Exact analytical solutions and corresponding Monte Carlo models for the problem of light transport in turbid media with continuous absorption and discrete scattering at the single scattering approximation

Although the radiative transport theory is widely used in various biomedical, ocean, and atmospheric optic problems, there are few light transport problems that can be solved analytically. Therefore, Monte Carlo (MC) numerical simulations are used in most practical applications. In this study, light transport problems in continuously absorbing and discretely scattering media for pencil-like incident beams were considered theoretically using the single scattering approximation. Strict and closed-form analytical solutions to these problems were derived and compared with МС numerical results. Two sets of probabilistic parameters for the MC algorithm were explored. The first was the classical set for media with continuous absorption and smooth scattering, while the second was the newly substantiated set for media with continuous absorption and discrete scattering corresponding to the analytical medium's model. It was shown that if the same model was used in MC simulations and the analytical approach, all of the results were identical. A divergence up to 10% between the obtained analytics and MC results in the case of continuous absorption and smooth scattering was observed.PostprintPeer reviewe

On-chip optical trapping with high NA metasurfaces

The project was supported by the European Research Council (ERC) under the European Union Horizon 2020 Research and Innovation Program (Grant Agreement No. 819346).Optical trapping of small particles typically requires the use of high NA microscope objectives. Photonic metasurfaces are an attractive alternative to create strongly focused beams for optical trapping applications in an integrated platform. Here, we report on the design, fabrication, and characterization of optical metasurfaces with a numerical aperture up to 1.2 and trapping stiffness greater than 400 pN/μm/W. We demonstrate that these metasurfaces perform as well as microscope objectives with the same numerical aperture. We systematically analyze the impact of the metasurface dimension on the trapping performance and show efficient trapping with metasurfaces with an area as small as 0.001 mm2. Finally, we demonstrate the versatility of the platform by designing metasurfaces able to create multisite optical tweezers for the trapping of extended objects.Publisher PDFPeer reviewe

Wavelength-controlled external-cavity laser with a silicon photonic crystal resonant reflector

This work was partially funded by the EPSRC, Scottish Enterprise, and the European Research Council under the Starting Grant 337508.We report the experimental demonstration of an alternative design of external-cavity hybrid lasers consisting of a III-V Semiconductor Optical Amplifier with fiber reflector and a Photonic Crystal (PhC) based resonant reflector on SOI. The Silicon reflector comprises a polymer (SU8) bus waveguide vertically coupled to a PhC cavity and provides a wavelength-selective optical feedback to the laser cavity. This device exhibits milliwatt-level output power and sidemode suppression ratio of more than 25 dB.Publisher PD

Two-tier manipulation of holographic information

The project was supported by the European Research Council (ERC) under the European Union Horizon 2020 research and innovation program (Grant Agreement No. 819346).Here we demonstrate the two-tier manipulation of holographic information using frequency-selective metasurfaces. Our results show that these devices can diffract light efficiently at designed frequency and environmental conditions. By changing the frequency and refractive index of the surrounding environment, the metasurfaces produce two different holographic images. We anticipate that these environmental dependent, frequency-selective metasurfaces will have practical applications in holographic encryption and sensing.Publisher PDFPeer reviewe

Photodynamic therapy offers a novel approach to managing miltefosine-resistant cutaneous leishmaniasis

Funding: Engineering and Physical Sciences Research Council of the UK (grants EP/R035164/1 and EP/L015110/1) and the Scottish Funding Council (ODA GCRF fund grant SFC/AN/12/2017).Cutaneous leishmaniasis (CL) is a neglected disease caused by Leishmania parasites. The oral drug miltefosine is effective, but there is a growing problem of drug resistance, which has led to increasing treatment failure rates and relapse of infections. Photodynamic therapy (PDT) combines a light source and a photoactive drug to promote cell death by oxidative stress. Although PDT is effective against several pathogens, its use against drug resistant Leishmania parasites remains unexplored. Herein, we investigated the potential of organic light-emitting diodes (OLEDs) as wearable light sources, which would enable at-home use or ambulatory treatment of CL. We also assessed its impact on combating miltefosine resistance in Leishmania amazonensis-induced CL in mice. Thein vitro activity of OLEDs combined with 1,9-dimethyl-methylene blue (DMMB) (OLED-PDT) was evaluated against wild-type and miltefosine-resistant L. amazonensis strains in promastigote (EC50 = 0.034 μM for both strains) and amastigote forms (EC50 = 0.052 μM and 0.077 μM, respectively). Cytotoxicity in macrophages and fibroblasts was also evaluated. In vivo, we investigated the potential of OLED-PDT in combination with miltefosine using different protocols. Our results demonstrate that OLED-PDT is effective in killing both strains of L. amazonensis by increasing reactive oxygen species and stimulating nitric oxide production. Moreover, OLED-PDT showed great antileishmanial activity in vivo, allowing the reduction of miltefosine dose by half in infected mice using a light dose of 7.8 J/cm2 and 1.5 μM DMMB concentration. In conclusion, OLED-PDT emerges as a new avenue for at-home care and allows a combination therapy to overcome drug resistance in cutaneous leishmaniasis.Peer reviewe

