Wavelength Light-emitting Diodes Research Articles

Comparison of different spectral ranges of UV-LED lighting for outdoor mosquito trapping in forested area in Thailand.

Mosquito surveillance is critical for actively tracking the location and monitoring population levels and the threat of mosquito-borne disease. Although light-emitting diodes (LEDs) light traps have grown in popularity, there is still a limited understanding of the application of light wavelengths for trapping nocturnally active wild mosquitoes in forest ecotypes. This study evaluated the performance of different UV wavelengths in trapping mosquito populations in a forested mountainous area in Nakhon Ratchasima province, Thailand. Traps with different UV wavelengths were deployed in 6 locations, following a 6 × 6 Latin square replicated 6 times over a total of 36 nights. Light traps were operated between 18:00 and 06:00 h from October 2022 to August 2023. Mosquitoes were separately collected from individual traps every 4 h at 22.00, 2.00, and 6.00 h. Mosquitoes were killed by placing in a freezer (- 20 °C) for at least 30 min and then were morphologically identified using illustrated keys for adult females. Traps fitted with the LED 365 wavelength light source were the most effective in capturing 790 (23.66%) of the total mosquitoes collected, followed by the UV fluorescent 632 (18.93%), with the other 4 LED wavelengths collecting between 16.89% (LED 385) and 12.64% (LED 375) of the mosquitoes. Culex was the most common genus, representing 56.00% of total mosquito abundance. LED 365 and LED 385 were comparable to the UV fluorescent traps (the standard reference). Optimal trapping times were during 18:00-22:00 h. Compared to the other wavelengths, LED 365 was significantly more effective at capturing Coquillettidia and Culex mosquitoes than the UV-based traps.

Developing a Multi-Spectral NIR LED-Based Instrument for the Detection of Pesticide Residues Containing Chlorpyrifos-Methyl in Rough, Brown, and Milled Rice.

A recent study showed the potential of the DA Perten 7200 NIR Spectrometer in detecting chlorpyrifos-methyl pesticide residue in rough, brown, and milled rice. However, this instrument is still lab-based and generally suited for point-of-sale testing. To provide a field-deployable version of this technique, an existing light emitting diode (LED)-based instrument that provides discrete NIR wavelength illumination and reflectance spectra over the range of 850-1550 nm was tested. Spectra were collected from rough, brown, and milled rice at different pesticide concentrations and analyzed for quantitative and qualitative measurement using partial least squares regression (PLS) and discriminant analysis (DA). Simulations for two LED-based instruments were also evaluated using corresponding segments of spectra from the DA7200 to represent LED illumination. For the simulation of the existing LED-based instrument (LEDPrototype1) fitted with 850, 910, 940, 970, 1070, 1200, 1300, 1450, and 1550 nm LED wavelengths, resulting R2 ranged from 0.52 to 0.71, and the correct classification was 70.4% to 100%. The simulation of a second LED instrument (LEDPrototype2) fitted with 980, 1050, 1200, 1300, 1450, 1550, 1600, and 1650 nm LED wavelengths showed R2 of 0.59 to 0.82 and correct classifications of 66% to 100%. These LED wavelengths were selected based on the significant wavelength regions from the PLS regression coefficients of DA7200 and the commercial availability of LED wavelengths. Results showed that it is possible to use a multi-spectral LED-based instrument to detect varying levels of chlorpyrifos-methyl pesticide residue in rough, brown, and milled rice.

