Traditional Ultraviolet Research Articles

Quantitative 31P NMR Spectroscopy Platform Method for the Assay of Oligonucleotides as Pure Drug Substances and in Drug Product Formulations Using the Internal Standard Method.

One of the most widely used techniques for the quantification of small interfering ribonucleic acid (siRNA) is the ultraviolet (UV) spectroscopy method. However, due to uncertainties in the extinction coefficient affecting the accuracy of the method and a sample preparation including several dilution steps, the purpose of this study was to explore the possibility of determining the content of siRNA by a platform method using quantitative 31P nuclear magnetic resonance (31P-qNMR) and the internal standard method. In this paper, acquisition time, selection of a suitable internal certified reference material, signal selection used for quantification, relaxation delay, and precision are discussed. In addition, the robustness of the method and the ability to apply this platform method to both drug substance (DS) and drug product samples is also discussed. Quantifications of siRNA determined by the 31P-qNMR platform method were on average 98.5%w/w when adjusting for the sodium and water contents. The data confirmed the applicability of 31P-qNMR in siRNA content determinations. The quantifications were compared to quantifications determined by the traditional UV spectroscopy method by F- and t-tests. The statistical tests showed that the platform 31P-qNMR method provided more accurate results (mass balance close to 100% w/w) compared to the traditional UV spectroscopy method when analyzing DS samples.

Flexible and transparent polylactic acid/hydrophobically modified nanobagasse cellulose/tannic acid/MXene films with highly efficient ultraviolet shielding

Ultraviolet (UV) radiation is potentially harmful to human health, while traditional petroleum-based conventional UV shielding materials can damage the environment, which necessitates the development of environmentally friendly transparent UV shielding materials. Ti3C2 (MXene) nanosheets were dispersed in a polylactic acid (PLA) matrix via the synergistic effect of hydrophobically modified nanobagasse cellulose (HC-NBC) and tannic acid (TA) to prepare solution-cast transparent UV shielding PLA/HC-NBC/TA/MXene (PLA/NTM) composite films with tunable bandgaps. The bandgap and UV shielding performance of the PLA/NTM composite films were regulated by varying the MXene addition amount. The bandgap of the PLA/NTM composite film with an MXene content of 1 wt% decreased to 2.37 eV, and the UVC, UVB, and UVA shielding ratios were 97.3, 96.9, and 90.8%, respectively. The visible light transmissibility of the PLA/NTM composite film was 41.8%, and its tensile strength increased by 58.4%. Furthermore, molecular dynamics simulations of the PLA/NTM composite system demonstrated that the hydrogen bonds between TA and HC–NBC synergistically promoted MXene dispersion in the PLA matrix, improving the UV shielding and mechanical properties of the PLA/NTM composite films. The findings of this study provide a new technical reference for the preparation of high-performance transparent UV shielding films.

Disinfection of wastewater by a complete equipment based on a novel ultraviolet light source of microwave discharge electrodeless lamp: Characteristics of bacteria inactivation, reactivation and full-scale studies

Ultraviolet (UV) light is widely used for wastewater disinfection. Traditional electrode-excited UV lamps, such as low-pressure mercy lamps (LPUV), encounter drawbacks like electrode aging and rapid light attenuation. A novel UV source of microwave discharge electrodeless lamp (MDEL) has aroused attention, yet its disinfection performance is unclear and still far from practical application. Here, we successfully developed a complete piece of equipment based on MDELs and achieved the application for disinfection in wastewater treatment plants (WWTPs). The light emitted by an MDEL (MWUV) shared a spectrum similar to that of LPUV, with the main emission wavelength at 254 nm. The inactivation rate of Gram-negative E. coli by MWUV reached 4.5 log at an intensity of 1.6 mW/cm2 and a dose of 20 mJ/cm2. For Gram-positive B. subtilis, an MWUV dose of 50 mJ/cm2 and a light intensity of 1.2 mW/cm2 reached an inactivation rate of 3.4 log. A higher MWUV intensity led to a better disinfection effect and a lower photoreactivation rate of E. coli. When inactivated by MWUV with an intensity of 1.2 mW/cm2 and a dose of 16 mJ/cm2, the maximum photoreactivation rate and reactivation rate constant Kmax of E. coli were 0.63 % and 0.11 % h−1 respectively. Compared with the photoreactivation, the dark repair of E. coli was insignificant. The full-scale application of the MDEL equipment was conducted in two WWTPs (10,000 m3/d and 15,000 m3/d). Generally 2–3 log inactivation rates of fecal coliforms in secondary effluent were achieved within 5–6 s contact time, and the disinfected effluent met the emission standard (1000 CFU/L). This study successfully applied MDEL for disinfection in WWTPs for the first time and demonstrated that MDEL has broad application prospects.