Organic light-emitting diodes as an innovative approach for treating cutaneous leishmaniasis

Funding: UK Engineering and Physical Sciences Research Council (Grant Number(s): EP/L015110/1).Antimicrobial photodynamic therapy (APDT) has been studied as a non-invasive therapy for treating cutaneous leishmaniasis to overcome challenges with current treatment, such as toxicity, resistance and need for in-patient hospital treatment. Organic light-emitting diodes (OLEDs) have emerged as an attractive technology that can provide wearable light-emitting materials that are conformable to human skin. This makes OLEDs ideal candidates for APDT by light-bandages for ambulatory care. In this work, we successfully develop suitable OLEDs to match the absorbance of three photosensitizers: methylene blue, new methylene blue, and 1,9-dimethyl-methylene blue to inactivate two Leishmania species in vitro: Leishmania major and Leishmania amazonensis. Parasites are treated either by LED (20 mWcm-2) or OLED (6.5 mWcm-2) at increasing photosensitizer concentrations at a radiant exposure of 50 Jcm-2. 1,9-Dimethyl-methylene blue is the most potent photosensitizer, killing both strains at nanomolar concentrations. We also explore the effect of different intensities from the OLEDs (0.7, 1.5, and 6.5 mWcm-2) and show that effective killing of Leishmania occurs even at very low intensity. These findings demonstrate the great potential of OLEDs as a new approach for ambulatory treatment of cutaneous leishmaniasis by APDT.Publisher PDFPeer reviewe

Flexible organic light-emitting diodes for antimicrobial photodynamic therapy

The authors are grateful to the European Research Council (grant 321305) and EPSRC (grant EP/L015110/1) for financial support. The authors would like to acknowledge EU grant Polythea (grant 764837) as well as support from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry of WUT.Bacterial infection is a serious and growing problem as antibiotic resistance grows leading to patient suffering, death and increased costs of healthcare. To address this problem, we propose using flexible organic light-emitting diodes (OLEDs) as light sources for photodynamic therapy (PDT) to kill bacteria. PDT involves the use of light and a photosensitizer to generate reactive oxygen species that kill neighbouring cells. We have developed flexible top-emitting flexible OLEDs with the ability to tune the emission peak from 669-737 nm to match the photosensitizer, together with high irradiance, low driving voltage, long operational lifetime and adequate shelflife. These features enable OLEDs to be the ideal candidate for ambulatory PDT light sources. A detailed study of OLED-PDT for killing S. aureus was performed. The results show that our OLEDs in combination with the photosensitizer methylene blue can kill more than 99% of bacteria, which indicates a huge potential for using OLEDs to treat bacterial infections.Publisher PDFPeer reviewe

Hybrid photonic crystal lasers

Energy efficient Wavelength Division Multiplexing (WDM) is the key to satisfying the future bandwidth requirements of datacentres. As the silicon photonics platform is regarded the only technology able to meet the required power and cost efficiency levels, the development of silicon photonics compatible narrow linewidth lasers is now crucial. We discuss the requirements for such laser systems and report the experimental demonstration of a compact uncooled external-cavity mW-class laser architecture with a tunable Si Photonic Crystal resonant reflector, suitable for direct Frequency Modulation.Postprin

Organic light emitting diode for in vitro antimicrobial photodynamic therapy of Candida strains

Funding: NSF grant 1545852 (OISE:PIRE-SOMBRERO)/CONACyT 251992.Organic light emitting diodes (OLEDs) are very attractive light sources because they are large area emitters and, can in principle, deposited on flexible substrates. These features make them suitable for ambulatory photodynamic therapy (PDT), in fact there are a few reports of in vitro or in vivo OLED based PDT studies for cancer or microbial inhibition but to our best knowledge, none against yeasts. Yeast infections are a significant health risk, especially in low income countries with limited medical facilities. In this work, OLED-based antimicrobial PDT (aPDT), using methylene blue (MB) as photosensitizer (PS), is studied to inactivate opportunistic yeast of four Candida strains of two species: Candida albicans and Candida tropicalis. Before aPDT experiments, fluconazole-resistance was evaluated for all strains, showing that both strains of C. tropicalis were resistant and both strains of C. albicans were sensitive to it. We found that is useful for aPDT and that 3 repetitive irradiations work better than a single dose while keeping the total fluence constant, and that this result applies whether or not the strains are resistant to fluconazole.PostprintPeer reviewe