The effect of different LED wavelengths used in the cultivation of Pleurotus ostreatus on quality parameters of the mushroom during the storage process

This study aimed to investigate the effects of light emitting diodes (LEDs) of different wavelengths (white, red, blue and green) used in Pleurotus ostreatus cultivation on post-harvest mushroom quality, storage process and maintenance of mushroom quality characteristics during storage. The mushroom was exposed to different LED wavelengths for 8 and 12 h per day during fructification period. The effects of these treatments were observed during post-harvest and storage periods, focusing on changes in color, weight loss, antioxidant capacity (FRAP), and total phenolic content (TPC). The harvested mushrooms were stored at 1 °C for 12 days, and samples were taken every 4 days to analyze mentioned parameters. After harvest, L*,a*,b* values of the fruiting bodies grown under different LEDs ranged 56.5 − 69.8, 2.0 − 3.84, 12.2 − 15.9 respectively, whereas TPC and FRAP values varied from 54.4 to 78.5 mg GAE/100 g fw and 6.14 to 7.59 µmol TE/g fw, respectively. The values of L*, a*, b*, browning index (BI), and yellowness index (YI) demonstrated a clear postponement of discoloration in the samples exposed to 8 h of red LED and 12 h of green LED compared to the control group at the end of the storage period. The TPC of the fruitbody cultivated under red LED (8 h per day) was markedly increased after 12 days (54.4 to 95.1 mg GAEs/100 g fw), but LEDs did not affect the maintenance of antioxidant capacity in P. ostreatus. The results showed that red LED applied for 8 h per day during the fructification period enhanced TPC with minimal effects on the color during cold storage.

The use of LEDs for the stomatal response, light compensation points, and storage of spinach and kale

The spectral composition of some light-emitting diodes (LEDs) reportedly results in higher crop yield, prevents wilting, and reduces thermal damage to plants. The use of LEDs for postharvest storage and shelf-life extension has been limited, but the potential of this technology will allow for greater applications in horticulture and the food industry. In this experiment, ‘Winterbor’ kale (Brassica oleracea) and ‘Melody’ spinach (Spinacia oleracea) plants were measured for the light compensation point and stomatal response under 14 different wavelengths of light ranging from 405 to 661 nm. Data collected from these measurements were used to select two different wavelengths of LEDs and determine the proper irradiance levels for an LED irradiance storage test on spinach and kale. Treatments comprising blue, red, and amber lights were effective at increasing the stomatal opening, while the green light resulted in reduced stomatal opening. For spinach, the light response curve showed that light compensation points at 500 nm and 560 nm were 65.3 and 64.7 μmol m−2 s−1, respectively. For kale, the light compensation points at 500 nm and 560 nm were 50.8 and 44.1 μmol m−2 s−1, respectively. For the storage test experiment at room temperature, kale and spinach were stored under four different treatments: dark treatment (control), standard white fluorescent light, 500 nm, and 560 nm LED wavelengths. For spinach, the moisture content was 70.1% at 560 nm and 53.7% for dark, moisture losses of 41.5% under the 560-nm treatment and 52.0% for the dark treatment. The fresh basis moisture content was 74.6% at 560 nm and 59.3% in the dark. Moisture loss under the 560 nm treatment was 39.6% while the dark treatment had a 54.0% moisture loss. A visual assessment scale was monitored, 560 nm resulted in the top visual quality for kale compared to the other treatments with the lowest visual quality under the dark treatment at day 4. For spinach, the visual quality for 560 nm treatment was statistically the standard white fluorescent light and 500 nm, with poor-quality product occurring by day 4 and the lowest-quality product occurring at day 5. The LED treatments improved the shelf life of spinach and kale, likely as a result of stomatal aperture closure, photosynthetic rate near the light compensation point and stability of the atmospheric moisture content. This study provides valuable information on the extension of the shelf life of leafy greens during storage. Reducing fresh produce waste in grocery stores will increase revenue, thereby benefiting the Canadian economy while providing social and environmental benefits that entail increased food security and reduced food waste.

Dynamics of carrier injection through V-defects in long wavelength GaN LEDs

The efficiency of high-power operation of multiple quantum well (QW) light emitting diodes (LEDs) to a large degree depends on the realization of uniform hole distribution between the QWs. In long wavelength InGaN/GaN QW LEDs, the thermionic interwell hole transport is hindered by high GaN barriers. However, in polar LED structures, these barriers may be circumvented by the lateral hole injection via semipolar 101¯1 QWs that form on the facets of V-defects. The efficiency of such carrier transfer depends on the transport time since transport in the semipolar QWs is competed by recombination. In this work, we study the carrier transfer from the semipolar to polar QWs by time-resolved photoluminescence in long wavelength (green to red) LEDs. We find that the carrier transfer through the semipolar QWs is fast, a few tens of picoseconds with the estimated room temperature ambipolar diffusion coefficient of ∼5.5 cm2/s. With diffusion much faster than recombination, the hole transport from the p-side of the structure to the polar QWs should proceed without a substantial loss, contributing to the high efficiency of long wavelength GaN LEDs.