Research Progress of the Application of UV Light-Emitting Diodes for Water Disinfection

With the increasing global demand for safe drinking water, the search for effective and economical water treatment technologies has become an urgent need. Ultraviolet (UV) light sterilization is a proven method for eliminating bacteria in water, but traditional UV systems often rely on mercury lamps, which pose potential environmental and health risks. In recent years, the development of UV-LED technology has offered a new solution for water treatment. This article provides a detailed explanation of the working principles, technological advantages, and applications of UV-LEDs in water treatment. By comparing them with traditional UV systems, UV-LEDs not only demonstrate lower energy consumption and longer lifespan, but also avoid the use of toxic mercury. Despite current challenges in cost and technological maturity, the environmental friendliness and efficiency potential of UV-LED technology indicate a promising market outlook. This article aims to provide a comprehensive review of UV-LED technology for practitioners and researchers in the water treatment industry, and to explore its future development directions.

Photochromic Uranyl-Based Coordination Polymer for Quantitative and On-Site Detection of UV Radiation Dose.

A highly sensitive detection of ultraviolet (UV) radiation is required in a broad range of scientific research, chemical industries, and health-related applications. Traditional UV photodetectors fabricated by direct wide-band-gap inorganic semiconductors often suffer from several disadvantages such as complicated manufacturing procedures, requiring multiple operations and high-cost instruments to obtain a readout. Searching for new materials or simple strategies to develop UV dosimeters for quantitative, accurate, and on-site detection of UV radiation dose is still highly desirable. Herein, a photochromic uranyl-based coordination polymer [(UO2)(PBPCA)·DMF]·DMF (PBPCA = pyridine-3,5-bis(phenyl-4-carboxylate), DMF = N,N'-dimethylformamide, denoted as SXU-1) with highly radiolytic and chemical stabilities was successfully synthesized via the solvothermal method at 100 °C. Surprisingly, the fresh samples of SXU-1 underwent an ultra-fast UV-induced (365 nm, 2 mW) color variation from yellow to orange in less than 1 s, and then the color changed further from orange to brick red after the subsequent irradiation, inspiring us to develop a colorimetric dosimeter based on red-green-blue (RGB) parameters. The mechanism of radical-induced photochromism was intensively investigated by UV-vis absorption spectra, EPR analysis, and SC-XRD data. Furthermore, SXU-1 was incorporated into an optoelectronic device to fabricate a novel dosimeter for convenient, quantitative, and on-site detection of UV radiation dose.

Availability of Adequate Photoprotection for Skin of Color.

The impact of ultraviolet (UV) light on the skin is well-established to have both immediate and delayed effects with increasing awareness of the impact of visible light (VL) on the skin with regardto photoaging and dyspigmentation. The effects of VL disproportionately impact the skin of color with regardto discoloration of the skin leading to guidelines for photoprotection that include the use of iron oxides in sunscreen products that impart a tint. Commercially available sunscreen products found in the suncare and sun protection displays at local stores, pharmacies, and grocery stores were cataloged, and ingredients were reviewed for the presence of iron oxides. Of the 410 commercially available sunscreen products cataloged, 1.7% of facial sunscreen products available offered iron oxides, and 0.5% of non-lip products offered shade matching. With only 1.7% of commercially available facial sunscreen products offering iron oxides in addition to traditional broad-spectrum UV protection, there is a clear gap in the market for iron oxide-containing sunscreen products to meet the photoprotection needs for the skin of color.

Epitaxial hexagonal boron nitride with high quantum efficiency

Two-dimensional (2D) hexagonal boron nitride (h-BN) is one of the few materials showing great promise for light emission in the far ultraviolet (UV)-C wavelength, which is more effective and safer in containing the transmission of microbial diseases than traditional UV light. In this report, we observed that h-BN, despite having an indirect energy bandgap, exhibits a remarkably high room-temperature quantum efficiency (∼60%), which is orders of magnitude higher than that of other indirect bandgap material, and is enabled by strong excitonic effects and efficient exciton-phonon interactions. This study offers a new approach for the design and development of far UV-C optoelectronic devices as well as quantum photonic devices employing 2D semiconductor active regions.

