel burning, transportation, and deforestation. It is also an asphyxiant and high exposure to it may lead to health effects in humans such as headaches, breathing difficulty, tiredness, coma, and elevated blood pressure. Therefore, in this paper, a carbon dioxide gas sensor with IoT using TiO2 is proposed to observe varying concentrations of carbon dioxide gas at room temperature. Three similar gas sensors were fabricated via screen-printing technology to compare their performance towards carbon dioxide. The hardware development consisted of an Arduino Uno R3 with ESP 8266 Wi-Fi module, wires, LCD display, red and green LEDs, and a 5V power supply. The ThingSpeak application was integrated with the gas sensor and hardware parts to monitor the carbon dioxide concentration in a real-time system. Gas sensor G1 produced the highest response and highest sensitivity with values of 2.120 and 0.245, respectively.

Green synthesis of cobalt oxide nanoparticles (Co3O4NPs): Characterization and green light-driven photocatalytic aerobic oxidation of alkyl and aryl sulfides to the corresponding sulfoxides

In recent years, cobalt oxide nanoparticles (Co3O4NPs) have garnered significant attention due to their unique properties and wide range of applications, particularly in catalysis and environmental remediation. This study focuses on the green synthesis of Co3O4NPs using garlic extract as a bio-reducing and stabilizing agent, marking the first instance of employing this eco-friendly and cost-effective method. The synthesized nanoparticles were characterized using various techniques including SEM, EDX, FTIR, XRD, UV–Vis DRS, and BET analysis, revealing their spherical morphology, elemental composition, surface area, and optical properties. The primary application investigated was the photocatalytic aerobic oxidation of alkyl and aryl sulfides to sulfoxides under visible green light irradiation. The study meticulously optimized the reaction conditions, evaluating the effects of different solvents, light sources, and catalyst dosages. The optimal conditions were found to be a MeCN:H2O (5:1) solvent system, green LED light (535 nm), and 10 mg of Co3O4NPs catalyst with the highest TON of 12.5. Under these conditions, the catalyst demonstrated high efficiency, achieving up to 95% yield of sulfoxides with various substrates. Furthermore, the reusability of the Co3O4NPs was assessed through multiple catalytic cycles, showing excellent stability and consistent performance. Mechanistic studies indicated that the photocatalytic activity involves the generation of reactive oxygen species (ROS) such as superoxide anion radicals (O2.-) and singlet oxygen (1O2), with both holes and electrons playing crucial roles in the oxidation process. This research highlights the potential of green synthesized Co3O4NPs as effective and sustainable photocatalysts for selective oxidation reactions, offering a promising approach for environmentally benign chemical processes. The findings pave the way for further exploration of bio-derived catalysts in various industrial applications, promoting greener and more sustainable practices in chemical synthesis.

The efficacy of light-guiding microneedle patch for stimulating hair growth in androgenetic alopecia.

Androgenetic alopecia (AGA) is the most common form of hair loss characterized by miniaturization of hair follicles. Low-level light therapy (LLLT) and microneedling have shown potential in promoting hair regrowth. This study aims to evaluate the efficacy of an innovative light-emitting diode (LED) helmet cooperated with a novel light-guiding microneedle patch (LMNP) for stimulating hair growth in AGA. In this randomized clinical trial, 16 AGA patients received treatments using light-guiding microneedle patches (LMNPs) illuminated by a LED helmet equipped with green (522nm) and red (633nm) LEDs, delivering 50mW/cm2 power and 40J/cm2 energy. Treatments were applied weekly for 24weeks, targeting the frontal recession area. The right side of the scalp was treated with green light and the left with red light, each combined with a LMNP featuring 900µm height needles at a density of 105 per square centimeter. Hair density and diameter, along with patient and physician satisfaction scores, were assessed monthly. Both red and green LED treatments with LMNP, significantly enhanced hair density and diameter. Satisfaction scores, as reported by both physicians and participants, increased over time. Comparative analyses revealed no statistically significant differences in average satisfaction scores or in changes in hair density and diameter between the groups by the end of the study. Additionally, no serious adverse effects were reported, highlighting the safety of the treatments. The combined Light sources which is portable LED helmet and LMNPs shows promise as a non-invasive, effective treatment for AGA, with similar efficacy between red and green wavelengths.

Photobiological response of mast cells to green and red light-emitting diodes (LEDs) in cutaneous burns.