Enhancing fucoxanthin production in Chaetoceros calcitrans under mixotrophic condition and LED wavelength shift strategy

This study addresses the challenge of achieving high fucoxanthin (Fx) productivity in Chaetoceros calcitrans under mixotrophic cultivation which often struggle to simultaneously increase biomass and Fx content. To overcome this, we investigated the potential of C. calcitrans for Fx production under mixotrophic conditions by investigating the interaction of organic carbon, light intensity, and light emitting diode (LED) color shifts during cultivation to optimize Fx production. Results revealed significant influences of various organic carbon sources on Fx productivity, with glycerol and glucose showing promising outcomes. Furthermore, the addition of external urea enhanced Fx content in mixotrophic cultivation. Response Surface Methodology (RSM) analysis highlighted the synergistic effect of light intensity and glycerol addition on Fx productivity. Most notably, shifting from white to blue LED during mixotrophic cultivation at the end of the exponential phase significantly increased Fx productivity in C. calcitrans to 3.2 mg L−1 d−1, representing a 1.3-fold enhancement compared to white LED sources. These findings underscore the potential of mixotrophic cultivation and LED color shifts as effective strategies for improving Fx productivity in diatoms.

(276) Light Emitting Diodes (LED) as a Potential Therapy for Erectile Function: A Preclinical Study in a Cavernous Nerve Injury Model

Abstract Introduction Erectile dysfunction (ED) induced by nerve injury including prostatectomy poorly responds to PDE5 inhibitor and requires invasive treatment. Light emitting diodes (LED) in some spectral range, is able to irradiate cells without overheating for its low energy consumption and to enhance mitochondrial metabolism, intracellular energy transfer, and thereby cell proliferation and tissue regeneration in some organs. We, herein, investigated whether and how LED therapy may improve penile erection in mouse cavernous nerve injury (CNI) - induced ED model Objective To identify the optimal LED parameters using molecular, histological, and erectile function analysis in cavernous nerve injury. Methods Eight week old male mice (n=120) were divided into 5 age-matched groups, a sham operation group receiving heat treatment, a CNI group receiving heat treatment, a CNI group receiving red light of LED (wavelength; 660 ±3% nm), a CNI group receiving near infrared light of LED (wavelength; 830 ±2% nm), and a CNI group receiving combination of both LED light. Mice were exposed to LED light for 30 minutes on the ventral side including penis for 5 consecutive days after CNI operation. Molecular study, histopathological analysis of the penis and erectile function test were done 2 weeks following the treatment in each subject. Results CNI group with heat treatment had much lower maximum and total ICP than sham control group. In contrast, three groups with LED light irradiation exhibited considerably improved maximum and total ICP, and the group with both LED treatments had the best erectile performance, reaching 90% of the sham surgery group. Histologically, mice treated with RED, NIR, or LED irradiation had more cavernous pericytes and endothelial cells than CNI mice after sham operation. In addition, all three CNI groups with various LED lengths improved neuroprotection and brain regeneration in CNI mice. All groups treated with LED showed increased expression of βIII-tubulin, neurofilament-1, and nNOS in cavernous tissue and dorsal nerve bundle. Additionally, LED treatment in three groups, particularly the combination group, significantly increased βIII-tubulin, S100, and myelin basic protein levels, indicating axonal integrity or expansion in the dorsal root and major pelvic ganglions. Molecular analysis of downstream signals of neural regeneration or angiogenesis showed that 3 groups with LED treatment increased phosphorylated PI3K, neurotrophic factors like BDNF, NGF, and NT-3, and angiogenic factors like angiopoietin1 and vascular endothelial growth factor in cavernous tissue and llpopolysaccharide-treated PC-12 cells. The TUNEL assay and BrdU staining of these tissue and cells showed lower cell apotosis and proliferation in LED-treated groups. Conclusions The results show that LED therapy with RED, NIR, preferably combination of each wavelength improves penile erection by neural progection or regeneration in cavernous nerve injury induced-ED. This noninvasive therapy may be useful in near future for ED refractory to PDE5 inhibitor. As far as we are aware, this is the first research to demonstrate the advantage of LED therapy, low level in sexual dyfunction field. Disclosure No.