Fast all-fiber ultraviolet photodetector based on an Ag-decorated ZnO micro-pillar.

There are urgent demands of ultraviolet (UV) photodetectors with high sensitivity and fast response due to the wide application of ultraviolet light in the fields of medical treatment, space exploration, optical communication and semiconductor industry. The response speed of traditional ZnO-based UV photodetectors is always limited by the carrier mobility and electrical resistance caused by the external circuits. Utilizing the all-optical detection method may replace the complex circuit structure and effectively improve the response speed of photodetectors. Here, a fast-response fiber-optic UV photodetector is proposed, where a ZnO micro-pillar is fixed on the end face of a fiber-tip and acts as a Fabry-Pérot interferometer (FPI). Under the irradiation of UV light, the photo-generated carriers change the refractive index of the ZnO micro-pillar, leading to a redshift of the interference wavelengths of the ZnO FPI. To enhance this effect, a discontinuous Ag film with an island-like structure is coated on the surface of ZnO micro-pillars through magnetron sputtering, and therefore the sensitivity of the proposed device achieves to 1.13 nm/(W·cm-2), which is 3.9 times higher than that of without Ag-decoration, due to the intensification of photo-carrier change with the help of the Schottky junction formed between Ag film and ZnO micro-pillar. Meanwhile, since the response speed of the proposed device is mainly determined by the temporal RI change of ZnO micro-pillar, the fiber-optic UV photodetector also shows very fast response with a rise time of 35 ns and a decay time of 40 µs. The demonstrated structure takes full advantage of optical fiber devices, exhibiting compactness, flexibility, fast response and immune to electromagnetic interference, which paves a new way for the next generation of photodetection devices.

A rheological approach for measuring cure depth of filled and unfilled photopolymers at additive manufacturing relevant length scales

We introduce a novel experimental method that uses an ultraviolet (UV) photorheometer to enable accurate and repeatable measurements of cure depth for a wide range of photopolymers. When exposed to UV irradiation within the rheometer, the cured thickness of the photoresin is measured by lowering the upper plate while monitoring the commensurate axial force. The encoder-measured distance is correlated with axial force to measure cure depth under different UV curing conditions. This technique enables precise measurements of photocured films thinner than 50 µm, which can then be used to establish working curve equations for photopolymerization-based additive manufacturing (AM) processes. This process is validated through the evaluation of three unique photoresins, including a commercially available VP stiff photoresin, a highly-viscous photoresin that cures into a “soft” gel, and a highly solids-loaded photoresin with particles that greatly limit maximum cure depth. In addition, the technique is employed to explore the impact of UV irradiance on curing behavior of photoresins. This technique enables measurement of AM process-relevant cure depths with process-relevant irradiance and wavelengths and has applications in advanced material development for a range of AM and traditional UV processing technologies. This technique meets identified gaps in current cure depth characterization techniques, including the need for automated instrumental approaches to reduce human error in measurements, the need to directly measure cure depths less than 150 µm, and the need to measure curing behavior at different UV irradiances/wavelengths. Due to the non-linear cure depth versus exposure behavior of some photoresins, it is important to directly measure cure depths at AM process-relevant sizes ( µm), as a working curve made from measurements of thicker films leads to more inaccurate predictions than those made from measuring thinner films.

Development of a geometrical model for the determination of the average intensity in a flow-through UV-LED reactor and validation with biodosimetry and actinometry

Ultraviolet (UV) treatment is widely used for water disinfection. The recent development and improvement of the light emitting diodes (LEDs) in the UVC range makes them an alternative to the traditional mercury vapor UV lamps in the middle or long term. Determining the UV intensity applied by a reactor is essential for evaluating its efficacy. Although doing so is relatively straightforward in simple laboratory reactors, such as a collimated beam reactor (CBR), its calculation for more complex devices, such as a flow-through reactor (FTR), requires indirect approaches. The objective in this study is determining the UV intensity in FTRs equipped with UV-C LEDs by utilizing indirect approaches such as the geometrical modeling of the intensity distribution, chemical actinometry, and biodosimetry using a CBR as a reference. With this method, the inactivation of four bacterial indicators in both the CBR and FTR have also been addressed. The three approaches that were used reported similar values of mean intensity with an average value of 0.86 mW cm−2. Determining the mean intensity enabled calculating the UV doses that were applied to the target water and then determining the inactivation kinetics parameters. The UV dose that was necessary to achieve four-log reductions from the initial bacterial concentration ranged from 5.8 to 17.5 mJ cm−2 depending on the target species. Additionally, the geometrical model developed in this study introduces new possibilities into the optimization of the reactor design.