This study assessed the effects of red and green LEDs on mast cells (MCs) in third-degree burns in 75 Wistar rats, divided into control, red LED (RED), and green LED (GREEN) groups. Animals were irradiated daily with RED (630 nm, 300 mW, 0.779 W/cm2, 9 J/cm2, 30 s) and GREEN (520 nm, 180 mW, 0.467 W/cm2, 60 J/cm2, 30 s). Histological sections stained with toluidine blue were analyzed for total and subtype MCs. Standardized MC counting was performed across the viable lesion area, considering lesion margins, through intact connective tissue and the integrity of skin appendages. No statistically significant differences in MCs 2 (with released granules and intact cell border) were found between groups. Irradiated groups showed increased total MCs at 7, 14, and 21 days (p < 0.05), with a decrease in MCs 1 (intact MCs) at all time points compared to control (p < 0.05). Significant changes in MCs 3 (with massive degranulation and partial or complete disintegration of the cell border) degranulation were noted in RED at 7, 14, and 21 days (p < 0.009) and in GREEN at 14 (p < 0.009) and 32 days (p < 0.028). Results suggest red and green LEDs modulate MC recruitment and degranulation in third-degree burns.

Solvent-regulated fabrication of Ni-MOF-based asymmetric supercapacitor device

An innovative solvent-controlled technique has been devised to fabricate Ni-BDC through the impurity-free-solvothermal method. X-ray diffraction analysis shows that the synthesized material has a triclinic phase and belongs to the P-1 space group. FESEM and TEM analyses elucidated the nanosheet-like morphology of Ni-BDC (NB1) in a 1:1 solvent mixture comprising of ethanol and DMF. In a three-electrode setup, NB1 displays an outstanding specific capacitance (CS) of 1124 F/g and remarkable cyclic stability (98.2 %) in a 2 M KOH aqueous electrolyte. Moreover, a device was constructed with a voltage range of 1.4 V, utilizing a positive electrode (NB1) in conjunction with a negative electrode composed of activated carbon (AC). The as-fabricated supercapacitor device displays a high capacitance of 359.3 F/g at a current density of 2 A/g, an impressive energy density of 97.8 Wh/kg at a power density of 484.2 W/kg. Three devices were linked in series, they collectively illuminated a green LED.

Photodynamic Therapy Using a Rose-Bengal Photosensitizer for Hepatocellular Carcinoma Treatment: Proposition for a Novel Green LED-Based Device for In Vitro Investigation.

Hepatocellular carcinoma (HCC) is one of the most common cancers worldwide. Despite new treatments, the HCC rate remains important, making it necessary to develop novel therapeutic strategies. Photodynamic therapy (PDT) using a Rose-Bengal (RB) photosensitizer (RB-PDT) could be a promising approach for liver tumor treatment. However, the lack of standardization in preclinical research and the diversity of illumination parameters used make comparison difficult across studies. This work presents and characterizes a novel illumination device based on one green light-emitting diode (CELL-LED-550/3) dedicated to an in vitro RB-PDT. The device was demonstrated to deliver a low average irradiance of 0.62 mW/cm2 over the 96 wells of a multi-well plate. Thermal characterization showed that illumination does not cause cell heating and can be performed inside an incubator, allowing a more rigorous assessment of cell viability after PDT. An in vitro cytotoxic study of the RB-PDT on an HCC cell line (HepG2) demonstrated that RB-PDT induces a significant decrease in cell viability: almost all the cells died after a light dose irradiation of 0.3 J/cm2 using 75 µM of RB (<10% of viability). In conclusion, the RB-PDT could be a therapeutic option to treat unresectable liver lesions and subclinical disease remaining in the post-resection tumor surgical margin.

Ultra-dense Green InGaN/GaN Nanoscale Pixels with High Luminescence Stability and Uniformity for Near-Eye Displays.

Ultra-dense (>4,000 pixels per inch) and highly stable full-color III-nitride nanoscale pixels are crucial for near-eye display technologies like virtual and augmented-reality glasses. In this context, InGaN-based long wavelength green microscale light-emitting diodes face major bottlenecks, such as low efficiency and inadequate wavelength stability. These challenges are associated with the presence of both nonradiative surface defects and the strain induced quantum-confined Stark effect. Herein, we report nanoscale pixelation of green InGaN/GaN LEDs incorporating strain-engineered ultra-dense nanowire (NW) arrays, corresponding to ∼36,000 pixels per inch. The NW pixel arrays exhibit a stable peak wavelength emission at ∼500 nm for over 3 orders of magnitude of injection current densities (from ∼4 A/cm2 to ∼1 kA/cm2). The observed wavelength stability enhancement (a reduced blue-shift of just ∼4 nm) directly results from the suppressed built-in electric field achieved by strain relaxation of the axial multi quantum wells in the NWs. Finite difference time domain simulations show that emission of the pixel array is significantly increased owing to the enhanced spontaneous emission rate (characterized by a high Purcell factor of ≈2) of the ultra-dense NWs. We have demonstrated top-down NWs, where each NW (diameter ranging down to 200 nm) shows excellent uniformity and light output characteristics in direct contrast to bottom-up grown NW heterostructures. The results of this study establish a viable route for realizing nanoscale pixels with high luminescence stability and wafer-scale uniformity with high (>20%) indium composition InGaN/GaN LED heterostructures, for next-generation near-eye displays.