Regeneration of African Violet in Response to Light Quality

Light-emitting diode (LED) technology is a form of artificial lighting that offers precise control over spectral composition, creating specific conditions for plant growth and development. However, the influence of various LED wavelengths on the regeneration characteristics in African violet (AV) has not been extensively explored. This study aims to investigate the changes in the regeneration traits of AV when exposed to different LED light colors within controlled conditions. In this study, AV leaf cuttings were prepared and subjected to white, red, blue, and red + blue light colors for a period of three months in a growth chamber. Afterward, they were transferred to the laboratory for further analysis. The results indicated that the AVs treated with red + blue colors exhibited the most significant improvement in several morpho-physiological traits of both the roots and shoots. The highest total biomass (2.96 g), shoot fresh weight (1.76 g), root dry weight (0.14 g), root volume (3.10 cm3), and shoot length (1.60 cm) were observed in this treatment group. Furthermore, the highest levels of photosynthetic pigments, such as chlorophyll a, chlorophyll b, and carotenoids (0.14, 0.12, and 3.80 mg g−1 f.w., respectively), were predominantly observed in the red + blue treatment group. In conclusion, this study introduces a novel methodology for optimizing lighting conditions to enhance the regeneration of African violets, shedding light on the potential for improving AV regeneration practices.

Application of Red and Blue LED Light on Cultivation and Postharvest of Tomatoes (Solanum lycopersicum L.).

Currently, light-emitting diode (LED) technology has produced a more energy-efficient and versatile technology as an artificial lighting system that can be applied in the agricultural sector. Artificial lighting technology has been proven to be effective in increasing the production of agricultural products, especially horticultural commodities. As one of the primary horticulture commodities, tomatoes are the most common crop produced in controlled environments with LED artificial lighting. The focus of this study is to describe the application of LED lights in tomato cultivation and postharvest. We provide an amalgamation of the recent research achievements on the impact of LED lighting on photosynthesis, vegetative growth, flowering, production, and postharvest of tomatoes. Red-blue (RB) lighting induces photosynthesis; increases the content of chlorophyll a, chlorophyll b, and carotenoids in tomato leaves; regulates vegetative growth in tomatoes; and increases the production of tomatoes. In postharvest tomatoes, blue LED lighting treatment can slowly change the color of the tomato skin to red, maintain hardness, and increase shelf life. Future research may be carried out on the effect of LED artificial lighting on tomatoes' phytochemical, antioxidant and other crucial nutritional content. Different LED wavelengths can be explored to enhance various bioactive compounds and health-promoting components.

Adjunctive effect of 470-nm and 630-nm light-emitting diode irradiation in experimental periodontitis treatment: a preclinical study.