Ocular and Facial Far-UVC Doses from Ceiling-Mounted 222 nm Far-UVC Fixtures.

Far-UVC radiation, defined in this paper as ultraviolet (UV) radiation with wavelengths from 200 to 235 nm, is a promising tool to help prevent the spread of disease. The unique advantage of far-UVC technology over traditional UV germicidal irradiation lies in the potential for direct application of far-UVC into occupied spaces since antimicrobial doses of far-UVC are significantly below the recommended daily safe exposure limits. This study used a ceiling-mounted far-UVC fixture emitting at 222 nm to directly irradiate an indoor space and then evaluated the doses received upon a manikin. Radiation-sensitive film was affixed to the head, nose, lip and eyes of the manikin, and the 8-h equivalent exposure dose was determined. Variables examined included manikin height (sitting or standing position), manikin offset from directly below the fixture, tilt of the manikin, the addition of glasses, the addition of hair and different anatomical feature sizes. Importantly, at the manikin position with the highest dose to eyes, the average eye dose was only 5.8% of the maximum directly measured dose. These results provide the first experimental analysis of possible exposure doses a human would experience from an indoor far-UVC installation.

A novel UV-LED hydrogen peroxide electrochemical photoreactor for point-of-use organic contaminant degradation

The degradation of organic contaminants is typically achieved by exposure of hydrogen peroxide (H2O2) containing influent to ultraviolet (UV) lamps as the source of radiation that can convert H2O2 to hydroxyl radicals (·OH), which oxidize organic pollutants. However, two factors prevent this process from being scaled down: the need to introduce H2O2, which requires special handling, and the use of bulky UV lamps, which have a high electric power consumption. In this work, an electrochemical cell was developed for the efficient in situ generation of H2O2 from water and atmospheric oxygen in a process called a two-electron oxygen reduction reaction (2e-ORR), so that the external addition of H2O2 is no longer needed. Moreover, the electrochemical cell was equipped with ultraviolet light-emitting diodes (UV-LEDs) to convert H2O2 to ·OH. The reactor exhibited a current efficiency of ∼90% for the H2O2 production at a flow rate of 50 mL min−1. The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was studied at 277 nm based on different operational parameters, such as UV fluence rate, initial concentration, and initial pH. A high degradation of >70% was obtained at a UV output of 900 mW. Our approach, the first of its kind, has novel features applied, including: optimal radiation distribution in the reactor by applying a new UV source, UV-LEDs that offer much more control for the radiation profile in the reaction system compared to traditional UV lamps, controlled hydrodynamics by implementing special flow channels to provide a more uniform residence time and offer enhanced mixing, and integrating UV reactor and electrochemical cell in a single unit which could lead to superior performance and space efficiency of the device. These features make the device very suitable for point-of-use (POU) water treatment applications to eliminate both microbial and chemical contaminants.

Laser-stimulated fluorescence reveals unseen details in fossils from the Upper Jurassic Solnhofen Limestones.

Laser-stimulated fluorescence (LSF) has seen increased use in palaeontological investigations in recent years. The method uses the high flux of laser light of visible wavelengths to reveal details sometimes missed by traditional long-wave ultraviolet (UV) methods using a lamp. In this study, we compare the results of LSF with UV-A-generated fluorescence on a range of fossils from the Upper Jurassic Solnhofen Limestone Konservat-Lagerstätte of Bavaria, Germany. The methodology follows previous protocols of LSF with modifications made to enhance laser beam intensity, namely keeping the laser at a constant distance from the specimen, using a camera track. Our experiments show that along with making surface details more vivid than UV-A or revealing them for the first time, LSF has the additional value of revealing shallow subsurface specimen detail. Fossil decapods from the Solnhofen Limestone reveal full body outlines, even under the matrix, along with details of segmentation within the appendages such as limbs and antennae. The results indicate that LSF can be used on invertebrate fossils along with vertebrates and may often surpass the information provided by traditional UV methods.