This study investigated the adjunctive effect of light-emitting diodes (LEDs) in the treatment of experimental periodontitis. Experimental periodontitis was induced by placing ligatures around the mandibular second, third, and fourth premolars of 6 beagles for 3 months. After ligature removal, periodontitis progressed spontaneously for 2 months. The animals' hemimandibles were allocated among the following 3 groups: 1) no treatment (control), 2) scaling and root planing (SRP), and 3) SRP with LED irradiation at 470-nm and 630-nm wavelengths (SRP/LED). The probing pocket depth (PPD) and gingival recession (GR) were measured at baseline, 6 weeks, and 12 weeks. The clinical attachment level (CAL) was calculated. After 12 weeks, histological and histomorphometric assessments were performed. The distances from the gingival margin to the apical extent of the junctional epithelium (E) and to the connective tissue (CT) attachment were measured, as was the total length of soft tissue (ST). PPD and CAL increased at 12 weeks compared with baseline in the control group (6.31±0.43 mm to 6.93±0.50 mm, and 6.46±0.60 mm to 7.61±0.78 mm, respectively). PPD and CAL decreased at 12 weeks compared with baseline in the SRP group (6.01±0.59 to 4.81±0.65 mm, and 6.51±0.98 to 5.39±0.93 mm, respectively). PPD and CAL decreased at 12 weeks compared with baseline in the SRP/LED group (6.03±0.39 to 4.46±0.47 mm, and 6.11±0.47 to 4.78±0.57 mm, respectively). The E/ST and CT/ST ratios significantly differed among the 3 groups (P<0.05). The clinical parameters and histologic findings demonstrated that 470-nm and 630-nm wavelength LED irradiation accompanying SRP could improve treatment results. Within the study limitations, 470 nm and 630 nm wavelength LED irradiation might provide additional benefits for periodontitis treatment.

Material classification based on a SWIR discrete spectroscopy approach

A crucial yet difficult task for waste management is the identification of raw materials like plastic, glass, aluminum, and paper. Most previous studies use the diffused reflection spectroscopy for classification purposes. Despite the benefits in terms of speed and simplicity offered by modern compact spectrometers, their cost and the need for an external, wide-spectrum source of illumination create complications. To address this issue, the present paper proposes a discrete spectroscopy method that utilizes short-wave infrared (SWIR) reflectance to identify waste materials, exploiting a small set of selected wavelengths. This approach reduces the complexity of the classification data analysis and offers a more practical alternative to the conventional method. The proposed system comprises a single germanium photodetector and 10 different light emitting diodes (LEDs). The LED wavelengths are selected to maximize the system sensitivity towards a set of seven different waste materials. Using a classification strategy relying on support vector machines, the proposed methodology reaches a classification accuracy up to 98%.

Effects of various light-emitting diode wavelengths on periodontopathic bacteria and gingival fibroblasts: An in vitro study

BackgroundIn recent years, light has been used for bacterial control of periodontal diseases. This in vitro study evaluated the effects of light-emitting diode (LED) irradiation at different wavelengths on both Porphyromonas gingivalis and human gingival fibroblasts (HGF-1). MethodsP. gingivalis suspension was irradiated with LEDs of 365, 405, 450, 470, 565, and 625 nm at 50, 100, 150, and 200 mW/cm2 for 3 min (radiant exposure: 9, 18, 27, 36 J/cm2, respectively). Treated samples were anaerobically cultured on agar plates, and the number of colony-forming units (CFUs) was determined. Reactive oxygen species (ROS) levels were measured after LED irradiation. The viability and damage of HGF-1 were measured through WST-8 and lactate dehydrogenase assays, respectively. Gene expression in P. gingivalis was evaluated through quantitative polymerase chain reaction. ResultsThe greatest reduction in P. gingivalis CFUs was observed on irradiation at 365 nm with 150 mW/cm2 for 3 min (27 J/cm2), followed by 450 and 470 nm under the same conditions. While 365-nm irradiation significantly decreased the viability of HGF-1 cells, the cytotoxic effects of 450- and 470-nm irradiation were comparatively low and not significant. Further, 450-nm irradiation indicated increased ROS production and downregulated the genes related to gingipain and fimbriae. The 565- and 625-nm wavelength groups exhibited no antibacterial effects; rather, they significantly activated HGF-1 proliferation. ConclusionsThe 450- and 470-nm blue LEDs showed high antibacterial activity with low cytotoxicity to host cells, suggesting promising bacterial control in periodontal therapy. Additionally, blue LEDs may attenuate the pathogenesis of P. gingivalis.

Blue Light-Emitting Diode Irradiation Without a Photosensitizer Alters Oral Microbiome Composition of Ligature-Induced Periodontitis in Mice.