UV/ozone irradiation manipulates immune response for antibacterial activity and bone regeneration on titanium

The immunomodulatory antibacterial activity and osteoimmunomodulatory properties of implantable biomaterials significantly influence bone regeneration. Various types of ultraviolet (UV) instrument are currently in use to greatly enhance the antibacterial activity and osteoconductive capability of titanium, it remains unclear how UV treatment modulates immune response. Compared to traditional UV treatment, the combination of low-dose ozone with UV irradiation is considered a new option to give benefits to surface modification and reduce the drawbacks of UV and ozone individually. Herein, the aim of this study was to elucidate the immune-modulatory properties of macrophages on UV/ozone-irradiated titanium that serve as defense against S. aureus and the crosstalk between immune cells and osteoblasts. Three different cell and bacteria co-culture systems were developed in order to investigate the race between host cells and bacteria to occupy the surface. In vitro immunological experiments indicated that UV/ozone irradiation significantly enhanced the phagocytic and bactericidal activity of macrophages against S. aureus. Further, in vitro and in vivo studies evidenced the favorable osteoimmune environment for osteogenic differentiation and bone formation. This research suggests vital therapeutic potential of UV/ozone irradiation for preventing the biomaterial-associated infections and achieving favorable bone formation simultaneously.

Recent advances on the application of UV-LED technology for microbial inactivation: Progress and mechanism.

Conventional technologies for the inactivation of microorganisms in food products have their limitations, especially changes in quality attributes that have led to quality deterioration, low consumer acceptance, impact on the environment, and potential health hazards (carcinogens). Ultraviolet (UV) light is an emerging promising nonthermal technology employed for microbial inactivation in water, liquid, and solid food products to curtail the limitations above. This review provides an insight into UV light-emitting diodes (UV-LEDs)' potential as an alternative to the traditional UV lamps for microbial inactivation in liquid and solid media. Also, the mechanisms of inactivation of lone and combined UVA-, UVB-, and UVC-LEDs were discussed. The strategies utilized to improve the efficacy between the UV-LED treatments at various wavelengths were summarized. Combining different UV-LEDs treatments at different wavelengths have a synergistic effect and suppression of microbial cell reactivation. The UV-LED-based advanced oxidation processes (AOPs) also have high germicidal action against numerous microorganisms and are efficient for the degradation of micropollutants. Among the UV-LEDs discussed, UVC-LED has the most antimicrobial effect with the most efficient micropollutants decomposition with regards to UV-LED-based AOPs. This review has provided vital information for future application, development, and customization of UV-LED systems that can meet the food and water safety requirements and energy efficiency.

Effect of Stereolithography 3D Printing on the Properties of PEGDMA Hydrogels

Stereolithography (SLA)-based 3D printing has proven to have several advantages over traditional fabrication techniques as it allows for the control of hydrogel synthesis at a very high resolution, making possible the creation of tissue-engineered devices with microarchitecture similar to the tissues they are replacing. Much of the previous work in hydrogels for tissue engineering applications have utilised the ultraviolet (UV) chamber bulk photopolymerisation method for preparing test specimens. Therefore, it is essential to directly compare SLA 3D printing to this more traditional approach to elucidate the differences in hydrogels prepared by each fabrication method. Polyethyleneglycol dimethacrylate (PEGDMA) is an ideally suited material for a comparative study of the impact that SLA fabrication has on performance, as the properties of traditional UV chamber-cured hydrogels have been extensively characterised. The present study was conducted to compare the material properties of PEGDMA hydrogels prepared using UV chamber photopolymerisation and SLA 3D printing. From the subsequent testing, SLA-fabricated hydrogels were shown to maintain similar thermal and chemical performance to UV chamber-cured hydrogels but had a higher compressive strength and tensile stiffness, as well as increased hydrophilicity. These differences are attributed to the increased exposure to UV light SLA samples received compared to traditionally UV chamber-cured samples.

Plasmon‐Enhanced InGaZnO Ultraviolet Photodetectors Tuned by Ferroelectric HfZrO

AbstractIndium–gallium–zinc oxide (IGZO) is widely used in liquid crystal panels, which are well suited for ultraviolet (UV) photodetectors due to a suitable bandgap and outstanding electrical properties. However, the poor performance for high dark current and low photoresponsivity limits practical applications of IGZO in UV photodetection. Here, a ferroelectric hafnium zirconium oxide (HfZrO) film is introduced to depress dark current and increase the sensitivity by strong ferroelectric‐localized field. Meanwhile, gold nanoparticles are used to enhance the photoresponsivity by localized surface plasmon resonance. With optimized designs, the photodetectors achieve a photoresponsivity of 714.6 A W–1, a dark current of 1.1 × 10−12 A, and a detectivity of 5.4 × 1012 Jones. Furthermore, the response time at rising and falling edge is as low as 40 and 10 ms, respectively. The performance of the photodetector is far beyond traditional IGZO UV photodetectors. This study establishes a new approach to produce ultraviolet photodetectors with high photoresponsivity, low dark current, high sensitivity, and fast response for further practical applications.