Objective: This study investigated the suppressive effects of blue light-emitting diode (LED) irradiation on bone resorption and changes in the oral microbiome of mice with ligature-induced periodontitis. Background: Wavelength of blue light has antimicrobial effects; however, whether blue LED irradiation alone inhibits the progression of periodontitis remains unclear. Methods: Nine-week-old male mice ligated ligature around the right maxillary second molar was divided into ligation alone (Li) and ligation with blue LED irradiation (LiBL) groups. The LiBL group underwent blue LED (wavelength, 455 nm) irradiation four times in a week at 150 mW/cm2 without a photosensitizer on the gingival tissue around the ligated tooth at a distance of 5 mm for 5 min. The total energy density per day was 45 J/cm2. Bone resorption was evaluated using micro-computed tomography at 8 days. Differences in the oral microbiome composition of the collected ligatures between the Li and LiBL groups were analyzed using next-generation sequencing based on the 16S rRNA gene from the ligatures. Results: Blue LED irradiation did not suppress bone resorption caused by ligature-induced periodontitis. However, in the LiBL group, the α-diversity, number of observed features, and Chao1 were significantly decreased. The relative abundances in phylum Myxococcota and Bacteroidota were underrepresented, and the genera Staphylococcus, Lactococcus, and Lactobacillus were significantly overrepresented by blue LED exposure. Metagenomic function prediction indicated an increase in the downregulated pathways related to microbial energy metabolism after irradiation. The co-occurrence network was altered to a simpler structure in the LiBL group, and the number of core genera decreased. Conclusions: Blue LED irradiation altered the composition and network of the oral microbiome of ligature-induced periodontitis in mice.

Influence of different LED wavelengths on retinal melatonin levels - A rodent study

BackgroundRetinal melatonin is crucial for neuroprotection. Exposure to light-emitting diodes (LEDs) affects retinal neurons, possibly influencing retinal melatonin levels. Hence, we aimed to quantify the retinal melatonin level with different LED wavelengths. MethodA total of 24 Sprague Dawley (SD) male rats were divided into four groups (n = 6 in each group) as normal controls (NC), blue light (BL), white light (WL), and yellow light (YL). The rats in the experimental groups were exposed to different wavelengths of LEDs for 28 days (12:12 h light-dark cycle) with uniform illumination of 450–500 lx. Following exposure, the rats were subjected to behavioral tests such as passive avoidance and elevated plus maze tests. Following the behavior tests, the rats were sacrificed, eyes were enucleated, and retinal tissue was stored at −80 °C. The homogenized retina was used for reactive oxygen species (ROS) and melatonin quantification using an enzyme-linked immunosorbent assay (ELISA) kit. ResultsPassive avoidance test revealed a significant difference across the groups (p < 0.0004). The BL exposure group demonstrated increased latency to enter the dark compartment (DC) and impaired motor memory. The elevated plus maze test revealed a significant difference across all the groups (p < 0.012), where the time spent in the closed arm was greater in the BL exposure group. Comparison of ROS levels revealed a significant difference across the groups (p < 0.0001), with increased nitric oxide concentrations in the experimental groups. Melatonin levels were significantly decreased in the light exposure groups (p < 0.0001) compared to the NC group. ConclusionCumulative exposure to different LED wavelengths resulted in increased anxiety with impaired motor activity. This was also complemented by the addition of oxidative stress leading to decreased melatonin levels in the retina, which might trigger retinal neuronal damage.

Reduction of nanoparticle size and promotion of cell membrane permeability by LED irradiation

To improve the efficiency of poly (D, L-lactic-co-glycolic acid) (PLGA) nanoparticles (NP) as a gene carrier for the transfection of human mesenchymal stem cells (hMSCs), we developed a light-emitting diode (LED)-induced gene delivery system. The size of NP produced at various LED wavelengths (blue, green, red, and NIR) was controlled in the colloidal state (a mixture of single particles and agglomerates). In addition, physical stimulation of cell membranes using two LED wavelengths (blue and near infrared (NIR)) altered their structure and facilitated the penetration of cells with extracellular substances. The reduction of NP size and increase in cell membrane permeability effectively increased gene delivery to cells and protein expression by improving transfection processes (cellular uptake, endosomal escape, and PEI-gene dissociation). The effects of 10 min irradiation at each LED wavelength were compared with those of the non-irradiated sample. The reduction of NP size by LED irradiation was confirmed using DLS, SEM, and Nanosight, and cell membrane permeability was assessed by confocal laser microscopy and FACS. Transfection efficiency was measured using confocal laser microscopy, FACS, and Western blot analysis. Among the tested LED wavelengths, NIR light irradiation was the most effective in reducing NP size and increasing cell membrane permeability. Conversely, blue light irradiation significantly increased gene delivery to cells by accelerating transfection processes. Thus, the LED-irradiation mediated NP dispersion method improved the delivery efficiency of PLGA NP as gene carrier, and by enhancing cell membrane permeability, extracellular substances that normally cannot easily penetrate the cell membrane were delivered in a timely and effective manner.

The effect of different LED wavelengths on the components and biosynthesis of isoflavonoid in sprout Astragalus membranaceus.

An artificial light source is the optimal element for studying the usability of the medicinal plant Astragalus membranaceus as a sprout vegetable. Based on artificial light source conditions, formononetin (FO) level was the highest (2.6 mg/L) in A. membranaceus exposed to white light emitting diode (LED) light, and calycosin (CA) level was the highest (3.09 mg/L) in the plant exposed to red LED light. According to the publicly available transcriptome data of LED-exposed sprout A. membranaceus LED, reference genes related to the content enhancement of FO, an isoflavone compound, and those related to the content enhancement of CA were selected. The expression patterns of these genes were assayed using qPCR. Among the genes related to FO enhancement, Gene-225190T showed the highest mRNA levels in cells of LED-white light-exposed sprout A. membranaceus; among the genes related to CA enhancement, Gene_042770T showed the highest expression under red LED light. Most genes related to the overall biosynthesis regulation of flavonoids of the upper concept of isoflavone were highly expressed in response to red LED light, and the transcriptional level of 4CL in response to red LED light was the highest. Based on these results, the artificial light sources that regulated the FO and CA contents in sprouts A. membranaceus were white and red LED lights, and the selected reference genes were capable of regulating isoflavone biosynthesis.

Antifungal efficacy of LEDs against major postharvest pathogens of litchi fruit in vitro and in vivo

Postharvest fruit diseases in litchi (Litchi chinensis Sonn.) caused by fungi are one of the major problems in the fruit industry. Light-emitting diodes (LEDs) technology is a promising alternative to fungicides to control postharvest fungal decay. This study aimed to evaluate the antifungal potential of LEDs against postharvest pathogens Geotrichum candidum and Fusarium sp. isolated from litchi fruit in vitro and in vivo. Results showed that violet light (410–420 nm) was more effective at inhibiting both fungi than other wavelengths of LED. The inhibition effect was dose-dependent, with spore germination completely inhibited and mycelial growth inhibited by about 65–79% when LED illumination for 10 h. In vivo assays demonstrated that LED reduced the population of G. candidum and Fusarium sp. by more than 2 log CFU/g (∼99%) on litchi fruit. However, different surface characteristics of the fruit produced different shielding effects on this technology. In addition, there were also species specificity in the inactivation effect, with Fusarium sp. being more resistant to LED than G. candidum. Notably, the antifungal efficacy at 25 °C was greater than at lower temperatures. These results demonstrate that LED holds great potential as a postharvest preservation technology for reducing the risk of fruit spoilage. The efficacy of treatment could be associated with multiple factors (e.g., wavelengths, exposure duration, temperature, fungal species, and fruit surface characteristics) and therefore needs to be well considered when applying the technique in food systems.