Polarization-insensitive and achromatic metalens at ultraviolet wavelengths

Ultraviolet (UV) light is widely used in nanofabrication and biomedical fields. However, in order to shape the wavefront of the UV beam, UV light needs to travel a relatively long distance in optical media that usually have strong UV absorptions. Thus the traditional UV lens is inefficient, costly, and easily aging under the radiation. Hopefully, dielectric metalenses represent a promising alternative. We design and numerically study a polarization-insensitive and achromatic metalens at UV spectra from 234 to 274 nm. The metalens consists of 1519 AlN nanopillars and its focal length is about 4.7 μm, with a <4.6 % alternation over the entire operating bandwidth, whereas the alternation of a chromatic metalens is 24.3%. More importantly, the focal length remains nearly the same (<0.02 % alternation) for not only linearly polarized light with different polarization angles but also for the left-handed and right-handed circularly polarized light as well. In addition, the designed metalens still has an excellent convergence ability even at 10-deg oblique incidence. This polarized-insensitive and achromatic metalens will greatly promote the development of UV photonic devices and UV nanophotonics.

Deep ultraviolet lasers for flow cytometry.

Modern flow cytometers require multiple laser wavelengths to excite the wide variety of fluorescent probes now available for high-dimensional analysis. Ultraviolet (UV) lasers (typically solid state 355 nm) have become a critical excitation source for the Brilliant Ultraviolet (BUV) series of polymer fluorochromes. The BUV dyes have pushed the number of fluorescent probes available for simultaneous analysis to nearly 30, allowing an unprecedented level of precision for immune cell analysis. However, immunologists are already seeking analyze more than 30 simultaneous parameters, requiring both new fluorochromes and corresponding laser wavelengths. A group of polymer dyes requiring deep ultraviolet (UV) excitation (~280-300 nm) is currently under development, allowing the expansion of high-dimensional cytometry beyond the current 30 color limit. In this study, we evaluated a newly available laser emitting at 280 nm as a possible laser source for exciting these dyes. Since deep UV polymer dyes are not yet available, we used quantum nanoparticles (Qdots) as a surrogate probe to assess the utility of this laser wavelength for flow cytometry. Deep UV laser light was found to excite Qdots as well as traditional UV sources. Deep UV 280 nm did not excite BUV dyes well, suggesting that BUV and deep UV polymers will be spectrally compatible with low crossbeam spillover issues. Deep UV excitation did excite considerable autofluorescence in the violet to blue range, a limitation that will need to guide deep UV fluorochrome development. A deep UV 280 nm laser may therefore be the next essential wavelength for high-dimensional flow cytometry. © 2018 International Society for Advancement of Cytometry.

An Inexpensive High-Temporal Resolution Electronic Sun Journal for Monitoring Personal Day to Day Sun Exposure Patterns.

Exposure to natural sunlight, specifically solar ultraviolet (UV) radiation contributes to lifetime risks of skin cancer, eye disease, and diseases associated with vitamin D insufficiency. Improved knowledge of personal sun exposure patterns can inform public health policy; and help target high-risk population groups. Subsequently, an extensive number of studies have been conducted to measure personal solar UV exposure in a variety of settings. Many of these studies, however, use digital or paper-based journals (self-reported volunteer recall), or employ cost prohibitive electronic UV dosimeters (that limit the size of sample populations), to estimate periods of exposure. A cost effective personal electronic sun journal (ESJ) built from readily available infrared photodiodes is presented in this research. The ESJ can be used to complement traditional UV dosimeters that measure total biologically effective exposure by providing a time-stamped sun exposure record. The ESJ can be easily attached to clothing and data logged to personal devices (including fitness monitors or smartphones). The ESJ improves upon self-reported exposure recording and is a cost effective high-temporal resolution option for monitoring personal sun exposure behavior in large population studies.