Performance Improvement of InGaN-Based Red Light-Emitting Diodes via Ultrathin InN Insertion Layer

The serious separation of electron–hole wavefunctions, which is caused by the built-in electric field, prevents electron–hole radiative recombination in quantum wells (QWs) in high-In-content InGaN-based red light-emitting diodes (LEDs). Here, we propose a staggered structure that inserts an ultrathin InN layer in the single quantum well (SQW) to reduce the piezoelectric polarization and suppress the quantum confined Stark effect (QCSE). We have numerically simulated the effects of SQW with the InN insertion layer (IL) on the energy band structure and electron–hole wavefunctions of the red LED. Owing to alleviated piezoelectric polarization and improved overlaps of electron–hole wavefunctions, the simulation results have revealed that the internal quantum well (IQE) of the red LED with InN IL exhibits 42% higher than that of the red LED with a square-shaped QW (SSQW) at 60 A/cm2, and the efficiency droop ratio of red LED with InN IL is 48% lower than that of red LEDs with SSQW. Furthermore, we have found that the position of InN IL can affect the energy states of carriers, which has a great influence on the IQE and peak emission wavelength of red LEDs.

Carrier dynamics in blue, cyan, and green InGaN/GaN LEDs measured by small-signal electroluminescence

We study the carrier dynamics for c-plane InGaN/GaN light-emitting diodes (LEDs) with various emission wavelengths near the green gap using a small-signal electroluminescence method. The LEDs were grown by Lumileds using state-of-the-art growth conditions. Radiative and non-radiative recombination rates are numerically separated, and the carrier recombination lifetime and carrier density are obtained. Experiment shows that the causes of efficiency reduction at longer wavelength in the present structures are injection efficiency decrease, radiative recombination rate decrease, and imbalance of the increase in Auger–Meitner and radiative terms due to the interplay between the carrier–current density relationship and the quantum-confined Stark effect (QCSE). The effects of QCSE, phase-space filling, and the carrier–current density relationship on efficiency reduction at longer wavelengths are examined separately with experimental data and Schrödinger–Poisson calculations. In addition, we confirm the scaling law between Cn and Bn under electrical injection and find that the increase in carrier density at a given current density is the primary cause for lower radiative efficiency at high current density in longer wavelength LEDs. Conversely, we do not observe a significant efficiency reduction at longer wavelengths from extrinsic material degradation.

On-chip mixing of cancer cells and drug using LED enabled 2D opto-wetting droplet platforms

Droplets of microliter size serve as miniaturized reaction chambers for practical lab on a chip (LoC) applications. The transportation and coalescence of droplets are indispensable for realizing microfluidic mixing. Light can be used as an effective tool for droplet manipulation. We report a novel platform for LED-based transport and mixing of cell-encapsulated microdroplets for evaluating dose response of cancer drugs. Microcontroller enabled LEDs (Light-emitting diodes) were used to actuate droplet movement on Azobenzene coated planar silicon substrates. Droplet transport was initiated by the spatial gradient in solid-liquid interfacial tension developed through LED triggered photoisomerization of Azobenzene substrate. Detailed UV-Visible characterization of Azobenzene molecule was performed for different LED light intensities and wavelengths. A complete standalone opto-wetting toolbox was developed by integrating various components such as a microcontroller, UV LED (385 nm), blue LED (465 nm), and Azobenzene coated photoresponsive substrate. 2D transport of DI water droplets (10–30 μl) along simple trajectories was demonstrated using this device. Subsequently, the proposed opto-wetting platform was used for performing drug evaluation through on-chip mixing of droplets containing cancer cells (A549—Lung cancer cells) and cancer drug (paclitaxel). Separate cell viability analysis was performed using MTT assays, where the cytocompatibility of Azobenzene and UV light (385 nm) on A549 cells were studied. The dosage response of paclitaxel drug was studied using both MTT (3-(4,5-Dimethylthiazolyl-2)−2,5-diphenyltetrazolium bromide) and live-dead cell assays. The results obtained indicate the potential use of our device as a cost-effective, reliable opto-wetting microfluidic platform for drug screening experiments.